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Physic 2 > Transducer Design > Flashcards

Transducer Design Flashcards

1
Q

Another name for ultrasound probe and it’s function

A

Transducer

Converts energy from electrical energy to acoustic energy and than acoustic energy back to electrical energy

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2
Q

Transducer

A

Piezoelectric crystal or element

Signal conversion device

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3
Q

Crystal

A

Piezoelectric material

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4
Q

Element

A

Another name for the piezoelectric crystal

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5
Q

Scan-head

A

Another name for transducer

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6
Q

Probe

A

Another name for transducer

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7
Q

Transducer assembly

A

Another name for transducer including the housing and internal circuitry

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8
Q

Housing

A

Contains all probe components

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9
Q

Backing material

A

A mixture of metal, plastic, or epoxy bonded to the back of the crystal

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10
Q

Crystal - in the probe

A

Ceramic element that piezoelectric properties

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11
Q

Matching layer

A

Used to reduce sound refraction from the skin

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12
Q

When and who discovered the piezoelectric principle

A

Jacque and Pierre curie in the 1880’s

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13
Q

What does the piezoelectric principle explain

A

Why some material can convert electrical energy to mechanical energy and vice versa

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14
Q

What are some of the natural materials that have piezoelectric properties that were used in early machines

A

Quartz
Lithium sulphate
Rochelle salt
Tourmaline

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15
Q

What are some of the man-made synthetic crystals that are used in modern day equipment

A 
Lead zirconate 
Lead titanate
Barium titanate 
Lead zirconate titanate (PZT)
Polyvinylidene Fluoride (PVFD)
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16
Q

What are the man-made ceramic synthetic crystals

A

PZT Barium Metaniobate

Barium Titanate

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17
Q

What are the man-made composite synthetic crystals

A

Epoxy with PZT inserts

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18
Q

What are the man-made polymer synthetic crystals

A

PVFD

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19
Q

How does the piezoelectric effect (direct) occur when a mechanical pressure is applied

A

The mechanical pressure deforms the crystal
This changes the orientation of the electric dipoles
This change produces a small electrical voltage

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20
Q

How does the reverse piezoelectric effect occur when a electrical voltage is applied

A

The electrical voltage changes the orientation of the dipoles causing the crystal to expand and contract

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21
Q

What are electric dipoles

A

The molecules with the crystal with a positive charge at one end and a negative charge at the other

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22
Q

How can any dipolar material be influenced

A

By a electrical or magnetic field

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23
Q

Can a random alignment of dipoles cause sufficient vibration when a electrical current is applied

A

No

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24
Q

Why is proper alignment of dipoles needed

A

It allows for a better vibration of the crystal

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25
Q

What must be considered when the crystal vibrates

A

That different modes of vibration may occur

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26
Q

What was the shape of the crystal in early probes

A

Disc

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27
Q

What were the two modes that the crystal could the vibrate in early probes

A

Thickness mode

Radial mode

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28
Q

Are the crystals in modern day probes shaped differently than early probes

A

Yes

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29
Q

What are the three modes of vibrations that crystals can vibrate in today’s probes

A

Thickness
Length
Width

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30
Q

What is the most desirable vibration in today’s probes

A

Thickness

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31
Q

Why are synthetic materials used in the production of crystals

A

Allows a more pure product to be developed because there are less imperfections

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32
Q

How are substance aligned so that they can enhance the piezoelectric properties for ultrasound production

A

A substance is heated beyond its Currie temp which forces the bonds between the molecules to weaken and when subjected to a electrical field the dipoles align accordingly and when the substance is cooled the bonds strengthen

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33
Q

What is the Currie temperature for PZT

A

350° Celsius

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34
Q

What does reheating do to synthetic crystals and why are probes not put into autoclaves

A

Reheating can potentially cause depolarization, which why probes are not put into an autoclave. Also the plastic would melt

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35
Q

What kind of bath are the substance subjected to that will cause the bonds to weaken

A

Oil bath

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36
Q

What determines what frequencies a probe can emit

A

The crystal

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37
Q

What are the different frequencies

A

Resonate
Driving
Operating
Harmonic

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38
Q

What is resonant frequency

A

The frequency that the crystal likes to ring at

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39
Q

What determines resonant frequency

A

Crystal material

Crystal thickness

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40
Q

What is another name for resonant frequency

A

Fundamental frequency

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41
Q

What is driving frequency determined

A

By the Alternating current (AC) voltage that is sent to the crystal

42
Q

What is driving frequency

A

The different frequency that a crystal can be forced to ring at because of the voltage being altered

43
Q

What is the operating frequency

A

The frequency that is being used to scan

44
Q

What is the Harmonic frequency

A

Two times the resonant frequency

45
Q

How are lower frequencies and higher frequencies of a crystal determined

A

By crystal thickness

46
Q

What produces lower frequencies

A

Thicker crystals

47
Q

What produces higher frequencies

A

Thinner crystals

48
Q

Thickness of the crystal which determine resonance frequency is equal to what

A

1/2 wavelength

49
Q

What is the relationship of crystal thickness to frequency

A

Proportional

Ex: doubled thickness = 1/2 f

50
Q

What is important when calculating crystal thickness

A

Speed of sound in the crystal as the constant

51
Q

What is a crucial part of transducer design

A

Backing material

52
Q

What is the backing material typically

A

Epoxy resin with metal powder (tungsten)

53
Q

Where is the backing material located on the crystal

A

On the back

54
Q

What’s another name for backing material

A

Damping block

55
Q

What is the purpose of the backing material

A

To reduce the SPL which will improve axial resolution

56
Q

What does the backing material do the amplitude of the wave

A

It reduces it, which reduces sensitivity

57
Q

Anything that improves the spl also

A

Improves the axial resolution

58
Q

What would happen if the amount of damping material increased

A

The length of the pulse will shorten

59
Q

What is another function of the damping material

A

Absorbing sound so that reflections don’t occur behind the crystal

60
Q

How does the damping material absorb sound

A

The Z value of the damping must be comparable to the element

61
Q

Typically how many cycles per pulse are produced as a result of the damping material

A

2-3

62
Q

What length of a pulse is ideal to improve resolution

A

Short

63
Q

What is dynamic damping

A

Is an electronic means to suppress the ringing of the crystal

64
Q

When is dynamic damping used

A

In Doppler

65
Q

What is the matching layer

A

Prevent sound from returning to probe before entering the patient

66
Q

Why is the matching layer important

A

The z value that the matching layer has between the crystal and the skin helps reduce the amount of reflection

67
Q

What is the potential problem of adding a matching layer

A

The reflections that can occur between them and the crystal

68
Q

What is the key to solving the problem of the matching layer

A

Cut the thickness of the matching layer in 1/4 of the wavelength

69
Q

What does 1/4 of the wavelength do

A

It helps create destructive interference of waves that reverberate between the matching layers

70
Q

Are there multiple matching layers used for the multiple frequencies that come out of the probe

A

Yes

71
Q

The many matching layers will accommodate multiple frequencies which will improve what

A

Improves the transmission and reception of a wide bandwidth of frequencies

72
Q

What is the gel considered as

A

A matching layer as it helps the sound transmit into the patient

73
Q

Does the gel have a z value between the last matching layer of the probe and the skin

A

Yes

74
Q

What method did older technology use for driving voltage

A

Spike voltage

75
Q

What method did newer technology use for driving frequency

A

Burst voltage

76
Q

What kind of current does spike voltage use to vibrate the crystal

A

Direct

77
Q

Direct current

A

Current from the pulse hits the crystal where one spike is equal to one pulse

78
Q

Another name for dc current

A

Saw-tooth voltage

79
Q

What type of current does burst voltage use

A

Alternating current

80
Q

Alternating current

A

Current from the pulser hits the crystal where one voltage burst is equal to one pulse

81
Q

Burst voltage

A

Looks like a sine wave

Frequency of the voltage determines the frequency of the probe

82
Q

In ac mode what determines the resonating frequency

A

Driving frequency of the voltage

83
Q

In dc mode what determines the resonant frequency

A

The driving frequency and the resonant frequency are always equal to each other

84
Q

Bandwidth

A

The range of frequencies that are produced by a pulse

85
Q

When a crystal rings at its resonant frequency what normally happens

A

A very small range of frequencies are produced

86
Q

What happens when the crystal is dampened

A

The pulse length shortens and a greater range of frequencies are emitted from the probe

87
Q

What does crystal thickness and material determine

A

The most efficient frequency to ring at

88
Q

Shorter the pulse

A

Wider the bandwidth

89
Q

What does a wider bandwidth mean

A

More options of what driving frequency can be chosen

90
Q

What does the size of the bandwidth and attenuation limit

A

The frequencies that the probe can be driven at

91
Q

Frequencies that have an amplitude of less than half of the resonant frequency are

A

Too weak to be used by the system

92
Q

6dB bandwidth

A

The useable bandwidth

Is equal to one half amplitude or 1/4 the intensity of the resonant frequency

93
Q

Fraction bandwidth

A

The common way to express the bandwidth of the probe

FB= bandwidth/ frequency

94
Q

Broadband design

A

A probe with a FB over 80%

95
Q

Quality factor

A

Another term for describing the band width of the probe

Q= frequency/bandwidth

The reciprocal of fraction bandwidth

96
Q

Low Q

A

Desirable for 2D scanning

97
Q

High Q

A

Colour Doppler
Pulsed Doppler
CW Doppler

98
Q

To optimize the 2D image

A

Use more damping to shorten the pulse

99
Q

An increased bandwidth means

A

A lower Q factor

100
Q

Modes requiring more sensitivity will benefit from

A

A narrower bandwidth or higher Q

101
Q

Reducing SPL

A

Increase in bandwidth

Physic 2 (5 decks)

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