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Two MOEMS Microphone Designs for Acoustic Sensing Applications

  • Berit S. Avset (a1), Kari A. H. Bakke (a1), Britta. G. Fismen (a1), Ib-Rune Johansen (a1), Henrik Rogne (a1), Håkon Sagberg (a1) and Dag T. Wang (a1)...

Abstract

Two different micro-optical microphones are presented. The first is based on interferometric read-out of a deflecting membrane, based on the Fabry-Perot principle. The sensing device is produced in Silicon by combining standard CMOS and MEMS processing. This ensures that high accuracy alignment and low cost production can be obtained. Optical sensor elements with a ring structure are included on one of the Fabry-Perot surfaces whereas the other surface is an optically transparent membrane. Light from an uncollimated light source such as a semiconductor laser or a LED, will form a ring pattern when transmitted through the membrane.

The other microphone principle presented is based on a diffractive lens. The structure has a metallic ring pattern separated from a reflecting membrane with an air gap. When the air gap is an odd number of quarter wavelengths of the impinging light, these surfaces form a binary phase diffractive lens. By placing a light source and a detector in the focal plane of the lens, the measured intensity will be highly sensitive to the position of the membrane. Similarly to the first microphone this device can be mass produced at low cost using micromachining techniques.

Results from prototype devices will be presented, proving both principles and showing excellent properties compared to expensive commercially available condenser microphones.

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References

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1 Bilaniuk, N. Optical Microphone Transduction Techniques, Applied Acoustics, volume 50, no. 1, pp 3563, 1997.
2 Greywall, D.S. Micromachined optical-interference microphone, Sensors and actuators, no 75, pp 257268, 1999.
3 Keating, D. Microphone engineering, Oxford Boston Focal Press, 1994.
4 Fismen, B. Grennberg, Avset, B. S. Rogne, H. Wang, D. Johansen, I-R., A novel micro-optical microphone based on the Fabry-Perot principle, presented at the Proc. MME, Sinaia, Romania, Oct. 2002.
5 Sagberg, H. Sudbø, A., Solgaard, O. Bakke, K.A. H., Johansen, I-R., Optical microphone based on a modulated diffractive lens. IEEE Phot. Techn. Lett. Volume 15 no 10, pp 14311433, 2003
6 Evensen, L. Westgaard, T. Avdeichikov, V. Carlen, L. Jakobsson, B. Murin, Y. Martensson, J., Oskarsson, A. Siwek, A. Whitlow, H. J. vanVeldhuizen, E. J. Westerber, L. Guttormsen, M., Thin Detectors for the CHICSi E-E Telescope, IEEE Trans. Nucl. Sci., volume 44, no. 3, pp 629634, 1997.

Two MOEMS Microphone Designs for Acoustic Sensing Applications

  • Berit S. Avset (a1), Kari A. H. Bakke (a1), Britta. G. Fismen (a1), Ib-Rune Johansen (a1), Henrik Rogne (a1), Håkon Sagberg (a1) and Dag T. Wang (a1)...

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