Chap 3 Flashcards
What is attenuation
A decrease in wave amplitude or intensity
Attenuation implies decrease
Absorption
A conversion of energy into heat w/in the medium
If the frequency of the wave is increased, the amount of energy lost to heat will
Increase
What is reflection
A propagated wave changing direction
What is the angle of incidence
The angle formed between the wavefront and the interface of the reflecting structure
The angle formed between the line perpendicular to the reflecting structure
What is normal incidence
Implies that the wavefront is parallel to the reflecting structure
W/ normal incidence, the angle formed between the wave direction and the normal line is 0 degrees
What is Angle of reflection
Same method as angle of incidence except using reflected wavefront
What is speculation reflection
Incidence angle always equals angle of reflection
Mirrors the incident angle
What is back scattering
Occurs when reflecting surface is rough
Reflection is redirected in random directions
What is Rayleigh scattering
Occurs when reflecting structures are very small w/ respect to the wavelength
Reflection off RBC
What is acoustic impedance
Z = P x C = mass/volume(density) x prop velocity
Has units of rayls
Large difference in impedance = a large reflection
What is the reflection equation
The amount of reflection increases with an increase of acoustic impendance
%reflected = (z2-z1/z2+z1)^2
What is the transmission equation
% transmitted = I trans/I total = 1 - [Z2-Z1/Z2+Z1]^2
If z2 = z1 there is no impedance mismatch, so no reflection
Of z2 is much greater than z1 there will be 100% reflection
What is refraction
The bending of the wave at the interface
Occurs due to a change in prop velocity
What is snells law
Predicts when refraction will occur and to what degree
Ci/Ct
The greater the difference between transmitted incident angles, the greater amount of refraction
What is the critical angle
The incident angle at which total internal reflection occurs
