• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.11a
• /
• pp.506-511
• /
• 2000

The aim of this study is to suggest a fundamental data to improve the sound insulation performance of floor. To achieve the aim of this study, 8 types of sound-absorbing and sound insulation materials were installed under the slab, and the floor systems were compared to the general floor system which was composed of slab, timber frame, gypsum board and wallpaper.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2009.05a
• /
• pp.555-558
• /
• 2009

In this paper, stealth technology is investigated with RCS(Radar Cross Section) reduction to minimize detection range of retroreflective echoes from enemy. Most RCS reduction comes from shaping. RAM(Radar Absorbing Materials) are applied only in areas where there are special problems. Therefore, we designed and fabricated a RAM that has absorption ability higher than 17 dB at 94 GHz for RF stealth in millimeter wave range. As a result, detection range of enemy can be reduced in the 62 percent range by using a developed RAM.

• Korean Journal of Materials Research
• /
• v.9 no.12
• /
• pp.1234-1239
• /
• 1999

Electromagnetic wave asorbing properties of the $Ni_{0.5}-Zn_{0.4}-X_{0.1}{\cdot}Fe_2O_4$, where X was replaced by substitution elements Cu, Mg, Mn, have been studied. The structure, shape, size and magnetic properties of the $Ni_{0.5}-Zn_{0.4}-X_{0.1}{\cdot}Fe_2O_4$ were analyzed by XRD, SEM, VSM. The relative complex permittivity, permeability, and electromagnetic wave absorbing properties were measured by Network Analyzer. The structure, shape, size and magnetization value of the $Ni_{0.5}-Zn_{0.4}-X_{0.1}{\cdot}Fe_2O_4$ were found to be similar in spite of substitution elements. The coercive force and hysteresis-loss showed maximum value when Mg was substituted for X. The dielectric loss(${\varepsilon}_r"/{\varepsilon}_r'$) was found to be maximum value when Mn was substituted for X. Also the magnetic loss(${\mu}_r"/{\mu}_r'$} was found to be maximum with Cu substitution. The electromagnetica wave absorbing property of the $Ni_{0.5}-Zn_{0.4}-X_{0.1}{\cdot}Fe_2O_4$-Rubber composite with 4mm thickness was excellent as over - 40dB at 9GHz, and the $Ni_{0.5}-Zn_{0.4}-X_{0.1}{\cdot}Fe_2O_4$-Rubber composite with 8mm thickness was over-40dB at 2GHz. Those composites also showed superior microwave absorbing properties.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.622-624
• /
• 2008

This investigation studies the effects of material properties and corresponding propagation wave types on optimal configurations of sound absorbing porous materials in maximizing the absorption performance by topology optimization. The acoustic behavior of porous materials is characterized by their material properties which determine motions of the frame and the air. When the frame has a motion, two types of compressional wave propagate in the porous material. Because each wave in the material make different influence on the absorption performance, it is important to understand the relative contribution of each wave to the sound absorption. The relative contribution of the propagating waves in a porous material is determined by the material properties, therefore, an optimal configuration of a porous material to maximize the absorption performance is apparently affected by the material properties. In fact, virtually different optimal configurations were obtained for absorption coefficient maximization when the topology optimization method developed by the authors was applied to porous materials having different material properties. In this investigation, some preliminary results to explain the findings are presented. Although several factors should be considered, the present investigation is focused on the effects of the material properties and corresponding propagation waves on the optimized configurations.

• Korean Journal of Metals and Materials
• /
• v.50 no.10
• /
• pp.769-774
• /
• 2012

Mg-x wt% $Fe_2O_3-y$ wt% Ni samples were prepared by reactive mechanical grinding in a planetary ball mill, and their hydrogen-storage properties were investigated and compared. Activations of $Mg-5Fe_2O_3-5Ni$ was completed after one hydriding (under 12 bar $H_2$) - dehydriding (in vacuum) cycle at 593 K. At n = 2, $Mg-5Fe_2O_3-5Ni$ absorbed 3.43 wt% H for 5 min, 3.57 wt% H for 10 min, 3.76 wt% H for 20 min, and 3.98 wt% H for 60 min. Activated $Mg-10Fe_2O_3$ had the highest hydriding rate, absorbing 2.99 wt% H for 2.5 min, 4.86 wt% H for 10 min, and 5.54 wt% H for 60 min at 593 K under 12 bar $H_2$. Activated $Mg-10Fe_2O_3-5Ni$ had the highest dehydriding rate, desorbing 1.31 wt% H for 10 min, 2.91 wt% H for 30 min, and 3.83 wt% H for 60 min at 593 K under 1.0 bar $H_2$.

• The Journal of Korean Academy of Prosthodontics
• /
• v.34 no.1
• /
• pp.151-167
• /
• 1996

Temporary soft liners can be used to prevent chronic soreness from dentures or to aid in its treatment are as adjuncts in tissue conditioning, for temporary obturators, and to stabilize baseplate or surgical stent. The purpose of this study was to evaluate the shock absorption properties of several temporary soft denture liners using a free drop test with an accelerometer. The materials tested inclued Coe-comfort, Softone, Tissue conditioner and Viscogel. The specimens were fabricated with the thickness of 1, 2, 3mm and were stored in distilled water at $37^{\circ}C$ for a day, 1, 2, and 3 weeks. Six samples were made with each material for each test condition and the shock-absorbing behavior was evaluated according to material, thickness and duration. The results were as following : 1. Softone of 3mm thickness stored for a day showed the most excellent shock absorbability. 2. The shock absorbing behavior of duration according to materials and thickness showed a day to be the highest and decreased in 1 week, 2 weeks and 3 weeks in that order(p<0.05). And there was no significant difference between durations in Tissue conditioner. 3. The shock absorbability of thickness according to materials and duration showed 3mm to be highest and decreased in the order of 2mm, 1mm(p<0.05). 4. In comparison of the shock absorbability of temporary soft denture liners according to thickness, there was statistically significant difference between Softone and Visocgel, Tissue conditioner, Coe-comfort / Viscogel and Tissue conditioner, Coe-comfort in 1,2mm thickness, and between Softone, Viscogel and Tissue conditioner, Coe-comfort in 3mm thickness (p<0.05).

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.55.2-55.2
• /
• 2012

Intensive theoretical and experimental studies have been carried out at Korean Institute of Science and Technology (KIST) on controlling the bio absorbing rate of the Mg alloys with high mechanical strength through tailoring of electrochemical potential. Key technology for retarding the corrosion of the Mg alloys is to equalize the corrosion potentials of the constituent phases in the alloys, which prevented the formation of Galvanic circuit between the constituent phases resulting in remarkable reduction of corrosion rate. By thermodynamic consideration, the possible phases of a given alloy system were identified and their work functions, which are related to their corrosion potentials, were calculated by the first principle calculation. The designed alloys, of which the constituent phases have similar work function, were fabricated by clean melting and extrusion system. The newly developed Mg alloys named as KISTUI-MG showed much lower corrosion rate as well as higher strength than previously developed Mg alloys. Biocompatibility and feasibility of the Mg alloys as orthopedic implant materials were evaluated by in vitro cell viability test, in vitro degradation test of mechanical strength during bio-corrosion, in vivo implantation and continuous observation of the implant during in vivo absorbing procedures. Moreover, the cells attached on the Mg alloys was observed using cryo-FIB (focused ion beam) system without the distortion of cell morphology and its organ through the removal of drying steps essential for the preparation of normal SEM/TEM samples. Our Mg alloys showed excellent biocompatibility satisfying the regulations required for biomedical application without evident hydrogen evolution when it implanted into the muscle, inter spine disk, as well as condyle bone of rat and well contact interface with bone tissue when it was implanted into rat condyle.

• Textile Coloration and Finishing
• /
• v.34 no.1
• /
• pp.38-45
• /
• 2022

Sound absorbing materials are being developed in various materials and shapes and they are being applied in many fields such as construction, transportation, civil engineering, and sound. Among many sound-absorbing materials, polyester fiber has no environmental problems and harmfulness, and is a material with good sound absorption properties while being inexpensive. So it is manufactured as a nonwoven sound-absorbing material and used in various fields. In this study, polyester dry-laid nonwoven with different basis weight were manufactured using three types of polyester staple fibers: regular solid, single-hole hollow, and low linear density. We focused on the effects of the properties of the fibers, which constitute nonwovens, on the sound absorption properties, and we considered the basis weight. As the basis weight of the nonwoven fabric increased, the pore size became smaller and the air permeability was lowered, but the sound absorption coefficient was higher. However, the single-hole hollow polyester fiber did not contribute to the increase of the sound absorption coefficient of the nonwoven. It was established that, lower fiber fineness caused the sound absorption coefficient of the nonwoven to be increased. It was also found that the increase in the sound absorption coefficient due to the application of low fineness appeared from a certain basis weight or more.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 2007.04a
• /
• pp.285-297
• /
• 2007

As the demands of environment protection increase, the pulp mold container is developed to substitute for the plastic cushion materials like EPS(expanded poly styrene). The water-absorbing ratio, tensile strength and compressive strength of pulp mold are important factors to evaluate its shock absorbing characteristics. The study was performed to investigate the effects of the mechanical property changes on the various conditions of temperature and relative humidity for pulp mold containers made of mixed materials on ONP(old newspaper) and OCC(old corrugated container). This study also is evaluated the optimized mixing ratio of materials for making pulp mold by analyzing the changes of physical properties according to a various procured temperature and relative humidity conditions. The results show that the water absorption ratio of sample increased significantly, and tensile strength decreased $20{\sim}30%$, compressive strength decreased $10{\sim}20%$ by increasing relative humidity condition. And the results show that the ONP 50% and OCC 50% was optimized mixing ratio according to the samples.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.04a
• /
• pp.163-167
• /
• 2009

In this study, the acoustic properties of ceramic sound absorbing materials with different thickness and bulk density were investigated in terms of characteristic impedance, propagation constant, and absorption coefficient. The well-known two-cavity method was used for evaluating those acoustic parameter values. Also, in order to validate the experimentally measured values, the results were compared with the results obtained from Chung and Blaser's transfer function method and SWR method. The experimentally measured values of normal absorption coefficients were generally agreed well with the corresponding values from the transfer function method and the SWR method. Based on the experimental results, the following conclusions could be made. The magnitude of the absorption coefficient and the frequency range of the maximum absorption coefficient were controllable by changing the thickness and bulk density of the sound absorbing materials.