Abstract:
An electronic hearing aid apparatus comprises a first component, a second component and a cable assembly for electrically connecting the first component to the second component. The first component includes a vibration sensor for sensing acoustic vibrations and generating a vibration signal based on the sensed acoustic vibrations, electronics for processing and amplifying the vibration signal and an output port for providing access to the amplified vibration signal. The second component includes an input port for receiving the amplified vibration signal and a vibration generator for generating vibrations based on the amplified vibration signal. The cable assembly conducts the amplified vibration signal from the output port of the first component to the input port of the second component. The cable assembly includes a first connector for electrically connecting to the first component, a second connector for electrically connecting to the second component and a flexible cable portion for electrically connecting the first connector to the second connector. In some embodiments, the cable portion has a stiffness of no more than about 7.0 Taber stiffness units. In one most preferred embodiment, the cable portion has a stiffness of no more than about 1.0 Taber stiffness unit.

Description:
FIELD 
     The present invention relates generally to hearing aids. More particularly, the present invention relates to an apparatus for reducing mechanical feedback between an in-the-ear (ITE) component and a behind-the-ear (BTE) component of a hearing assistance device. 
     BACKGROUND 
     For many hearing loss patients, bone conduction hearing aids offer a better solution than more conventional acoustic/air transmitting hearing aids. Indeed, for some patients, bone conduction hearing aids offer the only solution. Bone conduction hearing assistance generally involves vibration of the patient&#39;s mastoid bone to improve hearing perception. In a typical bone conduction hearing aid, sound sensed by a microphone is converted to an electrical signal and amplified. The amplified signal is then received by a small vibrator which vibrates the mastoid bone. 
     Strategic placement of the vibrator on the user is essential in order to achieve optimal results. For example, some bone conduction hearing aids teach that the vibrator should be placed against the skin behind the ear, while others teach placing the vibrator on the forehead. Still others teach surgical implantation of the vibrator directly into the mastoid bone for better transmission of vibration. One particularly effective approach has been to mount the vibrator on an ITE structural member. The structural member is inserted in the patient&#39;s ear canal so that the vibrator is positioned adjacent the mastoid bone. 
     In prior hearing aids, a relatively stiff electrical cable connected the ITE component containing the vibrator to a BTE component containing a microphone and processing electronics. The stiff interconnecting cable of prior units provided a pathway for vibrations from the vibrator to the microphone. These vibrations caused undesired feedback or “ringing” which is irritating to the patient. 
     What is needed, therefore, is an apparatus that reduces mechanical feedback between the ITE component and the BTE component of a hearing aid device. 
     SUMMARY 
     The above and other needs are met by an electronic hearing aid apparatus comprising a first component, a second component and a cable assembly for electrically connecting the first component to the second component. The first component includes a vibration sensor for sensing acoustic vibrations and generating a vibration signal based on the sensed acoustic vibrations, electronics for processing and amplifying the vibration signal to generate an amplified vibration signal, and an output port for providing access to the amplified vibration signal. The second component includes an input port for receiving the amplified vibration signal and a vibration generator for generating vibrations based on the amplified vibration signal. The cable assembly conducts the amplified vibration signal from the output port of the first component to the input port of the second component. The cable assembly includes a first connector for electrically connecting to the output port of the first component, a second connector for electrically connecting to the input port of the second component and a flexible cable portion for electrically connecting the first connector to the second connector. In some embodiments of the invention, the cable portion has a stiffness of no more than about 7.0 Taber stiffness units. In one most preferred embodiment, the cable portion of the cable assembly has a stiffness of no more than about 1.0 Taber stiffness unit. In some embodiments of the invention, the cable portion of the cable assembly comprises one or more woven wires, such as Litz wires. 
     In some embodiments, the first component of the hearing aid apparatus is contained in a housing configured to be worn behind the ear of a user. In some embodiments, the second component is contained in a housing configured to be worn in the ear of the user. 
     In some embodiments of the invention, the vibration generator of the second component comprises a bone-conduction vibrator configured to produce vibrations that are conducted by the second component to the mastoid bone of the user of the hearing aid apparatus. In some embodiments, the vibration generator of the second component comprises a receiver configured to produce airborne vibrations within the user&#39;s ear canal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages of the invention are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
         FIG. 1  is a side view of a bone conduction hearing aid device; 
         FIG. 2  is a sectional view of a patient wearing the hearing aid of  FIG. 1 ; 
         FIG. 3  is a side view of a vented in-the-ear member of a hearing aid device; 
         FIG. 4  is a functional block diagram of a hearing aid device; 
         FIG. 5  depicts an electrical cable assembly for connecting an in-the-ear component to a behind-the-ear component of a hearing aid device according to a preferred embodiment of the invention; 
         FIG. 6A  depicts the geometry of a Taber stiffness test for determining stiffness of a material; and 
         FIG. 6B  depicts a graph of bending angle versus bending resistance for a Taber stiffness test. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings wherein like reference characters indicate like or similar parts throughout,  FIGS. 1 and 2  illustrate a bone conduction hearing aid  10  in accordance with the invention. The hearing aid  10  preferably includes a behind-the-ear (BTE) member  12  for carrying elements needed to receive and process acoustic vibrations, and an in-the-ear (ITE) member  14  configured to receive signals processed by the BTE member  12  and convert those signals to corresponding vibrations that are conducted by the mastoid bone to a cochlea of the patient or user. BTE member  12  is in electronic communication with ITE member  16 . 
     In a preferred embodiment as shown in  FIG. 1 , the two members  12 ,  16  are connected by an electrical cable assembly  17 . Further details regarding a preferred embodiment of the cable assembly  17  are provided hereinafter. As an alternative to the wired assembly shown in  FIG. 1 , the BTE member  12  may include a radio frequency transmitter that wirelessly transmits processed signals to a receiver in the ITE member  16 . 
     With continued reference to  FIGS. 1 and 2 , ITE member  14  includes an insertion portion  16  for being inserted into the user&#39;s ear canal adjacent the mastoid bone  18 . Insertion portion  16  is preferably custom formed to closely fit the ear canal of the user, and  FIG. 2  shows the hearing aid  10  fully inserted in the patient&#39;s ear canal  20 . A non-insertion portion  22  adjacent to and connected with the insertion portion  16  is positioned in the concha  26  of the ear when the hearing aid  10  is in use. A non-surgically implanted vibrator  24  carried by (i.e., mounted on or in) the non-insertion portion  22  is in vibrational communication with the insertion portion  16 . Vibrations produced by vibrator  24  are conducted by the insertion portion  16  to the mastoid bone  18 . Thus, when insertion portion  16  is inserted in the ear canal  20 , the vibrator  24  is positioned in the concha  26 . This configuration is particularly advantageous for patients with ear canals that are too small to receive the vibrator  24 , including patients with congenital atresia where the ear canal is extremely narrow or completely closed off from the tympanic membrane  28 . For example, aural atresia occurs where there is an absence of the opening to the ear canal. Bony atresia occurs where there is a congenital blockage of the ear canal due to a wall of bone separating the ear canal from the middle ear space. For atresia patients, the concha  26  provides a location with sufficient space to receive the vibrator  24 . 
     As mentioned above, BTE member  12  is configured to receive and process acoustic vibration signals and to provide the processed signals to ITE member  14  for operation of vibrator  24 . External features of BTE member  12  shown in  FIG. 1  include an acoustic vibration sensor, or microphone  30 , for receiving acoustic vibration, and a volume control  32  for controlling the level of amplification provided by the hearing aid  10 . An optional programming port  34  may be included which connects to a computer for adjusting programmable electronic parameters, such as feedback control, gain and maximum output. Access to the hearing aid battery  36  is also provided. 
     The insertion portion  16  of the hearing aid  10  is preferably formed from a vibrationally conductive material suitable for transferring vibration produced by the vibrator  24  into the ear canal  20  and then to the mastoid bone  18 . Suitable materials include hard plastic, hard Lucite and acrylic. In a preferred embodiment, vibrator  24  is an electromechanical vibrator, such as a “moving coil” type. Piezoelectric and other vibrator types may also be employed in accordance with the invention. 
     Vibration produced by the vibrator  24  may be transferred through the cable  17  of the hearing aid  10  and picked up by the microphone  30 , producing undesirable feedback particularly at higher amplifications. Feedback may be controlled by coating or otherwise fabricating non-insertion portion  22  with a vibration attenuating material  23 , such as rubber. If electronic feedback reduction is desired, the programming port  34  is provided to enable adjustment of feedback control circuitry and other electro-acoustic parameters carried by BTE member  12 . 
     In operation, sound waves are received by the microphone  30  and the microphone  30  outputs a corresponding microphone signal. The microphone signal is amplified and the amplified microphone signal is provided to the vibrator  24 . Vibrations produced by the vibrator  24  are conducted by insertion portion  16  into the ear canal  20  and on to the mastoid bone  18 , which in turn transfers the vibration to a cochlea of the user to enhance hearing perception. Thus, sound perception in patients with hearing loss is improved. Conducting vibration into the ear canal  20  in close proximity to the mastoid bone  18  provides excellent transfer of vibration to a cochlea by way of the mastoid bone  18 . 
     The hearing aid  10  can function to improve hearing in either ear. For example, patients with conductive pathology in one ear can experience improved hearing perception by placing the hearing aid  10  in the ear with the conductive loss. Vibrations produced by the vibrator  24  are transferred by way of the mastoid bone  18  to the cochlea of the affected ear. The hearing aid  10  can also be used by patients with total loss of hearing in one ear. For such patients, the hearing aid  10  operates to transmit vibration output by vibrator  24  transcranially through the mastoid bone  18  from the bad ear to the good ear. Transcranial conduction of the vibrator output in this manner overcomes problems associated with the “head shadow” effect where sounds coming from the direction of the deaf ear are attenuated by the patient&#39;s head. 
     The hearing aid  10  can also be used to help patients that have certain conductive pathologies involving drainage from the ear. To enable the ear to properly drain, an ITE type hearing aid should be vented. Due to space constraints, it is very difficult to fabricate a bone conducting ITE hearing aid with a vent and a vibrator positioned in the ear canal.  FIG. 3  shows how ITE member  16  can be configured to assist patients with such conductive pathologies. A vent  50  is provided to enable air to enter the ear canal for proper drainage of the ear. Vibrator  24  is located on or in non-insertion portion  22  where space is not as limited as in insertion portion  16 . This configuration of ITE member  14  provides a treatment solution that was previously unavailable to patients with conductive pathologies that involve drainage of the ear. 
     The hearing aid  10  can even be used to improve hearing perception in individuals with no hearing loss in either ear. In extremely noisy environments, the hearing aid  10  can function both as a plug and as a filter which electronically filters the noise while allowing desired sound to be perceived. For example, aircraft maintenance personnel are commonly required to work in close proximity to aircraft while the engines are turning. Good communication among the maintenance crew is essential from a safety standpoint as well as to ensure the aircraft is in proper working condition. A hearing aid in accordance with the invention would be particularly useful in this type of noisy environment since it would block aircraft noise by acting as a plug, electronically filter the engines&#39; higher frequency noise components, and still allow the lower frequency human voice to be sensed and perceived by the user. 
     A functional block diagram of a hearing aid  10  according to the invention is shown in  FIG. 4 . Sound waves are received by the microphone  30  which outputs a microphone signal to the signal amplification circuitry  40 . The microphone signal is amplified by an amplifier within the signal amplification circuitry  40  and the amplified signal is sent to the vibrator  24  which produces vibrations corresponding to the amplified microphone signal. Electrical power is provided by a battery  42 . The level of amplification can be adjusted with the volume control  32 . 
       FIGS. 5A-5E  depict a preferred embodiment of the cable assembly  17  that provides electrical communication between the ITE member  14  and the BTE member  12 . In this embodiment, the cable assembly  17  comprises a highly-flexible cable portion  60  of length L having a first connector  52  at one end and a second connector  54  at the opposing end. In an exemplary embodiment, the first and second connectors  52  and  54  are manufactured by Plastics One, Inc. under model numbers 871 and 870, respectively. The cable portion  60  preferably comprises three wires twisted about each other and enclosed within an outer jacket. The three wires are electrically connected at their opposing ends to corresponding contacts  58   a ,  58   b  and  58   c  in the first connector  52  and contacts  56   a ,  56   b  and  56   c  in the second connector  54 . (See  FIGS. 5B and 5C .) As discussed in more detail below, the stiffness and vibration transmission characteristics of the cable portion  60  are determined by the structure and materials of the individual wires and the jacket that encloses the wires. 
     In a most preferred embodiment, the length L of the cable portion  60  is about 0.9 inch to about 1.4 inch. However, it will be appreciated that the invention is not limited to any particular length L of the cable portion  60 . 
     Although the cable portion  60  is depicted in  FIGS. 5A ,  5 D and  5 E, as straight when in use, the cable portion  60  may take on any shape as necessary to connect the ITE member  14  to the BTE member  12 . Also, although the connectors  52  and  54  are depicted as having a particular angular orientation with respect to the cable portion  60 , the connectors  52  and  54  may have any orientation with respect to the cable portion  60  as may be necessary to accommodate the connection of the connectors  52  and  54  to the ITE member  14  and the BTE member  12 . Thus, it will be appreciated that the invention is not limited to any particular shape of the cable portion  60  or any particular orientation of the connectors  52  and  54  with respect to the cable portion  60 . 
     In one preferred embodiment of the invention, each of the three wires comprising the cable portion is formed by weaving or braiding together multiple conductors that are each individually insulated by a polymer film. This type of wire construction is known in the art as “Litz” wire, which is derived from a German word (litzendraht) which means “woven wire.” In a most preferred embodiment, each of the three Litz wires comprising the cable portion  60  includes eight strands of 46 gauge wire, which results in a 38 gauge assembly. New England Wire Technologies Corporation is one manufacturer of such Litz wire cable assemblies. Although Litz wire is used in a preferred embodiment, other types of highly flexible wire could be used, such as tinsel wire or stranded copper wire. 
     In addition to the construction of the wires, the construction of the protective jacket enclosing the wires also affects the vibration transmission characteristics of the cable portion  60 . In the preferred embodiment, the protective jacket is formed of a relatively soft plastic which is molded around the wires in an extrusion process. This process leaves no air gaps between the wires and the jacket material. Such structure provides significantly better vibration dampening properties as compared to prior cable assembly structures which incorporated tubular sleeve jackets. 
     The woven wire construction of the conductors of the cable portion  60  provides a flexible structure that minimizes or dampens conduction of vibrations along the length of the cable assembly  17 . Eliminating—or at least significantly reducing—vibration conduction along the cable assembly  17  is key to reducing the unwanted feedback of vibrations from the ITE member  14  to the BTE member  12 . This advantage of the cable assembly  17  is particularly important in bone conduction hearing aid systems which generally present a more significant feedback problem along the interconnecting cable than do air conduction hearing aid systems. However, the vibration dampening properties of the cable assembly  17  are also advantageous in air conduction systems. Accordingly, it should be appreciated that the invention is not limited to any particular type of hearing aid system. 
     In preferred embodiments of the invention, cable portion  60  is highly flexible, having a Taber stiffness value of no more than about 7.0 Taber stiffness units, where the Taber stiffness value is determined as discussed below. In a most preferred embodiment, the stiffness of the cable portion  60  is less than 1.0 Taber stiffness unit. For example, the embodiment of the cable assembly  17  described above which has woven wire in the cable portion  60  has a Taber stiffness of 0.72 Taber stiffness units. By comparison, prior connector cables for connecting the ITE portion to the BTE portion of hearing aid devices have had Taber stiffness values of greater than 7.0 Taber stiffness units. 
     According to industry standards, Taber stiffness of a specimen is determined by applying a bending force F to the specimen at a known distance D from a clamping point and measuring how much force F is required to bend the specimen to a particular angle θ, such as 15 degrees. The measurement geometry is depicted in  FIG. 6A . Generally, stiffness of a specimen may be expressed by the relationship between the bending force F and the bending angle θ, as shown in  FIG. 6B . The slope of the curve in  FIG. 6B  is the bending stiffness. 
     Taber stiffness of a specimen may be determined using a stiffness tester such as the Model 150-E manufactured by Taber Industries, which outputs stiffness in Taber stiffness units (g·cm). Generally, such stiffness testers include a pendulum weighing system for determining the force F. With the specimen held in a specimen clamp at the center of rotation of the pendulum, force is applied to the lower end of the specimen by a pair of rollers. The rollers, which are attached to a driving disc located directly behind the pendulum, push against the specimen and deflect it from its initial vertical position. The pendulum applies increasing torque to the specimen as it deflects further from its initial position. The test point reading occurs when the pendulum is moved to a particular angle θ, such as 15°, relative to its original position. The stiffness value is then read from a dial pointer on the tester, or from a digital read-out on the tester. 
     It will be appreciated that the method described above is but one way to determine stiffness of a material. Other test methods may be used to determine stiffness, and the invention is not limited to any particular test method or unit of stiffness measurement. For example, stiffness may also be expressed in Gurley stiffness units, where the relationship between Taber units and Gurley units are set forth in industry-standard TAPPI Test Methods T543 and T489. 
     As discussed above, one preferred embodiment of the invention incorporates so-called “Litz” wire construction to provide reduced stiffness. However, it will be appreciated that other cable construction techniques may be used to provide low stiffness in the range discussed above. Thus, it will be appreciated that the invention is not limited to any particular type of wire or means for constructing the wire or cable. 
     The foregoing description of preferred embodiments for this invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.