P2I-2 Design of Steep Intensity Distribution for Acoustic Tweezer Using Multiple High Frequency Focused Transducers

Sharp intensity change around a focal point is one of the most essential elements for acoustic tweezers. This paper presents a method to create such intensity distribution by using multiple high frequency focused transducers. In addition to a 50 MHz tweezer transducer, 20 MHz holder transducers are needed for initial positioning of lipid particles into a water chamber. The results demonstrate that the arrangement can provide 3 dB beamwidth of 30 mum to ensure tweezer effect. Aperture sizes of holder and tweezer transducers are 4.4 mm and 2.8 mm, respectively. F-number of all transducers is 0.5. Peak intensity and pressure at the focus are calculated to be 35.4 W/cm² and 0.7 MPa under 1 mW of acoustic power. Tight focusing is required to minimize acoustic streaming, which undermines the tweezing by acoustic radiation forces. Based on the field distribution obtained from Field II, it is concluded that its large intensity gradient can generate the tweezer effect up to 340 pN in the vicinity of the focus.