SPI Prep > Transducer Structure > Flashcards

Transducer Structure Flashcards

(52 cards)

Study These Flashcards
1
Q

What are the highest to lowest impedance levels in regards to the transducer?

A

PE element
matching layer
gel
skin

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2
Q

What is the housing of the transducer?

A

protective metal or plastic shell that protects internal components and user/pt from electrical shock

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3
Q

What does the thickness of the matching layer = …

A

1/4of the wavelength

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3
Q

What is the housing lined with? Why?

A

thin sheet of metal (reduces outside interference/noise) THEN cork (reduces internal vibrations)

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4
Q

What is the matching layer?

A

plastic portion that protects the ELEMENT

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5
Q

What does the matching layer aim to improve?

A

the efficiency of sound transmission into and out of the body

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6
Q

How does the matching layer increase the amount of ultrasound transmitted into the patient?

A

its impedance is between that of the skin and element

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7
Q

How does ultrasound gel allow us to image?

A

reduces impedance mismatch, which decreases reflections at the skin barrier and increases sound transmission

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8
Q

What is the most commonly used PE element for transducers?

A

lead zirconate titanate (also most common man made material)

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9
Q

What determines the frequency that is emitted from the transducer?

A

acoustic properties of the element and ELEMENT THICKNESS

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9
Q

What is the role of the piezoelectric element?

A

converts electrical signals into acoustic pulses & vice versa

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10
Q

How does the PE element produce a sound wave?

A

when voltage is applied, the element expands and contracts (aka vibrates)

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11
Q

What is the transducer frequency also known as?

A

Operating or resonance frequency

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12
Q

The impedance of the PE element is about _______ times soft tissue.

A

20

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13
Q

How is probe frequency determined?

A

propagation speed of element (mm/microsec)/ (2x pe thickness (mm))

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13
Q

The higher the operating frequency, the better the….

A

axial and lateral resolution

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14
Q

The thicker the element, the _____ the operating frequency.

A

lower

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15
Q

When propagation speed is slower, what happens to the sound beam?

A

longer near zone and less beam divergence

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16
Q

When the element is wider, what happens?

A

decreases beam intensity
longer near zone
less beam divergence

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17
Q

What is the damping layer and its significance?

A

epoxy resin/cork/putty that is attached to the back of the element; reduces ringing by restriction the amount of crystal deformation during excitation

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18
Q

T/F: continuous wave probes do not have a damping layer.

19
Q

What are the 5 advantages of a damping layer?

Study These Flashcards
A
  1. shortens PD and SPL
  2. improves axial resolution
  3. increases bandwidth / lowest intensity detected
  4. decreases duty factor
  5. prevents low intensity waves from forming
20
Q

What is another name for the near zone? Far zone?

Study These Flashcards
A

near = fresnel
far = fraunhofer

21
Q

What is the near field?

Study These Flashcards
A

area of the image closest to the face of the transducer, ending at the focal zone

22
As the beam nears the focal zone, what happens to the beams diameter?
it decreases
23
When there is a ______ element diameter or _______ frequency, there is a longer near zone.
wider; higher
24
In a single element transducer, the beam width at the end of the near zone is equal to ....
1/2 of the element diameter
25
What is the end of the near zone also known as?
the natural focal depth
26
What is the far field?
area of the image farthest from the face of the transducer, starting at the focal zone
27
As the beam moves away from the focal zone, what happens to its diameter?
it increases (beam divergence)
28
When comparing the transducer diameter to the beam diameter deeper in the far field, which will be greater?
the beam diameter in far field
29
What is the focal zone?
narrowest portion of the beam
30
T/F: Half of the focal zone belongs to the near field and the other half belongs to the far field.
true
31
What is best at the portion of the focal zone?
image resolution (lateral)
32
What is the focal depth?
distance from the face of the transducer where the near and far fields meet
33
What kind of transducers will have the deepest natural focus?
High frequency and wide diameter
33
Natural beam focus relies on these two things...
frequency and element diameter
34
In unfocused single element transducers, what is the relationship between depth and frequency + diameter?
directly proportional higher frequency = deeper depth large diameter = deeper depth
34
In unfocused single element transducers, how can you calculate the depth of the beam?
depth (mm) = diameter^2 (mm) x transducer frequency (MHz)
35
In unfocused single element transducers, what produces a shallow focus?
small diameter and high frequency probes
36
How do you calculate beam width at level of natural focus?
1/2D (mm)
37
How do you calculate focal depth?
D^2 / 4(wavelength)
38
Define beam divergence.
The gradual spreading out of beam after focal zone
39
Divergence decreases with...
higher element frequency larger element diameter
40
What does beam divergence depend on?
distance x transducer frequency
41
What are CMUT transducers?
capacitative micromachined ultrasonic transducers
42
What are CMUT transducers made of?
capacitative cells with 2 plate conductors that are separated by a vacuum OR dielectric insulating material with a voltage source aka electrode
43
How are CMUT transducers "layered"?
From the back to front: backing material fixed electrode dielectric silicon layer vacuum cavity flexible membrane electrode acoustic window
44
What is the purpose of the flexible thin membrane between the fixed and top electrode in CMUT transducers?
no matching layer is needed since it's close. to the impedance of skin
45
The _____________ behind the membrane in CMUT transducers allows vibrations.
vacuum cavity
46
What increases the capacitance of the CMUT transducer?
the dielectric layer
47
Why is a backing layer than is similar to the dielectric silicon substrate necessary in CMUT transducers?
reduces reverberation caused by the membrane movement
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