Abstract:
A moisture-resistant, wideband microphone subassembly for a Behind-The-Ear (BTE) hearing device, provides a barrier to perspiration and rain, while maintaining a good frequency response. The microphone subassembly is contained in the case of the BTE hearing device and comprises a microphone, a boot, and a moisture-resistant membrane. The boot structurally supports the microphone, provides a moisture seal around the microphone case, and provides the microphone with isolation from vibrations in the case of the BTE hearing device. The membrane resists the passage of moisture, while providing an acoustic window permitting sound waves to reach the microphone. In one embodiment high compliance washers sandwich the membrane to improve frequency response. A preferred embodiment provides a substantially flat acoustic frequency response to beyond 10 KHz.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to hearing devices for aiding the hearing impaired and the profoundly deaf, and more particularly to a water-resistant microphone subassembly providing isolation from case-born vibrations, and wide band frequency response, for use in a Behind-The-Ear (BTE) hearing system. Such BTE system may form part of a cochlear stimulation system. 
     Cochlear stimulation systems are known in the art. Such systems are used to help the profoundly deaf (those whose middle and/or outer ear is dysfunctional, but whose auditory nerve remains intact) to hear. The sensation of hearing is achieved by directly exciting the auditory nerve with controlled impulses of electrical current, which impulses are generated as a function of transduced acoustic energy. The acoustic energy is picked up by a microphone carried externally (not implanted) by the person using the device and converted to electrical signals. The electrical signals, in turn, are processed and conditioned by a signal receiver and processor, also referred to as a Wearable Processor (WP), in an appropriate manner, e.g., converted to a sequence of pulses of varying width and/or amplitude. The sequence of pulses, or command words that define such sequence of pulses, is carried by an external cable running from the WP to an external headpiece positioned on the side of the patient&#39;s head. A magnet in the headpiece holds the headpiece in place on the head of the user. Such magnet also aligns the headpiece with a corresponding magnet in the an Implantable Cochlear System (ICS). Such ICS receives the command words or pulse sequence, and converts them to appropriate stimulation current pulses that are applied to the auditory nerve through an electrode array implanted in the cochlea, as is known in the art. 
     While known ICS systems have succeeded in providing the sensation of hearing to the profoundly deaf, they unfortunately also have the disadvantage of appearing unsightly due to the external cable running from the WP to the headpiece positioned on the side of the user&#39;s head. 
     The WP is typically worn or carried by the user on a belt or in a pocket. While the WP is not too large, it is likewise not extremely small, and hence also represents an inconvenience for the user. The cable which connects the WP with the headpiece is often a source of irritation and self-consciousness for the user. 
     The above-described aesthetic considerations and inconvenience of an external wire are addressed by U.S. Pat. No. 5,824,022, issued Oct. 20, 1998, for “Cochlear stimulation system employing Behind-The-Ear (BTE) Speech Processor With Remote Control.” The &#39;022 patent teaches a small single external device that performs the functions of both the WP and the headpiece. The external device is positioned behind the ear to minimize its visibility, and requires no cabling to additional components. The &#39;022 patent is incorporated herein by reference. 
     While the BTE device taught by the &#39;022 patent resolves the issues of aesthetics and inconvenience, the resulting device, and known BTE hearing aids, disadvantageously expose the microphone to perspiration and rain, resulting in frequent failures. Therefore, there is a need for a microphone assembly that provides resistance to moisture, while maintaining a good frequency response. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing a moisture-resistant microphone subassembly for Behind-The-Ear (BTE) hearing devices, with a substantially flat frequency response to 10 KHz. The microphone subassembly is comprised primarily of a microphone, a boot, and a moisture-resistant membrane. The microphone has an transducer aperture through which sound waves enter the microphone. The boot includes a microphone cavity and a sound port. The boot structurally supports the microphone, provides the microphone with isolation from vibrations in the case of the BTE device, and provides a seal against moisture seeping around the microphone body and into the transducer aperture of the microphone. The membrane resides in the microphone cavity between sound port and the transducer aperture, and resists the passage of moisture, while permitting sound waves to reach the transducer aperture. 
     In accordance with one aspect of the invention, a boot provides structural support to the microphone. The boot is made from a high compliance material and isolates the microphone from vibrations that might otherwise create false signals. In the absence of such isolation, events such as rubbing the case of the BTE device against hair or skin, could produce undesirable signals. 
     It is a feature of the present invention to provide a boot which includes a sound waves port and an microphone cavity. The microphone is situated in the microphone cavity. The fit of the microphone inside the microphone cavity provides a seal against moisture. The sound waves port connects with the microphone cavity to provide an acoustic path for sound waves (acoustic waves) to enter the transducer aperture of the microphone. 
     It is an additional feature of the present invention to provide a means for retaining the microphone in the microphone cavity. In one embodiment, the boot includes boot fingers at the rear of the microphone cavity. Once the microphone has been pushed into the microphone cavity, the boot fingers hold the microphone in place. In another embodiment, the boot includes a retaining flange around the rear of the microphone cavity. The compliance of the boot material allows the retaining flange to stretch to allow the microphone to be pushed into the microphone cavity. Once the microphone is in the microphone cavity, the retaining flange closes around the rear of the microphone to retain the microphone in the microphone cavity. 
     It is a further feature of the invention to provide a moisture-resistant membrane. The membrane separates the microphone from the environment and prevents moisture from reaching the microphone, but allows sound waves to reach the microphone. In a preferred embodiment, the membrane provides a stable, flat, wideband acoustic frequency response for the microphone subassembly. Advantageously, the resulting response is flat to beyond 10 KHz. 
     It is additionally a feature of the present invention that the microphone subassembly fit within a cavity of a BTE case. The cavity is located inside a front surface of the BTE device case, and includes a microphone port in the front surface to allow sound waves access to the microphone subassembly. A water deflector or shield is located just above the BTE sound port to deflect water from the microphone port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
     FIG. 1 depicts a typical Behind-The-Ear (BTE) hearing device on a user; 
     FIG. 2 shows a microphone subassembly in the case of a BTE hearing device; 
     FIG. 3 shows a boot of a microphone subassembly; 
     FIG. 4 depicts a cross section of a first embodiment of the microphone subassembly; 
     FIG. 5 depicts a cross section of a second embodiment of the microphone subassembly which includes washers in front of and behind the membrane; 
     FIG. 6 depicts a cross section of a third embodiment of the microphone subassembly which replaces the washer in front of the membrane with a step in the microphone cavity; 
     FIG. 7 depicts a cross section of a fourth embodiment of the microphone subassembly with a retaining flange to retain the microphone in the microphone cavity; 
     FIG. 8 illustrates a microphone subassembly with a boot which partially extends over the microphone; 
     FIG. 9 shows an embodiment of the partial boot with a retaining means and a microphone including cooperating surfaces; and 
     FIG. 10 shows the frequency response of the microphone subassembly for a preferred embodiment. 
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     The moisture-resistant microphone subassembly of the present invention provides Behind-The-Ear (BTE) hearing devices with improved performance and reliability. A BTE hearing device  10  is shown carried and resting on an ear  12  of a user in FIG.  1 . The BTE device  10  may either be a standard hearing aid, or the external electronics for an Implantable Cochlear Stimulation (ICS) system. In either case, a microphone is required to receive acoustic energy (i.e., sound waves) and convert the acoustic energy into an electronical signal for further processing. In order to receive the acoustic energy, the microphone must be open to at least some extent to the environment. 
     As can be seen in FIG. 1, the BTE hearing device  10  forms an arch that starts behind the ear  12  and reaches over the ear  12 . The BTE hearing device  10  ends near the top of the arch, and an earhook  8  continues the arch a short distance. In typical BTE hearing devices, the microphone resides in the BTE device  10  near the highest point of the arch, behind a microphone port  13 . While the microphone port  13  is advantageously positioned to receive sound in a natural manner (i.e., from the direction the patient is looking), the position also exposes the microphone to various moisture sources. Such moisture sources include rain, splashed water, perspiration, etc. Such moisture may not only degrade a microphone&#39;s performance, but in some instances it may render the hearing device inoperable. 
     A cross-section of a portion of a BTE device case  16  is shown in FIG. 2. A microphone subassembly  14   a  is positioned directly behind the microphone port  13 . A water deflector  18  is placed above the microphone port  13 . The water deflector  18  advantageously reflects large volumes of water attempting to enter the microphone port  13 . The microphone subassembly has an assembly front  15  which resides against the microphone port  13 , and an assembly rear  17  which resides within the BTE device case  16 . 
     A cross-section of a boot  20   a  of the microphone subassembly  14   a  is shown in FIG.  3 . The microphone subassembly  14   a,  is comprised of components assembled inside the boot  20   a,  and the boot  20   a  is mounted in the BTE case  16 . The exterior of the boot  20   a  is shaped to cooperate with the BTE device case  16  to retain the microphone subassembly  14   a  in the BTE device case  16 . Preferably, a boot shoulder  21  cooperates with an interior part of the BTE device case  16  to retain the microphone subassembly  14  in the BTE device case  16 . 
     The interior of the boot  20   a  comprises a microphone cavity  24 . A sound port  26  provides an opening into the microphone cavity  24 . The boot  20   a  is made from a commercially-available elastomeric material, such as KRATON G2712, or equivalent. The elastomeric material provides isolation from vibrations in the BTE case  16 . The sound port  26  extends from the assembly front  15  to the microphone cavity  24 . The microphone cavity  24  extends from the sound port  26  to the assembly rear  17 . The sound port  26  has the shape of a truncated cone, with a larger diameter, preferably about 0.040 inches, at the assembly front  15 , and a smaller diameter, preferably about 0.020 inches where the sound port  26  connects with the microphone cavity  24 . When the microphone subassembly  14   a  is mounted in the BTE case  16 , the sound port  26  is aligned with the microphone port  13  to provide an acoustic path for acoustic energy outside the BTE device  10  to enter the sound port  26 . The boot also includes boot fingers  32  at the assembly rear  17 , which boot fingers  32  partially encroach inwardly into the microphone cavity  24 . In a preferred embodiment the boot  20   a  is round, as is the sound port  26  and the microphone cavity  24 . Those skilled in the art will recognize that boots, microphone cavities, and sound ports may be made in a variety of shapes. Such other shapes, or combinations of shapes, are intended to come within the scope of the present invention, as defined in the claims. 
     The construction of one embodiment of the microphone subassembly  14   a  is shown in FIG. 4. A microphone  22  resides in the microphone cavity  24 . The microphone is preferably cylindrical and about 0.10 inches in diameter. The microphone cavity  24  radially surrounds the microphone  22  and is slightly undersized to provide a moisture-resistant fit between the microphone  22  and the microphone cavity  24 . The microphone  22  has a transducer aperture  40 , whereby acoustic energy enters the microphone  22 . In FIG. 4, and subsequent figures, the transducer apertures are depicted as a rectangular indentation into the microphone  22 . In many cases the acoustic aperture may simply be a hole or holes in the microphone  22 , and the rectangular indentation shown in the figures is only for purpose of showing the location of the acoustic aperture  40 . The present invention is intended to apply to microphones with all shapes of acoustic apertures. 
     The transducer aperture  40  is aligned with the sound port  26  to allow the acoustic energy entering the boot  20   a  to travel to the microphone  22 . A membrane  28  is positioned between the sound port  26  and the transducer aperture  40 . The membrane  28  is manufactured from a commercially-available moisture-resistant material, such as VERSAPOR 10000R, or equivalent. Such material provides resistance to moisture, but still allows acoustic energy to pass. The membrane is preferably round, preferably about 0.10 inches in diameter, and preferably about 0.010 inches thick. The microphone  22  is retained in the microphone cavity  24  by the boot fingers  32  at the rear of the boot  20   a.  An elastomeric sealant  30  is applied to the assembly rear  17  to provide additional moisture resistance. 
     A second embodiment of a microphone subassembly  14   b  is shown in FIG.  5 . The microphone subassembly  14   b  includes a boot  20   b  similar to the boot  20   a  in FIG.  4 . The boot  20   b  may be slightly longer than the boot  20   a  to allow for additional elements. The microphone subassembly  14   b  includes a first washer  34  and a second washer  36 , and a clamp  38 . The length of the boot  29   b  is such that once assembled, the washers  34  and  36 , and the membrane  28 , are in sufficient longitudinal compression to form a seal. The presence of the membrane  28  in the acoustic path may result in undesirable attenuation of the acoustic energy. A wideband acoustic response is desirable for the microphone subassembly in order to provide more natural sound to the patient. The membrane  28  acts as a series acoustic resistance and the equivalent acoustic volume of the microphone  22  acts as a shunt acoustic capacitance. In order to minimize the effects of the acoustic resistance of the membrane  28  on the wideband acoustic response, the membrane  28  is sandwiched between the first washer  34  and the second washer  36 . The inside diameter of the first washer  34  and the inside diameter of the second washer  36 , are made large to expose a substantial percentage of the surface area of the membrane  28  to acoustic energy. In a preferred embodiment, the inside diameters of the washers  34 ,  36  are about 0.07 inches which results in about half (i.e., 49% of the area of a 0.10 inch diameter membrane) of the surface area of the membrane  28  being exposed. The low series acoustic resistance results in a cutoff frequency that is beyond 10 KHz and insures a flat, wideband, acoustic response for the microphone subassembly  14   b.  The boot  20   b  is made from high compliance material and the microphone cavity  24  is slightly undersized axially relative to the microphone  22 . The first washer  34 , membrane  28 , and second washer  36 , are substantially the same diameter as the microphone  22 , which diameter is preferably about 0.10 inches. The first washer  34 , membrane  28 , and second washer  36  are preferably about 0.010 inches thick. The microphone subassembly  14   b  is assembled by pushing the first washer  34 , membrane  28 , second washer  36 , and microphone  22  into the microphone cavity  24 . The boot fingers  32  press against the microphone  22 , thus retaining the microphone  22  in the microphone cavity  24 . A ring shaped clamp  38  resides on the exterior of the boot  20   b,  over the boot fingers  32 , thereby increasing the retaining force that the boot fingers  32  apply to the microphone  22 . 
     Yet another embodiment of a microphone subassembly  14   c  is shown in FIG.  6 . The microphone subassembly  14   c  utilizes a third boot  20   c  similar to the boot  20   b  in FIG.  5 . However, the boot  20   c  replaces the washer  34  by providing a cavity step  42  between the membrane  28  and the sound port  26 . The use of the cavity step  42  advantageously eliminates one step in the assembly of the microphone subassembly  14   c.  The length of the boot  29   c  is such that once assembled, the washer  36  and the membrane  28 , are in sufficient longitudinal compression to form a seal. 
     A fourth embodiment of a microphone subassembly  14   d  is shown in FIG.  7 . The microphone subassembly  14   d  includes a fourth boot  20   d.  The boot  20   d  is identical to the boot  20   b  shown in FIG. 5 with the single exception that the boot fingers  32  have been replaced by a retaining flange  44 . The retaining flange  44  wraps around the opening of the microphone cavity  24 . The length of the boot  29   d  is such that once assembled, the washers  34  and  36 , and the membrane  28 , are in sufficient longitudinal compression to form a seal. 
     The four embodiments described in FIGS. 4,  5 ,  6 , and  7  include microphone subassemblies that are assembled by pressing a combination of washers, membranes, and microphones into a microphone cavity, wherein the washers, membranes, and microphones are kept in place by either the boot fingers  32 , or retaining flange  44 . Various other embodiments include elements identical to those recited for FIGS. 4,  5 ,  6 , and  7 , but vary by the addition of an attaching means exercised on the interfaces between the boot, washers, membranes, and/or microphones. The attaching means may be an adhesive or a thermal or ultrasonic bonding process. Any suitable commercially-available bonding agent or compound may be used, as long as the agent or compound is compatible with the boot, membrane, or washer material. Agents or compounds that are absorbed by the boot, membrane, or washer material, and substantially alter the physical characteristics of the material, would not be suitable. In one embodiment of a microphone subassembly, similar to the microphone subassembly  14   a  shown in FIG. 4, the attaching means is exercised between the boot  20   a  and the membrane  28 , thereby attaching the membrane  28  to the boot  20   a.  In another embodiment of a microphone subassembly, also similar to the microphone subassembly  14   a  shown in FIG. 4, the attaching means is exercised between the microphone  22  and the membrane  28 , thereby attaching the membrane  28  to the microphone  22 . Various other embodiments of the application of attaching means to the boot, washers, membranes, and/or microphones will be apparent to those skilled in the art and are intended to come within the scope of the present invention. 
     The embodiments of a microphone subassembly described above all include a boot which extends over the length of the microphone. A fifth embodiment of a microphone subassembly  14   e,  includes a partial boot  20   e  that only partially extends over the microphone  22 , as shown in FIG.  8 . The microphone subassembly  14   e  is very similar to the microphone subassembly  14   a  in FIG.  4 . Other embodiments of a microphone subassembly with a partial boot could also include one or two washers  34 ,  36 , or a cavity step  42  as shown in FIGS. 5 and 6. The microphone  22  could be retained by a friction fit, or held in by an adhesive. 
     A microphone subassembly  14   f,  which includes a second partial boot  20   f  with a cooperating microphone  22 ′, is shown in FIG.  9 . The partial boot  20   f  includes at least two second boot fingers  32 ′ that cooperate with the microphone  22 ′ to retain the microphone  22 ′ in the boot  20   f.  As in the case of the microphone subassembly  14   e,  the microphone subassembly  14   f  may be practiced with one or two washers  34  and  36 , and/or the cavity step  42  shown in FIGS. 5 and 6. 
     A representative plot of the frequency response of the microphone subassemblies  14   b,    14   c,  and  14   d  is shown in FIG.  10 . As can be seen in the plot, the frequency response is substantially flat beyond 10 KHz. (Note, the response shown in FIG. 10 is actually an inverse response, thus the response is shown as measuring beyond 10 KHz, whereas the actual (non-inverse) response would decrease beyond 10 KHz). 
     Those skilled in the art will recognize that the present invention may be practiced in many microphone subassembly configurations. The heart of the present invention is the use of a moisture-resistant membrane, and/or a subassembly construction utilizing a combination of washers and membrane, that provide both moisture resistance and/or wideband frequency response. An embodiment comprising variations to boot shape, microphone cavity shape, microphone retention means, sound port configuration, or other details, is intended to fall within the scope of the present invention. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.