The Signal Processing of the MEMS-based Analog Hearing Aid
Date Issued
2008
Date
2008
Author(s)
Lai, Chien-hsun
Abstract
In this thesis, a new analog hearing aid is proposed. The signals are processed in the time domain. The signals are treated by three stages as following： the anterior treatment stage, the channels filtering and adjusting stage, and the demodulation and output stage. In the anterior treatment stage, the signals received from the environment are filtered, amplified, and then modulated with the mixer. The modulated signals have higher frequency, equivalent to shorter wavelength, than the original ones. In the second stage, the modulated signals are filtered by a SFIT filter made by MEMS techniques and then adjusted the gain depending on the user’s hearing loss and the outside conditions. In the demodulation and output stage, signals are synthesizing and demodulating to drive the output speaker. The adoption of the mixer reduces the size of the channel filter in order to adapt to the micromachining techniques, leading to mass production and cost reducing.The behaviors of waves propagating in periodic piezoelectric substrates are the base for designing SFIT filters. From Floquet’s theorem, displacements and the electric potential can be expressed as the summation of infinite space harmonics series. The dispersion curves are solved from satisfying wave equations and periodic boundary conditions. The influences of periodic electrodes are analyzed and discussed separately, including various electric boundary conditions and mechanical effects. According to the results of wave analysis, plate wave filters are designed and used in the hearing aids.
Subjects
SAW
SFIT
Interdigital transducer
Hearing aids
Periodical structure
SDGs
Type
thesis
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