In previous papers [Baudoin et al., Sci. Adv. 5, eaav1967 (2019); Baudoin et al., Nat. Commun. 11, 4244 (2020)], our team demonstrated the possibility to trap and manipulate microparticles and cells selectively, in 2D and in a standard microfluidic environment with some spiraling interdigitated transducers (S-IDTs). These S-IDTs were designed as the phase hologram of specific wave structures called focused acoustical vortices. Here we explore theoretically with an angular spectrum code the 3D trapping capabilities of these transducers. We demonstrate: (i) that the field synthesized by S-IDTs creates a 3D radiation trap for microparticles and cells and (ii) that the trap can be moved axially by simply tuning the driving frequency. This work opens perspectives for 3D manipulation of cells with single beams acoustical tweezers.