• Journal of Magnetics
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• v.3 no.2
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• pp.64-67
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• 1998

Microwave absorbing properties of ferrite-epoxy composite (absorbing layer) attached on the carbon fiber polymer composite (reflective substrate) are analyzed on the basis of wave propagation theory. A modified equation for wave-impedance-matching at the front surface of absorbing layer including the effect of electrical properties of the quasi-conducting substrate is proposed. Based on this analysis, the frequency and layer dimension that produce zero-reflection can be estimated from the intrinsic material properties of the obsorbing layer and the substrate. It is demonstrated that the microwave reflectivity of carbon fiber composite has a strong influence on the microwave absorbance of front magnetic layer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.293-295
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• 2004

In this research, we suggest the effective technique that the thickness of slab isn't increased, and considering proper shock absorbing material and supporting point, we make the floating floor which has multi-supporting system floating floor. As the result, it is effective in reduction of heavy weight system as well as one of light weight

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.928-931
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• 2003

In this research, we suggest the effective technique that the thickness of slab isn't increased, and considering proper shock absorbing material and supporting point, we make the floating floor which has multi-supporting system floating nut. As the result, it is effective in reduction of heavy weight system as well as one of light weight

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.76-81
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• 2021

A plastic noise barrier is a structure installed to minimize noise, and it is composed of the main plate, sound-absorbing plate, and sound-absorbing material. Plastic noise barrier structures have several advantages compared to other products, such as light weight, anticorrosion, durability, easy assembly, rapid construction, and low costs. In this study, the main and sound-absorbing plates were manufactured through extrusion molding, and the sound-absorbing plate was finished with a press to improve the conventional injection molding. Extrusion molding dies and punch dies were designed, and a profile extrusion-molding system was developed. Thus, inexpensive and efficient sound-absorbing and main plates can be produced, and the noise barrier structure can be assembled rapidly. Additionally, a noise barrier structure with extended service life and excellent quality can be constructed by creating uniform free space to accommodate increased temperatures after assembly and installation.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.3
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• pp.144-151
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• 2002

This work focuses on finding out the noise source and the method of reducing the noise level of LPG(liquefied petroleum gas) fuel injector. The noise of LPG injector in operating condition is due to the impact between valve and valve seat. This study shows that if the revolution of engine is increased, the noise of LPG injector will be more serious but it is not nearly affected by the increment of fuel pressure. The source and transmission paths of noise are identified through the analysis of noise generation mechanism and noise spectrum. The sound absorbing material is tested to verify its efficiency of sound absorption thor the LPG injector. The effect of noise reduction of absorbing material is remarkable when the engine speed is high. Consequently two methods of reducing the noise level are suggested from the identified results. The one is to equip the absorbing material on the outer side of injector and the other is to coat with a soft material or equip a soft ring on the surface of impact.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.2
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• pp.91-95
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• 2000

A new damping composite materials with asphalt and EM absorber are studied for high advantage values. The composite Ni-Zn ferrite and dielectric PZT with a main material is well developed of EM absorbing, and is continuous maintained of origin character, damping absorbing. Experiments and calculation results are shown to act two points frequencies at 928MHz and from 2MHz to 4GHz below -l0dB The narrow band widths of ferrite change to broad band as insert of dielectric material, PZT good of EM wave absorbtion and broad band widths in multi layers with ferrite These are applied to develop of new material at new need frequencies.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.155-161
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• 2000

In this paper, we studied the relation between heat-treatment temperature of ferrite and electromagnetic wave absorbing properties of ferrite-rubber composite. The heat-treatment temperatures of ferrite are 1200 and $1300^{\circ}C$, 2 hr. As s result. it has been shown that the optimum heat-treatment temperature of ferrite for electromagnetic wave absorber are related to the chemical composition. And, we can control electromagnetic wave absorbing properties of ferrite-rubber composite by the control of heat-treatment temperature of ferrite.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.4
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• pp.58-64
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• 2001

Sound absorbing materials are applied to the exposed surfaces of curvet subway tunnel for the reduction of curving noise level. Before the treatment, acoustical engineering simulation is performed to predict the noise level reduction for different kinds and amounts of absorbing material. The principle of geometrical acoustics is utilized to perform the simulation efficiently and accurately. The noise bevels of the inside and outside of running car body are measured to find the noise level reduction. The average noise level reduction of 8 dB has been attained. It has been shown that the simulated results are comparable to the measured ones.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.689-694
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• 2013

A duplex stainless steel sheet with 1 wt.% gadolinium was fabricated for a neutron absorbing material with high strength, excellent corrosion resistance, and low cost as well as high neutron absorption capability. The microstructure of the as-cast specimen has typical duplex phases including 31% ferrite and 69% austenite. Main alloy elements like chromium (Cr), nickel (Ni), and gadolinium (Gd) are relatively uniformly distributed in the matrix. Gadolinium rich precipitates were present in the grains and at the grain boundaries. The solution treatment at $1070^{\circ}$ for 50 minutes followed by the hot-rolling above $950^{\circ}$ after keeping the sheet at $1200^{\circ}$ for 1.5 hours are important points of the optimum condition to produce a 6 mm-thick plate without cracking.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.2 no.2
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• pp.73-79
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• 2001

In this paper, the transmitted noise reduction performance of piezoelectric smart panels is experimentally studied. The proposed piezoelectric smart panels are comprised of plate structure on which piezoelectric sensor/actuators are bonded and sound absorbing material is provided. It is a combination of passive and active approaches utilizing a passive effect at high frequencies and an active effect at low frequencies. To prove the concept of piezoelectric smart panels, an acoustic measurement experiment is performed. An acoustic tunnel is designed and its acoustic characteristics are tested. Below 800Hz, the tunnel exhibits a plane wave guide characteristics. When an absorbing material is bonded on a single plate, a remarkable transmitted noise reduction in mid frequency range is observed except the first resonance frequency. By enabling the active control of single smart panel with negative feedback control. about 10dB noise reduction is achieved at the resonance frequencies. The double smart panel got 4dB at the first resonance frequency and has more potential to reduce the transmitted noise in a wide range frequency. Piezoelectric smart panels incorporating passive absorbing material and active piezoelectric devices is a promising technology for noise reduction in a wide range frequency.