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.
