Farfield of Pulsed Rectangular Acoustic Radiator

Abstract

As an example of a previously described theory for plane and gently curved radiators, the farfield of a rectangular pistonlike radiator is shown to be composed of four components of equal magnitude, each of which behaves as if generated at one of the corners. The magnitude of each component varies monotonically with increasing angle from the acoustic axis and is independent of the dimensions of the radiator. For the steady state, the vectorial superposition of components, taking account of the separations between the four effective sources, yields the familiar CW field, containing lobe structure. In the two normal central planes parallel to the radiator sides, the four components reduce to two, and on the acoustic axis they reduce to one. If instead of a CW signal a pulse is applied to the radiator, the field components arrive sequentially, according to the travel times from each of the corners to the field point. If the applied pulse is sufficiently short, these field pulses may be fully resolved. Successful experimental verification of the theory is described in which resolution was obtained of the two pulses in a central plane of a rectangular transducer.