Acoustic Levitation and Haptics: Ultrasound Manipulation Lecture

Creating a standing wave with two opposing 40 kHz transducers achieves levitation. The wave traps objects smaller than the wavelength at antinodes where pressure amplitude reaches a minimum. Designers compute the forces that hold the particle using the Gorkov Potential, which translates acoustic pressure and velocity fields into a force vector.

Algorithmic Approaches

The system employs a 40 kHz transducer array that controls phase and amplitude for each element. The “focal point” method delivers computationally cheap updates, reaching more than 40,000 frames per second. To generate complex shapes, the Gershberg‑Saxton algorithm solves the inverse phase‑retrieval problem: it iterates between the desired pressure pattern and the transducer constraints until the phase distribution converges. Pre‑computing constant matrices further speeds real‑time movement of levitated objects.

Multimodal Applications

Focusing ultrasound on a hand creates tactile sensations; the short 40 kHz wavelength produces a felt pressure that feels like wind or a light tickle on the palm. Modulating the amplitude of the same carrier wave embeds audible signals, making a levitated object appear to speak. The platform can levitate an object, deliver haptic feedback, and emit sound simultaneously, merging contact‑free manipulation with audio‑haptic interaction.

Industrial and Future Use Cases

Omnidirectional 3D printing leverages material‑agnostic levitation to deposit biological fluids or polymers from any direction, enabling multi‑material structures. High‑value seed inspection uses acoustic traps to isolate individual tomato seeds, allowing precise germination testing and sorting. Automotive designers explore contact‑free tactile dashboards, where users feel virtual buttons projected by ultrasound. Entertainment venues add immersive tactile layers to visual media, enriching audience experience.