A resume of the terrestrial levitation of liquid drops (and solid particles) in optimized, single-axis acoustic standing wave levitators is presented. It concentrates on a normalized theoretical description of drop displacement and deformation in the full dynamic range of the levitation safety factor Φ_s, which is the ratio of axial levitation force and sample weight. Sample properties like density ρ and surface tension σ are represented by the Bond number Bo. The Weber number We as the ratio of the acoustic radiation pressure and the capillary pressure defines the upper limit of the levitation range at critical acoustic Mach numbers Ma_(crit), where drops disintegrate. The theoretical considerations are backed up by some measurements with water drops in near ambient air at 20 and 58 kHz. An engineering concept for modular, single-axis acoustic levitators with sensor-controlled, calibrated resonance tuning is introduced. The levitators can easily be changed from a tube version with small required gas volume into an open version with free radial access to the sample, both optional with superimposed axial gas flow. Some recent terrestrial applications of acoustic levitators are listed.
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