Abstract
We propose and experimentally prove an algorithm for demodulation of interferometric signals, modified for use in a totally implantable hearing aid device. A fiber optic configuration, which generates two quasi-quadrature signals by a passive 3x3 coupler, for a non-contact detection of the middle ear ossicle vibration is employed. We simulated the ossicle vibration and large movements and demonstrated the effectiveness of the algorithm to compensate changes of the signal DC values and the phase shift introduced by the coupler. Applying the proposed algorithm we obtained the output signal stability better than 0.5 dB, and the system equivalent input noise of about 31 dB (A) SPL @ 1 kHz.
Highlights
The external microphone is usually employed in an implantable hearing aid, with different solutions regarding the signal transfer through the skin [1]
We propose and experimentally prove an algorithm for demodulation of interferometric signals, modified for use in a totally implantable hearing aid device
We applied the described algorithm to these pair of raw signals and got- the time varying DC levels, calculated as the running middle of the signal extrema, and the change of the coupler phase shift, which are presented in Fig. 2, versus the target position
Summary
The external microphone is usually employed in an implantable hearing aid, with different solutions regarding the signal transfer through the skin [1]. In a totally implantable hearing aid device (TIHA), the detection of sound should be performed completely inside the patient’s body [2]. The first TIHA clinical trials demonstrated 10-20 dB better functional gain, over the whole audiometric frequency, than the semi-implantable devices, a degradation of the initial sensitivity of the microphone is recognized, mainly due to the skin effect on the membrane [1]. In contrast to this approach, we propose a sound sensing system, based on a non-contact detection of vibration of the ossicles inside the middle ear (ME). In this article we are dealing with the requirements for signal stability, low noise and low power consumption, which are, along with small dimensions, biocompatibility and encapsulation, the main issues of a TIHA device
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