Optimization of the spark gap parameters for high power ultrasound applications

There is considerable interest in the industrial and commercial applications of High Power Ultrasound (HPU) generated using pulsed power techniques. These applications include metal peening, the treatment of ores and minerals before extraction, drilling technologies and the comminution and recovery of waste materials. In all of these applications, it is important to optimise the parameters of the discharge causing the shock wave in the working medium to maximise the efficiency of the treatment. It is possible to measure the intensity of the HPU output at distances relatively far from the discharge through the use of pressure sensors such as pinducers. However, due to the non linear attenuation of the HPU pulse as it passes through the working medium, it is difficult to relate these distant measurements to the behaviour in the active region close to the discharge. Techniques such as ball crusher gauges and Almen strips can be used in this near field region, but interpretation of the measurements is complex. In a research project at the University of Strathclyde, some applications of HPU to the treatment of waste to assist in recycling have been investigated. Two systems have been considered, slag from the manufacture of stainless steel and bottle glass. With the slag material, it is intended to separate stainless steel from the silicate matrix to permit its recovery. With the bottle glass, the intention is comminution of the material to allow it to be recycled in a more valuable form. Measurements of the efficiency of these processes have been made in terms of the mass of material processed versus the energy input as the parameters of the discharge gap have been varied. In parallel with this work, measurements have been made using pinducer sensors to determine the energy in HPU pulses generated by discharges under identical conditions. Correlations are made between the efficiency of material treatment and the intensity of the HPU pulse measured in the far field. It is hoped that this approach will allow the optimal gap parameters to be determined using pinducer measurements rather than time consuming trials based around materials processing.