Focus control of a concave ultrasonic gel lens

Optical image stabilization is a powerful tool for camera devices. This paper investigates a tunable lens using ultrasound and a transparent viscoelastic gel in which the focal point can be controlled in the radial direction. The lens has a simple structure and consists of four piezoelectric ultrasonic transducers, a glass disc, and a transparent silicone gel film. A four-phase drive of the lens at the resonant frequency generates the flexural traveling-wave mode, resulting in changes of the surface profile of the gel by acoustic radiation force. At a resonant frequency of 60.8 kHz, a concave shape was observed on the gel surface, indicating that a concave lens can be fabricated by controlling the driving frequency and the phase difference between the transducers. Optical characteristics of the lens were evaluated by ray tracing. The deformation displacement of the lens surface and the change in focal length increased with the voltage amplitude. The voltage ratio between the four transducers was changed, allowing the center position of the gel deformation and its focal position to be shifted in the radial direction, thus realizing image stabilization functions.