Ultrasonics - Part 1. Basic principles of sound

Sound waves are a form of mechanical energy that can only exist in solid, liquid or gas and not in vacuum. Two requirements for sustaining a vibration include mass and elasticity. Sound energy travels outwards from the source of the vibration as the oscillation of a particle of solid, liquid or gas disturbs the neighboring particles so that the neighbour takes up the oscillation. The disturbance which is called sound wave is transmitted in different modes, specifically, compression wave, shear wave, surface wave, lamb wave, and creeping wave.