An automobile airbag deploys thanks to an accelerometer — a sensor that detects sudden changes in velocity. Accelerometers keep rockets and airplanes on the correct flight path, provide navigation for self-driving cars, and rotate images so that they stay right-side up on cellphones and tablets, among other essential tasks.
A team of researchers has developed an accelerometer a millimeter thick that uses laser light instead of mechanical strain to produce a signal. Although a few other accelerometers also rely on light, the design of the new instrument makes the measuring process more straightforward, providing higher accuracy. It also operates over a greater range of frequencies and has been more rigorously tested than similar devices.
The optomechanical accelerometer is much more precise than the best commercial accelerometers and does not need to undergo the time-consuming process of periodic calibrations. In fact, because the instrument uses laser light of a known frequency to measure acceleration, it may ultimately serve as a portable reference standard to calibrate other accelerometers now on the market, making them more accurate. The accelerometer also has the potential to improve inertial navigation in such critical systems as military aircraft, satellites, and submarines, especially when a GPS signal is not available.
The device consists of two silicon chips with infrared laser light entering at the bottom chip and exiting at the top. The top chip contains a proof mass suspended by silicon beams, which enables the mass to move up and down freely in response to acceleration. A mirrored coating on the proof mass and a hemispherical mirror attached to the bottom chip form an optical cavity. The wavelength of the infrared light is chosen so that it nearly matches the resonant wavelength of the cavity, enabling the light to build in intensity as it bounces back and forth between the two mirrored surfaces many times before exiting. When the device experiences an acceleration, the proof mass moves, changing the length of the cavity and shifting the resonant wavelength. This alters the intensity of the reflected light. An optical readout converts the change in intensity into a measurement of acceleration.
The optomechanical accelerometer detects accelerations as tiny as 32 billionths of a g, where g is the acceleration due to Earth’s gravity. That’s a higher sensitivity than other accelerometers now on the market with similar size and bandwidth. With further improvements, the device could be used as a portable, high-accuracy reference device to calibrate other accelerometers without having to bring them into a laboratory.
For more information, contact Ben P. Stein at
Kifuniko cha hewa cha gari hufunguliwa kwa sababu ya kipima-haraka - kiashiria kinachogundua mabadiliko ya ghafula ya mwendo. Accelerometers kuweka roketi na ndege juu ya njia sahihi ya ndege, kutoa urambazaji kwa ajili ya magari ya kujiongoza, na kugeuka picha ili kubaki upande wa kulia juu ya simu za mkononi na vidonge, miongoni mwa kazi nyingine muhimu. Watafiti wa Marekani wametengeneza kifaa cha kupima mwendo (accelerometer) ambacho hutumia mwangaza wa laser badala ya nguvu za mitambo kutengeneza ishara. Ingawa accelerometers nyingine chache pia hutegemea mwanga, muundo wa chombo kipya hufanya mchakato wa kupima kuwa rahisi zaidi, kutoa usahihi wa juu. Pia inafanya kazi katika masafa makubwa ya masafa na imepimwa kwa ukali zaidi kuliko vifaa kama hivyo. Accelerometer optomechanical ni sahihi zaidi kuliko accelerometers bora ya kibiashara na haihitaji kupitia mchakato wa muda wa calibrations mara kwa mara. Kwa kweli, kwa sababu chombo hicho hutumia mwanga wa laser wa mzunguko unaojulikana kupima kasi, inaweza hatimaye kutumika kama kiwango cha kumbukumbu cha kubeba ili kusawazisha accelerometers nyingine sasa kwenye soko, na kuwafanya kuwa sahihi zaidi. Vifaa hivyo vinaweza pia kuboresha uwezo wa kuongoza ndege za kijeshi, satelaiti, na nyambizi, hasa wakati ambapo ishara ya GPS haipatikani. Kifaa hicho kina chips mbili za silicon na nuru ya laser ya infrared inayoingia kwenye chip ya chini na kutoka juu. Chip ya juu ina proof wingi kusimamishwa na silicon beams, ambayo inawezesha wingi kusonga juu na chini kwa uhuru katika majibu ya kasi. kioo coating juu ya ushahidi wingi na kioo hemispherical kushikamana na chip ya chini fomu upasuaji optical. Mzunguko wa infrared ni chaguo kwa njia ambayo karibu inalingana na resonant mwendo wa cavity, kuwezesha mwanga kujenga katika nguvu kama bounces nyuma na mbele kati ya mbili mirrored nyuso mara nyingi kabla ya kuondoka. Wakati kifaa uzoefu kasi, ushahidi wingi hatua, kubadilisha urefu wa shimo na kuhamisha resonant urefu wa wimbi. Hilo hubadili nguvu ya nuru inayorudiwa. Mtazamo wa macho hubadilisha mabadiliko ya nguvu kuwa kipimo cha kasi. Inasemekana kwamba kipimo cha mwendo wa dunia (opto-mechanical accelerometer) kinaweza kugundua mwendo mdogo kama g ya bilioni 32 (g) - g ni mwendo wa mwendo unaosababishwa na nguvu ya uvutano wa dunia. Hiyo ni unyeti wa juu kuliko accelerometers nyingine sasa katika soko na ukubwa sawa na bandwidth. Kwa kuboresha zaidi, kifaa hicho kinaweza kutumiwa kama kifaa cha kumbukumbu cha kubeba, cha usahihi wa juu ili kusawazisha vipimo vingine vya kasi bila kulazimika kuvileta kwenye maabara. Kwa maelezo zaidi, wasiliana na Ben P. Stein katika