Lesson 13 Flashcards

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1
Q

What happens to bandwidth when impedance decreases?

A

Increases

- also increasing sensitivity and resolution

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2
Q

What do we get when we lower impedance?

A

Less reflection

- more pulses go through solid tissues

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3
Q

What is damping material also known as?

A

Backing material

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4
Q

What does the damping material include? (2)

A
  1. Metal powder
    - tungsten
  2. Plastic/epoxy resin
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5
Q

Where is the damping material?

A

On the back of the element

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6
Q

What does the damping material do? (2)

A
  1. Reduces ringing
  2. Reduces cycles per pulse
    - faster decay time
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7
Q

What 3 thing do you need for the best resolution?

A
  1. Decreased PD
  2. Decreased SPL
  3. Increased bandwidth
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8
Q

Why do we use gel in ultrasound?

A

It gets ride of the air bubbles that have a low impedance

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9
Q

Why might we use damping material?

A

To decrease sensitivity

- have the ability to detect weaker echoes

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10
Q

What is an example of no damping material?

A

Continuous wave

  • better sensitivity
  • worse resolution
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11
Q

What is the case made from?

A

Usually the same material as the damping material

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12
Q

What does the case do? (2)

A
  1. Prevents moisture

2. Protects some of the internal structures

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13
Q

Where does the case absorb most of the energy?

A

From the sides of the crystals

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14
Q

What percentage of the matching layer is IRC?

A

80%

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15
Q

Matching layer

A

1-3 layers are used to reduce the large differences in impedances
- 20x in tissue

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16
Q

What is the thickness of each mathching layer?

A

1/4 of the wavelength

17
Q

What is the reason we use a matching layer?

A

Same as why we use gel

- to decrease impedance

18
Q

What does a transducer convert?

A

One form of energy to another

19
Q

What shortens and improves resolution? (2)

A
  1. Composites

2. Damping material

20
Q

What do matching layers and coupling media facilitate?

A

The passage of ultrasound across the transducer skin boundary

21
Q

What are single element transducers in the form of?

A

Discs

22
Q

What of the transducer element changes when voltage is applied to its face?

A

Its thickness

23
Q

What is the resonance frequency of an element determined by?

A

Its thickness

24
Q

What do the thinnest elements have?

A

The largest frequencies

25
Q

What kind of impedance does the matching layer have?

A

Intermediate impedance

26
Q

Composites

A

Mixtures of a piezoelectric ceramic and a nonpiezoelectric polymer