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Elektrisk felt og spenning

Elektrisk felt og spenning. Feltfordeling. s 1. Charged plates. -----------------------------------------------------------------. +++++++++++++++++++++++++++++++++++++. Fraden section 3.1 and 3.2. Adding a third plate. -----------------------------------------------------------------.

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Elektrisk felt og spenning

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  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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