Implantable Microphone Research Articles

Speech quality evaluation of subcutaneously implanted microphone using in vivo experiment.

The microphone in a fully implantable hearing device (FIHD) is generally implanted under the skin covering the temporal bone. However, the implanted microphone can be affected by the skin, which causes both sound attenuation and distortion, particularly at high frequencies. As the degree of attenuation and distortion through the skin is severe, speech quality evaluation parameters are needed for the received signal when designing an implantable microphone. However, the performance of most implantable microphones is only assessed based on the sensitivity and frequency response. Thus, practical indicators based on human auditory characteristics are needed for an objective evaluation of the performance of implantable microphones. In this study, a subcutaneously implantable microphone was designed, and its frequency response investigated using an in vivo experiment. Plus, to evaluate the objective indicators, the speech quality of the signals measured by the implanted microphone was calculated using a MATLAB program, and the indicators compared before and after implantation.

In vivo evaluation of mastication noise reduction for dual channel implantable microphone

Input for fully implantable hearing devices (FIHDs) is provided by an implantable microphone under the skin of the temporal bone. However, the implanted microphone can be affected when the FIHDs user chews. In this paper, a dual implantable microphone was designed that can filter out the noise from mastication. For the in vivo experiment, a fabricated microphone was implanted in a rabbit. Pure-tone sounds of 1 kHz through a standard speaker were applied to the rabbit, which was given food simultaneously. To evaluate noise reduction, the measured signals were processed using a MATLAB program based adaptive filter. To verify the proposed method, the correlation coefficients and signal to-noise ratio before and after signal processing were calculated. By comparing the results, signal-to-noise ratio and correlation coefficients are enhanced by 6.07dB and 0.529 respectively.

The measurement of transmission loss and absorption coefficient of the rat and porcine skin: Synthesizing artificial material for an implantable microphone test

With the advent of totally implantable hearing aids, the implementation and measurement of the microphone becomes an important issue. Engineers have to consider effects of the skin on the implantable microphone that did not exist in conventional hearing aid tests. In this paper, the transmission loss (TL) and absorption coefficient of rat and porcine skins were measured, and the synthesized skin was then implemented by using a gelatin gel that is widely used as an ultrasound phantom. From the measurement, the TL for rat and porcine skin was found to be 23.5±2.7dB and 30.4±2.8dB (mean±std) at 1kHz, respectively. Further, the absorption coefficients or the rat and porcine skin were measured as 0.029±0.011 and 0.031±0.012 at 1kHz, respectively. From the measurements, the TL values were found to be significantly increased at the high frequency and the absorption coefficients did not changed significantly in the 1–6kHz range. In additionally, the synthesized tissues also showed similar properties when compared with the animal experiments and they could be used to replace animal experiments for implantable microphones.

Feasibility test of implantable microphone at middle ear cavity

With the advent of implantable hearing aids, the implementation and acoustic sensing strategy of the implantable microphone becomes an important issue. Previously, implantable microphones were inserted under the skin, which causes loud noise signals from touching or moving the skin. In this reported work, mounting a microphone in a drilled hole to the middle ear cavity is proposed. This method does not cause any skin movement problems or aesthetic problems. Furthermore, surgical operation is easy because the microphone can be mounted onto the drilled bone and does not need to be clipped or attached to the ossicular chain. From guinea pig experiments (n = 5), the loss of transmission from the proposed microphone observed was only 1.17 ± 0.36 and 5.04 ± 0.84 dB (mean ± std.) for the 0.2-1 and 3-4 kHz bands. The lowest minimum detectable sound pressure was measured as 27.7 dB SPL (SNR: 6 dB) at 3150 Hz without pinna or canal effects.

Feedback characteristics between implantable microphone and transducer in middle ear cavity

With the advent of implantable hearing aids, implementation and acoustic sensing strategy of the implantable microphone becomes an important issue; among the many types of implantable microphone, placing the microphone in middle ear cavity (MEC) has advantages including simple operation and insensitive to skin touching or chewing motion. In this paper, an implantable microphone was implemented and researched feedback characteristic when both the implantable microphone and the transducer were placed in the MEC. Analytical and finite element analysis were conducted to design the microphone to have a natural frequency of 7kHz and showed good characteristics of SNR and sensitivity. For the feedback test, simple analytical and finite element analysis were calculated and compared with in vitro experiments (n = 4). From the experiments, the open-loop gain and feedback factor were measured and the minimum gain margin measured as 14.3dB.

Influence of the middle ear anatomy on the performance of a membrane sensor in the incudostapedial joint gap

There is a great demand for implantable microphones for future generations of implantable hearing aids, especially Cochlea Implants.An implantable middle ear microphone based on a piezoelectric membrane sensor for insertion into the incudostapedial gap is investigated. The sensor is designed to measure the sound-induced forces acting on the center of the membrane. The sensor mechanically couples to the adjacent ossicles via two contact areas, the sensor membrane and the sensor housing. The sensing element is a piezoelectric single crystal bonded on a titanium membrane. The sensor allows a minimally invasive and reversible implantation without removal of ossicles and without additional sensor fixation in the tympanic cavity.This study investigates the implantable microphone sensor and its implantation concept. It intends to quantify the influence of the sensor's insertion position on the achievable microphone sensitivity. The investigation considers anatomical and pathological variations of the middle ear geometry and its space limitations.Temporal bone experiments on a laboratory model show that anatomical and pathological variations of the middle ear geometry can prevent the sensor from being placed optimally within the incudostapedial joint. Beyond scattering of transfer functions due to anatomic variations of individual middle ears there is the impact of variations in the sensor position within the ossicular chain that has a considerable effect on the transfer characteristics of the middle ear microphone. The centering of the sensor between incus and stapes, the direction of insertion (membrane to stapes or to incus) and the effect of additional contact points with surrounding anatomic structures affect the signal yield of the implanted sensor. The presence of additional contact points has a considerably impact on the sensitivity, yet the microphone sensitivity is quite robust against small changes in the positioning of the incus on the sensor. Signal losses can be avoided by adjusting the position of the sensor within the joint.The findings allow the development of an improved surgical insertion technique to ensure maximally achievable signal yield of the membrane sensor in the ISJ and provides valuable knowledge for a future design considerations including sensor miniaturization and geometry.Measurements of the implanted sensor in temporal bone specimens showed a microphone sensitivity in the order of 1 mV/Pa.This article is part of a Special Issue entitled “MEMRO 2012”.

저작운동으로 인한 진동 잡음 신호의 경감을 위한 측두골 이식형 마이크로폰의 설계

A microphone for fully implantable hearing device was generally implanted under the skin of the temporal bone. So, the implanted microphone's characteristics can be affected by the accompanying noise due to masticatory movement. In this paper, the implantable microphone with 2-channels structure was designed for reduction of the generated noise signal by masticatory movement. And an experimental model for generation of the noise by masticatory movement was developed with considering the characteristics of human temporal bone and skin. Using the model, the speech signal by a speaker and the artificial noise by a vibrator were supplied simultaneously into the experimental model, the electrical signals were measured at the proposed microphone. The collected signals were processed using a general adaptive filter with least mean square(LMS) algorithm. To confirm performance of the proposed methods, the correlation coefficient and the signal to noise ratio(SNR) before and after the signal processing were calculated. Finally, the results were compared each other.

Implantable microphone with acoustic tube for fully implantable hearing devices

Fully Implantable hearing devices consist of a microphone that is implanted under the human skin. However after the implantation, the gain characteristics of the microphone are attenuated at the high frequencies because of the sound filtering effect of the skin and tissue. To solve this problems, we proposed an implantable microphone with an acoustic tube, which generates a resonance effect between the diaphragm and the acoustic transducer inside a case. By performing several experiments in water, it has been confirmed that the frequency response of the implantable microphone at high frequencies can be improved by use of the acoustic tube.

Active Vibration Attenuation For Implantable Microphone

The invention is directed to an implanted microphone having reduced sensitivity to vibration. In this regard, the microphone differentiates between the desirable and undesirable vibration by utilizing at least one motion sensor to produce a motion signal when an implanted microphone is in motion. This motion signal is used to yield a microphone output signal that is less vibration sensitive. In a first arrangement, the motion signal may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. Specifically, the motion signal may be scaled to match the motion component of the microphone output such that upon removal of the motion signal from the microphone output, the remaining signal is an acoustic signal.

이식형 마이크로폰과 진동체를 갖는 인공중이의 이득 보상을 위한 주파수 특성 고찰

ACROSS device, which is composed of an implantable microphone, a signal processor, and a vibrating transducer, is a fullyimplantable middle ear hearing device(F-IMEHD) for the recovery of patients with hearing loss. And since a microphone is implanted under skin and tissue at the temporal bones, the amplitude of the sound wave is attenuated by absorption and scattering. And the vibrating transducer attached to the ossicular chain caused also the different displacement from characteristic of the stapes. For the gain control of auditory signals, most of implantable hearing devices with the digital audio signal processor still apply to fitting rules of conventional hearing aid without regard to the effect of the implanted microphone and the vibrating transducer. So it should be taken into account the effect of the implantable microphone and the vibrating transducer to use the conventional audio fitting rule. The aim of this study was to measure gain characteristics caused by the implanted microphone and the vibrating transducer attached to the ossicle chains for the gain compensation of ACROSS device. Differential floating mass transducers (DFMT) of ACROSS device were clipped on four cadaver temporal bones. And after placing the DFMT on them, displacements of the ossicle chain with the DFMT operated by 1 <TEX>$mA_{peak}$</TEX> current was measured using laser Doppler vibrometer. And the sensitivity of microphones under the sampled pig skin and the skin of 3 rat back were measured by stimulus of pure tones in frequency from 0.1 to 8.9 kHz. And we confirmed that the microphone implanted under skin showed poorer frequency response in the acoustic high-frequency band than it in the low- to mid- frequency band, and the resonant frequency of the stapes vibration was changed by attaching the DFMT on the incus, the displacement of the DFMT driven with 1 <TEX>$mA_{rms}$</TEX> was higher by the amount of about 20 dB than that of cadaver's stapes driven by the sound presssure of 94 dB SPL in resonance frequency range.

Studies of MEMS Acoustic Sensors as Implantable Microphones for Totally Implantable Hearing-Aid Systems

There is a need for high-quality implantable microphones for existing semiimplantable middle-ear hearing systems and cochlear prosthesis to make them totally implantable, thus overcoming discomfort, inconvenience, and social stigma. This paper summarizes and compares the results of an in-vitro study on three design approaches and the feasibility of using microelectromechanical system acoustic sensors as implantable microphones to convert the umbo vibration directly into a high-quality sound signal. The requirements of sensors were selected including the ability to withstand large body shocks or sudden changes of air pressure. Umbo vibration characteristics were extracted from literature and laboratory measurement data. A piezoelectric vibration source was built and calibrated to simulate the umbo vibration. Two laboratory models of the acoustic sensor were studied. The model-A device, using electrets-microphone as the sensor, was designed and tested in the laboratory and on temporal bones. The results verify that the laboratory measurement is consistent with the temporal bone characterization and achieves a near flat frequency response with a minimum detectable signal of a 65-dB sound-pressure-level (SPL) at 1 kHz. The model-B sensor was then designed to increase the sensitivity and provide an easy mounting on umbo. The model-B device can detect 40-dB SPL sound in the 1-2 kHz region, with 100-Hz channel bandwidth. The results of model-A and model-B displacement sensors and the acceleration sensor are summarized and compared. A preliminary design of the implantable displacement sensor for totally implantable hearing-aid systems is also presented.

Dual feedback control system for implantable hearing instrument

The invention is directed to an implanted microphone having reduced sensitivity to vibration. In this regard, the microphone differentiates between the desirable and undesirable vibration by utilizing at least one motion sensor to produce a motion signal when an implanted microphone is in motion. This motion signal is used to yield a microphone output signal that is less vibration sensitive. In a first arrangement, the motion signal may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. Specifically, the motion signal may be scaled to match the motion component of the microphone output such that upon removal of the motion signal from the microphone output, the remaining signal is an acoustic signal.

Soft tissue placement of implantable microphone

Provided herein are systems and methods where an implantable microphone of an implantable hearing system is positioned at a location spaced from the surface of the patient's skull. More specifically, the microphone is mounted to soft tissue of the patient to at least partially isolate the microphone from skull-borne vibrations. Accordingly, by utilizing a soft tissue mount, the microphone may be made more sensitive to ambient sounds with reduced concern to amplification of non-ambient vibrations caused by skull-borne vibrations including, for example, transducer feedback, talking and/or chewing. The system will further include an auditory stimulation device that is located proximate to the skull of the patient and which is operative to stimulate an auditory component of the patient in accordance with an output signal generated by the microphone. A subcutaneously routed signal wire may extend between the implanted microphone and the auditory stimulation device.

Implantable microphone having sensitivity and frequency response

Implantable microphone devices that may be utilized in hearing systems are provided. An implantable microphone device allows the implantable microphone's frequency response and sensitivity to be selected. A microphone device with an increased membrane flexibility and a decreased acoustic compliance of the sealed cavity. Vibrations of a membrane are transmitted through a primary air cavity and through an aperture of a microphone. Keeping a flexible membrane and decreasing the sealed air cavity compliance are the preferred way to simultaneously increase overall sensitivity of the device, and move the resonance peak to higher frequencies.

Anatomical Vibrations That Implantable Microphones Must Overcome

The goal of this study was to measure the tissue vibration amplitude that would be associated with an implantable microphone. Totally implantable hearing devices have been desired by the hard-of-hearing community for some time. However, an implanted microphone must pick up desired acoustic signals in the presence of undesired signals, including vibration. To design an effective microphone, the level of tissue vibrations originating from anatomical sources and the implanted transducer must be understood. Using a laser Doppler vibrometer and an accelerometer, tissue vibrations were measured under the following conditions: (1) Normal control subjects during vocalization (n=4); (2) Vocalization and biological sounds measured on cranium and in soft tissue on normal subjects (n=6); (3) Transducer vibration measured on Otologics semi-implantable hearing device wearer (n=1) and human cadavers (n=4 ears). Anatomical noise vibrations are 20 to 25 dB greater in soft tissue for frequencies less than 1,000 Hz than on the cranium, whereas vibrations due to implanted transducers are 20 to 25 dB greater on the cranium than in soft tissue inferior to the mastoid. Chewing vibrations are 10 to 15 dB greater than vocalization on the mastoid. Mastoid vibration levels measured in patients are equivalent to those in cadavers. Vibration levels do not vary significantly with respect to location on the cranium next to the pinna. The greatest anatomical vibrations that an implanted microphone must overcome are because of vocalization in the soft tissue inferior to the mastoid and chewing vibrations on the mastoid. A human cadaver is an appropriate model for transducer cranial vibration studies. If the implantable microphone is placed on the cranium near the pinna, it makes little difference with regard to actual location.

High contact count, sub-miniature, full implantable cochlear prosthesis

A fully implantable cochlear prosthesis includes: (a) an implantable hermetically sealed case (100) wherein electronic circuitry including a battery and an implantable microphone (1), are housed, (b) an active electrode array (29) that provides a programmable number of active electrode contacts through which stimulation current may be selectively delivered to surrounding tissue, preferably through the use of appropriate stimulation groups, and (c) a connector (9) that allows the active electrode array to be detachably connected with the electronic circuitry within the sealed case. The active electrode array provides a large number of both medial contacts and lateral contacts, any one of which may be selected to apply a stimulus pulse through active switching elements included within the array. The hermetically sealed case within which the electronic circuitry, battery, and microphone are housed may be replaced, when needed, through minimally invasive surgery. Further, the electronic circuitry housed within the hermetically sealed case may be programmed, as needed, using acoustic signals from an acoustic remote control (106) and/or RF control signals from an external programmer (104).

Implantable microphone having improved sensitivity and frequency response

The present invention is a microphone device (108) with an increased membrane flexibility, and decreased acoustic compliance of sealed cavity (200). Vibrations of a membrane (202) are transmitted through a primary air cavity (206), and through an aperture (202) of a microphone (208).

Fluid filled microphone balloon to be implanted in the middle ear

An implantable microphone system, usable with a cochlear implant system or other hearing aid prosthesis, detects sound pressure waves (acoustic waves) at a movable member within the middle ear, e.g., the tympanic membrane or the stapes, through a fluid communication channel (20) established between the middle ear movable member and a microphone capsule (10). The microphone capsule (10) includes two compartments (11, 12) separated by a flexible diaphragm (13). One compartment (12) is in fluid communication with a thin-walled balloon, filled with a suitable fluid (30), positioned in contact with the movable member within the middle ear. The other compartment (11) is mechanically coupled through a suitable mechanical linkage (16) to a microphone sensor (14). The microphone sensor, in turn, is electrically connected to the cochlear implant system or other hearing aid prosthesis.

Implantable cochlear stimulator system incorporating combination electrode/transducer

A hearing aid system provides acoustic modulation of the fluid within the cochlea of the inner ear corresponding to a first frequency range of sensed acoustic signals, e.g., lower-to-middle frequencies of the audible range, and electrical stimulation of the cochlea corresponding to a second frequency range, e.g., high frequencies of the audible range. In a preferred implementation, a short electrode/transducer array is provided for use with the hearing system. Such array is adapted to be inserted into the basal region of the scala tympani of the cochlea. The electrode/transducer array includes a plurality of spaced-apart electrode contacts through which electrical stimulation is provided to stimulate ganglion cells located in the basal region of the cochlea, which cells are responsible for perceiving the higher frequencies of the acoustic energy. The electrode/transducer further includes an acoustic modulator as an integral part thereof, in fluid communication with an acoustic transducer, through which acoustic modulation may be coupled to the fluid within the cochlea, thereby allowing normal hearing processes to occur in the cochlea. In the preferred implementation, the lower frequencies of sensed acoustic energy are processed to provide modulation of the acoustic modulator. An implantable cochlear stimulator (ICS), including the acoustic transducer and coil, and implantable speech processor (ISP), including an implantable microphone, are used with the system. In an alternative embodiment, the acoustic modulator within the electrode/transducer array is used as a sensor, to sense fluid modulation within the cochlea resulting from a functioning middle ear, and the acoustic transducer converts such sensed fluid modulation to electrical signals, thereby providing the function of an microphone implanted in the cochlea.

Biomechanical Aspects in Implantable Microphones and Hearing Aids and Development of a Concept with a Hydroacoustical Transmission

The middle ear functions as a sensitive pressure receptor. This implies that it not only transmits sound pressure waves with molecule-sized vibrational amplitudes, but that it also reacts to the million times larger variations of ambient air pressure. This pressure induces movements of the tympanic membrane and of the attached ossicular chain of up to 1,000 microm. Any artificial device that contacts these sound-transporting elements, be it a receiver for an implantable microphone or a transducer for an implantable hearing aid, has to respect these two different modes of biomechanical behavior. A hydroacoustical transmission system has therefore been developed consisting of a water-filled flexible tube, which contacts the ossicular chain with a balloon tip, and which is connected to a piezo-electric transducer at its other end. This soft contact prevents a localized pressure load and does not restrain the free movement of the underlying ossicle during ambient pressure variations. Temporal bone experiments showed that the device transmits vibration energy in good acoustical quality. The device can also be used in a reverse mode, working as a microphone, for example for a totally implantable hearing aid or a cochlear implant. This microphone concept has the advantage that it incorporates the biologic sound receiving components (the tympanic membrane and the ossicular chain micromechanics) into a technical device.