Measurement of the Complex Reflectivity of Submerged Thin Plates at ObliqueIncidence Angles Using the Two-Sensor Intensity Technique

摘要

This study has involved the adaptation of the two-sensor acoustic intensitymeasurement method to an underwater environment. The intensity technique involves measuring the acoustic pressure at two closely spaced points. The average of the pressures approximates the pressure at the midpoint of the two sensors while the difference between the pressures and the application of the Euler's equation leads to an approximation for the acoustic particle velocity at the midpoint between the two sensors. These two quantities, the acoustic pressure and the acoustic particle velocity, are all that is needed to approximate the acoustic intensity and the acoustic impedance. The objective of this research was to develop the system and use it to measure the complex reflectivity of submerged thin plates at non-normal angles of incidence. The two-sensor technique has advantages over more conventional methods of measuring the reflectivity in that the sensors need only be positioned once during the test. This leads to a savings in effort and time for the experimenter. The source of acoustic energy used to ensonify the plates took form of a parametric or virtual and fire array. The parametric array is formed by exciting a transducer with a high frequency carrier signal which has been amplitude modulated with a low frequency signal. Keywords: Complex reflectivity, Plates, Intensity, Underwater, Parametric array. (jhd)