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CMI 350 > Ch.8 Transducers > Flashcards

Ch.8 Transducers Flashcards

1
Q

What is a transducer?

A

is any device that converts one form of energy into another

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2
Q

What two functions does the transducer perform?

A

Transmission
Reception

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3
Q

Transmission

A

electrical energy from the system is converted into sound

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4
Q

Reception

A

the reflected sound pulse is converted into electricity

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5
Q

Transducer Converts frm-to
ultrasound transmit
ultrasound receive
car engine

A

from To
electrical acoustic
acoustic electrical
chemical motion

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6
Q

Transducer Converts frm-to
Electric motion
Light bulb
Muscle

A

From To
electrical motion
electrical light & heat
chemical motion

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7
Q

what is the Piezoelectric effect?

A

describes the property of certian materials to create a voltage when they are mechanically deformed or when pressure is applied to them.

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8
Q

What is the reverse piezoelectric effect?

A

a process when piezoelectric materials change shape when a voltage is applied to them

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9
Q

What are piezoelectric materials?

A

materials which convert sound into electricity (and vice versa)
Also called:
piezoelectric
ferroelectric

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10
Q

What is the most commonly used piezoelectric material used in transducers ?

A

lead zirconate titanate (PZT)

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11
Q

What is the most commonly used piezoelectric material used in nature?

A

quartz and tourmaline

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12
Q

PZT synonyms 3

A

ceramic
active element
crystal

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13
Q

What are the seven components of a basic transducer?

A

Case
Electrical shield
Acoustic insulator
PZT or active element
Wire
Matching layer
Backing material (damping material)

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14
Q

Case

A

the cylindrical tube, constructed of metal or plastic, that protects the internal components of the transducer from damage. The case also insulates the patient from electrical shock

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15
Q

Electrical shield

A

A thin metallic barrier lining the inside of the case. The shield prevents spurious electrical signals in the air, unrelated to diagnostic information, from entering the transducer.

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16
Q

Electrical shield prevents

A

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

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17
Q

Acoustic insulator

A

A thin barrier of cork or robber that isolates or “uncouples” the internal components of the transducer from the case.

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18
Q

Acoustic insulator prevents

A

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

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19
Q

PZT or active element

A

Piezoelectric crystal shaped like a coin.

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20
Q

The characteristics of the sound beam emitted by the transducer are related to ________ of the ______ _______.
PZT is one-half ________ _____.

A

dimensions of the active element

wave length thick

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21
Q

Wire

A

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

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22
Q

The active element requires electrical contact (wire) so that during transmission, the voltage from the ultrasound system can cause the crystal to ______ and produce an ______ ______.

A

vibrate
ultrasonic wave

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23
Q

During reception, the crystal’s vibration produces a _______ that must return to the system for processing into a _____.

A

voltage
image

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24
Q

Matching layer

A

Positioned in front of the PZT at the face of the transducer. It is one-quarter wavelength thick.

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25
Q

What are the two functions of the matching layer?

A

1) Increases the efficiency of sound energy transfer btw the active element and the body.
2) Protects the active element

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26
Q

Backing Material
Crystal damping enhances what?

A

(damping element)
Bonded to the back of the active element, it reduces the “ringing” of the PZT.
-Axial Resolution

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27
Q

When an electrical spike excites the PZT, the backing material restricts the _ _ _ of ______.

A

the PZT deformation
The emitted sound pulse is dampened; thus it is short in duration and length

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28
Q

Transducer layers A-P? back to front?

A

case
Electrical shield
Acoustic insulator
Wire
Backing material
PZT
Matching layer
Acoustic insulator
Electrical shield

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29
Q

How thick is the matching layer? Active element?

A

1/4 wavelength thick
1/2 wavelength thick

30
Q

The matching layer and gel _____ the efficiency of sound transfer between the transducer’s _ _ _ and ____.

A

increases
PZT
skin

31
Q

Label in decreasing order of impedance:
PZT
Matching layer
Skin
Gel

A

PZT > matching layer > gel > skin

32
Q

The impedance of the PZT is about _ _ ____ greater than the impedance of ____.

A

20 times
skin

33
Q

The matching layer is designed with an impedance that is ______ that of the _____ _______ and the _____.

A

between
active element
skin

34
Q

The impedance of gel is _______ that of the ______ and _______.

A

between matching layer
biologic media

35
Q

What is the function of the gel?

A

it further increases the percentage of sound transmitted into out of the body.
described as coupling the transducer to the patient

36
Q

What are the two characteristics of the damping material?

A

high degree of sound absorption
acoustic impedance similar to PZT

37
Q

What are the consequences related to the use of a backing material?

A

decreased sensitivity
wide bandwidth
low quality factor

38
Q

Backing material not only _____ active element vibration during _______-, but also during _______ .

A

reduces
transmission
reception

39
Q

Why is decreased sensitivity by the backing material undesireable?

A

the transducers are less responsive to the tiny reflected sound waves returning from reflectors in the body.

40
Q

Transducers with damping material are less able to convert low-level ____ ______ into meaningful _____ _____.

A

sound reflections
electrical signals

41
Q

Resonant Frequency

A

a long pure tone of sound that vibrates freely for a long time at a single frequency

42
Q

The PZT is restricted from vibrating freely by the ____ ____ , and the pulse emitted by an imaging probe is a _____ duration sound “_____” rather than a steady ____ ____.

A

backing material
short
click
long
tone

43
Q

Bandwidth

A

is the range of frequencies in the pulse. It is the difference between the highest and lowest frequencies

44
Q

Imaging probes produce pulses that are identifies as ___ _______ or (_______).
Continuous wave doppler, do not use ______ ______ and produce ______ _____ pulses.

A

wide bandwidth
(Broadband)
backing material
narrow bandwidth pulses

45
Q

Long duration events are _____ bandwidth, whereas short duration events are ____ bandwidth.

A

narrow
wide

46
Q

Quality factor

A

is a unitless number that is inversely related to bandwidth.
Q-factor is the main frequency divided by the bandwidth.

47
Q

Q-Factor formula

A

Q-factor = main frequency / bandwidth

48
Q

Wide bandwidth probes have a ___ Q-factor.
Narrow bandwidth probes have a ___ Q-factor

A

low
high

49
Q

What is the relationship between Q-factor and pulse length?

A

directly related

50
Q

A short, damped pulse has a ____ Q-factor.
A longer, undamped pulse has a ______ Q-factor.

A

low
higher

51
Q

What are the 6 characteristics of imaging transducers?

A

1) Pulses with short duration and length
2) Uses backing material to limit ringing
3) Reduced sensitivity
4) Wide bandwidth or broadband
5) Lower Q-factor
6) Improved axial resolution

52
Q

What are the 6 characteristics of non-imaging transducers?

A

1) Creates continuos wave or pulses with long duration and length
2) No backing material
3) Increased sensitivity
4) Narrow bandwidth
5) Higher Q-factor
6) NO images created

53
Q

How is PZT created?

A

polarization
(created by exposing the material to a strong electrical field while being heated to a substantial temprature)

54
Q

What is the Curie temperature?

A

the temperature at which PZT is polarized

55
Q

What is the importance of the curie temperature?

A

if the polarized PZT is heated above the Curie temperature the crystal’s piezoelectric properties are destroyed. (called depolarization)

56
Q

Depolarization

A

the loss of piezoelectric properties (depolarized)

57
Q

Which method is used to clean transducers?

A

transducers should be disinfected with Cidex or other cold germicides.

58
Q

What determines the frequency of sound produced by a transducer?

A

differs depending on whether the transducer produces continuous wave sound or pulses

59
Q

Continuous wave produces

A

a continuous electrical signal that constantly excites or drives the active element in the transducer.

60
Q

The frequency of sound emitted by a continuous wave probe is equal to the?

A

frequency of the electrical signal

61
Q

Electrical frequency = _______

A

Acoustic frequency

62
Q

Pulse wave creates

A

a short duration electrical spike that travels thru the wire and strikes the PZT crystal in the transducer

63
Q

The frequency of sound created by the active element of a pulsed wave transducer depends upon the characteristics of what?

A

the active element in the transducer

64
Q

What 2 characteristics of the active element determine the frequency of sound created by a pulsed wave transducer?

A

1) Speed of sound in the PZT
2) Thickness of the PZT

65
Q

How does the speed of sound in PZT affect frequency?

A

the speed of sound in PZT and the frequency of sound are directly related

66
Q

What is the range of speed of sound in most piezoelectric materials?

A

from 4 to 6 mm/us
(4 times greater than the speed of sound in soft tissue)

67
Q

How does the thickness of the PZT crystal affect frequency?

A

PZT thickness and frequency are inversely related

68
Q

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

A

1/2 of the wavelength of sound in the PZT

69
Q

What are the two characteristics of high frequency pulsed wave imaging transducers?

A

1) Thinner PZT crystals
2) PZT with higher speeds

70
Q

What are the two characteristics of low frequency pulsed wave imaging transducers?

A

1) Thicker PZT crystals
2) PZT with lower speeds

71
Q

What is the formula for frequency (MHz) ?

A

(MHz) = sound’s speed in PZT (mm/us) / 2 x thickness (mm)

CMI 350 (11 decks)

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