Quantitative analysis of pulsed ultrasonic beam patterns using a schlieren system

The acoustic output from pulsed ultrasonic transducers has traditionally been analyzed with a hydrophone. Recently, a new faster technique has been developed using the principles of optical diffraction. This schlieren method allows the direct two-dimensional visualization of the ultrasonic beam as a pulse train. In order to obtain quantitative information in the form of temporal-average acoustic intensity, however, tomographic reconstruction has to be performed. In this study, tomographic reconstruction was achieved by acquiring 250 images over a 180/spl deg/ angle. Automation of the measurement was obtained by using a frame grabber, a stepper motor, and digital delays all controlled by an IBM-compatible computer. Comparisons of the schlieren results to those obtained by a hydrophone are made in terms of both the -3 dB beamwidths and axial profiles. The results demonstrate that the schlieren method may be a more time efficient alternative for the characterization of ultrasonic transducers.