A wire-based heating element is provided having first and second portions twisted about each other such that magnetic flux emitted from one portion is substantially cancelled by magnetic flux emitted from the other portion. A bonding material that fixedly connects the two portions of the heating element and restricts their movement relative to each other to thereby maximize the cancellation of magnetic flux. A substrate-based heating element is also provided having traces on opposed sides of a substrate and overlying each other to cancel magnetic flux. Electrical connection pads are located on the same side of the substrate, and the second trace extends passed the first trace to connect to the second connection pad. A lead connected to the first connection pad overlies the portion of the second trace that extends to the second connection pad to thereby cancel magnetic flux emissions from this portion of the second trace.

The present invention relates generally to electrically resistive heating elements and more particularly to heating elements configured such that emissions of magnetic flux from the heating elements are reduced.
Most electronic devices experience changes in operating characteristics based on their operating temperature. For most applications, these variations are slight and can either be ignored or compensated for through calibration. However, there are instances in which environmental temperature regulation is required to ensure proper operation of an electronic device. For example, in many space applications where temperatures are extremely cold, environmental temperature regulation is required. At these extreme temperatures, electronic components may have operating characteristics that are quite different from their operating characteristics at room temperature causing them to malfunction or provide erroneous readings. Further, temperature regulation is also typically required for components that are particularly sensitive to variations in temperature. One example of such a device is a precision fiber optic gyro (FOG). Precision FOGs are particularly sensitive to changes in temperature. In precision applications, changes in the operating temperature of only a few millidegrees can affect the performance of the gyros significantly.
In many applications, strip heaters are used in temperature control systems for providing heat to electronic devices. Strip heaters include a resistive element that generates heat when a current is applied thereto. The heating element is either an elongated wire or trace of resistive material deposited on a substrate. The heating element is typically arranged in a pattern over a defined area to thereby provide uniform heat over the defined area. When current is applied to the heating element, heat is emitted from the strip heater.
While strip heaters are considered an inexpensive and efficient means of providing heat to electronic devices for environmental temperature control, there are some drawbacks to these devices. Specifically, as known in the art, when a current is applied to an elongated wire or trace, a magnetic field or flux is emitted from the heating element. This magnetic flux is problematic for several reasons. In terms of public safety, studies have linked high magnetic flux emissions as contributing to increased risk of cancer and other health problems. In addition, in terms of electronic device design, magnetic flux emissions, even at substantially lower levels, are known to negatively effect the performance of electronics and some types of fiber optics. Stray magnetic flux can also introduce output changes, drift, or noise into electronic components, which can corrupt data signals in an electronic device.
The magnetic flux emitted from a wire having infinite length is defined by the equation:
B=(xcexc0i)/(2xcfx80d)
where:
xcex0=4xcfx80xc3x9710xe2x88x927 henries per meter;
i=amperes (AC and/or DC); and
d=distance from wire in meters.
As mentioned above, many conventional strip heaters employ elongated heating elements that are formed into patterns. These elongated heating elements can produce significant levels of magnetic flux. As seen from the equation above, the amount of flux emitted is inversely proportional to the distance d from the heating element. In most cases, the heating element is placed as close as possible to the item to be heated, thereby intensifying the amount of magnetic flux to which the element to be heated is subjected. Thus, although a strip heater element will serve to raise or regulate the operating temperature of the electronic device to a desired level, the magnetic flux emitted by the strip heater can adversely affect the electronic device""s operation.
Considerable effort, costs, and research is expended in electronic device design applications to shield devices from and eliminate sources of magnetic flux that may disrupt operation of the electronic device. For example, FIGS. 1A and 1B illustrate one conventional strip heater 10 having somewhat reduced magnetic flux emissions. As illustrated, the heater 10 includes a continuous heating element 12 that is folded in half to form two portions, 14 and 16. To reduce magnetic flux emissions, the two portions 14 and 16 are twisted about each other. When current is applied, as shown by the current arrows, current flows through the first portion 14 of the heating element 12 in one direction and through the second portion 16 in an opposite direction. In this configuration, because the current is the same magnitude through both portions, 14 and 16, magnetic flux emitted from the first portion 14 of the heating element is substantially cancelled by the magnetic flux emitted from the second portion 16.
Importantly, the amount of magnetic flux emission cancellation is related to the proximity of the first 14 and second 16 portions of the heating element to each other. In other words, the tighter the heating elements are twisted about each other, and the finer the elements are in terms of average diameter, the better the magnetic flux cancellation. Separations and air gaps between the first and second portions of the heating element, however, and the use of loosely wound, poorly-anchored, large diameter (0.010 inches or more) wires reduce the level of magnetic flux cancellation. As such, it is important to eliminate separations and air gaps between the first and second portions of the heating element for maximum magnetic flux cancellation.
Current heating element designs, however, do not properly address these problems. Specifically, for the most part, twisted heating element type strip heaters have been employed in heating blankets and similar applications. In these applications, heating elements are typically placed in the blanket material in a loose fashion. In this instance, the heating element is free to flex with the movements of the blanket. The flexing of a heating blanket also flexes the heating element allowing for separations and/or air gaps to form between the first 14 and second 16 portions of the heating element 12. For example, FIG. 1B illustrates a conventional heating element 12 in a flexed state. As can be seen, because the first and second portions are not fixed with respect to each other, air gaps 18 form in the flexed heating element, which thereby increase the amount of net magnetic flux emissions, (i.e., non-cancelled), by the heating element. While generally safe for human use, such heating blankets and similar devices can typically emit flux at levels tens or hundreds of times higher than many sensitive electronic devices can tolerate.
Some strip heating elements are substrate based, which means they are formed by depositing resistive traces on a substrate as opposed to wires. Advances have also been made to these substrate-based strip heaters to reduce magnetic flux emissions. In these systems, it is difficult to manufacture the heating element so that it has two portions twisted about each other. For this reason, conventional low flux substrate-based strip heater systems can be designed such that the resistance traces overlay each other on the opposed sides of the substrate. FIG. 2 illustrate a typical substrate-based strip heater system. Specifically, the strip heater system 20 includes a substrate 22 and first and second electrically resistive traces, 24 and 26. Importantly, the first and second traces are located on opposed sides of the substrate 22. The two traces each have opposed ends, (24a and 24b) and (26a and 26b), and bodies 24 and 26. Importantly, the bodies of each of the traces overlay each other in a corresponding pattern. Further, the opposed ends 24b and 26b are connected to each other by a via 28 extending through the substrate 22 to create a continuous heating element between the first ends 24a and 26a. In these systems, similar to the heating elements illustrated in FIG. 1A, current is applied to one end 24a of the trace and current (A.C. or D.C.) flows in opposite directions between the traces at any instant as shown by the arrows. This opposite flow causes a cancellation between the magnetic flux emitted by one trace and the magnetic flux emitted by the other trace.
Although these conventional substrate-based strip heating systems effectively reduce the amount of harmful magnetic flux emitted, present substrate-based strip heater designs do not maximize magnetic flux reduction. Specifically, as illustrated in FIG. 2, in many current substrate-based strip heater designs, the patterns of the first and second traces, 24 and 26, do not match each other at the location where they are connected to the via 28. Instead, there is a loop 30. This non-matching pattern area 30 results in a net magnetic flux emission between the portions, 32a and 32b, of the first and second traces, 24 and 26, because they do not sufficiently overly each other so as to maximize magnetic flux cancellation.
Additionally, for most substrate-based strip heater applications, it is advantageous to form connection pads, 34 and 36, on the same side of the substrate 22. To accomplish this, the contact pads 34 and 36, are offset from each other on the same surface, and the trace on the opposed surface, in this case the second trace 26, is redirected to the position of its corresponding connection pad 36. The trace 26 is connected to the connection pad 36 by a via 38 extending through the substrate. As illustrated, the pattern of the second trace 26 again diverges from the pattern of the first trace 24. Here again, because the patterns do not overly each other for the portion 32b, magnetic flux emissions are not effectively minimized.
In light of the problems with the conventional heating elements discussed above, the present invention provides both wire-based and substrate-based heating elements that effectively minimize the amount of magnetic flux emitted. Specifically, the heating elements of the present invention reduce the number of potential gaps, loops, and separations between the portions of a heating element that can cause a net magnetic flux emission.
For example, in one embodiment, the present invention provides a wire-based heating element having a body comprising first and second portions that are twisted about each other such that magnetic flux emitted from current flowing in one portion of the heating element is substantially cancelled by magnetic flux emitted from current flowing in the other portion of the heating element. Importantly, in this embodiment, the heating element further includes a bonding material that at least partially overlays the first and second portions of the heating element. The bonding material fixedly connects the two portions of the heating element that are twisted about each other together and restricts their movement relative to each other. This, in turn, reduces the potential for separations and/or air gaps between the first and second portions that would create a net magnetic flux emission by the heating element.
In addition to providing bonding material to fixedly connect the two portions of the heating element relative to each other, the present invention, in some embodiments, also provides a backing material for supporting the first and second portions of the heating element. More specifically, one embodiment of the present invention provides a backing material to which the first and second portions of the heating element are fixedly connected by the bonding material. In this embodiment, the backing material further reduces the amount of flex between the first and second portions of the heating element thereby minimizing the numbers of separations and/or air gaps that can be introduced between the first and second portions when the heating element is flexed. In a further embodiment, the backing material may further include an adhesive layer on a side opposite from the location of the heating element. The adhesive layer allows the heating element to be fixedly connected to a body to be heated by the heating element. Alternatively, the adhesive layer can be on the same side of the backing material as the heating element.
The present invention also provides embodiments in which the heating element itself is attached to the backing material in a serpentine pattern. The serpentine pattern effectively decreases the strain in the heating element due to tension forces that may be applied to the heating element during flexing. The pattern also provides for more uniform heating. In this embodiment, because the first and second portions of the heating element are fixedly bonded together and are further bonded to the backing material by the bonding material and because of the serpentine pattern of the heating element on the backing material, the present invention effectively minimizes the number of separations and/or air gaps that can be introduced between the first and second portions of the heating element that would create a net magnetic flux emission.
In some embodiments, the heating element of the present invention has a specific length corresponding to a desired heat output for the element. In these embodiments, the heating element may be required to fit within a selected area of the backing material to provide heat within that given area. In this embodiment of the present invention, the heating element, having a selected length L defines a serpentine pattern within the selected area having a width w and a length d. In this instance, the serpentine pattern creates zigzag portions that form triangles having a base 2xc3x97 and sides r. To properly fit the selected length L of the heating element in the selected area, the zigzag portions of the heating element have a selected triangle base width. Specifically, if the area of the backing in which the heating element is to be patterned has a width w and a length d and a heating element has an overall length of L, then half of the base length (x) of each triangle in the zigzag pattern will be defined by the following equation:
x=w[(L2/d2)xe2x88x921]xe2x88x921/2.
In addition to providing wire based heating elements, the present invention also provides substrate-based heating elements. The substrate-based heating elements of the present invention reduce the number of loops and gaps between the first and second portions of the heating element, thereby minimizing the amount of magnetic flux emissions. For example, in one embodiment, the present invention provides a substrate-based strip heater having first and second heating element traces respectively located on first and second opposed sides of a substrate. The first and second traces have at least one of a corresponding pattern and a corresponding position relative to each other, such that magnetic flux emitted from current flowing in the first trace is substantially cancelled by magnetic flux emitted from current flowing in the second trace. The heating element of this embodiment further includes a first connection pad located on the first side of the substrate in electrical communication with the first trace. Additionally, the heating element further includes a second connection pad also located on the first side of the substrate in electrical communication with the second trace. There are first and second leads respectively connected to the first and second connection pads for applying electrical current thereto.
Importantly, in this embodiment, for the first and second connection pads to be located on the same side of the substrate, the second connection pad is offset from the location of the first connection pad by a selected offset distance. In this instance, a portion of the second trace is offset from the position of the first trace in order to connect to the second connection pad. To reduce the magnetic flux emissions from the offset portion of the second trace, the first lead extends along the first surface of the substrate overlying the portion of the second trace that is offset from the first trace. As such, the magnetic flux emitted from the offset portion of the second trace is effectively cancelled by the magnetic flux emitted from the portion of the first lead that overlies the second trace.
For example, in one embodiment, the second connection pad is located at position in front the first connection pad, and the second trace extends past the position of the first connection pad to connect the second connection pad. In this embodiment, the second trace substantially overlies the entire length of the first trace so that the magnetic flux from the first trace is substantially cancelled by the magnetic flux emitted by the second trace. Further, the first lead of this embodiment extends from the first connection pad over the portion of the second trace that extends past the first connection pad to the second connection pad to thereby substantially cancel the flux emitted from this section of the second trace.

Heating elements with reduced stray magnetic field emissions


A rear wheel steering device for a vehicle has a steering control mechanism which steers rear wheels of the vehicle on the following formula: EQU TG.theta..sub.R =-K.sub.F .multidot..theta..sub.F +K.sub.R .multidot.V.multidot..psi.. where. TG.theta..sub.R : target steering angle of rear wheels PA0 .theta..sub.F : steering angle of front wheels PA0 V: vehicle speed PA0 .theta.: yaw rate PA0 K.sub.F, K.sub.R : coefficients determined by the properties of vehicle.. To achieve slip angle .beta.=0, the device further includes a vehicle condition detecting mechanism which detects various conditions of the vehicle, and a changing mechanism being connected with the steering control mechanism and the vehicle condition detecting mechanism for changing at least one of the coefficients K.sub.F, K.sub.R based on the conditions of the vehicle.

The present invention relates to a rear wheel steering device for a vehicle.
Conventionally, a four-wheel steering device for a vehicle which steers rear wheels in accordance with a vehicle speed and a steering angle of front wheels has been known in the art. In this device, the rear wheels are steered in the opposite direction at a low speed, and in the same direction at a high speed to the front wheels according to the steered angle thereof.
In this prior art, no problem occurs when turning a corner slowly with a gradual steering of the steering wheel at the initiation of a turn since necessary yaw rate (yaw angular velocity) is attained due to the difference of the steering angles between the front and the rear wheels. However, problems arise when turning the steering wheel abruptly since, with the rear wheels in the same orientation as the front wheels at a high speed, the vehicle moves in a diagonal direction and vehicle yaw rate is restricted. As a result, slip angle .beta. formed between the orientation of the vehicle and the moving direction thereof does not become 0 degrees, which will lead to a failure to meet the driver's desire to turn the vehicle.
DesirabIy, at the initial stage of steering in such a case, first the orientation of the vehicle should be changed, and then the rear wheels should be steered in the same orientation as the front wheel to stabilize the vehicle condition, thereby constantly achieving a slip angle .beta.=0.
To this end, a method of to steering the rear wheels according to the following formula has been proposed: EQU TG.theta..sub.R =-K.sub.F .multidot..theta..sub.F +K.sub.R .multidot.V.multidot..psi. (1)
where
TG.theta..sub.R : target steering angle of rear wheels PA0 .theta..sub.F : steering angle of front wheels PA0 V: vehicle speed PA0 .psi.: yaw rate PA0 K.sub.f, K.sub.R : constants determined by vehicle properties, for example, vehicle weight based on wheels, center of gravity balance of the vehicle. PA0 1.sub.1 : distance between gravity center of vehicle and axle of front wheels PA0 1.sub.2 : distance between gravity center of vehicle and axle of rear wheels. PA0 TG.theta..sub.R : target steering angle of rear wheel PA0 .theta..sub.F : steering angle of front wheel PA0 V: vehicle speed PA0 .psi.: vehicle yaw rate PA0 K.sub.F, K.sub.R : coefficients determined by the properties of vehicle.
In the above formula, K.sub.F and K.sub.R are determined by the following equation: ##EQU1## C.sub.1, C.sub.2 : cornering capacity W: weight
The formula shows that the steering angle of the front wheels functions as an element to steer the rear wheels in the direction opposite to the front wheels while a vehicle speed V and a yaw rate function as an element to steer the rear wheels in the same direction as the front wheels. Accordingly, at a low speed, the direction of the rear wheels become opposite to that of the front wheels since the value of the second term of the formula is small due to the low vehicle speed V. On the contrary, at a high speed, the direction of the rear wheels coincide with that of the front wheels since the value of the second term of the formula is large due to the increase in a vehicle speed V and a yaw rate. However, at the initial portion of the turn, the direction of the rear wheels is opposite to that of the front wheels because the value of the second term of the formula is yet small due to lower yaw rate during the initial stage of the turn.
As disclosed in the U.S. Pat. No. 4,412,594, a device which steers rear wheels in accordance with the output from a yaw rate sensor to compensate for disturbances such as side wind has been known in the art.
In the above formula, K.sub.F and K.sub.R are defined as constants. However, using these values as constants makes it difficult to control the rear wheels. For example, if, during a low speed, the steered angle of the front wheels is approximately at 35 degrees and the rear wheels are steered at the same angles as the front wheels, the vehicle will make a small excessively sharp turn with a resultant swerve of the rear end of the vehicle. Furthermore, drivers accustomed to driving 2-wheel steering cars wherein rear wheels are not steered may feel uncomfortable and uneasy in driving four-wheel steering cars.
According to the above formula, when the wheels are locked, for example, by the abrupt braking, vehicle speed V becomes 0 and the direction of the rear wheels becomes opposite to that of the front wheels. However, since at the initial stage of braking, vehicle speed V is not actually 0, the vehicle will be in an unstable state. In addition, during sudden deceleration, sudden decrease in the vehicle speed V causes the vehicle to move toward the unstable direction or an undesired direction for the driver, with a resultant failure to achieve improved control of the vehicle. Further, during acceleration, the same problem occurs when the wheel spin is occurring.
Above mentioned formula further involves the problem when practically applied to the rear wheel steering device. That is, during sudden acceleration and deceleration, the value of the first term of the formula becomes large, and consequently the element for controlling the rear wheels into the opposite direction to the front wheel becomes large. As a result, the vehicle will be placed in the unstable condition. In detail, when the vehicle speed V becomes 0 due to sudden braking, for example, the value of the second term of the formula becomes 0, and therefore the rear wheels will consistently be steered in the opposite direction. That means the rear wheels are in the direction opposite to the front wheels when the control of the vehicle is recovered in the driver's hands, which is not desirable transiently. Furthermore, even during the low speed running at the initial stage of the acceleration, the value of the first term of the formula should be small to achieve the stability of the vehicle condition since the driver does not require the turn of the wheels at that stage.
On the other hand, at a low speed, the value of the second term of the formula should be small. This is because when driving at a low speed, for example, while garaging a car, vehicle speed fluctuates substantially due to frequent change in the degree of acceleration, and relatively high vehicle yaw rate is generated due to the large steering angle. Under such circumstances, extent of degrees to which the rear wheels are steered opposite to the front wheels decreases to the contrary of the driver's desire to make a small turn. In addition, the driver may feel uncomfortable because of the frequent changes of the steering angle.
When practically applied to the rear wheel steering device of a vehicle, the method of controlling the rear wheels based on a vehicle yaw rate has an advantage over the conventional two-wheel steering device under a certain condition. That is the stable controllability of the vehicle under the condition that the change of speed of the vehicle yaw rate is within the fixed range while the rear wheels are securely steerable. However, the disadvantage lies in the difficulty of recovering the control of the rear wheels, once it is lost. For instance, according to the result of the test conducted to determine when the control of rear wheels is lost at the time of exceeding the peak of the cornering power C.sub.P (refer to FIG. 17) during the turn under the same road condition, four-wheel steering vehicle lost its control at a higher speed while two-wheel steering vehicle lost its control at relatively low speed. This indicates that the four-wheel steering vehicle lose its controllability while the kinetic energy of the vehicle is high, resulting in the subsequent difficulty of recovering the control. Accordingly, slip angle .beta.=0 cannot be obtained.

Rear wheel steering device for a vehicle


Garments to support a distended abdomen are described herein. For example the garment comprises an abdominal panel displaced beneath and in a position to support a distended abdomen, said panel being formed from an anisotropic elastomeric fabric that stretches in a latitudinal direction; side panels secured to a side of said abdominal panel, each side panel extending upwards and to a rear of said abdominal panel and being formed from an isotropic elastomeric fabric having a modulus of elasticity at least 1.5 times greater than said abdominal panel; and a back panel positioned over a lumbar region attached to said side panel.

It is known that abdominal distention due to excess weight causes pain. Though not limited to pregnancy, abdominal distention is especially encountered during pregnancy. In this respect, it is known that there is substantial weight gain during pregnancy, especially during the latter 20 gestational weeks. Weight increase during pregnancy may often reach 40 pounds or more with 70% of the increase occurring during the last 20 gestational weeks. This increase is largely due to water retention, an increase in fat reserve, and the weight of the fetus.
It is also known that during pregnancy, the joints, ligaments and muscle structure of the pelvis and spine are particularly lax. The increased joint laxity and elasticity allows an easier adaptation of the pelvic shape to the fetus.
Further, it is known that during pregnancy, due to changes in the hormonal state, relaxation of the ligament and tendon system occurs along with an increase in the level of the progesterone hormone. This relaxation affects the whole body and becomes particularly apparent at the sacroiliac joints and at the pubic symphysis resulting in a greater stretching of the ligaments and a corresponding increase in pain derived from the stress exerted by the swelling of the uterus. At the vertebral level, particularly in the lumbar tract, ligamentous laxity may cause microstrains against the articular facets resulting in lower back pain. Moreover, at the lower lumbar vertebrae and at the lumbosacral passage, where the compressive stress on the vertebral bodies and the vertebral disks concentrate, a greater rate of disk protrusions occurs. The latter are also enhanced by greater laxity of the posterior longitudinal ligament with resulting compression creating lower back pain.
The relaxation of the ligament system during pregnancy also causes a spreading apart of the pelvic bones. In particular, the diastasis of the pubic symphysis causes a symptomatology represented by pubic and lumbosacral nerve pain enhanced by motion making walking difficult.
The above described symptoms are very frequent during pregnancy with an incidence that tends to increase during the course of the pregnancy as the uterine volume and weight increase until reaching its maximum around the end of the eighth month when approximately three women out of four intensely suffer from these conditions.
There are many factors contributing to pain during pregnancy. As the dimension of the abdomen and weight of the uterus increase coupled with relaxation of the abdominal wall, the center of gravity shifts forwards causing lumbar stress. This results in modification of the spine morphology including an abnormal forward curvature of the spine in the lumbar region, a backward shifting of the sacrum causing a progressive verticalization of the lumbosacral angle, a stretching of the sacroiliac joints, and finally a stretching against the pubic symphysis. At times, also sciatic neuralgia from herniated disc-deriving discoradicular compression is developed. To compensate for the above, the shoulders, the neck and the head are brought backwards, and the pelvis is slightly rotated onto the femurs. These modifications in posture induce pregnant women to assume a typical waddling gait with overloading of the vertebrae and of the related intervertebral disks.
Many maternity garments, especially undergarments, have been developed over the years to better support women during pregnancy. For example, U.S. Pat. No. 5,094,648 discloses a maternity support top with a built in bra and with a two-inch bellyband that lifts weight off of the pelvis. This garment focuses only on the upper torso of a pregnant woman and does not address the hip or buttock area.
U.S. Pat. No. 5,702,286 discloses a back and abdominal support worn over the brassiere and under the panties with a supportive band under the abdomen. However, this garment does not smooth and support the hip and buttock areas, but only acts as a supportive piece, not a shaping or smoothing piece.
U.S. Pat. No. 7,181,755 discloses a knit fabric band that is worn over pants that are too tight or too loose, holding them in place. The band is worn as a single layer over the abdomen as it grows. The band, however, does not address the torso or the back and does not act as a support function. Additionally, the band does not provide a shaping function and does not improve the woman's silhouette.
U.S. Pat. No. 6,817,034 discloses a full body slip that shapes and supports the torso, smoothes the thighs, buttocks, and waist. However, an abdominal panel is only supported by a narrow strip and functions solely as a support for the belly. The design disadvantageously prevents the wearer from wearing pants because the full body slip is shaped in a tubular fashion, necessarily extending and reaching far down the leg.
Patent Application Publication No. 2009/0270012 discloses a mild support to shape a woman's body. The garment has a shoulder strap, a belly panel, a hip band, and two side panels, and a back panel made of high performance fabric with varying degrees of compression. Though providing improvement over similar garments such as those described above, it fails to provide full relief from all discomfort resulting from the distended abdomen.
From the above, it is apparent that known maternity support and under garments disadvantageously target only a specific area of the body and solves only a limited number of problem areas. Therefore, a need exists for an all-in-one garment that addresses several areas including the smoothing of a woman's profile, the improvement of her level of comfort, the provision of needed support in all areas impacted by the pregnancy and compliments desired aesthetics.

This patent is subject to a terminal disclaimer.


An adaptive clutter filtering for ultrasound color flow imaging is provided including an iterative algorithm that is used to select the best clutter filter for each packet of color flow data. If significant clutter motion is present, a high pass filter cutoff frequency is automatically set to suppress the clutter and associated flash artifacts. The cutoff frequency is chosen according to the frequency of the clutterxe2x80x94the lower the clutter frequency, the lower the cutoff frequency can be. If clutter frequencies are low, lower filter cutoffs allow for maximum low flow detection. In this manner, the filter cutoff frequency can be optimized based on the data for each pixel in the color flow image.

1. Field of the Invention
This invention relates to filtering in general and to filtering ultrasound data in particular.
2. Prior Art
Ultrasonic imaging is a frequently used method of analysis for examining a wide range of media and objects. Ultrasonic imaging is especially common in medicine because of its relatively non-invasive nature, low cost, and fast response times. For example, ultrasonic imaging is commonly used to detect and monitor the growth and health of fetuses, or to detect and assist in the diagnosis of liver and kidney pathology. Typically, ultrasonic imaging is accomplished by generating and directing ultrasonic sound waves (an ultrasonic beam or signal) into a medium under investigation using a set of ultrasound generating transducers and then observing reflections generated at the boundaries of dissimilar materials, such as tissues within a patient, also using a set of ultrasound receiving transducers. The generating and receiving transducers may be arranged in arrays and a single transducer may be used for both generating and receiving ultrasonic signals. The reflections are converted to electrical signals by the receiving transducers and then processed, using techniques known in the art, to determine the locations of echo sources. The resulting data is displayed using a display device, such as a monitor.
Typically, the ultrasonic signal transmitted into the medium under investigation is generated by applying continuous or pulsed electronic signals to an ultrasound generating transducer. In diagnostic imaging, the transmitted ultrasonic signal is generally in the radio frequency A) range of 1 MHz to 15 MHz, which corresponds to ultrasonic wavelengths in the range of 0.1 mm to 1.5 mm. The ultrasonic signal propagates through the medium under investigation and reflects off interfaces, such as boundaries, between adjacent tissue layers. Scattering of the ultrasonic signal refers to the deflection of the ultrasonic signal in many directions by interfaces that are much smaller than the ultrasonic wavelength. Attenuation of the ultrasonic signal is the loss of ultrasonic signal as the signal travels. Reflection of the ultrasonic signal is the bouncing off of the ultrasonic signal from an object (e.g., a vessel wall) that is similar in size or larger than the ultrasonic wavelength. Transmission of the ultrasonic signal is the passing of the ultrasonic signal through a medium. As it travels, the ultrasonic signal is scattered, attenuated, reflected, and/or transmitted. The portions of the reflected and/or scattered ultrasonic signals that return to the transducers are detected as echoes.
In the ultrasound art, steering refers to changing the direction of an ultrasonic beam. Aperture refers to the size of the transducer or group of transducer elements being used to transmit or receive an ultrasonic signal. The transmit aperture is the size of the transducer or group of transducers used to transmit an ultrasound signal, and receive aperture is the size of the transducer or group of transducers used to receive an ultrasound signal. Apodization refers to applying a weighting profile to the signals across the transducer aperture to produce ultrasound beams with reduced sidelobe spreading. Electronic focusing refers to applying relative time and/or phase shifts to signals across the transmit or receive transducer array elements to account for time-of-flight differences.
A conventional process of producing, receiving, and analyzing an ultrasonic signal (or beam) is called beam forming. The production of ultrasonic signals optionally includes apodization, steering, focusing, and aperture control. In conventional beamforming, RF echo data is acquired across a transducer array and processed to generate a one-dimensional set of echolocation data In a typical implementation, a plurality of ultrasonic beams are used to scan a multi-dimensional volume.
In electronic focusing, the transmit aperture of the transducer is apodized and electronically focused to form a transmit beam, and a large number (typically over 100) of transmit beams are generated and steered (as for a sector scan) along different scan lines to cover the entire scan plane.
To create two-dimensional (2D) B-mode images of tissue and 2D color flow images of moving blood, the echoes are detected and converted into electronic signals by the receive transducer aperture elements. Through parallel electronic channels the signals in different frequency bands are subject to amplification, digitization, frequency downshifting, apodization, focusing, steering and other filtering operations in order to generate echolocation data along the scan direction. Depending on the front-end architecture design, the order in which the above processing are performed may vary. Any processing such as amplification, which occurs before digitization would be implemented using analog electronic circuits.
In most ultrasound receivers, the echo signals are shifted down in frequency by means of frequency mixers and filters, to generate the in-phase (I) and quadrature (Q) signals which are centered at a much reduced RF frequency, but contain the same information bandwidth as the RF signals. For color flow processing, the RF spectrum is shifted down to baseband and the resultant I/Q components are also referred to as baseband components. The advantage of using I/Q echo components is that they can be digitized and processed at much lower sampling rates due to their reduced Nyquist bandwidths.
The I/Q echo data is furnished to the B-mode and color flow image processors for amplitude and motion detection respectively. For B-mode, the echo amplitude can be computed simply by taking the square root of I2+Q2. The detected data from different transmit events are compiled into 2D acoustic data sets, which are then converted by the scan-converter into X-Y format of, for example, 480xc3x97640 pixels (picture elements), for video display.
In B-mode imaging, the brightness of a pixel is based on the detected echo amplitude, whereas in color flow imaging, the color of a pixel is based on mean velocity and/or power of detected echoes from moving parts of the medium under investigation. In color flow imaging, the color flow image is formed within a region of interest (ROI), which is over-written onto the B-mode image by a video image processor such that, for example, the composite image depicts blood flow within the ROI according to a color scale, while surrounding stationary tissues are displayed in a gray-scale.
In color flow imaging, for each scan line within the user-specified ROI, a set of transmit beams are fired repeatedly at some pulse repetition frequency (PRF), in order to detect moving blood. Fundamentally, any motion of the medium under investigation relative to the ultrasound transducer produces the well-known Doppler effect in which the frequency of the reflected echo is shifted from that of the transmit frequency fo by an amount fd that is proportional to the target speed in the direction of the ultrasonic beam. That is, the frequency of the reflected signal is fo+fd. A medium under investigation that is moving towards the transducer will compress the incident ultrasonic wave thereby producing a positive Doppler frequency shift in the reflected echo. Conversely, a target that is moving away from the transducer will produce a negative Doppler frequency.
Mathematically, the Doppler frequency shift fd can be derived as follows. Suppose the target (e.g. red blood cells) is moving at velocity v, which makes an angle xcfx86 with respect to the sound beam. This means that the target velocity component in the direction of the sound waves is u=v cos(xcfx86). Over a short time interval xcex94t, the change in round-trip distance between the target and the ultrasonic source (transducer) is xcex94d=2uxcex94t. Assuming u less than  less than c (speed of sound), xcex94d translates into to a phase shift xcex94xcex8=2xcfx80xcex94d /xcex, where xcex=c/fo is the ultrasound wavelength. Hence, the Doppler frequency shift induced by target motion is
fd=xcex94xcex8/(2xcfx80xcex94t)=2fo(u/c)=2fo(v/c)cos(xcfx86).
In practice, Doppler frequencies due to blood flow in humans and animals are in the kHz range, which are much smaller than the transmit radio frequencies. A minimum of two transmit signals must be fired along each scan line in order to generate a measurable phase change between the returning echoes from two successive firings. At a Pulse Repetition Interval (PRI)=1/Pulse Repetition Frequency (PRF), the phase change between echoes from two successive firings is xcex94xcex8=2xcfx80fd/PRF. Color image processors create a color velocity image by estimating xcex94xcex8 for each acoustic point, and then converting it into either Doppler frequency or velocity unit, which is then mapped to a 2D pixel display image according to a color versus velocity or Doppler frequency scale.
Since the instantaneous phase of the returning RF echo from each transmission of an ultrasonic beam is equivalent to the angle of its baseband I and Q components; i.e., xcex8=tanxe2x88x921(Q/I), the phase change over two successive transmit and receive cycles is simply given by
xcex94xcex8=tanxe2x88x921(Q1/I1)xe2x88x92tanxe2x88x921(Q2/I2).
In practice, there are two significant challenges in producing a real-time color flow image. First, the echoes returning from moving blood are generally very weak, so typically a packet of several or more transmit and receive cycles are needed to detect flow along a particular scan line. Color Doppler velocity estimation then involves computing the mean phase change  less than xcex94xcex8 greater than  per PRI from the received echo signals. As will be defined in a later section, a common method of estimating  less than xcex94xcex8 greater than  is to evaluate the first-ordered autocorrelation function of {In,Qn} over the transmit packet (n=1, 2, 3 . . . ) for each acoustic point in the medium under investigation. In other words the autocorrelation is between all possible pairs of {In,Qn} and {Im,Qm} at the same position, where n and m represent different time indices within a color Doppler data packet.
The second practical challenge stems from the fact that the tissue medium, and especially bones and tissue layers that comprise the vessel walls of the insonified blood vessel, often produce very strong reflections that are orders of magnitude larger than the backscattered signals from blood. Without first removing the clutter, the I/Q data analysis would be dominated by clutter effects and will not reflect the desired flow signal properties. To compound this problem, the reflecting structures in the medium under investigation (such as the body) are often moving at low velocities (due to breathing and/or cardiac motion, for example), which means the corresponding clutter signals may also contain Doppler frequency components or phase changes that can register as xe2x80x9ccolor flashesxe2x80x9d in the color flow image.
In order to provide a common framework for understanding the clutter problem, and the new and existing solutions, it is helpful to visualize (FIG. 1) the flow signal component and any unwanted DC or low-frequency clutter component in the Doppler frequency domain (even though color flow image processors don""t actually need to compute the Doppler frequency spectrum from the input I/Q data.)
FIG. 1 is a plot 100 of spectra of clutter and flow components, and a High Pass Filter (HPF) frequency response. FIG. 1 shows frequency spectra of color flow I/Q data having a clutter spectrum 102, and a flow signal spectrum 104, and a HPF frequency response (HPF1) 106 plotted on an x-axis 108 and y-axis 110. X-axis 108 is in units of Hertz (Hz), and y-axis 110 is in units of decibels (dB). The signal spectra 102 and 104 are normalized in magnitude such that the clutter spectrum peak is 0 dB. For the HPF response HPF1106, 0 dB means the filter gain is unity at that particular frequency. In general, clutter spectrum 102 could be the frequency spectrum of a stationary object (such as a bone) and/or of the relatively slow motion of other objects within the medium under investigation. For example, clutter spectrum 102 in FIG. 1 represents the reflected signal that contains a very low Doppler frequency spectrum ranging from 0 to about 30 Hz, with the peak at about 15 Hz. Flow spectrum 104 represents the frequency spectrum of a typical flow from a fluid such as blood within a medium under investigation.
In the body, tissue motion may be caused by breathing, cardiac motion, or simply transducer motion due to the operator, which are generally of a lower speed than blood flow in detectable vessels. The average power of the clutter may be up to 40 dB stronger than the flow signal in the time domain, so that the peak of clutter spectrum 102 maybe 50 dB higher than that of flow spectrum 104.
Three approaches to clutter removal in conventional color flow imaging include using a High Pass Filter (HPF), using a Fast Fourier Transform (FFT), and using a clutter model. These are summarized as follows:
When using a HPF, having for example frequency response HPF1106, the ultrasound signal from the transducer is passed through a linear high pass Finite Impulse Response (FIR) or Infinite Impulse Response (IIR) filter in the time domain. A high pass filter response such as HPF1106 shows which frequency band is attenuated, and which frequency band is allowed to pass. The amplitude of the signal component at a given frequency is reduced by the HPF1106 response (e.g. xe2x88x9250 dB) at that frequency. For example at 460 Hz, the signal amplitude is reduced by xe2x88x928 dB or about 40%. In the frequency domain, clutter spectrum 102 tends to concentrate around the lowest frequency bins. HPF1106 is effective for rejecting the relatively low frequency clutter spectrum 102.
In FIG. 1, HPF1106 corresponds to the frequency response of a filter whose xe2x88x9250 dB stopband edge is at a normalized frequency (i.e., a frequency divided by PRF/2) of 10%.
When using an FFT, the FFT is taken of basebanded I/Q data samples and then the power in the lowest frequency bins is set to zero. This can be viewed as frequency-domain filtering, or a form of clutter modeling in which the data is projected onto a series of complex exponentials of various Doppler shift frequencies.
When using a clutter model (see U.S. Pat. No. 5,228,009, incorporated herein by reference) the part of data samples that represent the clutter (e.g., the time domain representation of clutter spectrum 102) is projected onto a set of low order orthonormal basis functions (e.g., Legendre polynomials), thereby forming a model or fitted curve of the clutter. Then the sum of projections (i.e., the fitted curve) is subtracted from the data samples thereby subtracting the modeled clutter from the data. Using the low frequency components of a frequency spectrum (which may have been obtained via an FFT) to represent the clutter is a special case of clutter modeling.
In all the above three approaches, appropriate parameters are selected that depend on the tissue velocity, such that only the clutter and not the blood flow signal is subtracted from the data or suppressed. Choosing the appropriate parameters is equivalent to choosing the cutoff frequency (and the order) of the high pass filter or to selecting the highest order for the basis functions in the clutter modeling approach. If the filter cutoff is always set high to reject the highest possible clutter frequencies, then some low flow signals may not be detected well. If the filter cutoff frequency is always set low, color flashes may result in the image whenever significant clutter power due to tissue motion is present above the cutoff frequency. Hence, various adaptive clutter suppression techniques have been proposed in the prior art as follows.
U.S. Pat. No. 6,309,357 uses two or more clutter filters of different frequency responses to process each color data packet in parallel and then select or combine the best results for velocity estimation. U.S. Pat. Nos. 5,349524 and 5,445,156 estimate clutter velocity and bandwidth using the standard autocorrelation method, and then either shift the clutter frequency down to DC before high pass filtering, or apply a complex filter with a notch at the estimated clutter frequency. U.S. Pat. No. 5,349,525 estimates the clutter velocity and bandwidth and excise the corresponding bins in the FFT spectrum of the data. U.S. Pat. No. 5,228,009 starts with the lowest order of basis functions (mean removal), computes and subtracts projections from the data onto the basis functions, and then checks the residual energy. The process is repeated for the next lowest order until residual energy falls below a predefined threshold.
In U.S. Pat. Nos. 5,349524, 5,349;525, and 5,445,156, the velocity estimation is performed twice for each packet or acoustic point in the color flow image. Specifically, the velocity estimation is performed the first time to estimate mean clutter velocity, and the second time to estimate the mean flow velocity after the clutter has been subtracted out. Also, the standard autocorrelation method involves a division and an arctangent operation, which are computationally expensive. In U.S. Pat. No. 5,228,009, as the order of filtering increases, the amount of computations required for computing the projection onto the basis function based on the least squares criterion also increases and is quite computationally intensive.
In U.S. Pat. No. 5,782,769, a high pass filter suitable for clutter from non-moving sources is applied prior to velocity estimation, and a separate nonlinear xe2x80x9cmin-maxxe2x80x9d filter is used across image frames to suppress color flashes that may result from tissue motion. While it is true that in general, color flashes can be rejected by such post processing or other simpler threshold techniques based on the total power and mean velocity estimates, if a weaker flow signal is also present, it will likely get thrown out with the flash artifact.
An adaptive clutter removal method is provided that can suppress color flash artifacts without compromising low flow detection. The method utilizes an adaptive high pass filter which is applied to the in-phase (I) and quadrature (Q) components of a given flow data packet prior to flow parameter estimation. The clutter may be detected and the cutoff frequency may be adjusted iteratively, may be adjusted on a point-by-point or region-by-region basis, and may be adjusted dynamically or in real time, while collecting the data for other acoustic points. For example, in an embodiment while data for one frame is imaged, a second frame is filtered, and a third frame is collected.
In an embodiment two criteria are used to detect the clutter, which are the magnitude of the total signal power being higher than a given threshold and the mean Doppler frequency (proportional to mean velocity) being lower than a given clutter frequency threshold. Ordinarily, calculating the mean frequency or phase change entails taking an arc tangent of the real and imaginary parts of the first order autocorrelation function of the I/Q data. However, determining whether the mean frequency change is less than a threshold does not require actually calculating the mean frequency change. Instead, in an embodiment, a check is performed to see if the real part times a multiplicative factor is greater than the absolute value of the imaginary part of the first order autocorrelation function. The multiplicative factor is determined by the ratio of a clutter frequency threshold to the pulse repetition frequency.
Although the method is equally applicable to I/Q flow data derived from 2D or 3D volume scanning based on conventional line-by-line beam forming, the preferred embodiment, for which this is a continuation-in-part, is referred to as area forming which is enabled by broadbeam technologies. Broad beam technologies refer to systems and methods that include or take advantage of techniques for generating a broad ultrasound beam from a single ultrasonic pulse, and analyzing the returning echoes to yield multidimensional spatial information.
The receive system architecture for the preferred broad beam system utilizes software running on a set of Digital Signal Processing (DSP) chips to perform all of the image processing operations after area forming. Although the adaptive clutter filter can also be implemented in hardware, the programmability and scalability of DSP chips provide an ideal match to the algorithmic nature of the adaptive clutter filter. For example, to achieve more optimal clutter filter performance, the number of iterations and high pass filter choices can be increased in concert with technological advances in the DSP chip family.
Area forming is the process of producing, receiving, and analyzing RF echoes from a medium under investigation, that optionally includes apodization, steering, focusing, and aperture control, where a two-dimensional set of echolocation data can be generated using only one ultrasonic beam. Nonetheless, more than one ultrasonic beam may still be used with the area forming even though only one is necessary. Area forming is a process separate and distinct from beam forming. Area forming may yield an area of information using one transmit and/or receive cycle, in contrast to beam forming, which typically only processes a line of information per transmit and/or receive cycle.
Volume forming is the process of producing, receiving, and analyzing an ultrasonic beam, that optionally includes apodization, steering, focusing, and aperture control, where a three dimensional set of echolocation data can be generated using only one ultrasonic beam. Nonetheless, multiple ultrasonic beams may be used although not necessary. Volume forming is a superset of area forming.
Multidimensional forming is the process of producing, receiving, and analyzing an ultrasonic beam that optionally includes apodization, steering, focusing, and aperture control. Using multidimentional forming a two or more dimensional set of spatial echolocation data can be generated with only one ultrasonic beam. Nonetheless, multiple ultrasonic beams may be used although not necessary. Multidimensional forming optionally includes non-spatial dimensions such as time and velocity.

System and method for adaptive clutter filtering in ultrasound color flow imaging


A system and method for inspecting a structure having a coating on at least one surface are provided. The system includes at least one ultrasonic sensor positioned proximate to the structure. Each sensor is capable of transmitting a shear wave toward the structure and receiving return signals in response thereto, wherein the shear wave includes at least one reference beam and at least one interrogating beam. The system further includes a data acquisition system in communication with the sensor for generating information indicative of the coating based on at least one return signal associated with the reference beam.

1) Field of the Invention
The present invention relates to non-destructive inspection and, more particularly, to non-destructive inspection of a structure for defects using an inspection system in conjunction with a data acquisition system.
2) Description of Related Art
It is frequently desirable to inspect structures to identify defects or flaws, such as cracks, discontinuities, voids, or porosity, which could adversely affect the performance of the structure. Non-destructive inspection ("NDI") of structures is typically utilized to thoroughly examine a structure without harming the structure or requiring significant disassembly. Non-destructive inspection is typically preferred to avoid the schedule, labor, and costs associated with removal of a part for inspection, as well as avoidance of the potential for damaging the structure. NDI is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, NDI is commonly used in the aircraft industry to inspect aircraft structures for any type of internal or external damage to, or defects (flaws) in, the structure. Inspection may be performed during manufacturing or after the completed structure has been put into service, including field testing, to validate the integrity and fitness of the structure.
Various types of sensors may be used to perform NDI. One or more sensors may move over the portion of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo (PE), through-transmission (TT), or shear-wave sensor may be used to obtain ultrasonic data, such as for thickness gauging, detection of laminar defects and porosity, and/or crack detection in the structure. Resonance, pulse-echo, or mechanical impedance sensors are typically used to provide indications of voids or porosity, such as in adhesive bondlines of the structure. High resolution inspection of aircraft structure is commonly performed using ultrasonic testing (UT) to provide a plan view image of the part or structure under inspection. Data acquired by sensors is typically processed and then presented to a user via a display as a graph of amplitude of the received signal. To increase the rate at which the inspection of a structure is conducted, a scanning system may include arrays of inspection sensors, i.e., arrays of transmitters and/or detectors.
Various coatings, such as paint, primer, adhesive layers, or corrosion inhibiting compounds, may be applied to metallic structures, complicating NDI of the structures. Generally, NDI techniques used on thicker structures are incompatible and unreliable for inspecting thinner structures having coatings. Thin materials may have relatively small flaws that would be acceptable in a thicker structure but that have a disproportionately large affect on the quality of a thin structure and, therefore, are desirably detected. With the detection of such smaller flaws, more noise and other spurious signals are also detected and analyzed which can lead to false results and render the NDI technique unreliable. Moreover, the complications upon NDI posed by a coating are also generally more pronounced with respect to thinner structures.
Generally, a robust NDI technique has an acceptable signal-to-noise ratio (i.e., 3-to-1) and is capable of identifying flaws, at least larger flaws, rather than spurious signals. However, a robust NDI technique may miss some smaller flaws since the signals generated by the smaller flaws may be considered noise. A sensitive NDI technique has a lower signal-to-noise ratio so as to identify smaller flaws, but is more prone to identify spurious signals as being indicative of a potential flaw since the spurious signals will sometimes exceed the signal threshold that has been established to define a flaw. Adding gain to a sensitive NDI technique in an attempt to detect smaller flaws amplifies spurious signals, as well as flaws, which leads to false rejections of structures. Conversely, reducing gain to a sensitive NDI technique provides a more robust inspection because less false signals will be identified to be indicative of flaws, but the inspection is less sensitive and not as many flaws, especially smaller flaws, will be identified.
Previous NDI techniques determined the attenuation of the worst case coating condition, generally the thickest possible coating of the most attenuative material, and compensated for the attenuation by adding gain. However, in practice this often leads to excessive gain settings on a structure that does not have the worst case coating condition. Excessive gain settings to offset attenuation created by a coating magnify the noise level, causing irrelevant signals to be mistaken for defects, particularly for thinner structures. As such, unwarranted repairs and a loss of confidence in the inspection technique may result. Moreover, paint stripping of the structure prior to an inspection due to the difficulty in inspecting thinly coated metallic structures has been an expensive alternative. However, without a reliable inspection system, this may be one of the few alternatives for inspecting the coated structure.
One type of NDI uses ultrasonic shear wave techniques. However, NDI using ultrasonic shear wave techniques causes several problems when inspecting thin structures having a coating applied thereon. The coating dampens the ultrasonic beam entering the structure as the ultrasonic beam bounces between opposing surfaces of the structure, which attenuates the ultrasonic energy until there is insufficient ultrasonic energy to detect flaws. In addition, ultrasonic shear waves entering the structure can convert to less well-behaved modes resulting in unpredictability in locating flaws within the structure. Moreover, modifying the coating thickness generates nonlinear attenuation effects (i.e., no change, small change, or large change in attenuation) such that modeling these effects is difficult. Without an accurate model, it is more difficult to use a gain compensation formula as would otherwise be employed by ultrasonic inspection techniques to account for coating thickness variations. Such a formula would also require a priori knowledge of the coating thickness on the structure to be tested, which is generally not known.
It would therefore be advantageous to provide an inspection system that is more reliable for inspecting thin structures having a coating. It would also be advantageous to provide an inspection system that is capable of compensating for attenuation and adjusting gain to compensate for a coating present on the structure. It would be further advantageous to provide an inspection system that is practical and economical.

Inspection system for inspecting a structure and associated method


A composite optical lens is disclosed. The composite optical lens includes a concave bottom surface adapted to receive light, reflective surface adapted to reflect the received light, and optical surface through which the reflected light leaves the optical lens. The concave bottom surface defines a concave cavity allowing placement of at least a portion of a light emitting device within the concave cavity. The concave bottom surface, the optical surface, or both may have predetermined optical finish to operate on the light such as diffusing or focusing the light. The reflective surface can be coated, designed, or both for total internal reflection effect.

The present invention relates to the field of packaging semiconductor devices, and more particularly to packaging light emitting diodes.
Light emitting devices (LEDS) such as light emitting diodes are often packaged within leadframe packages. A leadframe package typically includes an LED connected to thin metal leads where the LED and most of the leads are completely encapsulated within a plastic body. A part of the plastic body defines a lens. A portion of the leads connected to the LED extends outside the plastic body. The metal leads of the leadframe package serve as the conduit to supply the LED with electrical power and, at the same time, may act to draw heat away from the LED. Heat is generated by the LED when power is applied to the LED to produce light. The portion of the leads that extend out from the package body connects to circuits external to the leadframe package.
Some of the heat generated by the LED is dissipated by the plastic package body; however, most of the heat is drawn away from the LED via the metal components of the package. The metal leads are typically very thin and have small cross sections. For this reason, capacity of the metal leads to remove heat from the LED is limited. This limits the amount of power that can be sent to the LED. This, in turn, limits the amount of light that can be generated by the LED.
To increase the capacity of an LED package to dissipate heat, in one LED package design, a heat sink slug is introduced into the package. The heat sink slug draws heat from the LED chip, thus increasing the heat dissipating capacity of the LED package. However, this design introduces free space in the optical cavity of the package that needs to be filled with a refractive-index-matching clear encapsulant within the package to extract light from the LED chip. Unfortunately, the volumetric expansion and contraction of the encapsulant typically exceeds that of the space that contains it. Hence, as the temperature rises, the encapsulant expands and overflows or is oozed out from the cavity through vent holes. Further, when it cools, the encapsulant contracts, creating a partial vacuum inside the cavity, and thus causing air or moisture to be sucked in. Sometimes, voids are formed inside the encapsulant or it delaminates from various components that it comes into contact with. This adversely affects the light output and reliability of the package. Furthermore, this design commonly includes a pair of flimsy leads which are typically soldered by a hot-iron. This ironing process is incompatible with the commonly used SMT (Surface Mount Technology) electronic board assembly processes.
In another LED package design, leads of the leadframe are made of different thicknesses in various shapes and configurations and extend beyond the immediate edge of the LED package body. The package body is molded with transparent thermoset plastic which usually serves as the encapsulation material for the package. These leads are typically thicker than the leads of the LEDS of the previous design. The thicker lead is utilized as a heat-spreader and the LED chip is mounted on it. This arrangement allows heat generated by the LED chip to dissipate through the thicker leads which are connected thermally to an external heat sink. Unfortunately, this design is inherently unreliable due to large difference in coefficient of thermal expansion (CTE) between the plastic body, the encapsulant and the leadframe materials. Thus, when subjected to temperature cycles of, say, −40 C to 120 C, most or all components of the LED package experience high thermal stresses, especially at contact points. This frequently results in cracking of the LED chips, delamination of plastic body from the leads, breaking of bond wires, or a combination of these problems. In addition, the extended leads increase the size of the LED package size and footprint. The increased size prevents mounting of the packages in a dense cluster on a PCB (printed circuit board) to generate bright light for certain applications, for example, for automobile lighting or for general illumination.
Another disadvantage of the current high power leadframe package designs is that the thick lead material cannot be stamped into a fine circuit for flip-chip or mounting of several LED chips that can be addressed independently for color control.
Consequently, there remains a need for an improved LED package that overcomes or alleviates one or more of the shortcomings of the prior art packages.

Composite optical lens with an integrated reflector


A loudspeaker includes: a frame; a yoke fixed to the frame; a magnet fixed to the yoke; a plate fixed to an upper surface of the magnet which is opposite to a surface of the magnet which is fixed to the yoke; a vibratable voice coil arranged in a first magnetic gap formed between the yoke and the plate; a diaphragm having an outer-edge portion joined to the voice coil; and a support member supporting the diaphragm in a vibratable manner, and composed of edges, one end of each edge being fixed to the frame. The plate is composed of: a flat-plate part fixed to the upper surface of the magnet, and having, at an upper surface thereof, a planar portion extending from the outer-edge portion up to a predetermined distance; and a protruding part disposed on the flat-plate part excluding the planar portion, and protruding toward the diaphragm.

In recent years, with the spread of personal digital assistants and the spread of living style in which individuals personally enjoy video and music, demands for inner-ear headphones with high sound quality are increasing. The shape of an auditory pore into which an inner-ear headphone is inserted greatly varies among users. Therefore, in order to improve wearing sensations of many users, a small-size loudspeaker with a high degree of freedom in case design is demanded. In addition, as for a loudspeaker used in a receiver of a hearing aid, a small-size loudspeaker is demanded which has a wide frequency band for sound output, and causes a user to feel less discomfort or unpleasantness when it is inserted in his/her auditory pore.
As an example of a loudspeaker used for an inner-ear headphone or a hearing aid, a balanced armature type loudspeaker which is a kind of a magnetic loudspeaker is widely used. Although the balanced armature type loudspeaker can be reduced in size, since the displacement amplitude of an armature that drives a diaphragm is small because of the structure of the loudspeaker, it is difficult to reproduce a low-pitched sound which needs a large amplitude.
As a prior art literature relating to the present disclosure, Patent Literature 1 has been known, for example. Patent Literature 1 discloses a small-size electrodynamic loudspeaker capable of reproduction of low-pitched sound. In the loudspeaker, a support member that supports a diaphragm in a vibratable manner is composed of a plurality of edges, and a magnetic fluid fills a space between a voice coil and a plate, in a magnetic gap.

Loudspeaker, inner-ear headphone including loudspeaker, and hearing aid including loudspeaker

PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.


A steam system is provided with a steam trap including a Y-fitting having a single fluid inlet, a primary outlet for returning water to a boiler, and a secondary outlet for testing only, and a main valve in series with the primary outlet. Connected to the secondary outlet are an auxiliary valve and a replaceable test jet downstream of the auxiliary valve, the test jet terminating the auxiliary branch. Test jets of various sizes may be installed, and outflow through each visually observed or measured, until an optimum size is arrived at. A main jet of a corresponding size is then installed in the main valve.

This invention relates generally to pipe fitting, and more particularly to an improved steam trap for removing condensate from steam lines.
The inverted bucket condensate traps of older systems were replaced by fixed-orifice devices, exemplified by U.S. Pat. 3,715,870 and 3,877,895, placed directly in a steam line, to separate water from steam, and let mainly the water only return to a boiler. The orifice size, even if specified correctly initially, may change over the years due to corrosion. By that time, the manuals may have been lost, so trial and error is necessary to find the correct orifice size. Too large or too small an orifice results in system inefficiency. The need to change orifices was addressed by U.S. Pat. No. 4,426,213, which provided a standard device into which various-sized inserts could be installed. While this represented an improvement over fixed orifice plates, it was necessary to disassemble the steam line in order to change inserts.
To avoid the need to separate the steam line in order to install a new fitting, it was later proposed to include a ball valve in the system, and place a removable jet or orifice in the ball. A plug was provided in the valve housing so that, with the valve temporarily closed, the jet could be removed and replaced, without having to break down the line. Even with this arrangement, though, some experimentation was required, since one could not see flow through the valve, and had to make measurements of some kind, with the system stabilized, in order to determine whether the proper sized jet had been installed at each location.
Since large systems may have such orifices at hundreds of locations, it is important to make fitting an orifice a simple matter requiring a minimum of experimentation and labor.


An image display method, a display system, and a computer-readable storage medium are disclosed. The image display method includes: acquiring a first image; determining a first region and a second region in the first image; performing a first rendering algorithm on the first region in the first image and performing a second rendering algorithm on the second region in the first image, so as to obtain a second image, where a rendering resolution of the first rendering algorithm is greater than a rendering resolution of the second rendering algorithm; and displaying the second image.

Virtual Reality (VR) is a computer simulation technology which may create and experience a virtual world. The VR technology may be applied to many fields such as medical science, amusement, games, military astronautics, exhibitions and demonstration, or the like.
With development of display technologies, demands from human for a resolution of a display device raise increasingly. A product with a high resolution (such as a 4K resolution) requires a relatively large data transmission amount, thereby reducing a refresh rate of an electronic product. The VR technology is strict in the resolution, refresh rate, or the like, for example, the VR technology requires the refresh rate up to more than 90 Hz, so as to ensure that a user would not feel dizzy. Therefore, the data transmission amount has become an urgent problem in the VR technology.

Image display method, display system and computer-readable storage medium

BEIJING BOE OPTOELECTRONICS TECHNOLOGY CO., LTD.


A wireless device comprises a first wireless transceiver, a second wireless transceiver, and control logic. The control logic is coupled to the first wireless transceiver and the second wireless transceiver. The control logic is configured to determine whether to transmit protection frames (e.g., clear-to-send 2 self frames) based upon sequence numbers in frames received from another device.

As wireless technologies proliferate, mobile wireless devices incorporate a multiplicity of different wireless standards. For example, a cellular telephone can accommodate a cellular network (e.g., Universal Mobile Telecommunications System), a wireless local area network ("WLAN"), such as IEEE 802.11, and a wireless personal area network ("WPAN") (e.g., BLUETOOTH). Including WPAN access makes utilization of a wireless device more convenient by allowing use of wireless headsets and other short-range wireless appliances. Such phones are sometimes referred to as "smart phones."
Mobile wireless devices are sometimes capable of accessing multiple exclusive wireless networks. Such wireless networks can occupy adjacent or overlapping parts of the frequency spectrum. For example, both BLUETOOTH and IEEE 802.11b/g/n utilize the 2.4-2.5 GHz band. Access to the networks can be coordinated via time multiplexing or frequency multiplexing to reduce performance degradation caused by collisions that may occur when the networks are simultaneously accessed. However, such multiplexing is often at the cost of shorter medium time available to each radio and thus lower performance, as a radio may be blocked from transmitting or receiving packets temporally to avoid collisions.
One technique to coordinate the use of the wireless medium between different wireless protocols that may interfere with each other is through the use of a frame such as the CTS-2-Self (C2S) frame (CTS stands for Clear To Send). A C2S frame commands all other wireless stations on a wireless local area network (WLAN) that receive the C2S frame to avoid transmitting on the wireless network for a period of time indicated in the C2S frame itself. A C2S frame thus places a WLAN in a non-communication mode. Repeated transmissions of C2S frames therefore reduce the performance of a WLAN.

Selective protection based on sequence numbers in coexisting networks


Methods and apparatus for obtaining a vibrational circular dichroism (VCD) image using a discrete frequency infrared (DFIR) microscope are disclosed. The method includes generating a pulsed laser beam comprising a spectral frequency, which may be tunable; modulating the laser beam to generate circularly polarized light; illuminating a sample and collecting, and detecting an optical signal transmitted or transflected from the location of the sample. The detected signal is demodulated at, for example, both the pulse frequency and the sum or difference of the pulse frequency and the modulating frequency to obtain an intensity value that correspond to the absorbance, and a polarization-dependent value that corresponds to the VCD. Other configurations of the apparatus may be employed to measure VCB and VLD.

Infrared (IR) spectroscopic imaging has undergone innovations in recent years that have advanced to be used as an analytical technique. IR spectroscopic imaging is a non-destructive approach that directly images the distribution of chemical composition of samples. Contrast is derived from molecular structures which absorb optical frequencies that are resonant with the vibrational modes of the comprised functional groups. Each peak in the absorption spectrum may correspond to a characteristic, which together can be used for the identification and classification of spatially-and spectrally-complex samples. While IR vibrational frequencies span the mid-IR spectral range (for example, a wavenumber range of 800-4000 cm−1), the fingerprint region (for example, a wavenumber range of 800-1800 cm−1) has traditionally been critical for biological and polymeric sample identifications.
Chirality is an extrinsic geometric property, wherein the molecule forms a non-superimposable mirror image with its enantiomer. Such chiral pairs, also known as stereoisomers, are typically characterized as either right-handed or left-handed depending on the molecular structure. Many biomolecules essential for life are chiral and, in many cases, only one of the stereoisomers is typically effective for specific biological processes while its non-superimposable complement is either inactive, or at times, highly toxic. Further, in addition to chirality arising from structural arrangements, chirality of a molecule can also be conformational. Understanding chirality of tissues or physical samples is an important aspect of the discipline of biomedical sciences as well as other scientific fields. The composition as well as structural and/or conformational chirality plays a dominant role in the efficacy and kinetics of the molecular interactions. Understanding biological processes, specifically related to drug metabolism and disposition, informs purification and testing aspects of drug development pipelines, where about 56% of pharmaceuticals currently on the market are chiral and about 88% comprised of equimolar racemic mixtures, including common drugs such as Ibuprofen, Propranolol, and Pindolol. Moreover, the approved drugs by FDA for the recent COVID-19 pandemic, such as Remdesivir and its various counterparts, are also chiral. While absorption of light in the mid-infrared (IR) spectral region provides information about the molecular composition of a sample, the differential absorption of left circularly polarized (LCP) and right circularly polarized (RCP) light provides a way of quantifying its chirality, at least empirically. Specifically, Vibrational Circular Dichroism (VCD) spectroscopy optically measures this difference in attenuation (i.e. circular dichroism, CD), providing an accurate and convenient method to estimate chirality.
Over the last two decades, the availability of Density functional theory (DFT) models and instrumentation to compute and evaluate VCD spectra has furthered our scientific and analytical understanding of this concept. However, the experiments have largely been of homogeneous samples. Most often, these samples are aqueous solutions with measurements conducted in transmission mode.
A VCD spectrometer is an infrared spectrometer that can measure the CD associated with infrared vibrational absorption bands, by measuring the differential absorption of left- and right-circularly polarized infrared light. The signals are relatively small compared with the corresponding IR signals. Anisotropy factors ΔA/A of 10−4 to 10−5 are typical, where A is the absorbance and ΔA is the difference in absorbance for left- and right-circularly polarized light.
The simplest of these instruments is the dispersive VCD spectrometer. Other techniques involving Fourier transform (FT) VCD spectrometers are more complex, but share the same underlying conceptual basis as the dispersive VCD spectrometer.
Originally built around dispersive spectrometers, current VCD instruments rely on interferometry and the throughput and multiplex characteristics of FT-IR spectrometers. However, due to the small optical signal obtained, the FT-IR technique typically requires relatively long acquisition time, typically ranging from 30 min to several hours or more, to collect sufficient co-averages and achieve a signal-to-noise ratio commensurate for analysis. In particular, quantitative estimates of fractional secondary structure content and site-specific information for biopolymers remains a significant challenge with FT-IR spectrometers for VCD analysis. The weak, broadband optical source is spatially distributed over a large area degrading the performance of multipixel detectors and imaging spectrometers show a reduction in signal to noise ratio (SNR) compared to non-imaging spectrometers. The limited sensitivity of FT-IR imaging and long acquisition times needed for VCD is a combination potentially impractical of acquiring reliable measurements.
Uncompensated chromatic distortions may compromise the accuracy and repeatability of results. Measurements are made over large band of contiguous wavelengths rather than at specific frequencies of morphological interest. Furthermore, the long acquisition time and focal volume per measurement makes it difficult to perform sufficiently high throughput spatially resolved mapping for the purpose of generating micro- and macroscopic images.

Vibrational circular dichroism infrared spectroscopic imaging microscope

The Board of Trustees of the University of Illinois


A steam turbine (10) having an inner casing (11), in which a rotor (12) that can rotate about an axis (13) is arranged, a steam passage (14) being formed between the rotor (12) and the inner casing (11), in which steam passage there is a multi-stage arrangement of guide vanes (16) secured to the inner casing (12) and rotor blades (17) secured to the rotor (12), in which arrangement hot steam coming from an inlet (15) undergoes work-performing expansion. In a steam turbine of this type, the thermal loading of the rotor and/or inner casing, in particular when starting up, is reduced by virtue of the fact that at least in the steam passage (14) plate-like protective shields (18, 19, 20), which protect the surface of the rotor (12) or inner casing (11) beneath them from the direct action of the hot steam flowing through the steam passage (14), are arranged parallel and close to the surface of the rotor (12) and/or parallel and close to the inner surface of the inner casing (11).

1. Field of the Invention
The present invention deals with the field of steam turbines.
2. Brief Description of the Related Art
Steam turbine rotors and inner casings, when the turbine is starting up, are subject to high thermal stresses, in particular in the region of the inlet, from the relatively hot steam flowing past them, and these stresses limit the service life of the components and the start-up time.
Therefore, various proposals have already been made in the past as to how the rotors and inner casings of steam turbines can be cooled in the critical areas without additional, external devices.
U.S. Pat. No. 4,551,063 has disclosed a medium-pressure steam turbine in which cooling steam is removed at the outlet of the high-pressure turbine prior to the reheating and is routed out of an annular space located outside the steam passage, via axial bores in the rotor, into the first two stages of the turbine, where it is fed into the steam passage from the blade roots. A solution of this type can only be employed for high-pressure turbines but not for medium-pressure turbines.
In the case of a combined high-pressure/medium-pressure steam turbine disclosed by U.S. Pat. No. 5,149,247, the stator is divided into an external stator and an internal stator, which are separated from one another by an intermediate space. For cooling purposes, cooling steam is removed from the final stage of the high-pressure part and introduced into the intermediate space. A similar solution is also disclosed in U.S. Pat. No. 6,341,937. Neither solution prevents the whole of the inner stator being exposed to the live steam.
Finally, in U.S. Pat. No. 6,010,302, the rotor is provided with a central bore through which cooling steam which has been removed at the outlet of the high-pressure stage is routed. In this solution, cooling of the inner casing is not provided and is indeed not possible.


A measuring arrangement for fiber Bragg grating measurement points and particularly a measuring arrangement for two fiber Bragg gratings (FBG), wherein a first measurement point is subjected to tension and a second measurement point is subjected to pressure, or vice versa. The circuit arrangement includes a broadband light source, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, photodiodes and an optical delay element.

The Invention relates to a measuring arrangement for fiber Bragg grating measuring points and in particular to a measuring arrangement for two fiber Bragg gratings (FBG), with the first measuring point being subjected to tension and the second measuring point to pressure, or vice versa. Furthermore, the measuring arrangement should be inexpensive to manufacture and long-term stable.
Fiber Bragg grating sensors involve robust fiber optic measurement probes that are used in particular for high-resolution detection of strains. The measuring principle of such fiber Bragg grating sensors is based on the fact that a so-called fiber Bragg grating (FBG) is introduced in the direction of transmission of an optical waveguide for periodically changing the refractive index. This fiber Bragg grating acts like a frequency-selective filter, with the grating constants thereof being selected such that a very narrow-band intensity maximum is reflected as a peak when broadband radiating light is involved. The spatial spacing within the periodic sequence of the zones with different refractive index is decisive for the position (primary Bragg wavelength) of the intensity maximum. This is utilized for the use of measuring points with such fiber Bragg grating sensors preferably for the detection of strains. The position of the intensity maximum shifts, when a light guide is strained in the area of the periodic change of the refractive index. This shift in wavelength is a measure of the strain.
Various devices and methods are known from the prior art to measure the wavelengths or wavelength changes of the reflected intensity maxima and to determine the strain values therefrom.
With the so-called edge filter measuring method, the reflected light is guided across an optical filter, with the light transmission thereof changing with the wavelength. As a reflection peak changes its wavelength, the light intensity changes behind the edge filter, which can be measured using photodiodes. This method is simple, but has the disadvantages that it is only capable of evaluating a single fiber Bragg grating, but cannot illustrate a spectrum, and it shows substantial errors when exposed to scattered light.
In the so-called CCD charge-coupled device measuring method, the reflected intensity maximum is spectrally expanded and then projected onto a CCD line. The CCD line is read out and the wavelength of the reflection peaks is determined by association to the pixels of the CCD. This method can measure many fiber Bragg gratings on a fiber or waveguide but can also only illustrate the spectrum from only one fiber. Another limitation is that this method can only be operated with silicon CCDs at a reasonable cost. This means a restriction to the wavelength range around 800 nm. The inexpensive components from the telecommunications sector are therefore also not usable for this application, since these preferably operate in the wavelength range around 1550 nm.
Moreover, a measuring method with a tunable laser is known for detecting the respective wavelength or wavelength changes on fiber Bragg gratings. This measuring method does not use a broadband laser diode to generate light, but a laser that emits its entire radiation energy in a very small bandwidth of <0.005 nm. The wavelength of the laser is changed linearly over a measuring range of, for example, 1500 nm to 1600 nm and back again from 1600 nm to 1500 nm in the form of a triangular function. There are strong reflections at the respective peak wavelengths of the fiber Bragg gratings. The entire reflected spectrum of a fiber or a waveguide can be determined with a photodiode, which measures the radiation energy currently being reflected back during the tuning of the laser. As a result of the available high spectral energy of the laser, which energy concentrates on the very small bandwidth, very large measurement-to-noise ratios can be achieved that allow the energy of the laser to be distributed over many waveguides or fibers, so that the number of measuring points that can be connected overall can be very high. The measuring accuracy of this method is hereby also very high. When using many measuring points with fiber Bragg gratings, this measuring method has the disadvantage that a relatively wide wavelength range has to be scanned one after the other, which can lead to wavelength changes during the scanning time period, particularly in the case of dynamic measurements with a temporally variable strain curve. This results in time-dependent deviations, which can result in errors when comparing the measurement results.
From the article by S. H. Yun, D. J. Richardson and B. Y. Kim Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser, Optics Letters, vol. 23, p. 843-845, 1998, it is known to generate a repetition frequency of wavelengths of a light beam linearly ascending in the form of a measuring ramp. In particular, a repetition frequency of the wavelength variations of 250 Hz is mentioned, which describes only one advantageous aspect in fiber Bragg grating sensors.
The invention is based on the object to provide an improved measuring arrangement for determining fiber Bragg grating strain measurement signals, which measuring arrangement has a simple structure and is therefore cost-effective. Furthermore, the measuring arrangement should be stable over the long time.

Interrogator for two fiber bragg grating measurement points


A method for cutting nonmetallic materials such as wood, wood composites, and graphite composites using a ceramic composite router of unitary construction is disclosed. The ceramic composite material is comprised of an alumina matrix reinforced with silicon carbide whiskers.

The machining of nonmetallic materials such as wood, wood composites, and graphite composites is one of the most important and widely used processes in manufacturing. One of the most important machining operations is the use of routers to cut grooves in or finish the edges of a workpiece.
Routers, which are just one type of cutting tool, are manufactured in a number of different shapes and sizes. A double fluted router is shown in FIG. I. The mode of operation is essentially the same for all routers. The router mounts in the spindle of a rotary tool head and rotates about its longitudinal axis. The workpiece is moved into the router in a direction perpendicular to the longitudinal axis of the router. The cutting edge of the router meets the workpiece and cuts a groove as the workpiece is advanced. FIG. II illustrates this machining process.
The width of the groove cut by the router is equal to the diameter of the router. The depth of the groove is equal to the depth of cut, i.e. the distance from the top of the workpiece to the tip of the router. The cutting speed is the revolutions per minute (rpm) of the router. The feed rate is the rate of advancement of the workpiece measured in inches per minute (ipm).
A variety of materials have been used or suggested for routers, including tool steels, high speed steels, cast non-ferrous alloys, metal bonded carbides, and ceramics. The performance of these materials is measured by productivity, tool life, and cleanliness of the cut.
Productivity, which is the rate of removal of material from the workpiece, may be calculated based on the depth of cut, the width of cut, and feed rate. These three factors in turn are dependent on the cutting speed Tool life is measured in terms of the amount of material removed before failure. Failure occurs either suddenly by breakage or gradually by abrasion, corrosion, or dulling of the cutting edge. The cleanliness of cut is determined by the smoothness of the machined surface and by lack of defects such as burn marks.
Tool steel, high speed steel and cast non-ferrous alloys are restricted to relatively low cutting speeds because they all have critical temperature limitations. Carbide materials, such as tungsten carbide, can run at cutting speeds much higher than those of the steels. However, the carbides are often run at relatively low feed rates because they are relatively brittle and are susceptible to impact breakage Also, tungsten carbide suffers high-temperature corrosion as a result of the chemical interaction with the workpiece at the high temperatures generated when cutting materials such as wood or medium-density fiberboard. See Steward, "High Temperature Corrosion of Tungsten Carbide from Machining Medium-Density Fiber Wood", The Carbide and Tool Journal, January-February, 1986.
Ceramic materials, such as alumina, can operate at much higher speeds and temperatures than conventional steel and carbide materials. Ceramics, however, are even more brittle than carbides and tend to fracture catastrophically and unexpectedly when subjected to impact. Thus, ceramics can be operated only at quite low feed rates
References relating to the use of ceramics as cutting tools include U.S. Pat. Nos. 4,063,908 ("Ogawa"), 4,323,323 ("Lumby"), 4,343,909 ("Adams"), 4,366,254 ("Rich"), 4,526,875 ("Yamamoto"), 4,543,343 ("Iyori"), 4,554,201 ("Andreev"), and 3,514,828 ("Wale"); Japanese patent numbers 5,848,621 ("Yajima"), and 6,005,079 ("Mitsu Metal"); United Kingdom patent number 2,157,282 ("Santrade"); and pending U.S. patent application Ser. No. 830,773 ("Rhodes").
Of all these references, only Mitsu Metal, Santrade, and Rhodes suggest the use of whisker reinforced ceramics in cutting tools; and neither of these three disclose a method for cutting nonmetallic materials such as wood, wood composites, and graphite composite using a rotter comprised of alumina reinforced with silicon carbide whiskers. Rhodes, which is perhaps the closest reference, claims generally cutting tools comprised of alumina reinforced with silicon carbide whiskers It also discloses the use of such tools to cut metal.
Wale describes the use of ceramic or tungsten carbide as a cutting insert mounted by brazing or with adhesive on the flutes of high speed steel end mill cutters. The inserts are backed entirely by the highspeed steel center member.
It has been suggested that silicon carbide fiber reinforced ceramic can be used in various machine parts, including heat exchangers, molds, ,nozzles, turbines, valves and gears. See Japanese patents nos. 59-54680 and 59-102681. Such disclosures, however, are not particularly pertinent to the invention described herein, since such parts are not primarily subjected to impact stresses as part of their normal service environment. No mention is made of improved toughness or impact resistance nor are such properties of interest in the articles described.
It has also been disclosed that fracture toughness in ceramics can be improved by incorporation of silicon carbide whiskers into the ceramics Papers by Becher and Wei have described mechanisms for increase in toughness as related to whisker content and orientation. See Becher and Wei, "Toughening Behavior in SiC Whisker Reinforced Alumina", Comm. Am. Cer. Soc. (September, 1984); Wei, "Transformation Toughened and Whisker Reinforced Ceramics", Soc. Auto. Engrs., Proc. 21st Auto. Tech. Dev. Mtg., 201-205 (March, 1984); and Wei and Becher, "Development of SiC-Whisker-Reinforced Ceramics," Am. Ceram. Soc. Bull., p. 298-304 (February 1985). See also U.S. Pat. No. 4,543,345 ("Wei").
Neither the cited papers nor the Wei patent suggest the use of alumina reinforced with silicon carbide whiskers for cutting nonmetallic materials. Also, while these references disclose that alumina reinforced wit silicon carbide whiskers shows increased fracture toughness and flexural strength, they do not disclose thermal shock resistance, or the ability of the material to withstand the combination of severe shear, tensile, and compressive stresses and repeated impact loading experienced by a router.

Method for cutting nonmetallic materials

Advanced Composite Materials Corporation