Single Oscillating Bubble from Radiofrequency Fiber Electrode

The radiofrequency (RF) power in the 0.3∼30 MHz band is often used for coagulation, ablation, and modification of tissues in medicine while in the lower frequency band both shock waves and cavitation may occur, which has found applications in lithotripsy for stone fragmentation and water purification. In this study, we demonstrate that single oscillating bubble is produced at the electrode tip in cell culture medium, which avoids the random inception of cavitation in liquid. With high-speed image recordings and Fast Fourier Transform (FFT) spectrum analysis, the frequency of the bubble oscillations is found to be dependent on the driven radio frequency, electrode diameter and the supplied voltage. With microelectrodes that are incorporated into flexible fibers (2-6 Fr), sustained oscillation is generated in the frequency range of 5.7-17 kHz. The oscillation frequency decreases with the radio frequency and electrode diameter, while an optimum voltage exists to reach maximum frequency of bubble oscillation. The RF power supply also offers flexibility to control the bubble dynamics with different voltage waveforms, duty cycles and pulse repetition rate.