Development of compact fiber-optic microphones

• Published in: The Journal of the Acoustical Society of America 1999-02, Vol.105 (2_Supplement), p.999-999
• Main Authors: Cho, Young C., Gary, Charles K., Ozcan, Meric, George, Thomas
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.424823

Advanced pressure sensors have been developed at NASA Ames Research Center, using fiber-optic technology. The development includes: compact size microphone for aeroacoustic measurements in wind tunnels with minimized flow–sensor interaction, and compact size pressure sensors for real-time measurements of flow transition over an airfoil. A prototype pressure sensor was designed and fabricated with a silicon nitride diaphragm mounted on a miniaturized ferrule. The sensor has a 3-mm diameter. Preliminary tests demonstrated excellent performance. The frequency response is steady and uniform within the design frequency limit, 100 to 5000 Hz. Its sensitivity, measured in terms of signal-to-noise ratio, is almost 10 dB better than the best condenser microphone available in a similar size (0.125-in diameter), and is better than any existing fiber-optic pressure sensor by at least three orders of magnitude. The overall performance of this sensor exceeds the initial expectation. The compact size and light weight of these sensors provide several advantages. The small size could allow tens of hundreds of sensors to be used together for applications such as microphone arrays. The flow–sensor interaction is smaller, providing more accurate measurements of pressure fluctuation of air flows over flight surfaces.