全像式光學麥克風之設計與開發

Design and Development of a Holographic Optical Element Acoustic Microphone

丁律妏(Lu-Wen Ting)

指導教授 ： 黃光裕

國立臺灣大學/工學院/機械工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02608

摘要

市售麥克風以電容式或動圈式為主，無法在高電磁干擾與高射頻干擾的環境下運作，而光學麥克風以光作為傳遞訊號的特性可以避免惡劣環境的影響。本論文利用全像式光學讀取頭的量測技術，以其體積小且緊緻、聚焦光點小、解析位移小等優點開發一光學麥克風。
本論文以光路模擬軟體和聲學理論對光路和麥克風薄膜進行分析，透過光學分析模擬找出最適合搭配在光麥克風的透鏡組，並透過模擬結果設計出互相搭配的麥克風腔體和光路模組，並由光學讀取頭性能量測S曲線與線性區域範圍，得知聚焦誤差訊號與位移之關係。在麥克風薄膜分析上，透過分析軟體（COMSOL）可得知不同模態的薄膜震動情形，並由計算結果得知薄膜變形量的分析。
整合光學量測系統與聲壓感測系統，本論文以直徑4 mm與6 mm的圓形聚對苯二甲酸乙二酯(PET)鍍鋁薄膜作為聲壓傳遞介質，對全像式光學麥克風進行靈敏度、訊噪比、頻率響應及各頻率失真度的性能量測。其結果顯示全像式光學麥克風具備高敏感度的特性，薄膜直徑4 mm與6 mm的光學麥克風敏感度分別為-41.47 dB與-31.09 dB，兩者皆可量到高達30 kHz的超聲波。薄膜直徑4 mm與6 mm光學麥克風的訊噪比分別為33.91 dB與34.37 dB。在頻率響應方面分別可以清楚解析出薄膜直徑4 mm第一共振頻10823.1 Hz，第二共振頻19279 Hz；薄膜直徑6 mm第一共振頻6015 Hz，第二共振頻13339 Hz。其失真度在在10 kHz以內能達到在5 %以內。

關鍵字

光學麥克風 ； 頻率響應 ； 全像式讀取頭 ； 聚焦誤差訊號

並列摘要

Condenser microphones and dynamic microphones are the major products on the market. However, these microphones cannot be used under EMI and RFI environments. Optical microphones are immune to these harsh environments as the signal is transmitted by light. This thesis is to design and develop an optical microphone based on the holographic optical element (HOE) pickup head, which have many advantages including a small and compact volume, a small focusing spot size, and high displacement resolution.
Using optical simulation software and acoustic theory, this study analyzes the light path and the membrane characteristics of the microphones. We find the suitable lens system through simulation of optical analysis. Base on the reasons of simulation, we design a microphone cavity and light path modules that are high compatible. The HOE pickup head measures the S-curve and the linear response region of the microphone, which can then be used to obtain the relationship between focus error signal and displacement. By the analysis of COMSOL, the different vibration modes of the thin film are derived and used to confirm their deformation.
Integrating the optical measure system and acoustic sensors, the circular polyethylene terephthalate (PET) membrane with 4mm and 6mm diameter are used as the mediums for performance measurements. We carry out a serious of experiments for the sensitivity, the signal noise ratio, the frequency response and the frequency distortion of the holographic optical microphone. The results show that the optical microphones have high sensitivity. The sensitivities of the membranes are -41.47dB and -31.09 dB respectively. Both have the ability to measure supersonic waves with frequency as high as 30kHz. The noise ratios are 33.91 dB and 34.37 dB respectively. The frequency response of 4mm film induces the first resonance frequency of 10823.1 Hz, the second resonance frequency of 19279 Hz. The 6 mm film has the first resonance frequency of 6015 Hz, the second resonance frequency of 13339 Hz. In which distortion is achieved less than 5% under 10kHz.

並列關鍵字

optical microphone ； frequency response ； holographic pick-up head ； focus error signal

參考文獻

[2] Kots, A. and Paritsky A., “Fiber optic micropone for harsh environment”, SPIE, Vol. 3852, 1999, pp106-112.

[3] Sagberg, H., Sudbo, A., Solgaard, O., Bakke, K. A. H., and Johansen, I. R., “Optical Microphone Based on a Modulated Diffractive Lens”, IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 15, 2003, pp1431-1433.

[4] Bilaniuk, N., “Optical Microphone Transduction Techniques”, Applied Acoustics, Vol. 50, 1997, pp35-63.

[8] He, G. and Cuomo, F. W., “Displacement Response, Detection Limit, and Dynamic Range of Fiber-optic Lever Sensors”, Journal of Lightwave Technology, Vol. 9, 1991, pp1618-1625.

[9] Hu, A., Cuomo, F. W., and Zuckerwar, A. J., “Theoretical and Experimental Study of a Fiber Optic Microphone”, Journal of the Acoustic Society of America, Vol. 91, 1992, pp3049-3056.