The role of electric field in microfluidic heating induced by standing surface acoustic waves

The heating mechanism of standing surface acoustic waves (SSAWs) on a LiNbO₃ substrate has been experimentally studied. Three devices with different substrates were used to heat the drops with NaCl concentrations ranging from 0 to 1 g/l, respectively. The device with a glass substrate was used to shield acoustic waves. The device with an Au layer between the LiNbO₃ substrate and the droplet was used to shield the alternating current field. The results show that the thermal effect induced by SSAWs on the LiNbO₃ substrate is composed of the acoustothermal effect due to SSAWs and the electric field thermal effect (Joule heat) due to the alternating current field. The electric field thermal effect which is ignored in SSAW devices previously plays an important role in the thermal effect induced by SSAWs. These results provide a meaningful insight into the mechanism of SSAW-based heating, which is of great help to guide the effective use of the SSAW-based heating technique for various applications.