Jinpyo Jeon

On-demand magnetic manipulation of liquid metal in microfluidic channels for electrical switching applications

We report magnetic-field-driven on-demand manipulation of liquid metal in microfluidic channels filled with base or acid. The liquid metal was coated with iron (Fe) particles and treated with hydrochloric acid to have strong bonding strength with the Fe particles. The magnetic liquid metal slug inserted in the microchannel is manipulated, merged, and separated. In addition, corresponding to the repositioning of an external magnet, the liquid metal slug can be readily moved in microfluidic channels with different angles (>90°) and cross-linked channels in any direction. We demonstrated the functionality of the liquid metal in the microfluidic channel for electrical switching applications by manipulation of the liquid metal, resulting in the sequential turning on of light emitting diodes (LEDs).

Magnetic Liquid Metal Marble: Characterization of Lyophobicity and Magnetic Manipulation for Switching Applications

We report a “magnetic liquid metal marble” (MLMM) obtained by coating a liquid metals surface with micro/nano-sized ferromagnetic iron (Fe) particles, which enables on-demand, magnetic manipulation of a liquid metal droplet for switching applications. Among liquid metals, gallium-based liquid metal alloys have been developed for a variety of applications. However, most developed applications using the gallium-based liquid metal alloy only work on deformability because of its easy-wetting property stemming from surface oxidation. By coating the oxidized surface with the 45 μm or 45 nm diameter Fe particles, the MLMM exhibits non-wetting property investigated by evaluating apparent contact angles and sliding angles against various surfaces. On the Teflon-coated glass, the largest contact angle was measured to be ~169.0°, and the lowest sliding angle was obtained to be 17.2°, respectively. In order to move the 45-μm diameter Fe particles-coated MLMM, we measured the minimum required magnetic flux density of 150 gauss and demonstrated the magnetic control of the liquid metal marble to turn ON light emitting diodes. In addition, we investigated that hydrochloric acid-vapor treatment on the MLMM enhanced the lyophobicity (sliding angle of 9.4°), reduced the minimum magnetic flux density (150 to 107 gauss) to actuate it, and enabled electrical switching applicability even in silicon oil with shorter delay time and high mobility of the MLMM under the applied magnetic field.

Liquid lens based on electromagnetic actuation for high-performance miniature cameras

This paper presents a new design of tunable liquid lens operated by electromagnetic actuation for autofocus (AF) in miniature cameras and its optical performance is experimentally verified. When an electrical voltage is applied to an electric coil inside the electromagnetic system beneath the liquid lens, a magnetic field is generated around the electromagnetic system based on Faradays law of induction. The magnetic field is used to actuate a ring type neodymium magnet placed on the top of an elastic membrane in the liquid lens. Based on the proposed liquid lens, the measurement of the lens sag height with respect to an applied voltage is carried out. The lens sag height is linearly increased from -1 mm to 0.8 mm while the applied voltage is changed from 0 V to 50 V at a 5 V increment. The average sag height variation per voltage is about 32 μm. The focal length with respect to an applied voltage is also measured using a custom-built testing system consisting of a laser, a mirror, a liquid lens and a detection screen and compared with theory. Finally, the ability of the liquid lens to change its focal plane to distinguish two objects positioned at different distances is successfully tested.

Novel energy harvesting using acoustically oscillating microbubbles

When a bubble hanging on a piezocantilever is excited by an acoustic wave around its resonant frequency, it oscillates and simultaneously generates cavitational microstreaming around it. The microstreaming bends the piezocantilever with fine vibration, resulting in electric power generation from the piezocantilever. In this study, we explore the dynamic behaviors of an acoustically oscillating bubble on the flexible substrate as well as demonstrate applicability of the proposed system to practical applications such as energy harvesting and acoustic wave sensors. First, the effects of an applied frequency and bubble size on the dynamic characteristics of an acoustically oscillating bubble, such as maximum amplitude and resonant frequency, are experimentally investigated. The amplitude of an oscillating bubble is maximized at its resonant frequency, which is inversely proportional to its size. In addition, electrical voltage generated by a piezocantilever attaching with an oscillating bubble is measured at different applied frequencies, bubble sizes, and distances between the bubble and piezoactuator. The results show that the generated voltage is strongly affected by the applied frequency and is inversely proportional to the bubble size and the distance between the bubble and piezoactuator. Finally, the output voltage is almost linearly proportional to the number of bubbles.

On-chip separation method using a bubble for bio/micro-object manipulation

A novel on-chip bubble-separator has been developed where microparticles in an aqueous medium are separated and collected by size using an acoustically excited bubble as a mechanical filter. The concept of the bubble-separator is experimentally verified: bubble manipulation (generating and transporting operations) and micro-object manipulation (selectively capturing, carrying, and releasing operations). Optically induced bubble generation is firstly tested for different optical powers in a microfluidic chip with an amorphous silicon layer as an optically absorbent material. And bubble transportation is also demonstrated using optically induced thermocapillary effects. Micro-object manipulation is separately demonstrated using a bubble with two different sized glass and polystyrene particles in an aqueous medium. When a bubble is acoustically excited by a piezoactuator attached on the side of a chip, it oscillates and simultaneously captures large microparticles owing to the oscillating bubble induced radiation force but repels small microparticles due to the bubble induced cavitational microstreaming. Finally, the manipulation (separation and collection) of the mixture of two different sized glass particles is achieved using a bubble actuated by optical and acoustical excitation.