1. A little physics, and a few definitions

1.1 Vibrations

Vibration" refers to the oscillation of an elastic medium around its equilibrium position, involving three fundamental quantities:

• the kinetic energy of the medium set in vibratory motion ;

• the restoring energy resulting from the elasticity of the medium distorted by the vibration ;

• the frequency of oscillation, which is the number of deformation cycles in one second, and whose unit is the Hertz, noted Hz. The unit 1 Hz corresponds to a sinusoidal vibration with a period equal to one second. A vibration of 100 Hz therefore corresponds to a sinusoid with a period of 0.01 seconds.

Vibrations therefore affect all elastic solids,...