Chapter 3 Transducers - Notes

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1

Q-factor formuala

operating frequency/bandwidth

2

fractional bandwidth formula

bandwidth/operating frequency

3

Bandwidth formula

max frequency - min frequency

4

SPL

SPL = nc/f

5

NZL

NZL = (D^2 * f) / 6

6

speed of crystal

c = fo * (2 * thickness)

7

Operating frequency formula

fo = c/(2*thickness)

8

thickness formula

thickness = c/(2*fo)

9

Axial Resolution formula

1/2 SPL

10

If a transducer diameter is doubled, what happens to the NZL?

If a transducer diameter is doubled, the near zone length will quadruple?

11

If a transducer diameter is doubled, what happens to the depth of the focus?

If a transducer diameter is doubled, the focus is 4 times as deep.

12

If the operating frequency is doubled, what happens to the NZL?

If the operating frequency is doubled, the NZL is doubled.

13

focus beamwidth formula

focus beamwidth = 1/2 transducer diameter

14

True or False?

The U/S beam is razor thin.

False

beam has
length
width
height (thickness)

15

Transducer

device that converts energy from one form to another

16

electric motor

electricity to kinetic

17

people

chemical to kinetic

18

light bulb

electricity to light (heat)

19

Sound transducer

converts electricity to sound & vice versa

20

Audible transducer

speaker - electricity to sound
microphone - sound to electricty

21

amber - fossilized plant resin
quartz
rochelle salts
tourmaline

naturally occurring Piezoelectric materials

22

ceramics - lead zirconate titanante (PZT)
barium titanate
polyvinylidene fluoride (PVDF)

Man-made piezoelectric material

23

ferroelectric material

piezoelectric material

24

Piezoelectric principle

applied pressure (echo) comes back to the transducer, converted to electric energy.

25

Reverse Piezoelectric principle

when a matter is deformed by an applied voltage it produces a pulse.

when you control the electricity going in, you control the strength of the pulse.

26

What is the most commonly used piezoelectric material in U/S?

ceramics - lead zirconate titanante (PZT)

27

PZT

Piezoelectric element

28

ceramic

Piezoelectric element

29

crystal

Piezoelectric element

30

element

Piezoelectric element

31

Creation of Piezoelectric material

Heat to currie point
polling
cool it

32

polling

placing a material in a very strong electrical field while the material is at a high temperature

33

curie point

360 degrees

the temperature where piezoelectric materail loses it's piezoelectric properties.

34

Heat sterilize

Never

element will lose it's piezoelectric properties

35

when electricity is applied to PZT

vibrates then creates a mechanical longitudinal wave

36

Increases & decreases in alternating current change the voltage within the crystal

Piezoelectric Effect

37

One cycle of the operating (drive) voltage creates how many U/S pulses

2 or 3

38

How many cycles of (drive) voltage is required for Doppler?

5 to 30

39

Placing a material in a very strong electric field while the material is at a high temperature.

A) poling
B) curie point
C) piezoelectric
D) autoclaving

A) poling

40

Frequency of the driving voltage

equals the voltage of the sound produce by the transducer

41

preferred frequency

voltage of the sound produce by the transducer

42

operating frequency

voltage of the sound produce by the transducer

43

resonant frequency

voltage of the sound produce by the transducer

44

natural frequency

voltage of the sound produce by the transducer

45

What 2 things determine operating frequency

propagation speed of material - 4 to 6 mm/μs

thickness of the transducer - .2 - 1 mm

46

propagation speed of material

4 to 6 mm/μs

47

thickness of the transducer

.2 - 1 mm

48

thickness formula

thickness = .5λ

49

wavelength formula

λ = c/f

50

thickness (f)

thickness = .5c/f

51

Relationship between thickness and frequency

inverse

52

Relationship between thickness and wavelength

direct

53

pulses per second

PRF

54

voltage pulses per second

VRF

55

relationship between PRF & VRF

PRF = VRF

56

formula Pd

pd = nt

57

SPL formula

SPL = nλ

*decrease the number of cycles = decrease SPL

58

Dampening

card image

material placed behind the element which reduces # of cycles, Pd & SPL

59

What is dampening material made of

epoxy resin + tungstun
metal powder + plastic or epoxy.

60

What is the purpose of damping material?

short pulses create better images

damping material stops pulse

*think of grabbing a bell while it rings

61

dampening and axial resolution

dampening improves axial resolution

62

dampening and amplitude

dampening reduces amplitude

63

dampening and sensitivity

dampening decreases sensitivity

64

dampening and efficiency

dampening decreases efficiency

65

dampening and SPL

dampening decreases SPL

66

dampening and Pd

dampening decreases Pd

67

Which of the following is positive?

A) reduced amplitude
B) decrease # of cycles
C) decrease sensitivity
D) decrease efficiency

B) decrease # of cycles

68

impedance

propagation speed * density

69

what is the purpose of gel?

without gel 80% of intensity of a pulse is reflected off the skin

gel eliminates loss from reflection at the surface of the skin

70

Matching layer

card image

matching layer eliminates loss from reflection at the surface of the transducer

71

matching layer thickness formula

thickness = .25λ

or

thickness = .25c/f

72

list impedance from highest to lowest

element > matching layer > gel > skin

73

impedance of matching layer

halfway between element and skin

ex. if element is 16 rayls a skin is 1 rayl

matching layer is 8 rayls

74

What determines the matching layer λ?

A) c/f
B) f/c
C) c * f

A) c/f

75

Matching layer thickness .25λ.

What is f?

A) operating pulse
B) pulse repetition frequency
C) frame frequency

A) operating pulse

76

Matching layer thickness .25λ.

What is c?

A) soft tissue
B) piezoelectric element
C) matching layer material
D) gel
E) rubber

C) matching layer material

77

What type of transducers do not need damping?

continuous wave

therapeutic

78

what is most desirable to get the maximum sound into the tissue?

A) low impedance crystals
B) multiple matching layers
C) little damping

B) multiple matching layers

79

Bandwidth

card image

range of frequencies the transducer produces

80

bandwidth determined by

transducer and the machine electronics

81

relationship between Pd and bandwidth

inverse

82

bandwidth formula

max frequency - min frequency

83

middle frequency

center frequency

84

fractional bandwidth formula

bandwidth/operating frequency

85

Q factor

operating frequency/bandwidth

86

relationship between Q factor and bandwidth

inverse

87

Quality factor

unitless # describing the degree of damping

approximately the # of cycles in a pulse

88

low Q transducers

imaging transducers

decrease Pd
low SPL
low Q
widebandwidth

89

How many pulses in Q factor

1-3

90

when are transducers broadband?

fractional bandwidth is greater than 80%

91

Broadband transducers are ___________ sensitive.

less

92

Why are broadband transducers less sensitive

due to damping

93

The highest frequency is 6 MHz. The lowest frequency is 2 MHz. What is the bandwidth?

A) 2
B) 3
C) 4
D) 6
E) 12

C) 4

6 MHz - 2 MHz = 4 MHz

94

The highest frequency is 6 MHz. The lowest frequency is 2 MHz. if the center frequency is 4 what is the fractional bandwidth?

A) 1
B) 2
C) 4
D) 8
E) 16

A) 1

bandwidth/operating f

4 MHz / 4 = 1

95

Advantages of Broad bandwidth

*Multi-Hz transducers can be used
*duplex can use low frequency for Doppler & higher frequencies for B-mode
*dynamic frequency tuning - decreasing frequency with increasing depth
* harmonics can be used if bandwidth includes both frequencies

96

Types of Resolution

Detail
*axial
*lateral

Contrast

Temporal

97

Detail resolution

ability to detail fine detail
- the smaller the machine can image the better it is

Axial - depth
lateral - side
section thickness - side

98

What is detail resolution dependent on?

axial resolution
lateral resolution
matrix size
instrument electronics
display device

99

Axial resolution

ability to distinguish between two objects that lie next to each other in the depth plane.

100

Which is frequently better axial or lateral resolution?

axial resolution

101

What is axial resolution dependent on?

SPL

102

Synonyms for axial resolution

longitudinal resolution
range resolution
radial resolution
depth resolution

103

Units of axial resolution

mm

104

How does SPL improve axial resolution?

shortening the pulse length prevents the echoes from combining as they return to the transducer

105

How to improve axial resolution?

higher frequency
Decrease SPL by decreasing cycle or wavelength

106

Lateral resolution

minimum distance that two objects can lie side by side and still be seen as two objects

107

synonyms for lateral resolution

angular resolution
transverse resolution
azimuthal resolution

108

What is the prime factor for lateral resolution

beam width

109

lateral resolution varies with depth.
Where is it best?

at the focus or near zone.

110

Units of lateral resolution

mm

111

Symbol for lateral resolution

R L

112

primary method of reducing beam width

focusing.

113

How does focusing improve lateral resolution?

by decreasing beam width

114

Contrast resolution

the ability to see structures with different reflection intensity values as separate items.

115

Detail resolution is dependent on?

amount of memory
pre & post processing
decibel range
display system
detail resolution

116

Does urine have low or high impedance mismatch?

Low

117

Does bone have low or high impedance mismatch

high

118

SPL a function of

pulse duration
frequency
wavelength

119

SPW a function of

crystal diameter

120

Partial thickness artifact

partial volume artifact

(thickness) due to 3D aspect of transducer

121

Temporal resolution

the ability to accurately located moving structures at any particular instant in time.

resolution pertaining to time

122

Temporal resolution is dependent in time

Frame rate
depth of penetration
sector size
lines per frame
number of focuses
pulse repetition frequency

123

SPL

A) The ability to see two items side by side as separate
B) The ability to see two items above and below each other as separate items
C) The ability to see two separate events as separte events

B) The ability to see two items above and below each other as separate items

124

Huygens Wavelet

Produced by a tiny source
wave diverges into this shape

125

Huygens Principle

According to Huygens the hourglass shape of a sound beam is the result of constructive and destructive inference of many sound wavelets

126

Aperture

width of the beam

AKA width of the element

127

near zone

is the area from the transducer to the focus.

the area of convergence

128

focus

the smallest part of the beam

1/2 size of element

129

far zone

the area of divergence

is the area from the focus to the end of the beam.

130

What shape are sound waves produced by imaging transducers?

hourglass

131

What is the Fresnel zone?

Near zone

132

What is the Fraunhofer zone?

far zone

133

When does the beam stop divergence?

when it reaches its original size

134

What does width determine?

lateral resolution

135

What changes top to bottom?

lateral resolution

136

The width perpendicular to the scan plane determines what?

section thickness artifact.

137

Formula for axial resolution

1/2 SPL

138

Grating lobes

Significant intensity that travels out in some direction not included in the beam

139

What type of transducer causes grating lobes?

Array

140

What type of transducer causes side lobes

single element transducers

141

What are some other names for near field?

focal length
focal depth

142

What happens to the near field when you increase diameter?

increases

143

What happens to the near field when you increase frequency?

increases

144

NZL formula

Focal zone length

(f*d^2)/6

145

f 5 MHz d 5mm? 1 NZL

A) 4 mm
B) 4 cm
C) 125 mm
D) 125 cm
E) 2 mm
F) 2 cm

F) 2 cm

=(5*5^2)/6
=(5*25)/6
=125/6
=20 micrometer
=.02 cm

146

What is the relationship between near zone length and diameter?

direct

147

What is the relationship between near zone length and frequency?

direct

148

For and unfocused beam where are the intensities the highest?

at the focus

149

For and unfocused beam at any given point, Beam diameter is dependent on what?

frequency
element diameter
depth

150

When frequency is low beam divergence is __________.

wide

151

When frequency is high beam divergence is __________.

narrow

152

When diameter is high beam divergence is __________.

narrow

153

When diameter is low beam divergence is __________.

wide

154

Does a smaller frequency gives a shorter or longer near zone?

shorter

155

variable aperture

increases # of elements fired

156

What is the relationship between Beam divergence and frequency?

indirect

157

What is the relationship between Beam divergence and diameter?

indirect

158

Name the 3 way to focus a transducer

* curve the face
* add a lens
* phase the firing sequence electronically

159

What type of focusing are the following?

* curve the face
* add a lens

fixed
conventional
mechanical

160

Focal region

an area on either side of the focal point which is within 25& or 6 dB of SPL

161

Focused transducers and lateral resolution

worst lateral resolution due to mechanical focusing

162

what is the value of focusing?

to improve resolution

163

What improves lateral resolution?

decrease size of focal zone
decrease width of beam

164

Automatic scanning

method by which transducers rapidly collect information

*creating multiple adjacent scan lines
*rapidly
*repeatedly
*real time scanning - depends on frame rate

165

What are the two ways rapid motion is accomplished in real time scanning?

Mechanically
* motor unit
* fluid inside

Electronically
* no motor
* no moving parts
* no fluid

166

Mechanical Motion in fixed focus

mechanical steering has to fo with curvature of PZT

167
card image

1. linear array
2. sector steered
3. curved linear
4. vector

168

Electronic scanning sequence

because elements are fixed focus is fixed

all elements fired at once act as one pulse

fires element in sequence until one frame is built.

169

During electronic scanning phasing
If delay is from left to right pulse angle to the ___________.

right

170

What does phasing control?

beam direction
focus level

171

Haygens law

multiple spherical wavelengths create a wave form produce a wave and the wave travels in a direction - orthogonal to the wave form.

172

where are electronic phased delay patterns produced?

in the beam former

173

how does phasing control aperture?

some electricity is turned off. This changed the size of the element

174

How is focus changed with phasing?

by curving the pattern

175

phasing

When focus is great the focus is ___________.

shallow

176

Vector

sector with flat top

vector converted from a linear rectangular format into a vector format

177

Annular array

multiple circular elements with wobble motor sweeps across

178

What format are annular arrays displayed in?

sector

179

Annular arrays

Steering is mechanical or electronic?

mechanical

180

Annular arrays

focus is mechanical or electronic?

electronic

181

dynamic apodization

changing the amplitude as focusing & steering changes to decrease grating lobe

182

dynamic focusing

delay correction is changed "on the fly"

transducer sets listening focus, as you cnage the depth

183

dynamic aperture

using more or less elements to change the diameter of the entire face.