The Study Of Acoustic Signals Picked Up From Ossicular Chain By Floating Piezoelectric Microphone And Post-processing

OBJECTIVE:The purpose of the study was to research the possibility of picking up the acoustic from the different positions of the ossicular chain. A piezoelectric sensor, floating piezoelectric microphone, driven by acoustic vibration of the ossicles, is one possible design for a microphone for a totally implantable cochlear implant. The piezoelectric microphone, attached on the different positions of the ossicular chain, would pick up the vibration signals of the ossicular chain. The piezoelectric would transmit the vibration signals into the electrical signals, which will be helpful for studying the frequency curve of the ossicular chain’s vibration. According to the results of the study, we designed the new floating piezoelectric microphone.METHODS:(1) The floating piezoelectric microphones, fixed by spot-welders,5.0mm in length and1.5mm by1.2mm in rectangular cross section, were glued on the wind cap surface of the one testing speaker to pick up the acoustic, recorded by the Cool edit software, NI software and NI DAQ.(2) The frequency response of the floating piezoelectric microphone in various locations on the ossicular chain was analyzed by finite-element modeling and the3D reconstruction, in order to supply suggestions for the in vitro testing of fresh cadaver heads.(3) The piezoelectric microphone was placed at3various locations(the long process of incus; malleus; tympanic cavity) on the ossicular chains of5ears (3fresh cadavers) and stimulated by pure tones of different frequencies.(4) In the in vitro test, the delay time of the piezoelectric microphone is studied. Burst signals were given to the system of the in vitro test, while the NI equipment would record the input and out put signals simultaneously to compare the difference of the pulse time.(5) Study the platform of totally implantable cochlear implant prototype hardware, in order to analysis the signals from the FPM.(6)Based on the in vitro test, piezoelectric microphone was improved by a Soundbridge Clip, Tube feedthrough insulator and the laser capsulation, in order to improve the biocompatibility and the way of fixing.RESULTS:(1) The floating piezoelectric microphones could pick up the acoustic of the wind cap with the change of spot-welder from250Hz-8000Hz, with the NI software and NI DAQ, compared with the Cool edit software.(2) In the3D Modeling, the floating piezoelectric microphone could be attached on different positions of the ossicular chain with the small volume. Also, there was a flat frequency curve by picking up the vibration of the ossicular chain.(3) In vitro test, the floating piezoelectric microphone could pick up the vibration of the ossicular chain effectively and convert it into the electronic signals effectively both in the long process of incus and in the malleus. The average sensitivity of the FPM is-44.22dB rms ref1V at1000Hz in the long process of incus,-53.33dB rms ref1V at1000Hz in the malleus and-108.59dB rms ref1V at1000Hz in the tympanic cavity. The frequency curve is flat from1OOHz to6000Hz, decreasing on8000Hz.(4) Additionally, the frequency characteristics of the FPM are similar for the position of the long process of the incus and the malleus, especially at the frequency of500kHz and3000kHz.(5) We have tested the delay time of the FPM by picking up the tone burst, and found that the delay time was14.85ms in the test system.(6) The platform of totally implantable cochlear implant prototype hardware includes the high-frequency complementally encoding strategy and the virtual channel encoding strategy.(7) With the Ti clip and Laser capsulation, the new piezoelectric microphone can be attached on to the incus, without obvious Low-frequency interference, Resonance phenomenon and the short circuit of current.CONCLUSIONS:(1) The study proved the possibility of picking up the acoustic from the different positions of the ossicular chain in human by floating piezoelectric microphone.(2) The study also compared the frequency responses of the floating piezoelectric microphone in different positions of ossicular chain by3D reconstruction and in vitro test, which supplied the suggestion for choosing the better attached position.(3) With the development of the capsulation and the welding, the new floating piezoelectric microphone with laser capsulation is designed for the long-term implantation, which will be attached to the long process of the incus, with good capsulation and low interference, avoiding the error of handiwork.(4) The floating piezoelectric microphoneand the platform of totally implantable cochlear implant prototype hardware are expected to be used as an implantable middle ear microphone for the totally implantable cochlear implant. While, it is should be studied further on the signal’s processing, compensation and long-term research in the future for the totally implantable cochlear implant.