Luciola: A Millimeter-Scale Light-Emitting Particle Moving in Mid-Air Based On Acoustic Levitation and Wireless Powering.

In this paper, we present an approach to realize the levitation of a small object with an embedded electronic circuit. Luciola is a light-emitting particle with a diameter of 3.5mm and a weight of 16.2mg moving in mid-air in a 10.4cm x 10.4cm x 5.4cm space through acoustic levitation using two 40-kHz 17 x 17 ultrasonic transducer arrays placed face-to-face at a distance of 20cm and wirelessly powered by 12.3-MHz resonant inductive coupling. The novelty of this paper is the acoustically levitated electronic object by the combined application of ultrasonic levitation and wireless powering to the levitated electronic object. A new shape of the levitated object and a new placement of the receiver coil to simultaneously realize acoustic levitation and wireless powering are proposed, achieving a stable wireless powering to a rotating levitated object at the bottom of an acoustic potential. To enable the levitation of a particle, a custom IC chip is essential in reducing the size and weight of the particle. In the design of the custom IC chip, a new voltage detector circuit enabling an accurate voltage detection and a correct output during the start-up is proposed to achieve an intermittent lighting of the LED to increase the maximum distance between the transmitter and the receiver coil. Luciola is applied to a self-luminous pixel in a mid-air display and drawings of characters in mid-air are demonstrated.