When a sound of specific wavelength penetrates through a medium, the intensity is in inverse proportion to the distance squared (defined as R) it passed through.
The characteristic of ultrasound through medium is expressed as attenuation coefficient (a) as follows.
Intensity (I) on the distance (R) is represented in relation to that of incident beam (I0) as follows.
Formula (3) is expressed as the round trip distance to a sensor by using reflection coefficient (Kr) as follows.
¡Ø Reflection coefficient (Kr) is expressed as the relations between reflective sound intensity and incident sound intensity.
Za = acoustic impedance of air
Zo = acoustic impedance of the objec
The first pick of a signal obtained indicates the intensity when the laser first reached a specimen, the second, third and fourth picks the intensity when laser makes round trip to specimen, respectively. The thickness of a specimen ( §¤ ) is expressed in relation to the intensity of a signal obtained as follows.
Calculate RMS (root mean square) A for AN obtained, corresponding to the intensity level, I0, I1, I2, I3 and I4
It has been used by Generazio, where the change in diffraction of incident beam can be disregarded as follows.
Figure 1. Crystal droplet measurement system using ultrasound