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ACOUSTICAL PHYSICS > 2 Ch 8: Transducers > Flashcards

2 Ch 8: Transducers Flashcards

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1
Q

Define ‘transducer’.

A

Any device that converts one form of energy into another.

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2
Q

During ___, electrical energy from the system is converted into sound.

A

transmission

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3
Q

During ___, the reflected sound pulse is converted into electricity.

A

reception

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4
Q

This is the property of certain materials to create a voltage when they are mechanically deformed or when pressure is appiled to them.

A

The piezoelectric effect

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5
Q

This is the process of piezoelectric materials that change shape when a voltage is applied to them.

A

reverse piezoelectric effect

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6
Q

Materials which covert sound into electricity (and vice versa) are called…

A

piezoelectric or ferroelectric

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7
Q

The piezoelectric material commonly used in clinical transducers that are synthetic are…

A

lead zirconte titanate or PZT

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8
Q

PZT is also known as…

A

ceramic, active element, or crystal.

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9
Q

This cylindrical tube, constructed of metal or plastic, protects the internal components of the transducer from damage.

A

case

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10
Q

This insulates the patient from electrical shock.

A

case

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11
Q

This thin metallic barrier lines the inside of the case.

A

electrical shield

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12
Q

This prevents spurious electrical signals in the air, unrelated to diagnostic information, from entering the transducer.

A

electrical shield

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13
Q

This helps prevent electrical noise from contaminating the clinically important electrical signals used to create diagnostic images.

A

electrical shield

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14
Q

This is a thin barrier of cork or rubber that isolates or ‘uncouples’ the internal components of the transducer from the case.

A

acoustic insulator

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15
Q

This prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer.

A

acoustic insulator

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16
Q

This provides an electrical connection between the PZT and the ultrasound system.

A

wire

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17
Q

This requires an electrical contact so that during transmission the voltage from the u/s system can cause it to vibrate and produce an ultrasonic wave.

A

PZT or active element

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18
Q

This produces a voltage that must return to the system for processing into an image.

A

PZT or active element

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19
Q

This is postioned in front of the PZT at the face of the transducer.

A

matching layer

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20
Q

This increases the efficiency of sound energy transfer between the active element and the body.

A

matching layer

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21
Q

This protects the active element.

A

matching layer

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22
Q

How thick is the active element/PZT?

A

one-half wavelength

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23
Q

How thick is the matching layer?

A

one-quarter wavelength

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24
Q

This is bonded to the back of the active element.

A

backing material or damping element

25
Q

This reduces the ‘ringing’ of the PZT.

A

backing material or damping element

26
Q

This is commonly made of epoxy resin impregnated with tungsten filaments.

A

backing material or damping element

27
Q

When an electrical spike excites the PZT, this restricts the extent of PZT deformation.

A

backing material or damping element

28
Q

T/F? Crystal damping enhances axial resolution.

A

true

29
Q

The matching layer and gel ___ the efficiency of sound transfer betwen the ___ and the skin.

A

increase, transducer’s PZT

30
Q

T/F? Damping material has a low degree of sound absorption.

A

false, a HIGH degree

31
Q

T/F? Damping material has an acoustic impedance similar to PZT.

A

true

32
Q

The three consequences of using backing material are…

A
  1. decreased sensitivity
  2. wide bandwidth
  3. low quality factor
33
Q

During reception, tranducers with ___ are less able to convert low-level sound reflections into meaningful electrical signals.

A

damping material

34
Q

This is the range of frequencies in the pulse.

A

bandwidth

35
Q

Long duration events are ___ bandwidth, and short duration events are ___ bandwidth.

A

narrow, wide (broadband)

36
Q

This is a unitless number that is inversely related to bandwidth.

A

quality factor

37
Q

Main frequency divided by bandwidth equals…

A

quality factor.

38
Q

Because imaging probes used backing material and have a wide bandwidth, they are often referred to as…

A

low-Q.

39
Q

Transducers used in therapeutic u/s and continuous wave Doppler do not contain…

A

backing material.

40
Q

Transducers used in therapeutic u/s and continuous wave Doppler have…

A

narrow bandwidth and high-Q.

41
Q

A 3 MHz transducer with a bandwidth of 4 MHz has a Q factor of…

A

3/4 or .75.

42
Q

Q factor and pulse length are ___ related.

A

directly. The shorter the pulse, the lower the Q factor.

43
Q

This is the process of exposing material to a strong electrical field while being heated to a substantial temperature.

A

polarization

44
Q

The temperature at which PZT is polarized is called…

A

the Curie point or the Curie temperature.

45
Q

The loss of piezoelectric properties is called…

A

depolarization.

46
Q

This is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation.

A

sterilization

47
Q

This is the application of a chemical agent to reduce or eliminate infectious organisms on an object.

A

disinfection

48
Q

What determines the frequency of sound produced by a transducer?

A

Depends on whether it produces a continuous wave or a pulse.

49
Q

The frequency of sound emitted by a ___ probe is equal to the frequency of the electrical signal.

A

continuous wave

50
Q

What is the frequency of sound from continuous wave transducer when the transmitter creates a 6 MHz electrical signal?

A

6 MHz, electrical frequency = acoustic frequency

51
Q

The frequency of sound created by a ___ probe depends upon the characteristics of the active element in the transducer.

A

pulsed wave

52
Q

What characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?

A
  1. the speed of sound in the PZT

2. the thickness of the PZT

53
Q

The speed of sound in the PZT and the frequency of sound are ___ related.

A

directly. The faster the speed of sound in the PZT, the higher the frequency of sound.

54
Q

The pped of sound in most piezoelectric material ranges from…

A

4 to 6 mm/microseconds (about 4 times greater than the speed of sound in soft tissue).

55
Q

The PZT thickness and frequency are ___ related.

A

inversely. The thinner the PZT, the higher the frequency pulses.

56
Q

The thickness of PZT crystals in diagnostic imaging transducers range from…

A

0.2 to 1 mm.

57
Q

PZT sound speed (mm/microseconds) divided by twice the PZT thickness (mm) equals…

A

frequency (MHz).

58
Q

The thickness of the PZT crystal in a pulsed wave transducer is equal to…

A

one-half of the wavelength of sound in the PZT.

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