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Flashcards in Lesson 10 Deck (30)
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1

What does perpendicular incidence involve? (3)

1. Pulse echo techniques
2. Transmission
3. Impedance differences

2

What does oblique incidence involve? (5)

1. Angle of incidence
2. Angle of reflection
3. Angle of transmission
4. Refraction
5. Propagation speed

3

What does relfection and transmission depend on?

Impedance

4

What does refraction depend on?

Propagation speed

5

What happens to the echoes when a surface is rough?

It scatters

6

What are examples of specular reflection? (2)

1. Perpendicular incidence
2. Oblique incidence

7

Specular reflector

Mirror like

8

What are examples of specular reflectors in the human body?

Smooth, large boundaries
- sound will bounce back to the transducer and produce a strong echo

9

What is an example of not smooth/rough surfaces?

Heterogeneous tissues
- eg) liver tissue

10

When do you get scatter? (2)

1. In heterogenous tissues
2. When the target object is comparable or smaller than the wavelength

11

What do you get when a small wavelength hits a larger object?

Specular reflection

12

Does scattering help us?

Yes
- most times
- but typically want less scattering

13

What does scattering help us with?

Getting a good visual of the tissue parenchyma

14

What does scattering depend on? (2)

1. Frequency
2. Scatter size

15

What happens to scattering if you increase the frequency?

Will result in a decrease in wavelength and therefor have a decrease scattering

16

Backscatter

The echo information that comes back to the transducer

17

What happens with scattering in Rayleigh scattering as frequency increases?

Scattering increases

18

What is scattering intensity proportional to in Rayleigh scattering?

Frequency

19

What happens with scattering in Rayleigh scattering if you increase wavelength?

Frequency decreases which means scattering decreases

20

What is an example of a speckle?

Scattering

21

Scattering

Echo sound waves take different paths on the way back to the transducer

22

What 2 ways can waves come back from scattering?

1. Constructively
2. Destructively

23

Constructively speckle

The scatters reinforce each other
- adding 2 sound waves together

24

Destructively

The scatters partially (dont fully line up) or totally cancel each other
- they dont line up

25

What is another word for constructive interface?

In phase

26

What is another word for destructive interference?

Out of phase

27

What happens to the frequency if you double the transducer?

It goes up 16x

28

What appearance do speckles give off?

Grainy appearance

29

Acoustic speckle

A form of acoustic noise

30

What is acoustic speckle a result of?

Constructive and destructive interference of scattered sound waves