Fig. 6. 3D assembly of silica gel beads with holographic ultrasound fields.

(A) Arrangement of three sources (2.25 MHz) and target field (sample container hidden). (B) Intensity distribution (isosurface at 0.16 · max {I}) of the simulated field and its (C) radiation force potential $\text{Υ}$ for silica gel particles (isosurfaces at −0.1 · min {$\text{Υ}$}). (D) Hydrophone measurement of the sound pressure field. Isosurfaces at 0.4 · max {p} = 21.6 kPa. (E) Photo of the fixed 3D assembly of silica gel particles in cross-linked hydrogel. Subsequent images show rotated close-up views. Scale bar, 5 mm.