MEMS based multi-channel piezoelectric acoustic transducer for fully implantable cochlear implants

Yüksel, Muhammed Berat
This thesis presents multi-channel acoustic MEMS transducer that is able to work within the audible frequency range (250-5500 Hz) and mimic the operation of a cochlea by filtering incoming sound. This transducer is composed of eight thin film piezoelectric cantilever beams possessing different resonance frequencies. The transducer is well suited to be implanted in a middle ear cavity with an active volume of 5 x 5 x0.6 mm3 and 4.8 mg. Resonance frequencies and piezoelectric outputs of the beams are modeled by using Finite Element Method (FEM). Vibration experiments showed that the transducer was capable of generating up to 139.36 mVpp under 0.1 g excitation. Test results are consistent with FEM model on frequency (97%) and output voltage (89%) values. It was also tested with acoustical excitation in a test setup including artificial tympanic membrane and flexible connection equipment. In that case, it generated up to 50.7 mVpp under 100 dB Sound Pressure Level (SPL). Output voltages observed in acoustical and mechanical characterizations are the highest reported ones to the best of my knowledge. For the first time in the literature, acoustical transducer was excited with speech sound and recovered by using software. Spectrograms of recorded and recovered signals showed close patterns. Moreover, recovered sound was recognizable. Beside stand-alone tests, in-vivo and in-vitro tests have been conducted with stimulation circuits. This stimulation system can operate in 50 dB dynamic range. Finally, a new beam structure is proposed to improve hearing quality by expanding the covered bands as a future work.
Citation Formats
M. B. Yüksel, “MEMS based multi-channel piezoelectric acoustic transducer for fully implantable cochlear implants,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Electrical and Electronics Engineering., Middle East Technical University, 2020.