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SPI > Exam 3 - Lesson 5 > Flashcards

Exam 3 - Lesson 5 Flashcards

1
Q

Role of a transducer?

A

Converts electrical energy (voltage) to mechanical energy

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2
Q

What is Piezoelectricity?

A

property of crystals to generate voltage (electrical energy) to vibrate back & forth

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3
Q

What is the Reverse Piezoelectric Effect?

A

pressure generated when fluctuating voltage applied causing expansion in thickness (alternates btwn +/-)

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4
Q

Manufactured Piezoelectric material

A

Ceramics - PZT ( Lead Zicronate Titanate)

* Impedance of PZT is 30 - 40 Rayls

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5
Q

What is Poling?

A

strong electric field applied to PZT material at high temps. Molecules slide and align themselves

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6
Q

Cure point

A

Temp above which Pzt material loses its poling. Material becomes depoled so it can be used

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7
Q

What is the active element in a transducer?

A

The crystal

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8
Q

What determines the operating fq in PW?

A

Thickness of the crystal

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9
Q

Crystal thickness formula

A

λPZT / 2 …. thickness = half wavelength in PZT

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10
Q

What does the diameter of the crystal tell us?

A

sound beam width

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11
Q

Crystal width vs. fq

A

Inverse

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12
Q

Backing/ Damping material

A

dampens crystal vibrations to limit ringing.

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13
Q

If you increase damping, what will also increase?

A

Bandwidth (larger range of fq), Axil Res

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14
Q

How does backing affect impedance?

A

backing Z = PZT so prevents reflection

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15
Q

advantages of damping/ backing?

A

Shortens SPL, Increases axil res, and increases bandwidth

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16
Q

Matching layer

A

protects crystal & helps transmission from crystal / skin by matching impedances (z)

17
Q

Lens

A

focuses ultrasound beam to reduce slice thickness

18
Q

Transducer fq in CW

A

Transducer fq (5 MHz) = drive voltage fq (5 Mhz)

19
Q

Transducer fq in PW

A

short bursts (pulses) applied to crystal

20
Q

What is the operating fq in PW determined by?

A

Propagation speed (c) & thickness of crystal

21
Q

If you have a thinner crystal, what will your operating fq be?

A

higher fq ; shorter pulse

22
Q

Pulse length/ fq / bandwidth

A

Damping limits ringing - shortens SPL - widens bandwidth

23
Q

How to get transducer bandwidth?

A

Max fq - Min fq

24
Q

What is Quality Factor?

A

pureness of the beam (no range of fq’s)

25
Q

What do Imaging transducers need to emit for quality factor

A

short pulses (SPL) with wide bandwidths = low Q factor (wide range in fq)

26
Q

What has the best quality factor?

A

CW bc always ringing at same fq & has a narrow bandwidth. The closer you are to no variation, the increased quality factor.

27
Q

Transducer sensitivity

A

ability to detect reflectors at given depth (penetration)

28
Q

How are bandwidth and sensitivity related?

A

Inverse bc broad bandwidth = shorter pulse = high fq = less penetration or sensitivity

29
Q

CW beam shape

A

single flat disc (unfocused) crystal, no lens

Acoustic fq = voltage fq

30
Q

What does every beam start out as in CW?

A

every beam starts out at the same diameter as the crystal

31
Q

What is the narrowest point (natural focus) equal to?

A

Narrowest point = 1/2 crystal diameter

32
Q

Near Zone Length (NZL)

A

distance from transducer face to point of min. beam width

33
Q

NZL formula

A

NZL = diameter of transducer ^2 / 4x wavelength

34
Q

How is NZL related to diameter and fq?

A

^^ NZL = ^^ D/ Fq

35
Q

Far field (fraunhofer)

A

region deeper than natural focus where beam diverges

36
Q

Qualities of far field?

A

More uniform, less intensity = poor sensitivity & resolution

37
Q

Huygens Principle

A

sound waves propagate in spherical ripples. Most of the intensity is in the center of focus zone

*what forms hourglass shape

SPI (3 decks)

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