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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
A transducer with a 3Mhz main frequency produces a sound pulse that contains frequencies ranging from 1Mhz-5Mhz. What is the bandwidth?
4Mhz or 5Mhz-1Mhz = 4 Mhz
26
Quality factor
A unitless number Equals the quality of the tone
27
How are quality factor and bandwidth related?
inversely
28
quality factor formula
Main frequency/ bandwidth
29
Wide bandwidth have what kind of Q factor?
Low Q-factor
30
Narrow Bandwidth have what kind of Q-factor?
High Q-factor
31
What creates a better quality image High or low Q-factor?
Low Q-factor
32
Imaging TransducerCharacteristics
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
Non-Imaging Transducers Characteristics
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
A shorter dampened pulse has what kind of Q-factor?
Lower Q-factor
35
A longer dampened pulse has what kind of Q-factor?
Higher Q-factor
36
Curie Temperature
The Temperature at which PZT is polarized. 500 degrees.
37
depolarization
The loss of piezoelectric properties due to exposure to high temperatures.
38
Sterilization
destruction of all microorganisms by exposure to extreme heat. Transducers should never be sterilized!
39
Disinfection
application of a chemical or agent to reduce or eliminate infectious organisms. Transducers should be disinfected.
40
How are pulse duration and bandwidth related?
inversely related
41
How are pulse length and pulse duration related?
Directly related
42
How are PZT and frequency related?
inversely related
43
Thick crystals have what type of frequency?
low frequency
44
Thin crystals have what type of frequency?
High frequency
45
Characteristics of High Frequency Pulsed wave imaging Transducers
1. Thinner PZT crystals 2. PZT with higher speeds
46
Characteristics of low frequency pulsed wave imaging transducers
1. Thicker PZT crystals 2. PZT with lower speeds.
47
Frequency (MHz) formula
sound's speed in PZT (mm/us)/ 2 x thickness (mm)
48
Which type of transducer has a greater Q-factor, therapeutic or imaging?
Therapeutic
49
Which type of transducer has a greater bandwidth, continuous wave or imaging?
Imaging transducers have a wider bandwidth
50
What is the purpose of attaching the backing material to the PZT?
to improve image quality
51
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?
6 MHz. 8MHz-2MHz = 6MHz
52
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?
The resonant, main or center frequency is 5 MHz
53
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?
0.8 Q factor is resonant frequency / bandwidth. 5MHz / 6 MHz

Ultrasound Physics (10 decks)

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