Electromagnetically driven liquid lens

This paper presents a new design of tunable liquid lens. The lens was operated by electromagnetic actuation for autofocusing (AF) in miniature cameras and its optical performance was experimentally verified. An electrical voltage was applied to an electric coil inside an electromagnetic system beneath the liquid lens to generate a magnetic field around the electromagnetic system according to Faraday's law of induction. The magnetic field was used to actuate a ring-type neodymium magnet placed on the top of an elastic membrane in the liquid lens. The sag (sagittal) height of the liquid lens was measured as a function of the applied voltage. The sag height of the lens increased linearly from −1 mm to 0.8 mm when the applied voltage was changed from 0 V to 50 V at 5 V increments. The average variation of the sag height per volt was about 32 μm. The focal length was also measured with respect to the applied voltage by using a custom-built testing system consisting of a laser, mirror, liquid lens, and detection screen. The measured focal length values were compared with the theoretical ones. For imaging tests, a single-object focusing test was first performed by using a sheet of paper with a check pattern. Furthermore, the ability of the liquid lens to distinguish two objects positioned at different distances by changing its focal plane was successfully tested. Finally, the response times of the liquid lens for actuation and relaxation were measured by a high-speed camera and were found to be about 900 ms.