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MEMS based Optical Microphone


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MEMS based Optical microphone

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MEMS based Optical Microphone

  2. 2. OUT LINE…  Introduction  Optical microphone  Microphone structure  Fabrication  Future work  Implementation  Advantages  Conclusion
  3. 3. INTRODUCTION  Optical microphones posses innate resistance to electro magnetic interference & harsh environments.  MEMS technology provides a promising implementation for optical microphones.  Here, we discuss the design & characteristics of an intensity modulated optical level microphone.
  4. 4. OPTICAL MICROPHONE TRANSDUSER SCHEMES Introduced by Nykolai Bilaniuk in 1996  3 properties of light could be modulated. They are Intensity Polarization Phase 
  5. 5. Optical Microphone Classification Based on Transduction Mechanism
  6. 6. INTENSITY MODULATION Intensity modulating optical microphone can be sub- divided into a) Radiated wave intensity modulating microphone b) Evanescent wave intensity modulating microphone
  7. 7. Radiated Wave Intensity-modulating Microphone Types.
  8. 8. Evanescent Wave Intensity-modulating Microphone Types.
  9. 9. POLARIZATION MODULATION  Polarization modulation type devices alter the polarization of the light when in the presence of an acoustic field. TWO SUBCATEGORIES. a layer of liquid crystals is subjected to acoustic field induced shear stresses, which modulate the polarization of the light passing through.  “a moveable dielectric plate interacts with the evanescent field of a waveguide excited with both TE and TM modes,
  10. 10. Polarization Modulating Microphone Types.
  11. 11. PHASE MODULATION  A mechanism that changes either the physical length or the refractive index of an optical test path and recombining the result with the signal from a reference path. The two defined subgroups  Grating type devices  Interferometric devices.
  12. 12. Grating-Type Phase Modulating Microphone Types.
  13. 13. Interferometric Phase Modulating Microphone Types
  14. 14. MICROPHONE STRUCTURE The intensity-modulated optical microphone can be divided into four major physical parts.  MEMS chip  Optical fibers  Light source  Detection electronics
  15. 15. Block Diagram of the Optical Microphone
  16. 16. MEMS Chip  2.5mm X 2.5 mm silicon chip with a micro machined 1 mm diameter silicon nitride diaphragm Cross Section of the MEMS Chip.
  17. 17. Fiber Bundle in the MEMS Chip - Cross Section
  18. 18. Optical Fibers  The optical fibers selected for the optical microphone are the Thorlabs AFS105/125Y multimode optical fibers.  Used fibers  The for both transmit (Tx) and receive (Rx) cores of each fiber are color-coded, and surrounded by a white ring representing the cladding.
  19. 19. End View of the Optical Fiber Bundle
  20. 20. Optical Fibers in Steel Tubing
  21. 21. Optical Fiber Bundle Drawing.
  22. 22. Light source  The light source used by this optical microphone is the HP8168B Tunable Laser Source.  The maximum output power of the laser at 1550 nm is 0.515 mW.  An alternate laser source or an LED source could be used in place of the HP8168B.
  23. 23. Detection Electronics There are three schemes for use as detection electronics.  unreferenced output technique.  the referenced output technique.  Heterodyne modulation
  24. 24. FABRICATION OF THE OPTICAL MICROPHONE The fabrication of the optical microphone consists of two parts:  The MEMS optical diaphragm chip Fabricated by MEMS Exchange  The fiber bundle.
  25. 25. MEMS Exchange Process Both mask and wafers were purchased through the MEMS Exchange Wafers Used for Optical Microphone Fabrication
  26. 26. Packaging Process Abeysinghe et al. Packaging Technique.
  27. 27. Beggans et al. Packaging Technique.
  28. 28. Kadirval Packaging Technique.
  29. 29. Proposed Package for the Optical Microphone.
  30. 30. Proposed Optical Microphone Array Package.
  31. 31. FUTURE WORK  Future generation version of the optical microphone could be implemented with a single, large-core, highNA fiber (instead of a fiber bundle) using an LED as a light source to improve stability and frequency response.  A laser can provide 1000 times more power than an LED source when used as a light source in an intensity-modulated lever microphone.  Since the performance of a MEMS device is application specific, multiple packages and an array packaging technique should be developed to take advantage of the small size of the MEMS device.
  32. 32. IMPLIMENTATION Microphone Components
  33. 33. IMPLIMENTATION PHONE-OR Fibre Optical Microphone
  34. 34. ADVANTAGES  Pressure Gradient Accuracy  EMI/RF Immunity  Bandwidth (typically from 1Hz to 10kHz)  Dynamic Range (at least 85dB.)  Signal to Noise Ratio (SNR) in the order of 70dB.  Total Harmonic Distortion (THD) is less than 1% at 94dBre20μPa over the entire frequency bandwidth.  Sensitivity of the FOM is 100mV/Pa for the pressure microphones and 1.94 mV/(Pa/m) for the pressure gradient microphones.
  35. 35. CONCLUSION     MEMS-based intensity-modulated optical microphone is an excellent choice for applications with harsh environmental or size constraints. Optical MEMS microphones are currently marketed as a surveillance technology, as an EMI and RFI immune technology, and as a suitable technology for use in automobile voice recognition systems It is also possible to design the optical microphone with a significantly higher sensitivity and lower MDS by sacrificing frequency response and reducing the upper limit of the microphone’s dynamic range. more sensitive, fiber geometries are required to make an intensity modulated optical microphone suitable for aeroacoustic measurements.
  36. 36. References    S. D. Senturia, Microsystems Design. New York: Kluwer Academic, 2001. N. Bilaniuk, "Optical Microphone Transduction Techniques," Applied Acoustics, vol. 50, pp. 35-63, 1997. V. P. Klimashin, “Optical Microphone,” Pribory i Tekhnika Eksperimenta, no. 3, pp. 135-137, May 1979.
  37. 37. THANKS….