Lesson 8 (Part 1) Flashcards
What is the opposite of reflection?
Transmission
Reflection
The throwing back by a body or surface of light, heat or sound without absorbing it
What happens at each point boundary with perpendicular incidence? (2)
- Some of the sound is reflected
2. Some of the sound beam goes through
What is another word for perpendicular incidence?
90 degree incidence
IRC
Intensity reflection coefficient
Intensity reflection coefficient
Is the ratio of the intensity of the reflected wave relative to the incident (transmitted) wave
Incident pulse
Is a pulse where the incident moves towards (i.e., approaching) the boundary with the pole
Reflected pulse
A pulse with an upward displacement will reflect off the end and return with a downward displacement
- an echo
Transmitted pulse
The amplitude is representative of the energy carried by a wave
What is the equation for IRC?
IRC = echo intensity/incident sound intensity x 100%
ITC
Intensity transmission coefficient
Intensity transmission coefficient
Is a measure of how much of an electromagnetic wave (light) passes through a surface or an optical element
- can be measured for amplitude or intensity
What is the formula for ITC?
ITC = transmitted intensity/ incident sound intensity x 100%
What is the relationship between impedance and density / propagation speed?
Directly proportional
Where is impedance the highest?
In solid structures
- eg. bone
Where is impedance the lowest?
In air
What does impedance depend on?
Densities
What does it mean when you have a higher difference in impedance?
A brighter echo
What does IRC + ITC equal?
100%
What is the % of transmitted pulses?
80%
What is the % of reflected pulses?
20%
How much goes through and how much is reflected depends on what?
Impedance
What is the formula for impedance?
z = p x c z = impedance p = density c = propagation speed
What is the unit for impedance?
Rayls
- kg x m / m^3 x s
Does each tissue have its own impedance?
Yes
What is the formula for acoustic impedance mismatch?
delta z = z2 - z1
What does the amount of reflection depend on?
delta z
What is the formula for IRC? (involving impedance)
IRC = (z2-z1 / z2+z1)^2
What does delta z decide?
If the echo will appear bright or dark
What does increase in delta z mean?
Brighter echo
