Angle-dependent spectral distortion for an infinite planar fluid–fluid interface

Abstract

Angle-dependent spectral distortion (ASD) refers to the change in complex spectrum of the signal from the receiving transducer due to change in angular orientation of the reflecting target, i.e., from normal incidence to some non-normal incidence. The ASD for a fluid–fluid infinite planar interface (IP–ASD) is numerically determined for the cases of a planar piston, spherically focused piston, and nondiffracting (J0 -Bessel) transducer geometries. The numerical algorithm employed is based on an equivalent image transducer. Reception of the acoustic pulse is performed using discrete surface integration, based on 3-D surface mesh generation strategies. Numerical simulations, together with experimental results, are presented for the above transducers for various geometries, reflector distances, and misalignment angles. The results indicate that the IP–ASD significantly alters the spectrum of the received acoustic pulse, and thus must be taken into consideration for quantitative ultrasonic measurements. Finally, the numerical simulations have revealed that the nondiffracting transducer produces distinct peaks in the magnitude IP–ASD that enable precise estimates of misalignment angle to be obtained.