Beams, interfaces, reflection, refraction Flashcards
What is Incident Intensity?
The sound wave’s intensity immediately before it strikes a boundary.
What is Reflected Intensity?
The intensity of the portion of the incident sound beam that, after striking a boundary, returns back from where it came.
What is Transmitted Intensity?
The intensity of the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that is was traveling.
What are the units of all intensities?
W/cm2
There is conservation of energy at the boundary. How does this affect incident (starting) intensity?
Incident intensity = reflected intensity + transmitted intensity
What happens to ultrasound energy?
(e.i., what causes attenuation?)
Reflection
Scattering
Absorption
Most ultrasound energy is lost to _______?
Absorption
What is the interface?
The boundary between two media having different acoustic Z.
If the two media are the same Z, what is the reflection?
Echos are created by ___?
Zero. No echo.
∆Z
If the two media have a very big ∆Z, how does this affect the echo?
Bigger ∆Z, means more reflection:
Stronger echo. Very little transmission.
At a boundary between two soft tissues, a small ∆Z means:
Not much reflects. Small echo.
A lot transmits.
At a boundary between two soft tissues, a very
big ∆Z means:
Very big echo. Reflection is near total.
Very little transmits.
What is normal incidence?
When the incidence sound beam strikes the boundary at exactly 90º.
Some synonyms for normal incidence are:
Perpendicular. Orthogonal.
Right angle. 90 degrees.
When does oblique incidence occur?
When the incident sound beam strikes the boundary at any angle other than 90º.
True or false:
For incidence to be oblique, the angle must equal 90º.
False.
The angle must not equal 90º.
What does oblique mean?
Not at right angles or perpendicular.
What type of incidence is this?
Sound striking a boundary at normal incidence.
What type of incidence is this?
Sound striking a boundary with oblique incidence.
What is IRC?
Intensity Reflection Coefficient;
the proportion (percentage) of intensity
that is reflected.
What is ITC?
Intensity Transmission Coefficient;
the proportion (percentage) of intensity
that travels on beyond the interface.
What is a coeffiecient?
A number that relates variables;
a constant relationship.
Name two ways to find IRC:
- You know the impedances of the two media
- You know the intensities of the two media
As a sound beam strikes a boundary, energy is conserved, and 100% of the intensity must be accounted for. The following relationship applies:
100% = IRC (%) + ITC (%)
If the reflected and transmitted intensities are added, the result must be the ____ ____.
Incident intensity
If the IRC and ITC are added,
the result must ____ ____.
Must equal 100%
A sound wave with a intensity of 50 W/cm2 strikes a boundary and is toally reflected.
What is the intensity reflection coefficient?
Since the wave is totally reflected, the intensity reflection coefficient is 100%.
A sound wave with an intensity of 50 W/cm2 strikes a boundary and is totally reflected.
What is the reflected intensity?
Since the wave is totally reflected,
intensity is 50 W/cm2.
What is the equation used to calculate
intensity reflection coefficient when given the impedances?
What is the equation used to calculate
intensity transmitted coefficient when given the intensities?
