醫用光纖式聲壓感測器

Optical Fiber Microphone

馮郅文(Tze-Weng Fong)

指導教授 ： 蔡正倫

中原大學/工學院/醫學工程研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200004

摘要

聲音是傳遞週遭環境訊息的方法之一，麥克風可做為換能器，將聲波轉換成易處理的電子訊號，然而並非一般的麥克風(如電容式麥克風)都可適用於所有的環境，在強電磁場或是射頻干擾的惡劣環境中易產生雜訊，使用光學式麥克風當作檢測器便可解決此問題。
本研究採用穩定度高且亮度佳的雷射二極體為光源，配合塑膠光纖及塑膠材質反射膜製成直徑7mm的光纖麥克風。實驗以單光纖的擺設方式做為雙光纖的設置依據，再利用雙光檢測膜振動時的光反射變化，並以差動電路檢測微弱的聲頻訊號以提高檢測的靈敏度。結果顯示當光源及檢測光纖之間呈20度角時，可得到較佳的靈敏度，其檢測靈敏度為6.7mV/μm，且在2.2kHz的共振頻率量測聲頻訊號時，其失真度為0.19%。
本研究以非導磁性的材質製作完成價格低廉、體積小的光纖麥克風，在電磁場中完全不受到干擾，且由光纖為媒介，傳導光訊號遠離磁場後再進行電路檢測，以避免磁場干擾電子電路。該光纖麥克風可應用於聲磁式氧氣濃度量測，改良成為主流型氧氣濃度感測器，以協助臨床醫療的診斷與監測。

關鍵字

光纖麥克風 ； 氧氣濃度量測 ； 振動 ； 音頻 ； 電磁場干擾 ； 位移

並列摘要

Sound is kind of method to transmit information from the surrounding environment, and microphone is the transducer that can transfer the sound wave to the electric signal. However, not all of the microphones could work suitably in any places, such as the condenser microphone, when it work at the heavy electromagnetic fields or RFI, the harsh environment will generate noise easily, but using the optical microphone could solve these problems.
In this study, an optical fiber microphone was made with laser diode as its light source that have high steadiness and brightness, the light is guided by plastic optical fibers. Place of two fibers were depend on the set up of single fiber from previous experiment. In order to eliminate the effect of scattering property in membrane, two optical fibers were use to detect the difference of light reflection at nearby positions. Sensitivity was also improved by detecting signal with a differential amplifier. The best sensitivity was 6.7 mV/mm when the source and receiving fibers were hold with 20 degree between them, and the diameter of microphone could reach 7mm. The T.H.D was 0.19% in measuring the acoustic signal at resonance frequency of 2.2kHz.
Optical fiber microphone was made with the non-magnetic material, it not only cost less but small size and never be interfered at the electromagnetic fields. Optical signal was guided by optical fibers keep the electromagnetic fields away that avoid interference the circuit. An optical fiber microphone could be applied to measure the acoustic signal in an acoustomagnetic oxygen sensor, it was useful to clinical diagnose or monitor.

並列關鍵字

Displacement ； Audio signal ； Vibration ； Oxygen concentration measurement ； EMI ； Optical fiber microphone

參考文獻

1. Cheng-Lun Tsai, “Paramagnetic oxygen measurement using an optical-fiber microphone,” Sensors and Actuators B, Vol. 73, pp.211-255, 2001.

2. N. Bilaniuk, “Optical Microphone Transduction Techniques,” Applied Acoustics, Vol. 50, No. 1, pp.35-63, 1997.

6. Alexander Kots, Alexander Paritsky, “Fiber optic micropone for harsh environment,” Harsh Environment Sensors Ⅱ, Phone-Or Ltd.,1999.

7. Yuan Libo, “Analysis of the compensation mechanism of a fiber optic displacement sensor,” Sensors and Actuators A, Vol. 36, pp.177-182, 1993.

8. John L. Remo, “Solid state optic vibration/displacement sensor,” Opt. Eng. Vol. 35, pp.2798-2803, 1996.