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Flashcards in Lesson 13 Deck (26)
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1

What happens to bandwidth when impedance decreases?

Increases
- also increasing sensitivity and resolution

2

What do we get when we lower impedance?

Less reflection
- more pulses go through solid tissues

3

What is damping material also known as?

Backing material

4

What does the damping material include? (2)

1. Metal powder
- tungsten
2. Plastic/epoxy resin

5

Where is the damping material?

On the back of the element

6

What does the damping material do? (2)

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

7

What 3 thing do you need for the best resolution?

1. Decreased PD
2. Decreased SPL
3. Increased bandwidth

8

Why do we use gel in ultrasound?

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

9

Why might we use damping material?

To decrease sensitivity
- have the ability to detect weaker echoes

10

What is an example of no damping material?

Continuous wave
- better sensitivity
- worse resolution

11

What is the case made from?

Usually the same material as the damping material

12

What does the case do? (2)

1. Prevents moisture
2. Protects some of the internal structures

13

Where does the case absorb most of the energy?

From the sides of the crystals

14

What percentage of the matching layer is IRC?

80%

15

Matching layer

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

16

What is the thickness of each mathching layer?

1/4 of the wavelength

17

What is the reason we use a matching layer?

Same as why we use gel
- to decrease impedance

18

What does a transducer convert?

One form of energy to another

19

What shortens and improves resolution? (2)

1. Composites
2. Damping material

20

What do matching layers and coupling media facilitate?

The passage of ultrasound across the transducer skin boundary

21

What are single element transducers in the form of?

Discs

22

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

Its thickness

23

What is the resonance frequency of an element determined by?

Its thickness

24

What do the thinnest elements have?

The largest frequencies

25

What kind of impedance does the matching layer have?

Intermediate impedance

26

Composites

Mixtures of a piezoelectric ceramic and a nonpiezoelectric polymer