Three-dimensional variable-focus liquid lens using acoustic radiation force

Abstract

A liquid lens was fabricated with a focal point that can be varied in the axial and radial directions. We have been developing a variable-focus liquid lens that employs acoustic radiation force and does not contain any mechanical moving parts. Our liquid lens is more compact and has a faster response than conventional mechanical lenses. Rapid scanning of its focus at 1 kHz has been realized by excitation with an amplitude-modulation (AM) signal. The liquid lens consists of a cylindrical acrylic cell (inner diameter: 10 mm; thickness: 3 mm), two immiscible liquids with different refractive indices (water and silicone oil), and an annular piezoelectric lead zirconate titanate transducer with four electrodes. The oil-water interface functions as a lens surface and it can be deformed by the acoustic radiation force generated by the transducer; this enables the lens to act as a variable-focus lens. The variation of the oil-water interface was observed by optical coherence tomography. The laser beam path through the lens was calculated by ray-tracing simulations. The oil-water interface could be deformed and its focal point could be varied in three dimensions by controlling the input voltages of the PZT electrodes. The displacement angle in the radial direction was approximately 3° when two of the electrodes were excited by an input voltage of 45 V at a frequency of 1.9 MHz. The dynamic performance of the lens was investigated using a high-speed cam- era. Excitation by AM signals with a phase difference caused the hemispherical water droplet to oscillate, enabling the focus to be scanned in the axial and radial directions.

Tunable Liquid Lenses: Emerging Technologies and Future Perspectives

“…The lens's response time was 6.7 ms. Then, they used a four‐phase actuator to generate an axisymmetric sound pressure field and cause an axisymmetric deformation of the optical interface in the liquid lens. [ 194 ] The ultrasonic drive could quickly focus the change, but the response speed was limited by the weight of the liquid. The smaller the droplet volume was, the faster the response speed was.…”

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…[311][312][313][314][315][316][317][318][319][320][321] High-power ultrasound is used to produce physical or chemical effects in a medium, such as sonoprocessing (e.g., the promotion of physical dissociation and chemical decomposition and the onset of nucleation and grain refinement of solidified metals), [322][323][324][325][326][327][328][329] streaming (e.g., the design of ultrasonic pumps and the improvement of their performance), [330][331][332] and manipulation (e.g., the manipulation of particles and the development of variable-focus liquid lenses). [333][334][335][336][337][338] High-power ultrasound is also used for energy conversion. For example, a recent class of engines that converts heat to sound energy and vice versa without moving parts (e.g., the design of thermoacoustic systems and the improvement of their efficiency) [339][340][341][342][343] and welding techniques that can join plastics or thin films by converting friction and vibration energy into heat [344][345][346] have actively been researched.…”

Relationship between liquid crystal layer thickness and variable-focusing characteristics of an ultrasound liquid crystal lens

“…1) Despite the need for small, thin camera modules with a high-speed response, it is difficult for conventional camera modules with moving mechanical parts to meet these requirements. Our group has developed variable-focus lenses using acoustic radiation force and immiscible liquids, 2,3) viscoelastic gels, 4,5) and liquid crystal (LC), 6,7) which have no moving mechanical parts. LCs are in a material state between a liquid and a solid and exhibit both liquidity and optical anisotropy.…”