The influence of edge waves in local surface skimming longitudinal wave generation using a focused PVDF transducer

Abstract

Acoustic microscopy is extensively used for high-frequency imaging and material characterization. In a focused ultrasonic transducer, the presence of edge waves from the edge of the transducer is usually considered a disadvantage. For high-frequency imaging applications, the edge waves adversely affect the quality of the image. This paper discusses edge wave's influence on generating a surface wave in bulk metal samples using a limited aperture PVDF transducer. Acoustic microscopy-based defocusing experiments are conducted on aluminum, stainless steel, copper, and brass samples. A detailed wave-path analysis is done to understand the different wave components in a signal as obtained from defocusing experiments. The travel path of each wave component is analytically obtained and compared with the experimental results. The different wave modes observed in the experiments are identified by overlaying the analytical plots on the experimentally obtained B-scans. A good correlation is obtained between the experimental and analytical results. The surface wave velocity of the samples is calculated using the time-resolved method, and the percentage of error in the measurement is estimated. The challenges for using this method in measuring surface wave velocities in samples with bulk longitudinal velocities [Formula: see text] are also discussed.