| Popis: |
Selected predictions of the Resonance Scattering Theory (RST) were experimentally investigated at NSWC's Hydroacoustic Measurements Facility during the summer of 1984. Elastic cylinders and cylindrical shells of various thicknesses and aspect ratios were placed in a water‐filled redwood tank 30 ft in diameter and 20 ft deep, and were insonified by trains of 1‐ms sinusoidal pulses. The frequencies were varied between 50 and 500 kHz. The signal from a hydrophone, located between the projector and the objects, was sampled at three judiciously chosen time‐gated windows to yield the strengths of the incident wave, of the backscattered echo, and finally of the free‐vibration target reradiation. Spectral recordings showed that the penetration of sound energy into the object is maximized when the input frequency matches one of the natural frequencies of the object. This is manifested in large dips in the spectral displays of the reflected echoes. The spectral display of the reradiation plot shows sharp rises at t... |
