Experimental Study on Measuring Reflection Coefficients at Oblique Incidence Using the Inverse Filter

The experiments on measuring reflection coefficients at oblique incidence using the inverse filter are discussed. The spatio-temporal focusing at the position of the hydrophone can be achieved with the reverberations decreased by retransmitting the inverse signal estimated from the underwater acoustic channel and the circuit channel using the inverse filter technique. In this paper, the inverse filter is applied to suppress the influence of the reverberations when the measurements of the reflection coefficients at oblique incidence for passive materials are performed in a limited space. The feasibility of the inverse filter applied to measure the reflection coefficients at different oblique incident angles was demonstrated by the experiments performed with a steel plate sample inside a cylindrical tank. To accurately record reflected signals with arbitrary incident angles, a device was designed. The results show that the inverse filter is valid for the measurement of reflection coefficients at oblique incidence in the measuring frequency ranges from 0.5 to 10 kHz and the measuring incident angle ranges from 0° to 75°.