Abstract
The characteristics of materials for underwater acoustics are frequently evaluated by measuring the complex (modulus and phase) reflection and transmission coefficients of panels with respect to the frequency. Using these measurements, which can be obtained accurately for normal incidence excitation, two methods of determination of the complex sound speed of the longitudinal wave of the tested material are presented here. Both methods use experimental results on the test panel measurements and theoretical expressions. The first one uses the information in a frequency range and can lead to the density, the thickness (which can be useful under hydrostatic pressure measurements), and the complex velocity of the longitudinal wave of the tested material. The second one uses the information at a given frequency and leads only to the complex velocity of the longitudinal wave. The variation of the complex velocity along the frequency in the sonar frequency range can be obtained using these methods. The accuracy of this determination is studied numerically for different kinds of the materials. Experimental results obtained on three test panels confirm the conclusions of the<eb;normal;j> theoretical study. Used as examples were the variations of the speed of sound in P foam and anechoic-like materials in the range 1.5–20 kHz.
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