Fabrication and Estimation of Novel Micro Liquid Rotor that Operates with Surface-Acoustic-Wave

Abstract

A micro liquid rotor that operates with surface acoustic waves (SAWs) was proposed and fabricated. The liquid rotor has two interdigital transducers (IDTs) that generate SAWs, in order to increase efficiency of rotating the liquid. The IDTs were fabricated by patterning Al/Cr on a LiNbO₃ substrate. As the IDT parameters, we used a stripline pitch of 200μm, 20 stripline pairs and an aperture size of 2mm. A liquid pool in the rotor is a round shape of 4mm diameter, and its depth is 200μm. A sidewall of the liquid pool was made of SU-8 on the substrate. As characteristics of the liquid rotor, we investigated relationships between electric power applied to the IDTs and angular velocity of the liquid or its temperature. For applying the electric power to the IDT, we used a burst voltage waveform that has sine frequency of 19.6MHz and duty ratio of 10%. Through experimentation we showed that the angular velocity or the temperature increase with increasing the electric power. In addition, we also found that a response time of the angular velocity is faster than that of temperature of the liquid. When the fabricated liquid rotor was applied electric power of 2W, the liquid of 5μl rotated at 330rad/s (3,100rpm) and its temperature reached 65°C.