The method of derivation is as follows:
Transfer function of a Oberst beam. This beam is fixed at one end and free in the other. This beam, composed of the material that we want to characterise, is excited at the fixed extremity and the response is measured by a non intrusive method, in this case, by a laser vibrometer.
The transfer functions are the basis for a program developed by Cidaut. This program finds, in an iterative way, the optimised properties which make the calculated functions approximate to the measured ones.
For each resonance, a value of the searched property is obtained and, from them, the material behaviour curve can be obtained.