A MINIATURE OMNIDIRECTIONAL MICROPHONE WITH SUPERIOR PERFORMANCE

  • Superior SNR (80 dB)
  • Highly compact, surface-mount design
  • Robust optical interferometer that yields performance advantages without compromising size

USING OPTICS TO ENHANCE PERFORMANCE OF OMNIDIRECTIONAL MICROPHONE TECHNOLOGY

Conventional microphones measure the motion of a compliant diaphragm using capacitive transduction. Criteria for high-fidelity motion detection conflict with criteria for low levels of thermal mechanical noise, or Brownian motion. This design conflict limits the SNR achievable by conventional MEMS microphones. Silicon Audio integrates optical interferometers with low-power, low-noise electronics to realize unprecedented performance in our omnidirectional microphones.


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HOW THE OPTICS WORK IN AN OMNIDIRECTIONAL MICROPHONE

At Silicon Audio, our optical detection approach uses a semiconductor laser to illuminate a system with a surface that splits a portion of the beam, while allowing a portion of light to reflect from a pressure-sensitive diaphragm. Through the interference of these light waves, extremely high displacement detection resolution is achieved. This, in-turn, results in extreme sound pressure resolution and high SNR, up to 80 dB, for an omnidirectional microphone.


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ULTRA-SMALL SURFACE-MOUNT DESIGN OF AN OMNIDIRECTIONAL MICROPHONE

As shown in the prototype image to the left (photographed from the back through the KOH etch cavity), our omnidirectional microphone achieves a surface-mount form-factor consistent with the smallest MEMS microphones today. Realization of successful microphones calls upon our expertise at Silicon Audio in microfabrication of MEMS elements, optoelectronic integration of photodiodes and semiconductor light sources, and acoustical packaging and modeling.  


RESEARCH BEHIND OUR OMNIDIRECTIONAL MICROPHONE

D. Kim and N. A. Hall, "Towards a Sub 15-dBA Optical Micromachined Microphone," The Journal of the Acoustical Society of America, vol. 135, pp. 2664-2673, May 2014.

D. Kim, C. T. Garcia, B. Avenson, and N. A. Hall, "Design and Experimental Evaluation of a Low-Noise Backplate for a Grating-Based Optical Interferometric Sensor," Journal of Microelectromechanical Systems, vol. PP (99), pp. 1-1, March 2014.

M. L. Kuntzman, C. T. Garcia, A. G. Onaran, B. Avenson, K. D. Kirk, and N. A. Hall, "Performance and Modeling of a Fully Packaged Micromachined Optical Microphone," Journal of Microelectromechanical Systems, vol. 20(4), pp. 828-833, August 2011.

N. A. Hall, M. Okandan, R. Littrell, B. Bicen, and F. L. Degertekin, "Simulation of Thin-Film Damping and Thermal Mechanical Noise Spectra for Advanced Micromachined Microphone Structures," Journal of Microelectromechanical Systems, vol. 17(3), pp. 688-697, June 2008.

N. A. Hall, M. Okandan, R. Littrell, B. Bicen, and F. L. Degertekin, "Micromachined Optical Microphone Structures with Low Thermal-Mechanical Noise Levels," The Journal of the Acoustical Society of America, vol. 122(4), pp. 2031-2037, October 2007.

N. A. Hall, B. Bicen, M. K. Jeelani, W. Lee, S. Qureshi, F. L. Degertekin, and M. Okandan, "Micromachined Microphones with Diffraction-Based Optical Displacement Detection," The Journal of the Acoustical Society of America, vol. 118(5), pp. 3000-3009, November 2005.

M. Okandan, N. Hall, B. Bicen, C. Garcia, and F. Degertekin, "Optical Microphone Structures Fabricated for Broad Bandwidth and Low Noise," in 2007 IEEE Sensors, Atlanta, GA, 2007, pp. 1472-1475.


MORE ABOUT THE CORE TECHNOLOGIES

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MEMS

The omnidirectional microphone highlights Silicon Audio’s expertise in MEMS and our familiarity with the attributes of silicon microfabrication that, in combination with optical and electronic elements, result in superior sound and vibration sensing.

Our MEMS experience...

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Optics

At Silicon Audio, our achievement of substantial improvements in fidelity and SNR, compared with other commercial MEMS microphones, is grounded in a deep understanding of advanced optics-based motion-detection principles.

Our OPTICS experience...


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Optimized Circuit Design

Unique circuit design challenges are introduced in the realization of the first commercial optical microphone, including photocurrent to voltage converters and closed loop actuation electronics.

Our OPTIMIZED CIRCUIT DESIGN experience...

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Acoustics

The optical microphone is free of many acoustical design constraints imposed on more conventional microphones, and advanced acoustical models are used to exploit this new space and achieve breakthrough performance.  

Our ACOUSTICS experience...