acoustic emission

Acoustic emission refers to the production of sound waves by a material under stress, or the sound waves themselves. This phenomenon occurs when materials release elastic energy, often due to the formation of microcracks.1

Sound waves, in general, propagate as spherical wavefronts, with each point on a wave acting as a source of new spherical waves. This is described by Huygens' principle. The principle of superposition allows multiple waves to occupy the same space without interfering with each other.2

A key characteristic of sound propagation is acoustic impedance, which is the ratio of acoustic pressure to volume velocity. It measures how easily a sound wave travels through a medium. When a sound wave encounters a medium with a different acoustic impedance, an impedance mismatch occurs, causing some of the wave to reflect and some to transmit. This mismatch can affect how efficiently a sound source radiates sound.2