Reflection + Refraction

how is reflection generated?

sound strikes a tissue of different impedance

sound may be from __ and _

specular reflectors, non-specular reflectors

interface

boundary between two different tissues with different impedances

reflections come from

specular reflectors or echos resulting from scattering

incident sound

sound from tdx to interface

reflected sound

sound returning from interface

transmitted sound

sound that passes through interface

the bigger the —- the greater the reflection

impedance mismatch

2 things needed to have reflection at an interface

impedance mismatch and normal incidence

reflection is about how much sound is — and —

reflected and transmitted

how do we measure how much sound is transmitted and reflected?

look at the intensities or percentage of reflected/transmitted sound

what’s reflected + what’s transmitted must =

amount of incident sound

intensity units

mW/cm²

an echo will only return to tdx is there’s an — —

impedance mismatch

normal incidence is also known as

perpendicular incidence, orthogonal, right angle, 90 degrees

normal incidence occurs when the angle of incidence is — to the interface between the media

90 degrees

angle of reflection is always equal to —

angle of incidence

intensities of reflected and transmitted sound depend on — and —

impedance mismatch and incident intensity

if the impedances of two media are the same is there reflection?

no

It =

transmitted intensity

Ii =

incident intensity

Ir =

reflected intensity

incident intensity =

transmitted intensity + reflected intensity

oblique incidence occurs when

angle of incidence is not perpendicular

3 types of attenuation

reflection, absorption, scattering

the greater the impedance difference, the greater the — of —

degree of reflection

the greater the reflection, the — sound can be transmitted

less

3 interfaces

air, bone, soft-tissue

soft tissue to soft tissue interface percent reflection

1%

soft tissue to bone interface percent reflection

50%

soft tissue to air interface percent reflection

100%

intensity reflection coefficient

percentage of sound reflected at the interface

intensity transmission coefficient

percentage of sound that continues through the medium and is NOT reflected

reflection is determined by what two factors?

angle of incident sound beam and impedances of both media

if sound is totally reflected, then ITC is — and IRC is — with normal incidence

0%, 100%

formula for IRC

= Ir/ Ii = [Z2+Z1/Z2-Z1]²

if impedance between 2 media are the same, what is the IRC

zero, no reflection without different impedances

unit for IRC

unitless, it’s a percentage

in normal incidence and 2 media with same impedance reflection is —

no reflection, angle of incidence = angle of transmission

with normal incidence and 2 media of different impedances, reflection —

occurs, angle of reflection = angle of incidence

in oblique incidence, does an echo return to the source?

no because the angle is not at 90 degrees

with reflection we need — and —, we get — or —

impedance mismatch, mandatory 90 degree angle; intensities or % reflected/transmitted

what question does refraction ask

what is the angle of transmitted sound?

refraction two things

propagation speed mismatch and oblique incidence

when sound hits an interface with oblique angle of incidence, a change in — between materials causes refraction

propagation speed

refraction

change of direction of sound on other side of the interface

angle of transmission = angle of incidence if — = —

C1 = C2

second material through which the sound is passing has a SLOWER VELOCITY than the first material, angle of transmission will be — than the angle of incidence

SMALLER or LESS THAN

second material through which sound is passing has a FASTER propagation speed than the first material , the angle of transmission will be — than the angle of incidence

LARGER or greater than

if C2 is 1800 m/s and C1 is 1200 m/s the angle of transmission will be — than the angle of incidence

greater than

C2 is 1200 m/s and C1 = 1600 m/s then angle of transmission is — than angle of incidence

less than

sound propagates with normal incidence through medium with propagation speed 2500 m/s and strikes a tissue with a propagation speed of 2100 m/s. what is the angle of transmission

angle of transmission = to angle of incidence since it’s normal incidence

what is the name of the law that describes refraction at an interface

Snell’s law

refraction is dependent on both the angle of incidence and — of the two media

propagation speed

if the angle of incidence is 90 degrees is there refraction?

no

with refraction we need —, — angle, and get

propagation speeds, oblique, angle of transmitted beam