CLAIM OF PRIORITY 
     The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Ser. No. 61/142,177, filed on Dec. 31, 2008, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to microphones for hearing assistance devices, and more particularly to a microphone having an electroactive (conductive) polymer. 
     BACKGROUND 
     Hearing instruments generally offer both an omnidirectional and directional mode of operation. The omnidirectional mode is executed with a single omnidirectional microphone. The directional mode is often executed with a single, passive, differential microphone having both a front and rear acoustical conduit. The rear conduit may contain an acoustical resistance in the form of a screen or mesh that is engineered to provide a fixed sensitivity pattern such as a cardioid, hypercardioid, etc. Two separate microphones are thus used to provide the two modes of operation in a hearing instrument. There exists, therefore, a need for a system to provide both modes of operation in a smaller profile, at lower cost, with the option of adjusting the acoustical resistance by adjusting the orifice dimensions electromechanically. There also exists a broad class of materials referred to as electroactive, conductive, or conjugated polymers that can be electrically controlled to produce large linear, volumetric, or bending strains when configured as an actuator under a DC voltage. These electroactive polymers (EAP) can be configured to operate as an acoustical valve in a small, low-cost, omni and directional microphone system. 
     SUMMARY 
     The above-mentioned problems and others not expressly discussed herein are addressed by the present subject matter and will be understood by reading and studying this specification. 
     One embodiment of the present subject matter includes an apparatus, including: a microphone to convert sound into a signal; and an electrically adjustable shutter including conductive polymer, the shutter in acoustic communication with the microphone and configured to provide an adjustable acoustic resistance to the microphone. Variations include conductive traces adapted to apply an electric signal to the conductive polymer. In some embodiments a diaphragm in acoustic communication with the shutter configured to detect acoustic energy is included. Different positions of the microphone and shutter are provided in various embodiments. Different types of hearing assistance devices are configured with the apparatus in various embodiments. In various embodiments a first and second conduit configuration of varying spacings are employed. In various embodiments a conductive mesh is used in conjunction with the apparatus. 
     The present subject matter also provides methods including, but not limited to a method for operating a microphone in a hearing assistance device, including measuring acoustic energy detected by a diaphragm in acoustic communication with a shutter via a conduit, and controllably adjusting an acoustic resistance of the shutter with an electric signal to change directionality of the microphone. In some embodiments the method further includes applying the electric signal to stacked electroactive polymer membranes to control the acoustic resistance. In some embodiments, the method includes applying the electric signal to a linear longitudinal or bending biomorph to control the acoustic resistance. 
     One embodiment of the present subject matter includes an apparatus for controlling the acoustic resistance of sound traveling through a sound conduit by having an EAP actuator located within the sound conduit extending from a microphone to the exterior of a hearing-aid housing. 
     The present subject matter includes several variations. In some embodiments, the EAP actuator is contained within a housing that is designed to mate with an existing microphone. In additional embodiments, the EAP actuator is at least partially adapted to an existing microphone but may alternatively be integrated within the microphone itself. 
     Additionally, an embodiment of the present subject matter includes an apparatus for a hearing assistance device, the apparatus having a hearing aid housing containing a microphone, a sound conduit acoustically sealed to the aperture in the hearing aid housing containing an electrically adjustable EAP shutter to control acoustic resistance traveling through the sound conduit. In addition, a method of adjusting the acoustic resistance of the shutter to change directionality of a microphone is provided. 
     This Summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and the appended claims. The scope of the present invention is defined by the appended claims and their equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are illustrated by way of example in the figures of the accompanying drawings. Such embodiments are demonstrative and not intended to be exhaustive or exclusive embodiments of the present subject matter 
         FIG. 1  shows a microphone having two air channels and a shutter, according to one embodiment of the present subject matter. 
         FIG. 2  shows a microphone with a shutter as assembled within the faceplate for a hearing aid, according to one embodiment of the present subject matter. 
         FIG. 3  illustrates an assembly of a shutter mechanism and microphone, according to one embodiment of the present subject matter. 
         FIG. 4  is a perspective view of a shutter adaptor assembly, according to one embodiment of the present subject matter. 
         FIGS. 5A and 5B  show a electroactive polymer assembly, according to one embodiment of the present subject matter. 
         FIG. 6  illustrates a microphone having built-in shutter capability, according to one embodiment of the present subject matter. 
         FIG. 7  is a flow diagram illustrating the method of adjusting acoustic resistance, according to one embodiment of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the present invention refers to subject matter in the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. References to “an”, “one”, or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more than one embodiment. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined only by the appended claims, along with the full scope of legal equivalents to which such claims are entitled. 
     The present subject matter is directed toward microphones. Among the many applications of microphones there are included hearing assistance devices. Such applications include a microphone used in a configuration of one or more passageways, or conduits, adapted to allow propagation of acoustic wavefronts. Some systems are designed to filter or attenuate the sound transmitted through the conduit as a means to control the sounds heard by the user. For instance, some hearing aids provide a fixed filter maintained within the conduit to limit certain frequencies within a given range, thereby blocking unwanted frequencies, or noise, that falls outside this range. This method does not provide the ability to change the filter response, once installed, reducing its adaptability to a changing user&#39;s needs. In various embodiments, the present subject matter provides a solution which provides electrical adjustability. Additionally the present subject matter maintains a low profile for application in hearing assistance devices and reduces cost. 
       FIG. 1  shows an illustration of an air conduit assembly  100 , including a microphone  112 , a first sound conduit  110 , a shutter  105 , and a second sound conduit  106 . The illustration further shows an aperture  129  within the shutter  105 , which may include a fixed opening size or allow adjustability. In one embodiment, the air channel assembly  100  can be sized to fit within a hearing assistance device, or hearing aid. It is within the scope of the present subject matter for the distance between the first conduit  110  and second conduit  106  to be at least 0.25″. In accordance with one embodiment, the distance between the first conduit  110  and second conduit  106  is about 0.41″. 
       FIG. 2  provides a perspective view of a sound module  200  and additional components that comprise the air conduit assembly, similar to that shown in  FIG. 1 . This configuration comprises a rear conduit  210  within housing  202  which extends between a rear opening  208  and a shutter  216 . The shutter  216  is adapted to provide an acoustic seal with microphone  212 . At the base of the shutter  216  is an electrical interface plate  224 , having electrical contacts  225 . The outer surface of the microphone  212  contains solder pads  218 ,  220  and  222  for electrical connectivity. On the side of the microphone  212  that is opposite the shutter  216  is a front sound conduit  206  within housing  202 . The front conduit  206  extends between the sound port, or aperture  214  of microphone  212  and front opening  204 . 
     In one embodiment the sound module  200  is sized to fit within the faceplate of a hearing aid. In various examples, the hearing aids which house the sound module  200 , are shaped to fit almost completely within the ear canal. This configuration is known in the art as a completely-in-the-canal (“CIC”) configuration. Optional configurations within the scope of the present subject matter extend beyond such embodiments using CIC housings. According to one embodiment of the present subject matter, the hearing aid which houses the sound module  200  is designed to fit at least partially within the ear canal. This configuration is known in the art as an in-the-canal (“ITC”) configuration. In one embodiment of the present subject matter, the hearing aid which houses the sound module  200  is designed to fit at least partially behind an ear. This configuration is known in the art as a behind-the-ear (“BTE”) configuration. 
     In some hearing aid designs, the front sound conduit  206  and rear sound conduit  210  are integrated within the housing  202 . As such, in embodiments having the front sound conduit  206  or rear sound conduit  210  integrated within the housing  202 , the front opening  204  and the rear opening  208  define an aperture in the hearing aid housing  202 . Overall, the present subject matter includes embodiments in which the sound conduits provide an acoustically-sealed passageway for sound to propagate through the hearing aid housing  202 . 
     In various examples, the conduits comprise hollow tubing, suited for acoustic seal attachment between the opening of the hearing aid housing  202  and microphone  212 , or equivalent assembly. Some embodiments include conduit tubing which is made of a conformable substance equivalent to rubber. 
       FIG. 3  illustrates one configuration of a shuttered microphone assembly  300 , similar to that shown in  FIG. 2 . This embodiment includes a microphone  312  having at least one aperture  314  and solder pads  318 ,  320  and  322  for electrical connectivity. The electroactive polymer (“EAP”) assembly includes retaining clip  326 , inside of which fits a biomorph actuator with an EAP back membrane  332  and an EAP front membrane  334 . The EAP back membrane  332  and EAP front membrane  334  are positioned between two low-density compliant fillers, front pillow  328  and back pillow  330 . In one embodiment, the low-density filler, similar to front pillow  328  and back pillow  334 , are formed from gel or foam material that is easily conformable in response to bending deflection in the EAP actuator, thereby creating an adjustable acoustic valve opening. In various embodiments, the adjustable acoustical valve&#39;s dimensions are controlled to provide an adjustable acoustical resistance, thereby providing an adjustable polar sensitivity pattern. 
     In another embodiment shown in  FIG. 3 , acoustical resistance mesh  336  is attached on the exterior of microphone  312  to cover the rear microphone aperture (not shown). When EAP the EAP actuator assembly is opened, the acoustic wavefront propagates through resistance mesh  336  and into microphone  312 . 
     Acoustical mesh  336  is engineered to provide a fixed acoustical resistance, thereby providing a fixed polar sensitivity pattern. 
     According to one embodiment of the present subject matter, module housing  316  is used to contain the EAP assembly, which includes retaining clip  326  with EAP back membrane  332 , EAP front membrane  334 , front pillow  328  and back pillow  330 . The side of module housing  316  contains an aperture  317  for establishing acoustic communication between the EAP material, including top membrane  332  and bottom membrane  334 , and the microphone  312 . Base plate  324  is attached to the base portion of the module case  316  and further contains electrical contact  325  for supplying electrical potential to the EAP top membrane  332  and EAP bottom membrane  334 . In one embodiment, the applied potential to contact  325  will induce a density change within the EAP material, resulting in an adjusted acoustic resistance. 
       FIG. 4  shows a perspective view of an EAP actuator assembly  400 , according to one embodiment of the present subject matter. Microphone  401  includes front spout  403  which can be adapted to fit any particular aperture size to which microphone  401  will mate. Microphone  401  further includes rear aperture  415  for providing acoustic communication to be transmitted to the conductive polymer assembly, comprising back membrane  432  and front membrane  434 , positioned between front pillow  428  and back pillow  430 . The actuator housing  405  is used to hold the conductive polymer assembly and align it over the rear aperture  415  of microphone  401  and to fit over at least a portion of microphone  401  and sufficient to seat the conductive polymer assembly against aperture  415 . In some embodiments, the actuator housing  405  is plastic. In additional embodiments, shutter adaptor assembly  400  is metal. Some embodiments include a shutter adaptor assembly  400  made from machined steel. 
       FIG. 5A  shows a perspective view of an EAP membrane assembly  500 , according to one embodiment of the present subject matter. The EAP membrane  502  includes two electrical trace anodes  504  and two electrical trace cathodes  506 . Each trace is bonded to EAP membrane  502  via metal deposition, conductive ink, or any other equivalent process.  FIG. 5B  shows a side view of an EAP actuator assembly  550  in an actuated/open state, according to one embodiment of the present subject matter. A top EAP membrane  334  is stacked above a bottom EAP membrane  336  to form an EAP actuator  550 . Each electrical trace anode  504  is aligned externally on EAP actuator  550 , and each electrical trace cathode  506  is aligned internally on EAP actuator  550  to create a common cathode. Voltage potential  510  is applied to common anode  504  and common cathode  506 , thereby causing the EAP actuator  550  to open, thereby creating sound conduit  520 . It will be appreciated by those of ordinary skill in the art that other actuator configurations, including linear longitudinal or bending biomorph, can be used to create sound conduit  520 . 
       FIG. 6  illustrates one configuration of a microphone  612  having the conductive EAP actuator integrated within the microphone  612  itself. Aperture  615  allows sound waves to propagate into microphone  612 . Solder pads  618 ,  620  and  622  provide electrical connectivity to microphone  612 . The additional solder pads  627  and  629  represent the electrical connectivity for actuator control as provided by supporting control circuitry. 
       FIG. 7  shows a flow diagram  700  illustrating the method of adjusting acoustic resistance, according to one embodiment of the present subject matter. The method includes a measuring step  702  for measuring the acoustic energy detected by the diaphragm in acoustic communication with a shutter. The method further includes an adjusting step  704  for controllably adjusting the acoustic resistance of the shutter to change directionality of the microphone. One should note that the present subject matter is useful in a variety of applications to include use with existing hearing aids, new hearing aids, use as new assemblies for attachment to housings, use as retrofit kits, and other uses. In various embodiments, the present subject matter includes components made from plastic or rubber and in some instances there may be a need to include an acoustic seal, such as o-rings. O-rings made from rubber fall within the present scope of such embodiments, however additional materials are also possible. Further, some embodiments include a washer. Some of these embodiments include a washer having a low durometer rubber. Other sealing methods, including films, adhesives, compression fittings, and other sealing technologies additionally fall within the present scope. 
     The present subject matter includes hearing assistance devices, including but not limited to, cochlear implant type hearing devices, hearing aids, such as in-the-ear (ITE), in-the-canal (ITC), completely-in-the-canal (CIC), behind-the-ear (BTE), and receiver-in-the-ear (RIC) type hearing aids. It is understood that behind-the-ear type hearing aids may include devices that reside substantially behind the ear or over the ear. Such devices may include hearing aids with receivers associated with the electronics portion of the behind-the-ear device, or hearing aids of the type having receivers in the ear canal of the user. It is understood that other hearing assistance devices not expressly stated herein may fall within the scope of the present subject matter. 
     This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of legal equivalents to which such claims are entitled.
One embodiment of the present subject matter includes an apparatus, including: a microphone to convert sound into a signal; and an electrically adjustable shutter including conductive polymer, the shutter in acoustic communication with the microphone and configured to provide an adjustable acoustic resistance to the microphone. Variations include conductive traces adapted to apply an electric signal to the conductive polymer. In some embodiments a diaphragm in acoustic communication with the shutter configured to detect acoustic energy is included. The present subject matter also provides methods including, but not limited to a method for operating a microphone in a hearing assistance device, including measuring acoustic energy detected by a diaphragm in acoustic communication with a shutter via a conduit, and controllably adjusting an acoustic resistance of the shutter with an electric signal to change directionality of the microphone.