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Exploring Electric Fields, Voltage, and Electret Microphone Technology

This document delves into the principles of electric fields and voltage distribution, specifically in the context of charged plates and the effects of introducing a third plate. It also addresses the sensitivity and construction of Brüel & Kjær systems, as well as the behavior of external loads under varying frequencies. Additionally, it examines electret microphones, their energy-harvesting capabilities, and key characteristics such as diaphragm stiffness and operational principles. The document is a valuable resource for understanding electrostatic devices and their applications.

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Exploring Electric Fields, Voltage, and Electret Microphone Technology

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Presentation Transcript

  1. Elektrisk felt og spenning

  2. Feltfordeling

  3. s1 Charged plates ----------------------------------------------------------------- +++++++++++++++++++++++++++++++++++++ Fraden section 3.1 and 3.2

  4. Adding a third plate ----------------------------------------------------------------- + + + + + + + + + + + + + + + + + + + + + s s1 ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ +++++++++++++++++++++++++++++++++++++

  5. (12.2) V ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ Disconnecting and moving the plate ----------------------------------------------------------------- + + + + + + + + + + + + + + + + + + + + + s s1

  6. Feeding a load V f

  7. Construction Brüel og Kjær

  8. Sensitivity Membrane tension Compression of air T V0=A s0

  9. Frequency response Low tension only log V log f

  10. Transfer functions log V = log s * V log f log f f Pressure  Displacement Displacement  Voltage Pressure  Voltage

  11. Response examples http://www.bksv.com/pdf/Bp0100.pdf

  12. Electret microphones • Are passive • Can harvest energy • No DC response (S(f=0)=0) • Two main variants: • Electret diaphragm • Cheap • Stiffness dominated by back volume • Electret backplate • Stable • Stiffness dominated by membrane tension • Can be used in reverse -> Electrostatic loudspeakers Are linear (p~V)

  13. dB scale 2 bar 2 Pa 20 µPa 20 µPa

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