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Ultrasound Physics > Week 7 Transducers > Flashcards

Week 7 Transducers Flashcards

Transducers

1
Q

A transducer

A

converts one form of energy into another

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2
Q

During transmission, electrical energy is converted into

A

sound

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3
Q

During reception, the reflected sound pulse is converted into

A

Electricity

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4
Q

Piezoelectric effect

A

The property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them.

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5
Q

Reverse Piezoelectric Effect

A

When Piezoelectric materials change shape when a voltage is applied to them.

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6
Q

Components of a transducer

A

Case
Wire
Electric Shield
Acoustic insulator
PZT/ Active Material
Matching Layer
Backing Material/ Damping element

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7
Q

Case

A

Protects the internal components

Insulates the patients from electric shock

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8
Q

Electrical Shield

A

Thin metallic barrier lining inside of the case

Prevents outside electrical signals from entering the transducer

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9
Q

Acoustic Insulator

A

Thin cork or rubber barrier

“Uncouples” the internal components of the transducer from the case.
Prevents vibrations.

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10
Q

Wire

A

Provides electric connection between the PZT and the ultrasound machine.

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11
Q

Backing Material/ Damping element

A

Reduces pulses, improving axial resolution.

Bonded to the back of the active element.

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12
Q

Matching Layer

A

Positioned in front of the PZT.

Improves sound transmission into the tissues.

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13
Q

The impedance of PZT is….

A

20 x’s greater than the impedance of skin.

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14
Q

Decreasing order of Impedance

A

PZT>matching layer>gel>skin

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15
Q

Matching layer and gel

A

increase the efficiency of sound transfer between the transducers PZT and the skin

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16
Q

The Active element is

A

1/2 wavelength thick

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17
Q

The Matching layer is

A

1/4 Wavelength thick

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18
Q

Long Pulses

A

degrade axial resolution and create less accurate images

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19
Q

Backing Material

A

substantially reduces PZT vibrations.

Allowing short pulses and producing enhanced axial resolution.

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20
Q

Characteristics of Backing material

A

High degree of sound absorption

Acoustic impedance similar to PZT.

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21
Q

Consequences of using backing material

A
  1. Decreased sensitivity
  2. Wide bandwidth
    3.Low quality factor
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22
Q

Decreased sensitivity refers to….

A

During reception, transducers with damping material are less able to convert low level sound reflections into meaningful electrical signals

23
Q

Bandwidth

A

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

24
Q

Narrow Bandwidth

A

Do not contain a backing material.

Are used in therapeutic ultrasound or continuous wave.

25
Q

A transducer with a 3Mhz main frequency produces a sound pulse that contains frequencies ranging from 1Mhz-5Mhz. What is the bandwidth?

A

4Mhz or

5Mhz-1Mhz = 4 Mhz

26
Q

Quality factor

A

A unitless number

Equals the quality of the tone

27
Q

How are quality factor and bandwidth related?

28
Q

quality factor formula

A

Main frequency/ bandwidth

29
Q

Wide bandwidth have what kind of Q factor?

A

Low Q-factor

30
Q

Narrow Bandwidth have what kind of Q-factor?

A

High Q-factor

31
Q

What creates a better quality image High or low Q-factor?

A

Low Q-factor

32
Q

Imaging TransducerCharacteristics

A
  1. Pulses with short duration and length
  2. Uses backing material to limit ringing
  3. Reduces sensitivity
  4. Wide bandwidth/ broadband
  5. Lower Q-Factor
  6. Improved Axial Resolution
33
Q

Non-Imaging Transducers Characteristics

A
  1. Creates continuous wave pulses
  2. No backing material
  3. Increased sensitivity
  4. Narrow bandwidth
  5. Higher Q- factor
  6. Cannot create an image
34
Q

A shorter dampened pulse has what kind of Q-factor?

A

Lower Q-factor

35
Q

A longer dampened pulse has what kind of Q-factor?

A

Higher Q-factor

36
Q

Curie Temperature

A

The Temperature at which PZT is polarized. 500 degrees.

37
Q

depolarization

A

The loss of piezoelectric properties due to exposure to high temperatures.

38
Q

Sterilization

A

destruction of all microorganisms by exposure to extreme heat.
Transducers should never be sterilized!

39
Q

Disinfection

A

application of a chemical or agent to reduce or eliminate infectious organisms.

Transducers should be disinfected.

40
Q

How are pulse duration and bandwidth related?

A

inversely related

41
Q

How are pulse length and pulse duration related?

A

Directly related

42
Q

How are PZT and frequency related?

A

inversely related

43
Q

Thick crystals have what type of frequency?

A

low frequency

44
Q

Thin crystals have what type of frequency?

A

High frequency

45
Q

Characteristics of High Frequency Pulsed wave imaging Transducers

A
  1. Thinner PZT crystals
  2. PZT with higher speeds
46
Q

Characteristics of low frequency pulsed wave imaging transducers

A
  1. Thicker PZT crystals
  2. PZT with lower speeds.
47
Q

Frequency (MHz) formula

A

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

48
Q

Which type of transducer has a greater Q-factor, therapeutic or imaging?

A

Therapeutic

49
Q

Which type of transducer has a greater bandwidth, continuous wave or imaging?

A

Imaging transducers have a wider bandwidth

50
Q

What is the purpose of attaching the backing material to the PZT?

A

to improve image quality

51
Q

A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the bandwidth?

A

6 MHz.

8MHz-2MHz = 6MHz

52
Q

A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz. What is the main frequency?

A

The resonant, main or center frequency is 5 MHz

53
Q

A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest is 8 MHz.What is the Q-factor?

A

0.8

Q factor is resonant frequency / bandwidth.

5MHz / 6 MHz

Ultrasound Physics (10 decks)

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