Hyung-Kun Lee

Application of ionic polymer-metal composites for auto-focusing compact camera modules

Step-motor, piezo, liquid lens and voice coil motor (VCM) have been thought as good candidates for actuators in auto-focusing compact camera module (CCM). Currently, VCMs take possession of big place in auto-focusing CCM market. However, VCMs have limitations in developing thin, low-power CCMs. Therefore, ionic polymer-metal composites (IPMCs) could be thought as one of the best candidates in developing auto-focusing CCM due to their well-known characteristics such as low-power consumption and large displacement. It is required that fast bending response (20 μm/20 ms) and large blocking force (800 mgf) should be achieved for the practical applications of IPMCs in developing auto-focusing CCM. Here, we present the method for increasing IPMCs bending response and displacement by anisotropic plasma treatment. Furthermore, we demonstrate the fabrication of a prototype of CCM actuated by IPMC and its remarkable low power consumption.

A narrow bandwidth microstrip bandpass filter with symmetrical frequency characteristics

This paper proposes a band-pass filter (BPF) with two transmission zeros based on a combination of parallel coupling and end coupling of half-wave transmission lines. The fabricated BPF exhibited a narrow bandwidth and two transmission zeros near the pass-band due to the end-coupled and shielding waveguide. At the center operation frequency of 60 GHz, the 20 dB bandwidth of the BPF is 1.0 GHz, which is almost 2% of the center operation frequency, and the insertion loss is 3.12 dB. Two transmission zeros reach approximately 40 dB at 58.5 and 62.5 GHz. The simulation results almost agree with the measured results.

Wideband aperture coupled stacked patch type microstrip to waveguide transition for V-band

A compact aperture coupled patch type microstrip-to-waveguide transition at V-band is proposed and fabricated using LTCC(Low Temperature Co-fired Ceramic) process. It uses the aperture coupled microstrip feed and the parasitic patch antenna radiating into the waveguide to improve the insertion loss and the bandwidth. As a result of experiments, low transmission loss and high return loss are realized at the design frequency of 60 GHz. For a 10 dB return loss, a relative bandwidth of 13.8% is obtained for a fabricated back to back transition.

Humidity-independent conducting polyaniline films synthesized using advanced atmospheric pressure plasma polymerization with in-situ iodine doping

This study reports on the synthesis and characterization of conducting polyaniline (PANI) thin films when using advanced atmospheric pressure plasma jets (APPJs). A simple method for synthesizing conducting polymers (CPs) with humidity-independent characteristics is introduced using advanced APPJs and an in-situ iodine doping method. In the case of ex-situ I2 doping, a humidity effect study showed that increasing the relative humidity produced significant changes in the electrical resistance (R) of the PANI, indicating strong humidity-dependent characteristics similar to conventional CPs. In contrast, in the case of in-situ I2 doping, the R and sensitivity of the PANI remained essentially unchanged when increasing the relative humidity, except for a very low sensitivity of 0.5% under 94% relative humidity. In addition, the R for the PANI with in-situ I2 doping showed no aging effect, while the R for the ex-situ-doped PANI increased dramatically over time. Thus, it is anticipated that the use of in-situ do...

Ionic Polymer-Metal Composites (IPMCs) Containing Cu/Ni Electrodes and Ionic Liquids for Durability

We describe the fabrication of ionic polymer-meal composites (IPMCs) containing Cu/Ni electrode as an electrode material and ionic liquid as an electrolyte. Cu/Ni is notorious for vulnerability to oxidation and acid. The authors have investigated best candidate of ionic liquids for this vulnerable electrode. This new IPMC shows increased displacement and blocking force compared to that of conventional IPMC containing Pt electrode and ionic liquid due to increased stiffness of resulting IPMC and size effect of mobile cations. In this research, the effect of ionic liquid was investigated by monitoring displacement and blocking force of IPMCs depending on the type of ionic liquids.

A model of the IPMC actuator using finite element method

Ionic polymer-metal composite (IPMC) is an attractive actuator among many electro-active polymers. In order to improve the performance of IPMC actuator, an IPMC actuator with the patterned surface was proposed. It is named the patterned IPMC actuator. In order to make use of its maximum effect, it is needed to establish a valid mathematical model. Among many models of IPMC actuator, the grey box modeling proposed by Kanno et al. was suited to model the patterned IPMC actuator. In this paper, we applied the grey box model based on Kannos model. Theoretical and experimental results demonstrate that the model is practical and effective enough in predicting the bending displacement partly.

5.5.2 Response/Recovery Behaviors of Solid Electrolyte CO2 Gas Sensors Depending on Reference Materials

Effects on response and recovery behaviors depending on reference materials such as lithium cobalt oxide (LiCoO2) and lithium manganese oxide (LiMn2O4) as well as lithium titanate (Li2TiO3) were investigated by fabricating the sensor composed of those reference materials and a sensing material Li2CO3 on a solid electrolyte Li3PO4. Selection of the reference materials was adopted from cathode materials in lithium ion battery field because of the similar working mechanism. The results showed that LiMn2O4 and LiCoO2 as the reference materials were effective in enhancing ΔEMFs/decade value and recovery time of the sensors compared to Li2TiO3, which might come from the facile lithiation of the reference materials, LiMn2O4 and LiCoO2, resulting from their unique crystal structures.

Performance enhancement of IPMC by anisotropic plasma etching process

Ionic Polymer-Metal Composites (IPMCs) of EAP actuators is famous for its good property of response and durability. The performance of Ionic Polymer-Metal Composites (IPMCs) is an important issue which is affected by many factors. There are two factors for deciding the performance of IPMC. By treating anisotropic plasma etching process to 6 models of the IPMCs, enhanced experimental displacement and force results are obtained. Plasma patterning processes are executed by changing the groove and the land length of 6 patterns. The purpose of the present investigation is to find out the major factor which mainly affects the IPMC performance. Simulations using ANSYS have been executed to compare with the experimental results about the values and the tendency of data. Experimental and simulating data of the performances seem to have similar tendency. In the next part of the paper, we observed the other properties like capacitance, resistance and stiffness of 6 plasma patterned IPMCs. And we observed that the stiffness is the major factor which affects the performance of IPMCs. As we seen, our problem has been reduced to investigate about the property of stiffness. We suggest that the stiffness is largely changed mainly because of the different thickness of Platinum stacked of the groove and the land part which are produced by anisotropic plasma etching processes. And we understand that anisotropic plasma patterned IPMCs of better performance can be applied to various applications.

Preisach modeling of IPMC-EMIM actuator

The IPMC-EMIM actuator is an improved IPMC actuator to replace the water by stable ionic liquids (1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EtMeIM][TA])). Just as a general IPMC actuator which uses the solvent of water has hysteresis, so do the IPMC-EMIM actuator exhibits hysteresis like other smart materials such as piezoceramics (PZT), magnetostrictive materials, and shape memory alloys (SMA). Hysteresis can cause it to be unstable in closed loop control. The Preisach Model has been used to model the hysteretic response arising in PZT and SMA. Noting the similarity between IPMC-EMIM and other smart materials, we apply the Preisach model for the hysteresis in the IPMC-EMIN actuator. This paper reviews the basic properties of the Preisach model and confirms that the Preisach model of IPMC-EMIM actuator is possible.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.