Seung-Yop Lee

Biologically inspired humidity sensor based on three-dimensional photonic crystals

This letter presents a biomimetic humidity sensor inspired by the humidity-dependent color change observed in the cuticle of the Hercules beetle. A thin-film-type humidity sensor with nanoporous structures (three-dimensional photonic crystals) mimicking the spongy multilayer in the beetles was designed and fabricated using the colloidal templating method and a hydrophilic surface treatment. The visible color of the fabricated humidity sensor changes from blue-green to red as the environmental humidity increases. The wavelength of reflected light that is predicted by Bragg’s equation considering the effect of water absorption shows a good agreement with experimental results.

Theoretical modeling, experiments and optimization of piezoelectric multimorph

This paper deals with the static and dynamic electromechanical responses of piezoelectric layered structures (multimorphs). Based on the Bernoulli?Euler plate model including the dynamics of piezoelectric, electrode and substrate layers, we obtain the natural frequencies, maximum displacement and resultant force of a symmetric cantilevered multimorph. The proposed theoretical model is verified by experiments using a 20-layered PZT (plumbum?zirconate?titanate) multimorph, and it is compared to the conventional bimorph model. Experimental results agree with the analytical predictions on the natural frequencies and vertical displacement. With the analytical solution for multimorph, we investigate the effects of the layer number and the layer thickness on natural frequency, maximum deflection and output force. It is found that there exists an optimum number of piezoelectric layers to maximize the transverse deflection. There also exists a specific value of the thickness ratio between piezoelectric and structure layers to maximize both the tip deflection and force.

Carbon nanotube-graphene composite for ionic polymer actuators

In this paper, we develop a new ionic polymer‐metal composite (IPMC) by replacing a typical platinum or gold electrode with a multi-walled carbon nanotube (MWNT)‐graphene based electrode. A solvent of MWNT and graphene is formed on both sides of the ionic polymer membranes as electrodes by means of spray coating and baking. Then, the ionic liquid process is performed for actuating in air. The four kinds of IPMC samples with different MWNT‐graphene ratios are fabricated with the same solid Nafion film. Experimental results show that the IPMC with a pure MWNT based electrode exhibits higher displacement compared to the conventional IPMC with a platinum electrode. Also, the increment of the ratio of graphene to the MWNT‐graphene electrode decreases the resultant displacement but increases the fundamental natural frequency of the polymer actuator. (Some figures may appear in colour only in the online journal)

Magnetic properties of gapless semiconductors: PbPdO2 and PbPd0.9Co0.1O2

PbPdO2 is a new class of gapless semiconductors, which is extremely sensitive to external influences such as temperature, magnetic field, and carrier doping, because of their peculiar band structure. With varying temperature, a broad transition from a high-temperature metallic behavior to a low-temperature insulating behavior was observed at TMI=100 K in the electrical resistivity, which is related to the thermally assisted excitation near the Fermi level due to its gapless band structure. By doping 10% Co for Pd in PbPdO2, the number of hole charge carriers was increased by ten times, and the transition temperature was increased to TMI=150 K. When applying a magnetic field, a ferromagnetic component was found at low temperatures in the magnetization curves of both materials, in addition to diamagnetic background signals for PbPdO2 and paramagnetic background signals for PbPd0.9Co0.1O2. In the low temperature regime, the slope of magnetoresistance is negative, while it is changed into positive with a quad...

A mobile auto-focus actuator based on a rotary VCM with the zero holding current

In this work, an auto-focus actuator moving lens in mobile phone cameras is developed by applying a rotary VCM (voice coil motor). A novel inclined cam structure is used to convert the rotational motion by the VCM by into the linear motion of the focusing lens. The new focusing design enables the zero holding current required to maintain the lens module in the focusing position as well as the reduction of the module thickness. This paper presents the theoretical analysis and optimal design for the VCM actuator, cam structure and preload spring. We manufacture a prototype module with the size of 9.9x9.9x5.9 mm(3). The experimental results agree with the theoretical predictions and meet the required specifications for mobile camera applications.

A piezoelectric actuator with a motion-decoupling amplifier for optical disk drives

In this paper, an optical pick-up actuator is studied using a multilayered PZT (lead‐zirconate‐titanate) for possible application to slim and small-form-factor optical disk drives or mobile devices. A theoretical modeling and analysis of the PZT actuator including the dynamics of piezoelectric, electrode and substrate layers are performed to estimate the dynamic properties such as natural frequencies, resultant forces and maximum displacements. In particular, we suggest a novel stroke-amplifying structure enabling the decoupled tracking and focusing motions actuated by four parallel multimorphs. A flexure hinge mechanism is used as the displacement amplifier to extend the allowable stroke of the actuator. Experimental results using a cantilever actuator agree well with the analytical predictions. Based on the theoretical and experimental investigations, we have designed the final model of the optical pick-up actuator with a height of 2.5 mm, showing that the moving range is ±400 μm at 15 V in the focusing direction, which is appropriate for slim or small-form-factor optical disk drives. (Some figures in this article are in colour only in the electronic version)

A Miniaturized Tadpole Robot Using an Electromagnetic Oscillatory Actuator

In this paper, we propose a miniaturized tadpole-like robot using an electromagnetic oscillatory actuator. The electromagnetic actuator has a simple structure with a moving-magnet type and the body size is 13 mm (length) × 11 mm (height) × 10 mm (width). A tail has the thickness of 100 μm and the length of 20 mm which is twice of the body-length (BL). The tail attached to the oscillatory actuator generates undulatory propulsion for the forward swimming. Moreover, the tadpole robot enables the change of the direction by controlling input signal patterns applied to the oscillatory actuator. Prototypes of the tadpole robot have been manufactured and the thrust force and swimming speed are measured to evaluate the performance of the biomimetic robot in water at various tail-beat frequencies. The maximum thrust force is 42 mN at the tail-beat frequency of 30 Hz with voltage of 3 V, enabling the tadpole robot to swim at the speed of 210 mm·s−1 (6 BL·s−1). The tadpole robot can also change its moving direction with the angular velocity of 21 deg·s−1 at the half pulse pattern of 30 Hz.

Design of a slim-type optical pick-up actuator using PMN-PT bimorphs

In this paper, a new optical pick-up actuator is proposed using PMN-PT (lead magnesium niobate–lead titanate) bimorphs for slim and small form factor optical disk drives. We suggest a novel structure enabling both tracking and focusing motions by changing the moving directions of the two parallel bimorphs. A cymbal-type flextensional structure is used as a displacement amplifier in order to meet the stroke requirement for optical pick-up actuators. We have performed the theoretical analyses for the bimorph actuator and displacement amplifier to predict the resultant force and displacement. The proposed actuator based on PMN-PT bimorphs and displacement amplifier has been manufactured, and the experimental results are compared to the analytical predictions. Experimental results agree well with the analytical predictions, showing that the cymbal structure amplifies the displacement twice and the focusing stroke is 52 µm at 10 V.

Direct experimental verification of the sound-induced tunable resonance on a flexible electrorheological layer

The tunable behaviors of low-frequency sound waves transmitted through a flexible electrorheological (ER) layer with plastic-aluminum electrodes are investigated. It shows that, within 80–210 Hz, the sound-pressure level (SPL) decreases with the electric field E, while within 210–300 Hz, the SPL increases with E. The vibration displacement of the ER layer surface is directly measured via a laser Doppler vibrometer. It reveals that two resonance modes exist on the ER layer and all the modes are tunable via the electric field. Around the first resonant frequency of 100 Hz, the vibration displacement decreases with the increase of E, while around the second resonant frequency of about 180 Hz, the vibration displacement increases with E. The consistently varying characteristics with respect to the electric field imply an intrinsic relation between the vibration of the ER layer and the sound transmission. The relation is further qualitatively explained by the vibration-radiation model. The tunable resonance ef...

Bioinspired Segment Robot with Earthworm-like Plane Locomotion

In this paper, a miniaturized segment robot using solenoids is developed to mimic the plane locomotion of earthworms. The bioinspired robot is composed of five segmented bodies, and one segment has two solenoid actuators. This robot can move linearly and it can also turn due to the pair of solenoid actuators that facilitate the earthworm-like peristaltic locomotion. We have designed a miniaturized solenoid with a permanent magnet plunger in order to increase the total electromagnetic force. A theoretical analysis is performed to predict the linear and turning motions of each segment, and the optimal profiles of input signals are obtained for fast locomotion. Experiments are then conducted to determine the linear and turning motions of the segment robot. It takes about 0.5 s for the five segments to complete one cycle of the peristaltic locomotion. In experiments, the segment robot is shown to have the linear and angular velocities of 27.2 mm·s−1 (0.13 body-length per second) and 2 degrees per second, respectively.