On Low-Power Droplet Manipulator Employing High-Frequency Surface Acoustic Waves

A droplet manipulator working with low driving power was developed by using the surface acoustic wave (SAW) technology. The manipulator was driven at a relatively high frequency of 350MHz to increase the SAW power density. First, a single phase unidirectional transducer (SPUDT) was designed. Because of its low insertion loss of 1.5 dB and high directivity of 10 dB, the SPUDT successfully conveyed a 100 nl water droplet with RF input power of 18 dBm (60 mW). Second, the SPUDT design was extended to a curved transducer to focus and launch the SAW energy into the narrow waveguide. Owing to the increased SAW power density, the required SAW power was reduced to 15 dBm (30 mW) for the 100 nl droplet manipulation. In addition, fabrication of liquid injectors was discussed for the formation of tiny droplet.