Abstract

Schlieren photography provides an excellent method for the observation of acoustic shock phenomena in water. The shock waves were generated using an electromagnetic acoustic transducer (EMAT) and a focusing lens. The discharge of 81 J through the EMAT device produces acoustic transients with a peak pressure of 20 MPa, a period of 6 µs, and acoustic energy densities in the region of 0.106 mJ/mm². The ratio of peak-positive-to-peak-negative pressure was approximately 3. The conventional two lens, parallel beam Schlieren system was illuminated by a Q-switched ruby laser giving the system a spatial resolution of 30 µm for shock transients in water. At maximum sensitivity the system was capable of detecting pressure changes of approximately 300 Pa. Located at the focus within the Schlieren observation area was a simulation kidney stone, manufactured from a mixture of plaster and microballoons by HMT GmbH. Figure 1 shows the Schlieren image of the transmitted and reflected components associated with the interaction of a shock wave with the simulation material. The stone is right of centre and the focusing lens surface is just visible on the far left. The insert shows the Schlieren image of the incident shock wave in which the bright components represent the alternating compression and rarefaction cycles of the wave. Shock propagation is from left to right. The transmitted shock wave during its passage through the material has become attenuated to such an extent that only the main compression and rarefaction cycles are seen. Also present within the field is cavitation, its appearance being most marked on the front face of the block.

© 1994 IEEE