類比分頻式助聽器之信號處理研究

The Signal Processing of the MEMS-based Analog Hearing Aid

賴建勳(Chien-hsun Lai)

指導教授 ： 周元昉

國立臺灣大學/工學院/機械工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.10200

摘要

本篇論文提出一種新型的類比式助聽器，信號處理皆在時域中進行，利用斜指插換能器的特性，設計一個可分頻調整各頻道權重的濾波器，依需求彈性調整通帶之頻率響應，應用在助聽器之聽力損失補償。此外，由於聲音信號的頻率較低，因此使用混波器將待處理的聲頻信號調變至較高頻率後，才送入濾波器中進行濾波，處理完成的信號再加以解調，轉換為聲頻信號輸出，有效縮小濾波器之尺寸。

週期性電極的壓電結構之中的波傳行為，為設計助聽器濾波器之基礎，論文中分析週期壓電半無限域中的表面聲波波傳，以及週期壓電平板中的板波波傳，再延伸至週期疊層平板之中的波傳行為。由壓電材料的本構方程式以及統御方程式推導出波動方程式，週期性壓電結構下之波傳通解，可由無限多個空間諧波的線性組合來表示，經由同時滿足波動方程式和邊界條件，得到壓電結構中波傳的色散關係，以及位移場和電位的分佈。其中分析了短路電極和開路電極，以及電極的質量及彈性效應等邊界狀況，探討不同的邊界狀況對於波傳的影響。

根據先前獲得的結果，再以Delta-function模型得到指插電極的轉移函數，設計板波濾波器，應用在助聽器中之聽力損失補償，其後，規劃濾波器之製程步驟，採用微機電技術製作成品，並搭配混波器製作助聽器之信號處理電路。最後，使用頻譜分析儀進行量測，並探討助聽器在音頻之特性表現。

關鍵字

表面聲波 ； 斜指電極 ； 指插電極 ； 助聽器 ； 週期性結構

並列摘要

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.

並列關鍵字

SAW ； SFIT ； Interdigital transducer ； Hearing aids ； Periodical structure

參考文獻

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