An entirely soft varifocal lens based on an electro-hydraulic actuator

Abstract

Varifocal lenses have been promptly developed but show many shortcomings in the area of artificial pupils, such as rigid frames, prestress and large structures. This paper presents an entirely soft varifocal lens to adapt to the increasingly ingenious soft robotic structures. Such a varifocal lens is mainly composed of a PDMS frame, a liquid dielectric and a pair of flexible electrodes. The stable focal length of the lens varies from 533.5 to 49.4 mm by applying DC voltages from 3 to 12 kV. Surprisingly, a novel ‘jump’ phenomenon is found in the varifocal lens at the moment of power-on. Then, the varifocal effects are studied under alternating voltages with a square wave, a triangle wave or a sine wave. The varifocal range remains basically stable after repeated cycles under alternating voltages. As the frequency increases, the range of the focal length change also gradually decreases and becomes more stable. As a result, the stable focal length of the lens is able to vary as wide as from 690.3 to 24.5 mm by applying square waveform voltages from 1 to 8 kV at a frequency of 10 Hz. The proposed lens is simple, thin and flexible, which is expected to develop the artificial eyes of soft robots.