Abstract:
A partially implantable hearing assistance system, having: an external unit ( 10 ) to be worn at least in part in a user&#39;s ear canal ( 12 ), a device ( 14 ) for capturing audio signals from ambient sound, an audio signal processing unit ( 16, 18 ) for generating first intermediate signals from said audio signals, and at least one electroacoustic output transducer ( 20, 20 A) in order to make the user&#39;s eardrum ( 46 ) vibrate according to the first intermediate signals; and an implantable unit ( 22, 122 ) having an input transducer ( 42 ) located in the user&#39;s middle ear for capturing second intermediate signals from the vibration of the eardrum ( 46 ), an actuator ( 26, 60 ) for stimulating the user&#39;s hearing, and a driver unit ( 48, 148 ) for transforming the second intermediate signals into an input signal to the actuator ( 26, 60 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a partially implantable hearing assistance system comprising means for capturing audio signals from ambient sound, means for processing audio signals and an implantable actuator for stimulating the user&#39;s hearing according to processed audio signals. 
         [0003]    2. Description of Related Art 
         [0004]    A partially implantable hearing aid typically comprises an external unit to be worn at the head close to the ear, which usually comprises a microphone for capturing ambient sound, a power source (battery), an audio signal processing unit and a transmitter, and an implantable unit comprising a receiver and the actuator, which may be a middle ear implant, such as an electro-mechanical transducer, or a cochlear implant (i.e., a simulation electrode). Usually, the audio signals/audio data and power are transmitted via an inductive coupling RF (radio frequency) link from the transmitter to the receiver. An example of such a partially implantable cochlear stimulation system is found in U.S. Patent Application Publication 2007/0260292 A1, while U.S. Pat. No. 6,005,955 relates to a partially implantable hearing aid comprising an implantable output transducer which is a piezo-electrical transducer mechanically coupled to an ossicle after opening of the ossicular chain. 
         [0005]    U.S. Pat. No. 5,456,654 relates to an implantable electro-magnetic transducer for a hearing aid, wherein a magnet fixed to the eardrum generates an alternating magnetic field which is captured by an implanted coil. 
         [0006]    It is difficult to transmit both audio data and power via a RF link, since efficient transmission of power requires a high-quality factor of the antenna, whereas, by contrast, a sufficiently high data transmission rate of audio signals requires a large bandwidth. Typically, commercially available hearing aids have an RF link which realizes a compromise between these two requirements, resulting in high power consumption which, in turn, results to large, unattractive form factors (usually two or three batteries of the size 675 are necessary). As a consequence, small children hardly can wear BTE (Behind-the-Ear)-type devices and their ears may get deformed by the weight of the device. The use of two different RF frequencies is not very attractive, since the two antennas required then have a negative impact on complexity and size of the device. Transmission frequencies in the GHz range would result in small antennas; however, adsorption by the human body is too high at such high frequencies. 
         [0007]    Percutaneous power transmission is considered to be necessary, since the capacities of implantable batteries are relatively low and the number of charge cycles limited. 
         [0008]    International Patent Application Publication WO 2009/047370 A2 relates to a partially implantable hearing aid, wherein the audio signals/audio data are transmitted from the external unit to the implantable output transducer via an optical link through the eardrum, while power is transmitted via an inductive link. 
         [0009]    French Patent FR 1.113.759 relates to a hearing aid, wherein audio signals captured from ambient sound are transmitted via bone conduction as ultrasound signals to an ultrasound receiver located in the mouth of the user at the teeth. 
         [0010]    U.S. Patent Application Publication 2007/0270675 A1 relates to an implantable medical device comprising a percutaneous acoustic link from a pulse generator to an implanted chemical sensor. U.S. Patent Application Publication 2005/0261741 A1 relates to a device for ventricular resynchronization pacing therapy including an acoustic link to an implanted pacemaker. 
         [0011]    U.S. Patent Application Publication 2004/0200281 A1 relates to a MEMS accelerometer sensor for a middle ear implant. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the invention to provide for a partially implantable hearing aid, which avoids the need for bulky external parts of the system. It is a further object to provide for a corresponding hearing assistance method. 
         [0013]    According to the invention, these objects are achieved by a partially implantable hearing assistance system and a method as described herein. 
         [0014]    The invention is beneficial in that, by transmitting the audio signals/audio data via an acoustic link using the eardrum to the implantable unit, the power consumption of the system can be reduced, since the power link can be separated from the data link and hence can be optimized. Due to reduced power consumption of the system, the size of the external unit can be reduced. In addition, the size of the externally visible part of the system can be minimized due to the design of the external unit which is to be worn at least in part in the user&#39;s ear canal. Preferably, the external unit is designed as a CIC (completely-in-the-canal), ITC (in-the-canal), ITE (in-the-ear) or mini-BTE with ex-receiver. 
         [0015]    Typically, the audio signals/audio data will be transmitted via the acoustic link in a manner that they are not perceivable by the patient. This can be achieved by selecting the frequencies and levels of the acoustically transmitted intermediate signals according to the individual hearing loss of the user. In this regard, the present invention is particularly useful for patients suffering from profound hearing loss, for example, patients having a need for a cochlear implant (CI) or a device for direct mechanical stimulation of the cochlea, since in this case there is sufficient “free” bandwidth in the higher audio frequency range for acoustic transmission. 
         [0016]    Preferably, the input transducer acting as the receiver of the acoustic link is an accelerometer fixed at an ossicle. Thereby, the natural impedance transformation of the middle ear (from air to bone) acts on the input transducer (a microphone located in the middle ear would not “see” this impedance transformation; in particular, a microphone located in the middle ear would have low sensitivity in the high audio frequency range due to the very strong decay of the transfer function from the free sound field to the middle ear at high frequencies (second order low pass)). 
         [0017]    Preferably, the audio signals are compressed prior to transmission by reducing audio signal components which would not result in perceivable stimulation of the patient&#39;s hearing by the implantable actuator. For example, if the actuator is a cochlear implant, only those frequency bands of the audio signal would be transmitted which play a role in the stimulation by the cochlear electrode, namely the maxima of the envelope function in the time domain and in the frequency domain. 
         [0018]    Further, the audio signals preferably are “pre-distorted” prior to transmission via the acoustic link in order to adapt the payload and the available transmission bandwidth. The available frequency range and the available volume range are limited not only by the technical parameters (available transmission power, available receiver sensitivity, channel properties, etc.), but in particular also by the hearing loss of the patient. 
         [0019]    Multi-frequency modulation may be used for acoustic link, wherein within the available bandwidth a plurality of frequency bands is defined and for each frequency band the available volume range is calculated according to the individual hearing loss. The lower limit is given by the weakest acoustic intermediate signal which can be detected by the input transducer, and the upper limit is given by the strongest acoustic signal which still is not perceivable by the patient. It may also be required, to transpose information from one frequency band to another to achieve the required overall performance. 
         [0020]    The acoustic link may be used for digital signal transmission or for analog signal transmission. 
         [0021]    These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic view of an example of a partially implantable hearing aid according to the invention comprising an electro-mechanical actuator; 
           [0023]      FIG. 2  is a view like  FIG. 1 , but showing an example of a partially implantable hearing aid according to the invention comprising a cochlear implant; and 
           [0024]      FIG. 3  is a schematic illustration of available bandwidth and volume range together with the individual hearing loss of the patient. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIG. 1  shows a system that comprises an external unit  10 , which is designed as a modified CIC hearing aid and which is to be worn in the user&#39;s ear canal  12 . The external unit  10  comprises a microphone arrangement  14 , an audio signal processing unit  16 , a power amplifier  18  and an electroacoustic output transducer (loudspeaker)  20 . The microphone arrangement  14  may comprise at least two spaced-apart microphones (not shown) in order to provide an acoustic beam-forming capability. The audio signal processing unit  16  processes the audio signals provided by the microphone arrangement  14  and supplies the processed audio signals as first intermediate signals to the amplifier  18  which drive the speaker  20 . The external unit  10  also comprises a battery (not shown) which may be rechargeable. The audio signal processing unit  16  may be implemented by an ultra-low power hearing instrument DSP (Digital Signal Processor). Thus, the external unit  10 , apart from the type of audio signal processing (which will be explained below), essentially corresponds to a CIC hearing aid. 
         [0026]    The system also includes an implantable unit  22  comprising an implanted audio signal unit  24 , an electro-mechanical actuator  26  and a power management unit  28 . 
         [0027]    The power management unit  28  comprises a power receiving coil  30 , a power management circuitry  32  and a rechargeable battery  34 . The battery  34  is charged via percutaneous inductive power link  36  by an external charging adapter  38  comprising a power transmission coil  40  which transmits power to the power receiving coil  30  of the power management unit  28 . The rechargeable battery  34  should be dimensioned for lasting at least a full day and it should be possible to recharge it within a few hours; charging must be feasible during normal operation of the hearing aid or at night. Preferably, the rechargeable battery  34  is designed in thin-film lithium technology or conventional Lithium ion technology. The power management unit  28  serves as a power supply for the implantable audio signal unit  24  and the actuator  26 . 
         [0028]    The implantable audio signal unit  24  comprises an input transducer  42  located in the middle ear cavity as a receiver for the acoustic signals emitted by the speaker  20 , which acoustic signals make the eardrum  46  and the ossicular chain (not shown) vibrate. The implantable audio signal unit  24  also comprises a decoder/driver unit  48  which serves to drive the actuator  26 . The input transducer  42  serves to capture second intermediate signals from the vibration of the eardrum (and the resulting vibration of the ossicular chain), and the decoder/driver unit  48  serves to transform the second intermediate signals into an input signal to the actuator  26 . 
         [0029]    The speaker  20  and the input transducer  42  serve to realize an acoustic link for transmitting audio signals and/or audio data signals from the external unit  10  to the implantable unit  22 . 
         [0030]    Not only the input transducer  42 , but also the other components of the entire unit  24  may be located in the middle ear cavity. 
         [0031]    In the embodiment of  FIG. 1 , the actuator  26  is an electromechanical (electro-magnetical or piezo-electric) transducer which is coupled via a coupling element  52  to a middle ear component  54 , namely an ossicle or the cochlear wall. The actuator  26  may be designed, for example, as a floating mass transducer (FMT) fixed at one of the ossicles or as a direct acoustic cochlear stimulator (DACS) directly acting on the cochlear wall, i.e., footplate, oval window, round window or any artificial opening of the cochlear. In some of the cases, there would be a need to interrupt the ossicular chain mechanically or decouple the dynamic range still in use. 
         [0032]    Alternatively, the actuator may be a cochlear electrode  60  (indicated in dashed lines in  FIG. 1 ) which replaces the electromechanical actuator. 
         [0033]    An alternative embodiment of an implantable unit  122  is shown in  FIG. 2 , wherein only the input transducer  42  is located in the middle ear cavity, while the decoder function and the driver function are integrated within the power management unit  128  as a decoder/driver unit  148  which supplies electrical stimulation signals to a cochlear electrode  60  via a wire  66 . The input transducer  42  is connected to the decoder/driver unit  148  via a wire  65 . 
         [0034]    Usually, the power management unit  28 ,  128  is located within an artificial cavity created in the mastoid region or directly on the bone behind the ear. 
         [0035]    According to modified embodiments of  FIGS. 1 and 2 , the external unit  10  may be designed as a modified BTE hearing aid (BTE hearing aid with ex-receiver), wherein the speaker  20  is located in the ear canal  12  and is connected by wire to the part worn behind the ear. Alternatively, the external unit  10  may have the design of an ITC or ITE hearing aid. 
         [0036]    Usually, the input transducer  42  is mechanically coupled to the eardrum or the ossicular chain. Preferably, the input transducer  42  is an accelerometer attached to the ossicular chain. Such embodiment is beneficial in that then the natural impedance transformation caused by the middle ear from air to bone acts on the transducer  42 . Alternatively, the input transducer  42  may be a piezo-transducer attached to the ossicular chain after cutting the ossicular chain (an example of such a transducer is found in U.S. Pat. No. 6,005,955) or a magnet which is attached to the ear drum  46  and cooperates with an implanted coil (an example of such a transducer is found in U.S. Pat. No. 5,456,654). An artificial malleus may be used for transmitting the vibrations of the eardrum  46 . 
         [0037]    The acoustic link of the present invention preferably is used for transmitting audio data signals from the external unit  10  to the implantable unit  22 ,  122 , i.e., the first intermediate signals are first audio data signals, and the second intermediate signals are second audio data signals, with the second audio data signals, apart from transmission losses, corresponding to the first audio data signals. The audio data signals may be digital or analog. In the case of digital signals, a multi-frequency modulation method may be used for parallel multi-channel transmission in order to achieve a sufficiently high bit transmission rate. Also in the case of analog data transmission, the first audio data signals may be divided into a plurality of frequency bands, wherein each frequency band corresponds to a certain frequency range of the audio signals and each frequency band is for feeding a separate channel of the actuator, wherein the level of each frequency band corresponds to the stimulation amplitude of the respective channel as caused by the actuator. In case of a cochlear electrode as the actuator, each channel corresponds to a different stimulation site within the cochlea. 
         [0038]    By pre-distorting the audio signals prior to transmission via the acoustic link, the payload and the available transmission bandwidth are adjusted. In particular, the available frequency range and the available dynamic range are limited not only by the technical circumstances, but also by the individual hearing loss. In the case of analog data transmission, the level of each of the frequency bands of the first audio data signals is limited according to the hearing loss of the user in such manner that the respective stimulation of the ear drum by the speaker  20  in the respective frequency range will not be perceived by the user. The minimum level of each of the frequency bands is adjusted in such a manner that the signal in the respective frequency band still can be captured by the input transducer  42 . 
         [0039]    Also for digital signal transmission the first audio data signals may be generated by selecting frequencies and levels in a manner that the vibration of the user&#39;s ear drum caused by the speaker  20  is not perceivable by the user, wherein the levels and frequencies preferably are controlled according to the individual hearing loss of the user. 
         [0040]    In general, prior to the pre-distortion of the signals, the audio signals may be compressed in order to reduce the data which need to be transmitted. Such compression is achieved by removing audio signal components which will not result in perceivable stimulation of the user&#39;s hearing by the actuator  26 . To this end, the audio signals may be divided into a plurality of frequency bands and those bands will be removed which will not result in perceivable stimulation of the user&#39;s hearing by the actuator  26 . 
         [0041]    An example of the band-width and volume range available for data transmission via the acoustic link is shown in  FIG. 3  for a typical individual hearing loss at high audio frequencies. 
         [0042]    In order to avoid—in case that the external unit  10  does not have a specifically attributed shape—the inadvertent use of a hearing aid which is not associated with the specific implantable unit  22 ,  122  as the external unit  10 , the acoustic link may be provided with a specific code which allows the implantable unit  22 ,  122  to identify the respective external unit  10 . To this end, the external unit  10  may be adapted to change the modulation frequencies in a cyclic manner or in a random manner. In this case, the first audio data signals are generated in a manner that redundant data, such as a check sum, is included in the first audio data signal. The implantable unit  22 ,  122  may be designed such that it works only if it has recognized the correct external unit  10 . 
         [0043]    According to a modification of the embodiments described so far, the system may be designed as a bi-modal instrument, wherein a first portion of the audio signals is processed in a manner that the vibration of the user&#39;s ear drum  46  caused by the speaker  20  according to such processed first portion of the audio signals is perceivable by the user as sound, while only a second portion of the audio signals is used to generate the first audio data signals in the manner described above. In this case, the system works both as a conventional electroacoustic hearing aid and as a partially implantable hearing aid. Preferably, the low audio frequencies are used for conventional acoustic stimulation of the user&#39;s hearing, and the higher audio frequencies are used for stimulation via the implantable actuator  26 . The reason is that usually the hearing loss is more pronounced at high frequencies. For such bi-modal embodiments, the single speaker  20  may be replaced by two speakers (as indicated by an additional speaker  20 A drawn in dashed lines in  FIGS. 1 and 2 ), wherein the first speaker  20 A is used for the conventional acoustic stimulation and the second speaker  20  is used for the acoustic data link. In addition, two separate signal processors may be used for the conventional acoustic stimulation channel and the acoustic data link channel. It is mentioned that a conventional digital hearing aid is well suited for analog audio data transmission via the acoustic link, since a digital hearing aid as such is already a multi-channel compressor which can be easily adjusted to compress and pre-distort the audio signals in the manner described above with regard to multi-channel audio data transmission 
         [0044]    It is also noted that the acoustic link of the present invention could be used not only for audio data, but also for “base band” signal transmission via the acoustic link; i.e., there is no modulation of the audio signals prior to transmission. In this case, the audio signals received by the input transducer  42  will undergo the necessary audio signal processing in the implantable audio signal unit  24  prior to being supplied as input to the actuator  26 . While thereby the external unit  10  can be simplified, the signal processing in the implantable audio signal unit  24  usually will be more complex. 
         [0045]    While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.