ch 9 transducers

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  1. transducer
    device that converts one form of energy into another
  2. transducer transmission
    electrical energy to mechanical
  3. transducer reception
    mechanical to electrical
  4. 2 dimensions of crystal
    • width (diameter)
    • thickness (a/p)
  5. reverse piezoelectric effect
    definition and syn
    property of a material to change shape when an electrical voltage is applied to it

    • Happens on TRANSMISSION
    • ferroelectric
  6. piezoelectric effect
    property of a material to create a voltage when mechanically deformed (pressure is applied)

    Happens on RECEPTION
  7. natural piezoelectric materials
    • quartz
    • tourlamine
    • rochelle salts
  8. man made piezoelectric materials
    • PZT- Lead Zirconate Titate
    • Barium Titinate
    • ends in "ate"
  9. synonyms for piezoelectric material
    • crystal
    • active element
    • ceramic
  10. polarization
    • to make piezoelectric by putting under a high temperature
    • place in an electrical field
    • ions line up + with + - with -
    • cool rapidly and ions stayi n the same place
  11. curie point
    temperature to polarize or depolarize
  12. depolarization
    if piezoelectric material is put back in high heat
  13. transducer sterilization/disinfecting
    • autoclave- heat sterilization
    • disinfect- with chemicals - Cidex
  14. case
    • metal or plastic
    • insulates internal components from damage
    • insulates pt from shock
  15. electrical shield
    • think metallic barrier lining inside of case
    • prevents spurious signals in air from entering transducer
    • and contaminating clinical electrical signals
  16. acoustic insulator
    • thin barrier of cork or rubber that internal components from the case
    • prevents vibrations from inducing electrical voltage in the pzt
  17. pzt or active element
    • crystal itself
    • shaped like a coin
    • characteristics of sound beam related to dimensions of element
    • PZT is 1/2 wavelegnth thick
  18. wire
    provides electrical connection btwn PZT and us system
  19. matching layer
    • infront of PZT
    • increases efficiency of sound energy transfer btwn element and body
    • protects active element
    • 1/4 wavelegnth thick
  20. backing/damping material
    • back of element
    • reduces ringing of pulse
    • made of epoxy resin impregnated with tungsten filaments
    • restricts pzt deformation
    • creates short duration of pulse
    • enhances axial resolution
  21. impedance of PZT compared to skin
    pzt impedance 20xs greater than skin

    would reflect right back if no matching layer
  22. decreasing order of impedance
    • pzt
    • matching layer
    • gel
    • skin
  23. backing material characteristics
    • high degree of sound absorption
    • acoustic impedance similar to PZT
  24. consequences of backing material
    • decreased sensitivity
    • wide bandwidth
    • low quality factor
  25. decreased sensitivity
    less able to convert low level sound reflections into meaningful electrical signals in reception
  26. bandwidth
    the range or difference between the highest and lowest frequencies in the pulse
  27. short pulse
    ? bandwidth
  28. backing material and bandwidth
    wide bandwidth
  29. continuous wave and bandwidth
    narrow bandwidth
  30. quality factor
    unitless number related to bandwidth

    qf = main frequency/ bandwidth
  31. quality factor and bandwidth
    inversely related
  32. wide bandwidth probe has...
    narrow bandwidth probe has..
    • wide= low quality factore
    • narrow= high quality factor
  33. imagine probes have high bandwidth and
    low q factor
  34. q factor is directly related to
    pulse legnth

    • short and low
    • long and high
  35. duty factor of continuous wave
  36. 2 elements of continuous wave
    • always sending and always recieving
    • no image produced
  37. continuous wave has no
    damping or listening time
  38. sound frequency of cw probe
    = electrical frequency
  39. imaging transducers
    • high wide bandwidth
    • low Q
  40. q factor number
    unitless and less than 1
Card Set:
ch 9 transducers
2012-03-15 21:33:34

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