(A and B) 3D and 2D schematics for illustrating the mechanism of an AFBH-based elliptical substrate device. (A) Inset: A photo of a fabricated device with a piezoelectric transducer [disc-like lead-zirconate-titanate (PZT)] bonded at the left focal point of an elliptical PMMA substrate. (C) Left: A simulated flexural wave field (out-of-plane displacement amplitude |uz|) in the solid domain at an excitation frequency of 163 kHz. Right: The corresponding acoustic streaming field with drag forces illustrated by red arrows. (D) Distributions of 10-μm fluorescent polystyrene particles in an AFBH before applying acoustic waves and after 3 min of acoustic waves. Scale bars, 500 μm. For this experiment, the excitation voltage, frequency, droplet volume, and initial particle concentration are 10 Vpp, 163 kHz, 20 μl, and 8.25 × 105 ml−1, respectively. (E) A simulated flexural wave field and an acoustic streaming field at an excitation frequency of 141 kHz. (F) Distributions of 10-μm fluorescent polystyrene particles in an AFBH before applying acoustic waves and after 3 min of acoustic waves. Scale bars, 500 μm. For this experiment, the excitation voltage, frequency, droplet volume, and initial particle concentration are 10 Vpp, 141 kHz, 20 μl, and 8.25 × 105 ml−1, respectively.