  Holographic acoustical tweezers (HAT) based on Archimedes-Fermat spiraling
InterDigitated Transducers (S-IDTs) are a versatile tool for the selective
manipulation of microparticles [Baudoin et. al., Sci. Adv., 5: eaav1967 (2019)]
and cells [Baudoin et. al., Nat. Commu., 11, 4244 (2020)] in a standard
microfluidic environment. These binary active holograms produce some focused
helical wave, with the ability to trap particles at the vortex core. Yet, all
the studies conducted with S-IDTs have so far been restricted to 2D
manipulation only. Here we show (i) that 3D radiation trap for microparticles
and cells can be obtained with spiraling tweezers with sufficiently large
aperture and (ii) that the particles can be displaced axially by simply tuning
the driving frequency, without any motion of the transducer. This work opens
perspectives for 3D cells and microparticles manipulation with single-beam
acoustical tweezers.
