Generating focused pressure wave with ultrasound piezotranducers

Bubbles induced by blast waves or shocks are speculated to be the major cause of damages in the cells. We have studied the impact of the bubbles and shock waves generated by underwater discharges [1]. Microbubbles were found indeed to induce noticeable cell detachment from the cell substrate, changes in focal adhesion and biomechanics [2]. To better understand the bubble mechanism, we would like to see a “focused” pressure wave, which allows us to clearly differentiate the impact region from the non-impact region on a cell coverslip or 3-D tissue culture. Such pressure wave generation needs to be low profile in order to be placed in a microcuvette under the microscope. A piezoelectric transducer system was designed to meet the need. The system uses a spherical piezoelectric transducer that has a focal point to deliver pressure waves to cells. The transducer system was driven by a push-pull amplifier that uses two power MOSFETs so that an alternating waveform of frequency (2.1 MHz) was produced. The RF signals modulated in a pulse mode produced by a signal generator were amplified by an RF amplifier to trigger the two MOSFETs. The drain-source voltages were tested not exceeding 500V. Applying an oscillating voltage to the transducer at the frequency of resonance resulted in the generation of pressure waves and bubbles in the water. Pressure measurements were performed using a fiberoptic hydrophone.