Measurements based on sound speed measurement
1. First possibility:
Sound speed is calculated immediately from the time of flight
measurement, the user must decide, if he is observing longitudinal or
transversal wave (this is not difficult, but requires some experience
and basic knowledge). It is necessary to know the path length in
material (sample dimension).
2. Second possibility uses the measurement of refraction angles:
Fom Snellius formula:
alfa - angle of incidence
ß - refraction angle
v1 - sound speed in medium1
v2 - sound speed in medium 2
If the user measures the refraction angles for each wave and knows the
sound speed for one medium (normally water), he will be able to
calculate the sound speed of the wave in the second medium - sample.
If the measurement was made for more than one angle, it is possible to
use averaging.
Additionaly it is possible to measure the acoustic impedance of material:
Impedance is the product of sound speed and density. And following
formulas are valid
Reflection coefficient:
Where: Io - intensity of reflected wave
Ip - intensity of encountering wave
Transmission coefficient:
where: Iz - intensity of refracted wave (coming through)
Measurement of amplitudes of reflected wave under different angles or
reflacted and reflected wave gives the possibility to measure the
impedance and density.
Further it is possible to calculate mechanical parameters of material
from measured sound speeds and density of material.
Following formulas are valid:
Sound speed of longitudinal and
transversal wave:
Where ro - density, and delta i mi are
Lame constants.
From Lame constants and material density it is possible to calculate all
other material constants.
