Directional point receivers: the sound and the theory

An acoustic vector sensor is described as a directional receiver that measures pressure (p) and all three components of acoustic particle velocity (u, v, w) at a collocated point. Another device, a dyadic sensor, measures in addition to acoustic pressure and the particle velocity vector, the gradients of acoustic particle velocity (the sum of the pure spatial derivatives of the velocity components being proportional to instantaneous density). Directional receivers provide a means to detect and localize acoustic sources. In an array configuration, directional elements can be used to eliminate discrete noise sources or to provide an equivalent acoustic baffle. A simple formulation is given to describe the directivity of multi-order directional receivers; and it is shown that, in theory, a single point sensor can be highly directive. In practice, however, additional self-noise mechanisms will likely limit the capabilities of directional sensors.