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Piezoelectric crystals

This comprehensive guide explores piezoelectric crystals, their mechanical and electrical axes, and various vibration types in applications like microphones. It covers materials such as Seignette salt and PZT, types of piezoelectric plates, and configurations of piezoelectric bimorphs. A special focus is given to the classification of microphones including pressure, velocity, and mixed types. Additionally, it describes microphone sensitivity, directivity, and the impact of diffraction on performance characteristics, making it an essential resource for understanding electroacoustics.

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Piezoelectric crystals

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  1. Piezoelectric crystals Optical axis Z Mechanical axis Y Electrical axis X Plate with X-cutting KNT (Seignette salt) Quartz

  2. Vibration types of piezoelectric plates Compressional – longitudinal Compressional – thickness Shear – longitudinal Shear - thickness

  3. Piezoelectric materials • acid amonium phosphate (ADP) • Seignette-Rochelle’s salt (KNT) • barian titanete (BAT) • lead titanete zirconato (PZT) • polymers • vinylidene polyfluoride

  4. Piezoelectric bimorphs Bending bimorph Torsional (twisting) bimorph

  5. Piezoresistive transducer Housing Membrane Beam Piezoresistor

  6. Wheatstone’s bridge with piezoresistors

  7. Carbon (coal) transducer Membrane Semispherical electrode Coal pulver chamber Fixed electrode

  8. ELECTROACOUSTICS PART IVMICROPHONES

  9. Microphones – the general classification • Pressure mics – the electrical response is caused by variations in pressure of actuating sound wave • Velocity mics – the electrical response corresponds to particle velocity resulting from the propagation of sound wave through acoustic medium  the difference in pressure between two points in space  pressure gradient • Pressure-velocity mics – a combination of the above

  10. Microphones • Pressure microphones • carbon mics • condenser mics • piezoelectric mics • moving conductor mics (dynamic – moving coil)

  11. Microphones • Velocity mics • ribbon dynamic mics (with both sides of membrane actuated by the sound wave) • condenser mics (with both sides of membrane actuated by the sound wave)

  12. Microphones – kind of transducer • Dynamic microphones (moving coil, ribbon) • Condenser microphones („real” condenser, electret)

  13. Sensitivity of microphone • Sensitivity in free field • Sensitivity in diffused field • Pressure sensitivity

  14. Other parameters • Output impedance • Frequency response • Directivity (polar pattern) • Noise level

  15. Pressure microphones

  16. Carbon microphone

  17. Microphones – the voltage (at open circuit)

  18. Dynamic pressure microphone

  19. Frequency response

  20. Diffraction effect and its correction

  21. bass-reflex system

  22. bass-reflex system (cont.)

  23. Helmholtz resonator

  24. Helmholtz resonator (cont.)

  25. Condenser microphone

  26. Condenser microphone

  27. Electret microphone

  28. Ce Equivalent circuit

  29. Preamplifier for condenser mics

  30. Frequency responses Diffractional effects diaphragm The aperture for pressures equalization

  31. Gradient microphones – basic idea d

  32. Polar pattern of gradient mic

  33. Condenser gradient mic

  34. Equivalent circuit

  35. Pressure –gradient microphones

  36. Polar patterns (directivity)

  37. Polar patterns

  38. Variable polar patterns

  39. Cardioid condenser microphone with 2 membranes

  40. The schematic action of condenser cardioid microphone w. 2 diaphragms

  41. Equivalent circuit

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