Ultrasonic micromanipulation of small particles in liquid using VHF-range leaky wave transducers

New ultrasonic micromanipulation techniques for small particles based on the radiation forces of high-frequency ultrasound are proposed, using VHF-range leaky wave transducers. A newly developed leaky wave transducer with beamwidth compression consists of a floating-electrode-type unidirectional interdigital transducer and a LiNbO
₃
substrate. It has many advantages: no impedance matching scheme between liquid and substrate, efficient generation of higher-frequency ultrasonic waves into a small-scale liquid system, and isolation of interdigital electrodes from liquid. The experimental leaky wave transducer with narrow beam width of 120-μm shows a conversion loss of 5.8 dB at 97.5 MHz. Transportation and trapping of 50-μm-diameter glass spheres in water are confined by preliminary experiments in the frequency range of 50 to 100 MHz