Nonlinear Detection of a Low-Frequency Plane Wave by a Directional Circular Piston Beam.
NAVAL RESEARCH LAB WASHINGTON D C
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Westervelts prediction 1963 that an acoustic signal of low frequency can be detected by a parametric endfire array--i.e., by nonlinear interaction with a pump beam of high frequency--is analyzed for the case of a plane wave of low frequency incident on a highly directional beam from a circular plane piston used as a pump. The piston beam is centered on the z axis, with which the plane wave makes a small angle psi. To first-order perturbation theory, the z component of particle velocity for the interaction component at the difference frequency is proportional to the product of the piston beam function, as calculated at the difference frequency, and the response function of a truncated endfire array of length z, along the z axis, as calculated at the low frequency. Hence the receiving directivity of the system is determined only by the endfire response function, regardless of the pistons properties. Author
- Acoustic Detection and Detectors