• Structural Engineering and Mechanics
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• v.82 no.2
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• pp.259-270
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• 2022

The paper investigates the residual stresses arising in a thermoviscoelastic cylinder as a result of layer-by-layer deposition of material on its lateral surface. Internal stresses are caused by incompatible deformations that accumulate in the assembly as a result of joining parts with different temperatures. For the analysis of internal stresses, an analytical solution to the axisymmetric quasi-static problem of thermoelasticity for a growing cylinder is constructed. It is shown that the distribution of residual stresses depends on the scenario of the surfacing process. In this case, the supply of additional heat to the growing body can significantly reduce the unevenness of temperature fields and reduce the intensity of residual stresses. The most effective is uneven heating, which can be realized, by the action of an alternating current with a tunable excitation frequency. The temperature and residual stresses fields on the growing surface is analyzed numerically for Titanium and Copper materials.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.200-204
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• 2008

Coherent tunable terahertz generation was demonstrated in periodically poled stoichiometric lithium tantalate crystal via difference frequency generation of femtosecond laser pulses. Simultaneous forward and backward terahertz radiations were obtained around 1.35 and 0.63 THz, respectively at low temperature. By cooling the crystal to reduce losses caused by phonon absorptions, the generated THz bandwidth was as narrow as 23GHz at the center frequency of 0.63 THz. The measurement result of temperature-dependent showed gradual intensity increase of the generated terahertz pulse and red shift of the center frequency as the temperature decrease from 291 to 143 K, but insignificant reduction of the spectral bandwidth. Furthermore, the stoichiometric crystal was very suitable for the suppression of THz loss at low temperature compared to the congruent $LiNbO_3$ crystal.

• Journal of the Korean Magnetics Society
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• v.16 no.5
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• pp.234-239
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• 2006

We measured the microwave permeability in the frequency range of 100 MHz$\sim$9 GHz in the exchange biased CoFe/MnIr films. The results were analyzed based on the Landau-Lifshitz-Gilbert theory. The initial permeability and ferromagnetic resonance frequency was tuned by controlling the CoFe thickness and unidirectional anisotropy. The tunable range of ferromagnetic resonance frequency was up to 20 GHz in the thin CoFe layer of 1.5 nm. The CoFe/MnIr films showed the high permeability and low loss properties in the microwave frequency range. Thus, this material could be applied to the microwave devices.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.508-517
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• 2004

We described a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 5GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator We developed a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterened Cr films on glass substrates. We measured the reflection coefficient of different metal thin film samples with the same thickness of 300m and compared with theoretical impedance respectly. By tuning the tunable screw coming through the top cover, we could improve sensitivity, signal-to-noise ratio, and spatial resolution to better than $1{\mu}m$. To demonstrate the ability of local microwave characterization, the surface resistance of metallic thin films has been mapped.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.33-41
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• 2011

To substitute TLS in the hybrid system which is combined with Sagnac interferometer and fiber bragg grating (FBG) it is necessary to investigate how the laser source (TLS and CW) and sensor material variate the response of fiber optic sensor. Two different hollow cylinder type mandrel materials are proposed which are PTFE and PTFE+carbon and 18 m optical fiber is wounded at the mandrel surface. CW laser source experiments had been done in the oil tank which is filled with transformer oil in the 1 kHz~20 kHz frequency range. Also Sagnac interferometer fiber optic sensor is combined with FBG called hybrid system and TLS used as a light source. Based on the experimental results PTFE sensor showed more higher magnitude of detection signal rather than carbon sensor and this result is agreement with the McMahon's theoretical results. Phase variation is inversely proportional to the elastic modulus of the mandrel material. In PTFE fiber sensor, tunable laser source showed more higher performance rather than CW case. Therefore, TLS fiber optic sensor can be applied to the hybrid system which is combined with Sagnac and FBG.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.43-50
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• 2004

For the simultaneous measurement of strain and damage signal a fiber Bragg grating sensor system with a dual demodulator was proposed. The dual demodulator is composed of a demodulator using a tunable Fabry-Perot filter measuring the low-frequency signal with large magnitude such as strain and the other using a passive Mach-Zehnder interferometer detecting the high-frequency signal with small amplitude such as impact or damage signal. Using the proposed fiber Bragg grating sensor system, both the strain and damage signals of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundreds of kilohertz at the instant of matrix crack propagation in the 90 degree layer in composite beam.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.95-102
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• 2004

For the simultaneous measurement of strain and damage signal, a fiber Bragg grating sensor system with a dual demodulator was proposed. One demodulator using a tunable Fabry-Perot filter can measure low-frequency signal such as strain and the other demodulator using a passive Mach-Zehnder interferometer can detect high-frequency signal such as damage signal or impact signal. Using a proposed fiber Bragg grating sensor system, both the strain and damage signal of a cross-ply laminated composite beam under tensile loading were simultaneously measured. Analysis of the strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were induced due to transverse crack propagation in the 90 degree layer of composite beam and vibration with a maximum frequency of several hundreds of kilohertz was generated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1132-1137
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• 2011

MRE(magneto-rheological elastomers) is a material which shows reversible and various modulus in magnetic field. Comparing to conventional rubber vibration isolator, MREs are able to absorb vibration of broader frequency range. These characteristic phenomena result from the orientation of magnetic particles named carbonyl iron powder(CIP) in rubber matrix. In this paper, simulation on variation rate of shear modulus for anisotropic MRE due to volume fraction of CIP and an effective permeability model was applied to predict the field-induced shear modulus of MREs. Also, the variation rate of shear modulus for anisotropic MRE was derived using magneto-mechanical theory. Based on Maxwell-Garnett mixing rule, the increment of shear modulus was calculated to evaluate the shear modulus of MREs with column structure of CIP due to induced current. The simulation results on variation rate of shear modulus can be applied to the variable mechanical system of MRE such as tunable vibration absorber, stiffness variable bush and mount.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.234.2-234.2
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• 2015

Recently, the electromagnetically-induced transparency (EIT)-like effect in metamaterials has attracted enormous interest. Metamaterial analogs of EIT enable promising applications in slow-light devices, low-loss metamaterial, quantum optics, and novel sensors. In this work, we experimentally and numerically studied a bilayer metamaterial for controllable EIT-like spectral response at microwave frequencies. Bilayer metamaterial consists of two snake-shape resonators (SSRs) with one and two bars. The transmission spectra were measured in a frequency range of 4 - 8 GHz in an anechoic chamber at normal incidence. It is found that two SSRs in the metamaterial are activated in bright modes, and the coupling between two bright modes leads to the EIT-like effect, which results in the enhanced transmission at 5.61 GHz. Furthermore, we confirm that the EIT-like feature could be controlled by adjusting the geometric parameters of metamaterial structure. Our work provides a way to tunable EIT-like effect and various potential applications including filters, sensors, and other microwave devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04a
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• pp.197-200
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• 2000

All-optical NOR logic device was realized by use of two pump signals with a single wavelength and a semiconductor optical amplifier(SOA). Specially, Mach-Zehnder(MZ) modulator was used for an external modulation of the pump signals. To obtain the sufficient gain saturation of the SOA, pump signals are amplified by an Er-doped fiber amplifier(EDFA) at the input of the SOA. Pump and probe signals are obtained from a DFB laser diode(${\lambda}_p$=1554 nm) and a tunable laser diode(${\lambda}_s$=1535 nm), respectively. The operation characteristics of the NOR logic device are successfully measured and demonstrated at the modulation frequency of 4.83 MHz.