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Wearable devices have attracted increasing attention for development of personal healthcare. In this study, three-dimensional porous carbon aerogels reinforced polydimethylsiloxane nanocomposites with controllable and hierarchical open, semi-open and closed cell structures were developed for multifunctional wearable heating and sensing devices. This investigation reveals that the microstructures of the aerogels play a critical role in determining nanocomposites properties, particularly their heating and sensing performances. As thermotherapy heaters, the nanocomposite with semi-open cell structure is observed with the highest energy transduction efficiency (equilibrium temperature ∼138.9 °C under only 5 V) compared to the nanocomposites with open and closed cell structures, due to the well-defined conductive network and structural stability. As stimuli-responsive sensors, compared to the nanocomposite with closed cell structure, the nanocomposites with open and semi-open cell structures are observed with higher sensitivity (gauge factor ∼369.03) and much better repeatability, benefiting from their structural integrity. Finally, the nanocomposite with semi-open cell structure was investigated for practical potential on human body. Experimental results demonstrated the uniform temperature distribution and reliable sensitivity as a multifunctional wearable device. Therefore, by controlling and optimizing the microstructure of carbon aerogels, the nanocomposites with tailored microstructure could be exploited for various engineering applications including emerging multifunctional wearable devices.

본 연구는 전자기 음향 공진을 이용하여 강선의 인장력 측정 타당성에 대한 연구이다. 강선은 공장, 교량, 건축물 등 대형 구조물의 프리스트레스 구조물로 널리 사용된다. 따라서 강선의 인장력 측정 기술은 구조물의 건전성과 안전성을 확보한다는 측면에서 기술 개발의 중요성이 대두되고 있다. 본 논문에서는 전자기 음향 공진을 이용하여 강선의 인장력에 따른 공진주파수를 측정하였다. 전자기 음향 공진은 비접촉식 공명 초음파 분광법으로 정확도가 높은 공진주파수 측정이 가능하다. 실험결과 공진주파수의 변화를 관찰하였다. 결과적으로 전자기 음향 공진을 이용한 강선의 인장력 측정의 타당성을 확인하였다.

건식 초음파 유량계는 기존 배관설비를 변경하지 않고 유량이 측정 가능하므로 산업현장에서 많은 주목을 받고 있다. 하지만 기존 건식 초음파 유량계는 압전 방식의 초음파 변환을 이용하므로 배관-유량계 접촉 문제, 낮은 신호대잡음비, 협소한 적용 온도 구간 등의 한계를 지니고 있다. 본 연구에서는 압전 원리 대신 전자기음향변환원리를 이용한 초음파 유량계를 제안하고 전자기 음향 트랜스듀서 적용에 따른 시간차법을 이용한 유량산출 모델을 제시하였다. 이를 바탕으로 1MHz의 중심주파수를 갖는 전자기음향트랜스듀서(EMAT) 기반 초음파유량계를 제작하였다. 제안한 유량계와 유량산출모델의 검증을 위해 실배관 시험을 수행하였다. 기존 전자식 유량계의 성능과 비교를 통해 제안한 EMAT 기반 초음파유량계의 타당성을 확인하였다.

Simultaneous substitution of Ba and/or Ti into Pb(Zn1/2W1/2)O3 was attempted in order to investigate the development of a perovskite structure. Precursor powders of the B-site components were separately prepared and post-reacted with the remaining components to assist the perovskite formation. The low formation yields of perovskite at Pb(Zn1/2W1/2)O3-rich compositions increased continuously with increasing substituent levels. Dielectric constant and loss values of the sintered ceramics were measured, followed by microstructure examination.

Herein, amino-functionalized monodisperse polymeric microcapsules were prepared via Schiff-base reaction between polyethyleneimine (PEI) and glutaraldehyde (GA) using a microfluidic approach. The GA encapsulated in the microcapsules leaked through thermal-induced microcracks at the shell of the microcapsules, and then the leaked GA caused crosslinking of the PEI molecules onto the shell without any further treatments. The success of amino-functionalization and the surface morphology of the microcapsules were demonstrated by Fourier transform infrared spectroscopy, scanning electron microscopy, and optical microscopy. Due to the presence of abundant amine groups in the PEI molecules on the shell, the amino-functionalized microcapsules serve as an effective adsorbent for heavy metal ions (HMI). The as-prepared microcapsules were evaluated as adsorbents to remove Cu2+, Cd2+, and Zn2+ ions from the aqueous solution under varying process parameters such as pH, contact time, and metal ion concentration. The adsorption capacity of the microcapsules for Cu2+, Cd2+, and Zn2+ was measured and fitted using the Sips isotherm model. After completion of HMI adsorption, the microcapsules were readily separated from the aqueous suspension by an external magnetic field. In addition, the cyclic adsorption–desorption efficiency of the amino-functionalized microcapsules was almost maintained for five times.

Suberin is a natural polyester providing the impermeability and mechanical damping of the plant cell walls. It is fascinating because ester bonds in the suberin can be easily hydrolyzed to provide various functional chemical precursors for further applications. This study investigates an unprecedented way to tailor energy-absorbing capabilities in silica-reinforced styrene-butadiene rubber (SBR) composites by introducing depolymerized suberin derivatives (DSDs) extracted from cork and potato periderm. The filler–matrix couplings were experimentally and analytically investigated through dynamic mechanical analysis (DMA) and the Huber–Vilgis model. The DSDs modified silica–polymer interfaces seem to offer a substantial increase in strength, toughness, and energy-absorption by nearly 47 %, 336 %, and 126 %, respectively, compared to bis(3-triethoxysilylpropyl)-tetrasulfide (TESPT)-coupled elastomers, without sacrificing the modulus. These findings could inspire natural materials enabled composite design for high energy-absorbing materials and provide a breakthrough in utilizing natural resources for next-generation structures such as urban air mobility or autonomous electrical vehicle, which typically require multifunctional performances including lightweight, high strength, and energy-absorbing capability.

In the manufacturing process of steel rod, a number of micro-scale defects occur along the axial direction on the surface of the rods. To prevent failures in advance, a method to detect the micro-scale cracks remaining on the surface of rod is required. This work employs an Electromagnetic acoustic transducer (EMAT) to evaluate the cracks of the wire rods with the noncontact Ultrasonic reverberation spectroscopy (URS). The resonance at the cross section of the cylindrical rods is generated by horizontally polarized shear waves driven in the circumferential direction. Through a series of URS experiments, changes in the resonant frequency, the amplitude of the resonant peak, and the attenuation of the ultrasonic reverberation were observed at intact and defected parts of specimens. The results showed that the URS technique may be one of the effective tools to detect the axial surface microcrack with its depth of a few tens of micrometers.

The emerging wire-shaped supercapacitors (WSSs) have motivated tremendous research interests in energy storage devices. However, challenges still exist in the pursuit of high-rate performance WSS. Here, a graphene fiber made from chemical vapor deposition grown laminated graphene sheet is adopted to form a WSS which exhibits an exceptional rate capability with a relaxation time constant of 1.4 ms, smallest among WSSs reported to date. Furthermore, the resulting WSS can be charged-discharged at a high scan rate of 100 V s −1 while maintaining good capacitive behavior. When the scan rate increased by 5000 times, from 20 mV s −1 to 100 V s −1 , the graphene fiber based WSS maintains 38.6% of its original capacitance. After 10,000 galvanostatic charge-discharge cycles, the specific capacitance retains over 105%, demonstrating a long cycle stability.

Herein, we demonstrate clipping distortion suppression of directly modulated multi-IF-over-fiber links using a simple shunt diode predistorter. The...

Electroplastic phenomenon has been demonstrated by that the elongation increases remarkably during deformation under electric current without a significant elevation of temperature due to Joule heating. Since the 1960s, the electroplasticity has been actively investigated; however, an exact explanation of the mechanism has been lacking. In this study, the origin of electroplasticity in metallic materials is elucidated based on first principle calculation, finite element simulation and experimental approaches. First principle calculations on a system that includes a grain boundary, which is the general defect in polycrystalline metallic materials, show that a charge imbalance near defects weakens drastically atomic bonding under electric current. The electroplastic behavior could be well reproduced with a small-scale, microstructure-based finite element simulation, which incorporates an effective temperature near defects under electric current. The effective temperature under electric current reflects the weakening of atomic bonding due to charge imbalance. In addition, the weakening of atomic bonding was confirmed by measuring the elastic modulus under electric current, which is inherently related to the atomic bonding strength. It can be said that the mechanical properties under electric current ultimately depend on the existing defects in metallic materials.

A non-invasive ultrasonic flowmeter transmits a shear wave into the wall of the pipe hosting the fluid. The shear wave is typically generated through a plastic wedge by the mode conversion of a longitudinal wave excited by a PZT element. Because of a big impedance mismatch between a plastic wedge and a metal pipe, however, conversion efficiency is not high. In this study, we propose a novel metal wedge equipped with an elaborately-designed mode-converting metamaterial slab and show that the designed wedge can fully transmit longitudinal-to-shear mode converted waves into a metal pipe. The design principle and mode-conversion efficiency of the meta-slab wedge and experimental results are presented. The designed meta-slab wedge was used for experiments performed with a water-flowing rectangular pipe and the flow velocity measurement sensitivity with it was increased several times compared with that based on a conventional wedge. Through this study, a metamaterial wedge is found to be a useful alternative to improve mode-converting transmission efficiency in ultrasonic applications.

Secondary solvents are utilized in post-processing procedures, such as the solvent post-treatment and post-deposition of polymer protecting and dielectric layers, and their effects on the morphology, molecular ordering, and charge-transport characteristics of poly (3-hexylthiophene) (P3HT) thin films have been investigated by systematically varying the polarity, viscosity, and solubility of co-solvent systems (i.e., chloroform/hexane, chloroform/methanol, and DCB/n-heptanol). During the solvent post-treatment, the P3HT films are preferentially dissolved by a co-solvent in the following order: DCB/n-heptanol

Longitudinal strips are suggested as a new device that can significantly increase the aerodynamic performance of a low Reynolds number airfoil at post-stall angles of attack. Its mechanism relies on the generation of corner vortices that delay flow separation on the airfoil suction surface.

In this study, we used the Finite element method (FEM) based on continuum mechanics, instead of molecular dynamics, to design and analyze an ultra-small mass nanomechanical sensor using Single wall carbon nanotube (SWCNT). We tested the validity of the FEM modeling technique based on continuum mechanics by comparing its analysis results with those of molecular dynamics modeling. After developing an elastic continuum shell model having an effective thickness, Young’s modulus, and Poisson’s ratio, we proved the superiority of the implemented analysis technique by comparing its resonance frequency with that of the molecular dynamics model. Additionally, using the developed model, we established various design parameters for a resonator and observed the parameter-dependent changes in frequency characteristics of the resonator.

In this study, we developed a fiber-optic temperature sensor (FOTS) based on a silicone oil and an optical time domain reflectometer (OTDR) to apply the measurement of a coolant leakage in the nuclear power plant. The sensing probe of the FOTS consists of a silicone oil, a stainless steel cap, a FC terminator, and a single mode optical fiber. Fresnel reflection arising at the interface between the silicone oil and the single mode optical fiber in the sensing probe is changed by varying the refractive index of the silicone oil according to the temperature. Therefore, we measured the optical power of the light signals reflected from the sensing probe. The measurable temperature range of the FOTS using a Cu-coated silica fiber is from 70℃ to 340℃ and the maximum operation temperature of the FOTS is sufficient for usage at the secondary system in the nuclear power plant.Key Words : Fiber-optic temperature sensor, Silicone oil, OTDR, Fresnel reflection, Coolant leakage †Corresponding Author : School of Biomedical Engineering,College of Biomedical & Health Science, BK21 Plus Research Institute of Biomedical Engineering, Konkuk University, KoreaE-mail : bslee@kku.ac.kr* School of Biomedical Engineering, College of Biomedical & Health Science, BK21 Plus Research Institute of Biomedical Engineering, Konkuk University, Korea** Department of Organic Materials & Fiber Engineering, College of Engineering, Soongsil University, KoreaReceived : August 11, 2015; Accepted : October 29, 2015

Insert parts in insert injection molding used to be deformed by pressure developed during the molding process. The plastic deformation of insert parts caused by injection pressure during insert injection molding for electric power plugs cannot be predicted by conventional injection molding analysis methods. In this study, the injection-structural coupled analysis was carried out to predict the plastic deformation of insert parts. Injection pressure developed during the molding process was calculated by the injection molding analysis software and was mapped onto the grid surface of the inner tube model for structural analysis as boundary conditions. The effect of process parameters such as injection time, melt temperature, and holding pressure on the injection pressure and the deformation of the inner tubes was examined to find the proper molding condition. The result from the analysis was compared to the insert injection molding experiment. Furthermore, the diameters of sub-runners in the multi-cavity mold of the power plugs were optimized to prevent the deformation of the inner tubes by the unbalanced filling of the melt into the linear arranged cavities using the injection-structural coupled analysis.

Recently, carbon materials such as carbon nanotubes and graphene have been proposed as alternatives to indium tin oxide (ITO) for fabricating transparent conducting materials. However, obtaining low sheet resistance and high transmittance of these carbon materials has been challenging due to the intrinsic properties of the materials. In this paper, we introduce highly transparent and flexible conductive films based on a hybrid structure of graphene and an Ag-grid. Electrohydrodynamic (EHD) jet printing was used to produce a micro-scale grid consisting of Ag lines less than 10 μm wide. We were able to directly write the Ag-grid on a large-area graphene/flexible substrate due to the high conductivity of graphene. The hybrid electrode could be fabricated using hot pressing transfer and EHD jet printing in a non-vacuum, maskless, and low-temperature environment. The hybrid electrode offers an effective and simple route for achieving a sheet resistance as low as ∼4 Ω per square with ∼78% optical transmittance. Finally, we demonstrate that transparent flexible heaters based on the hybrid conductive films could be used in a vehicle or a smart window system.

We demonstrate the improvement of the transmission performance based on intermixing noise mitigation techniques in a multiple intermediate-frequency-over-fiber (IFoF) based mobile fronthaul. The interaction between fiber chromatic dispersion and frequency chirp of the directly modulated laser generates the second-order distortion that degrades the performance of multi-IFoF transmission system. To avoid second-order distortion, we use intermediate frequency (IF) spacing optimization and octave-confined frequency plan schemes in which intermixing noise would be generated in the out of signal band and would not affect the quality of transmitted signal. For bandwidth efficient transmission of radio signal over mobile fronthaul link, we employ the dispersion compensation technique to suppress the intermixing noise sufficiently. For realization of the multi-IFoF based mobile fronthaul, we experimentally investigate the transmission performances of 48-, 72- and 144-IF carriers of the long term evolution-advanced (LTE-A) signals mapped with 64-quadrature amplitude modulation (QAM). It is clearly observed that the intermixing noise is suppressed owing to dispersion compensation technique and overall system performances are improved by IF spacing optimization and octave-confined frequency plan. As a result, we successfully transmit 144-IF carriers of the LTE-A signal with less than 8% error vector magnitude (EVM) over 20-km single-mode fiber (SMF) within only 3 GHz bandwidth. (C) 2017 Optical Society of America

In this study, two fiber-optic sensors were fabricated to measure water level and temperature using optical fibers, a coupler, a Lophine and an OTDR (optical time-domain reflectometer). First, using Fresnel's reflection generated at the distal-ends of each optical fiber, which was installed at different depth, we measured the water level according to the variation of water level. Next, we also measured the temperature of water using a temperature sensing probe based on the Lophine, whose absorbance changes with the temperature. The measurable temperature range of the fiber-optic sensor is from 5℃ to 65℃ because the maximum operation temperature of the optical fiber without a physical deterioration is up to 80℃.

Recently, much attention has been paid to nonlinear ultrasonic technology as a potential tool to assess hidden damages that cannot be detected by conventional ultrasonic testing. One nonlinear ultrasonic technique is measurement of the resonance frequency shift, which is based on the hysteresis of the material elasticity. Sophisticated measurement of resonance frequency is required, because the change in resonance frequency is usually quite small. In this investigation, the nonlinear electromagnetic acoustic resonance (NEMAR) method was employed. The NEMAR method uses noncontact electromagnetic acoustic transducers (EMATs) in order to minimize the effect of the transducer on the frequency response of the object. Aluminum plate specimens that underwent three point bending fatigue were tested with a shear wave EMAT. The hysteretic nonlinear parameter , a key indicator of damage, was calculated from the resonance frequency shift at several levels of input voltage. The hysteretic nonlinear parameter of a damaged sample was compared to that of an intact one, showing a difference in the values.

In microfludic biosensor applications, many kinds of magnetic particles have been employed due to their bioaffinity property, so the appropriate manipulation of magnetic microparticles is important. In this work, we demonstrated the alignment of magnetic beads (diameter 2.8 μm) and nanowires (length ≤ 6 μm & diameter ≈ 50 nm) using ultrasonic standing wave (USW) in a steel-acrylic microfluidic channel (660 μm width) in the aim of concentrating them to a sensor area to enhance the performance of a sensor. Ultrasonic standing wave field generates the radiation force to concentrate microparticles at the pressure nodal planes. To generate a standing wave inside the channel, an ultrasound of 2.25 MHz resonance frequency was applied as a resonance frequency of the channel. Moreover, it was demonstrated here that the position of the aligned magnetic particles could be controlled by changing the applied frequency. These successful alignment and position control can be a milestone for future research which targets to improve the sensitivity of microfluidic sensors using magnetic particles.

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack’s position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.

In this study, we investigated the dispersion characteristics of guided waves in thin films. Dispersion curves are essential for understanding not only the behavior of ultrasonic waves, but also the mechanical properties of thin films. Matrix techniques are presented for modeling ultrasonic waves in multilayered structures before being used to calculate the dispersion curves for Al-steel and Al-composite specimens. When compared with the dispersion curves obtained using the commercial program (Disperse), the dispersion curves generated from the transfer matrix method show its validity. These developed methods are used to obtain dispersion curves for Al thin films deposited on a Si substrate. The resulting dispersion curves enable observation of both dispersive and non-dispersive behavior for the guided waves, depending on the thickness of the thin films.

Recently microfluidic manipulation of live cell has been attracting attention because it is necessary for fast and accurate bioassays of cells within miniaturized devices like a lab-on-a-chip. This work concerns the alignment, translocation and concentration of live cells in a microfluidic channel by utilizing an ultrasonic standing wave. Among many ultrasonic manipulation methods, the technique using frequency swept ultrasound which was proposed in a previous study offers excellent particle manipulation performance, but that has been demonstrated only for biocompatible polystyrene microspheres with several different diameters, not actual biological cells. However, the technique needs to be verified for real cells because sizes and properties are little different with each other. Thus, in this work, the feasibility of using the ultrasonic frequency sweep method to manipulate live Nb2-11 cells was investigated experimentally The cells were aligned in a plane, moved to one side of a channel, and finally filtered out by sending them to one outlet with ultrasound. The frequency region of the applied ultrasound was between 1.75 MHz and 3.05 MHz. From experimental results, the cell behavior showing perfect alignment, almost perfect translocation and hence considerable aggregation proved the feasibility of using the frequency sweep method though the force acting on the Nb2-11 cells are much smaller than the force acting on polystyrene beads due to the differences in their sizes and mechanical properties.

We proposed and demonstrated high efficient pre-spectrum sliced seed lights (PS-SL) for serving low-cost seeded wavelength division multiplexing passive optical network (WDM–PON). The PS-SLs reused backward amplified spontaneous emission light which were generated by an Erbium doped fiber amplifier (EDFA) to improve output characteristics. The power, flatness and bandwidth of seed signal from the proposed PS-SL were sufficient to serve multiple seeded WDM–PON OLTs. We experimentally demonstrated the feasibility of the PS-SL with multiple seeded WDM–PONs over 20 km transmission. In addition, the PS-SL was tolerated to these ranges of environmental conditions since no data error was observed after 48 h. We anticipated a considerable reduction in the seed light cost per channel for multiple WDM–PONs because the seed light cost was shared by multiple WDM–PON OLTs.

Many studies have been conducted on the filtration of microparticles using the acoustic radiation force of ultrasonic standing wave. The present work concerns a flow-through particle filtration method by utilizing frequency varying ultrasound. The periodical frequency sweep of the ultrasonic standing wave translocates particles across a microchannel, where particles in fluid flow are filtrated without barriers. The present filtration technique in a microfluidic channel was proposed conceptually in the 1990s. However, its experimental realization on actual particles in a microfluidic channel has not been carried out in a notable way. Several sizes of polystyrene microspheres (10 μm to 90 μm) and silicon carbide (SiC) particles (37 μm) suspended in water were applied as a test sample. For filtration of those particles, a Y-branched microfluidic channel with one inlet and two outlets was made out of steel and acrylic as a form of modulized device. Ultrasound of a few MHz in band frequency (1.75 MHz to 3.05 MHz) was transmitted into one side of the channel wall to generate a standing wave field in fluid flow. The periodical frequency sweep operation showed successful filtration performance, whereby particles in water flowed into one outlet and purified water flowed into the other outlet of the Y branch of the channel.

The surface microcrack over a few tens of micrometers is one of severe problems of a steel wire rod to lead to the failure of the final products, so the method to evaluate crack depth has been required to develop. This work investigates the feasibility of electromagnetic acoustic resonance (EMAR) for this problem. EMAR is the method for measurement of resonant features using electromagnetic acoustic transducer (EMAT). Generally, EMAR is sensitive to small variation of the structures and easy to apply it to the industrial field because of the feature of noncontact measurement. Through several EMAR experiments, the change of the resonant frequencies and attenuation in reverberation has been observed. The results confirms that the surface cracks of around 100 micrometer depth can be detected successfully with the present method.

The film bulk acoustic resonator (FBAR) is one of filter devices for information and communication and is expected to apply to biosensor because of its excellent resonance characteristics. This study was conducted to analyze the factors affecting the resonance characteristics of FBAR by modeling and simulation. The acoustic Bragg reflector type FBAR (ABR-FBAR) consisting of piezoelectric thin film such as ZnO, top and bottom electrodes, acoustic reflector and substrate was assumed. The mathematical model describing the input impedance of ABR-FBAR was derived and verified by PZT element with ABR structures. The design parameters for ABR-FBAR factors such as thickness of electrode, and number, order and thickness of ABRs were analyzed by simulation of the derived model.

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Resistance of metal depends on temperature. Therefore, the metal can be used as a temperature sensor with a reference resistor. The reference resistor is connected serially and the voltages of the sensor metal are measured after applying DC voltage. However, it is not easy to keep the reference resistance constant while measuring temperatures. We studied the temperature dependence of resistance of oxide material to apply it to the bridge type temperature sensor which is insensitive to the environmental temperature. We made bridge type temperature sensor with oxide material and metal. The novel temperature sensor does not need a reference resistor, and composed of oxide and metal. Therefore, we could remove error induced by environmental temperature variation. Moreover, the novel bridge type temperature sensor provides higher sensitivity than conventional sensor structure. By different thermal coefficient of the oxide material, it was possible to remove an external reference resistance. The proposed bridge type temperature sensor is a self-reference temperature sensor which is insensitive to the environmental temperature.

자기변형 패치 트랜스듀서는 강구조물 자체의 자기변형성을 이용하여 탄성초음파를 발생시키던 기존의 방법에서 발전되어 자기변형성이 구조물에 비해 훨씬 더 큰 재질을 구조물에 부착하여 탄성초음파를 가진 또는 측정함으로써, 구조물의 재질과 무관하게 적용이 가능하고 출력 및 민감도의 비약적인 향상을 추구할 수 있다. 더불어 구조물에 Key Words : Bulk Shear Wave(체적전단파), Ferromagnetic Patch(강자성 패치), Magnetostrictive Transducer(자기변형 트랜스듀서), Radiation Pattern(방사 패턴) 초록: 최근 가공성이 우수하고 강한 자기변형성을 가진 강자성 패치가 소개되면서, 이를 이용한 탄성초음파 변환 연구가 활발하다. 이러한 자기변형 패치 트랜스듀서는 SH파와 비틀림파 등 전단파 변환 성능이 우수하여 비파괴평가 분야에서 많은 주목을 받고 있지만, 지금까지 관련 연구가 유도초음파 변환에 집중된 반면 체적초음파에는 아직 적용이 된 예가 없다. 본 연구에서는, 자기변형성이 큰 재질 중 하나인 철-코발트 합금을 이용한 체적전단파 트랜스듀서를 제안하고자 한다. 제안한 트랜스듀서는 강자성 패치, 코일, 영구자석, 요크를 포함하여 모듈형으로 설계되었고, 실험을 통해서 파형 및 방사 패턴 등을 측정하였다. 결과적으로, 제안한 트랜스듀서는 신호대잡음비 및 방사패턴 면에서 상당히 우수한 성능을 보임을 확인하였다. Abstract: Recently, the results of many studies have clarified the successful performance of magnetostrictive transducers in which a ferromagnetic patch is used for the transduction of guided shear waves; this is because a thin ferromagnetic patch with strong magnetostriction is very useful for generating and detecting shear wave. This investigation deals with bulk shear wave transduction by means of magnetostriction; on the other hand, the existing studies have been focused on guided shear waves. A modular transducer was developed; this transducer comprised a coil, magnets, and a thin ferromagnetic patch that was made of Fe–Co alloy. Some experiments were conducted to verify the performance of the developed transducer. Radiation directivity pattern of the developed transducer was obtained, and a test to detect the damage on a side drill hole of a steel block specimen was carried out. From the results of these tests, the good performance of the transducer for nondestructive testing was verified on the basis of the signal-to-noise ratio and narrow beam directivity.

For efficient non-destructive ultrasonic inspection in plate/shell structures, the development of a guided-wave based method using transducers having good beam directivity, high power and little dispersion is important. To this end, a damage inspection strategy using a set of specially-designed magnetostrictive patch transducers capable of generating beam-focused, non-dispersive shear-horizontal waves is proposed. In the present ultrasonic pitch-catch inspection, only a few single transducers need to be installed around an inspection area. To convert measured wave signals by the transducers into two-dimensional images, a relatively simple yet effective data-processing technique suitable for the employed transducer setting is developed. Sets of experiments were conducted on rectangular plates having one or two circular holes with a diameter of 1 mm or 3 mm. For all experiments, the Gabor-shaped ultrasonic pulses having the center frequencies of 250 kHz and 360 kHz were used. Nomenclature n A = region of influence for a grid point n. s c = shear wave speed. D = interval between solenoids in PSA (Planar Solenoid Array). , () n ij E t = envelope of the voltage output signal at a specific arrival time t from i to j via n. f = center frequency. G = spacing between virtual grid points. n h = the size of n A .

Oxide material can make transparent devices with transparent electrodes. We developed a transparent oscillator and rectifier circuits with oxide TFTs. The source/drain and gate electrodes were made by indium thin oxide (ITO), and active layer made by transparent material of IGZO (Indium Gallium Zinc Oxide) on a glass substrate. The RC oscillator was composed of bootstrapped inverters, and 813kHz oscillation frequency was accomplished at VDD = 15V. For DC voltage generation from RF, transparent rectifier was fabricated and evaluated. This DC voltage from rectifier powered to the oscillator which operated successfully to create RF. For data transmission, RF transmission was evaluated with RF from the transparent oscillator. An antenna was connected to the oscillator and RF transmission to a receiving antenna was verified. Through this transmission antenna, RF was transmitted to a receiving antenna successfully. For transparent system of RFID, transparent antenna was developed and verified sending and receiving of data.

Poly(ethylene terephthalate) (PET) fabric/poly(3,4-ethylenedioxythiophene) (PEDOT) composite with stable and high electrochemical activity was fabricated by chemical and electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) on a PET fabric in sequence. Effects of polymerization conditions on the following characteristics of the composite were studied: electrical conductivity and surface morphology. The electrochemical properties were also investigated by cyclic voltammetry and cyclic charge/discharge experiments. The specific volume resistivity, electrical conductivity and specific discharge capacitance of the composite were 0.034 Ω-cm and 25 S/cm, and 54.5 F/g, respectively.

Thiophene-based π-conjugated polymers have been widely used in p-channel OTFTs due to their high charge carrier mobility. SPQT-12 which has dodecylsulfanyl side-chain was synthesized by Stille polymerization. The polymer was characterized by 1H NMR, GPC, UV-Vis spectroscopy, and cyclic voltammetry. Molecular weight (Mn) of SPQT-12 was 10,000 (PDI = 1.7), and SPQT-12 were readily soluble in common organic solvents. In the film state, SPQT-12 showed absorption with λmax at 553 nm and optical band gap of 1.87 eV. A mobility of 1.0 × 10−3 cm2/Vs, an on/off ratio of 5.8 × 103 and threshold voltage of −11 V have been obtained with OTFTs using SPQT-12.

PbTiO 3 and/or BaTiO 3 were systematically introduced into Pb(Zn 1/2 W 1/2 )O 3 and resultant phase developments in terms of perovskite formation were investigated. Ceramic powders were prepared via a B-site precursor route to further assist the perovskite formation. Weak-field dielectric properties of the sintered samples were examined. For Pb(Zn 1/2 W 1/2 )O 3 -rich compositions, multiphase ceramics resulted and formation of monophasic perovskite turned out to be not successful even by the B-site precursor method. Values of the perovskite formation yield and the maximum dielectric constant increased with increasing fractions of the substituent species.

Warpage issues are of concern for flip chip Ball Grid Array (FCBGA) package reliability on thin substrates. Despite advantages in electrical performance of thin substrates, FCBGA warpage hampers reliability of the solder balls making up the ball grid array. Warpage and plastic strain of both the FCBGA package and solder balls are calculated under assembly conditions. Temperature dependent material properties were investigated using finite element analysis. FEM calculations of thermal deformation and equivalent plastic strain of solder balls considered to determine overall reliability of the solder balls. Solder ball plastic strain decreased with substrate core thickness. This can explain why solder ball reliability decreases with substrate thickness. Substrate surface warpage fluctuated significantly as core thickness decreased due to reduced stiffness. In addition, it is possible that solder balls and surface mounted components can be affected by surface fluctuations. Although thinner substrates have advantages in terms of electrical performance, high warpage is a critical root cause of package failure. Despite these tradeoffs, developing thinner substrates while avoiding warpage is a forefront issue.

The hypothesis that health effects associated with coal combustion fly-ash particles are exacerbated by the simultaneous presence of iron and soot was tested through two sets of experiments. The first set created prototype particles from complete and partial combustion, or oxygen free pyrolysis of a high iron Illinois bituminous coal in an externally heated drop-tube furnace. The second experiment created prototype particles consisting of iron and soot in various concentrations from doped ethylene Burke–Schumann flames. Size-classified samples from the coal tests were separated into coarse (>2.5 lm), fine (0.5–2.5 lm) and ultrafine (

material was synthesized by electrospinning method to obtain optimal particle size() without carbon coating or ball milling. This material showed an orthorthombic structure with Pnma space group without any impurities, such as FeP or , in the XRD pattern. The particle morphology and particle shape were observed by SEM analysis. Li/ cell showed a high initial discharge capacity of 135 mAh/g, at current density of with a cut-off voltage of 2.8 to 4.0V. This cell exhibited a perfect cycle performance over 99.9% cycle retention rate up to 50 cycles.

A new type of Li1−xFe0.8Ni0.2O2-LixMnO2 (Mn/(Fe+Ni+Mn)=0.8) material was synthesized at 350 °C in an air atmosphere by a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li1−xFeO2-LixMnO2 ((Fe+Ni+Mn)=0.8) with much reduced impurity peaks. It was composed of many large particles of about 500–600 nm and small particles of about 100–200 nm, which were distributed among the larger particles. The Li/Li1−xFe0.8Ni0.2O2-LixMnO2 cell showed a high initial discharge capacity above 192 mAh/g, which was higher than that of the parent Li/Li1−xFeO2-LixMnO2 (186 mAh/g). This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles. We suggest a unique role of doped nickel ion in the Li/Li1−xFe0.8Ni0.2O2-LixMnO2 cell, which results in the increased initial discharge capacity from the redox reaction of Ni2+/Ni3+ between 2.0 and 1.5 V region.