The generation of negative pressure waves for cavitation studies

A technique for producing strong focused negative pressure waves in water is described. The method is based on the phase inversion of the planar shock wave from an electromagnetic transducer. This is achieved by reflection and focusing at a pressure release boundary. The acoustic concentrator has a phase inverting central element and a phase maintaining annular mirror. Focal pressures of approximately -16 MPa from an initial +5 MPa EMAT source have been measured and the focal volume was found to be approximately the same as that obtained with a conventional ultrasonic lens. The electromagnetic transducer and the parabolic concentrator is an excellent source of cavitation bubbles in water. The focused negative wave has been observed using high speed laser-lit Schlieren photography.