ch 9 transducers

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transducer

device that converts one form of energy into another
transducer transmission

electrical energy to mechanical
transducer reception

mechanical to electrical
2 dimensions of crystal
- width (diameter)
- thickness (a/p)
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
piezoelectric effect

property of a material to create a voltage when mechanically deformed (pressure is applied)

Happens on RECEPTION
natural piezoelectric materials
- quartz
- tourlamine
- rochelle salts
man made piezoelectric materials
- PZT- Lead Zirconate Titate
- Barium Titinate
- ends in "ate"
synonyms for piezoelectric material
- crystal
- active element
- ceramic
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
curie point

temperature to polarize or depolarize
depolarization

if piezoelectric material is put back in high heat
transducer sterilization/disinfecting
- autoclave- heat sterilization
- disinfect- with chemicals - Cidex
case
- metal or plastic
- insulates internal components from damage
- insulates pt from shock
electrical shield
- think metallic barrier lining inside of case
- prevents spurious signals in air from entering transducer
- and contaminating clinical electrical signals
acoustic insulator
- thin barrier of cork or rubber that internal components from the case
- prevents vibrations from inducing electrical voltage in the pzt
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
wire

provides electrical connection btwn PZT and us system
matching layer
- infront of PZT
- increases efficiency of sound energy transfer btwn element and body
- protects active element
- 1/4 wavelegnth thick
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
impedance of PZT compared to skin

pzt impedance 20xs greater than skin

would reflect right back if no matching layer
decreasing order of impedance
- pzt
- matching layer
- gel
- skin
backing material characteristics
- high degree of sound absorption
- acoustic impedance similar to PZT
consequences of backing material
- decreased sensitivity
- wide bandwidth
- low quality factor
decreased sensitivity

less able to convert low level sound reflections into meaningful electrical signals in reception
bandwidth

the range or difference between the highest and lowest frequencies in the pulse
short pulse
? bandwidth

wide
backing material and bandwidth

wide bandwidth
continuous wave and bandwidth

narrow bandwidth
quality factor

unitless number related to bandwidth

qf = main frequency/ bandwidth
quality factor and bandwidth

inversely related
wide bandwidth probe has...
narrow bandwidth probe has..
- wide= low quality factore
- narrow= high quality factor
imagine probes have high bandwidth and

low q factor
q factor is directly related to
pulse legnth
- short and low
- long and high
duty factor of continuous wave

100%
2 elements of continuous wave
- always sending and always recieving
- no image produced
continuous wave has no

damping or listening time
sound frequency of cw probe

= electrical frequency
imaging transducers
- high wide bandwidth
- low Q
q factor number

unitless and less than 1

Author:	rbeacr
ID:	141830
Card Set:	ch 9 transducers
Updated:	2012-03-15 21:33:34
Tags:	transducers
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Description:	transducers
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