Ultrasonic microparticle trapping by multi-foci Fresnel lens

This paper describes an acoustic tweezers consisting of a multi-foci Fresnel lens on 127 μm thick PZT sheet, designed to capture micron-sized particles. The multi-foci Fresnel lens was designed to have similar working mechanism as that of an axicon lens to generate an acoustic Bessel beam and, correspondingly, to generate negative axial radiation force capable of trapping one or more microparticle(s). The fabricated acoustic tweezers successfully trapped lipid particles ranging in diameter from 50 to 200 μm and microspheres ranging in diameter from 70 to 90 μm at a distance of 2 to 5 mm from the tweezers without any contact between the transducer and microparticles.