Electromagnetically driven liquid iris

•A new type of tunable liquid iris based on electromagnetic actuation is proposed for miniature cameras for mobile devices.•To investigate the effect of a magnetic field on a ferrofluid used as a shutter, contact angle modification and transportation of a sessile ferrofluid droplet are tested.•A MEMS-based tunable liquid iris (9mm×9 mm×2mm) is realized. The aperture diameter can be varied from 1.72mm to 1.09mm. This paper presents a tunable liquid iris based on electromagnetic actuation for miniature cameras in mobile devices such as smart phones and pads. To investigate the effect of a magnetic field on a ferrofluid, contact angle modification and transportation of a sessile ferrofluid droplet are tested using a neodymium magnet and an electric coil. The variation in the contact angle of the ferrofluid droplet is 21.3° for the neodymium magnet and 18.1° for the electric coil. In addition, transportation of the ferrofluid droplet is also demonstrated using the neodymium magnet and the electric coil. As a proof of concept, a pretest of a tunable iris operated by electromagnetic actuation is conducted by using a hollow cylinder cell. Initially, the ferrofluid is in a relaxed state, so the cylinder cell shows the largest aperture (4.06mm). When an electric current is applied to an electric coil wound around the outside of the cylinder cell, the ferrofluid, which is initially placed in the hydrophobic sidewall inside the cylinder cell, is actuated and pulled to the center. The aperture diameter under the applied current is modified from 4.06mm at 0A to 3.21mm at 2.0A. Finally, a tunable iris, consisting of two connected circular microchannels, is realized using MEMS technology. The iris size is 9mm×9mm×2mm, and the aperture diameter can be varied from 1.72mm at 0A to 1.09mm at 2.6A. The response times of the iris for actuation and relaxation are measured by a high-speed camera and found to be 250ms and 450ms, respectively.