• 센서학회지
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• 제25권5호
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• pp.371-376
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• 2016

A self-powered piezoelectric energy harvester was developed for the application in wireless sensor node. The energy harvester was evaluated with power generation characteristics for the wireless sensor node for structural diagnosis of the electric power system. The self-powered wireless sensor node was set to measure temperature, vibration frequency of the electric power system. A piezoelectric harvester composed of 7 uni-morph cantilevers (functionalized as 6 generators and 1 vibration sensor) was connected to be an array and revealed to produce significantly high output power of approximately 10 mW at 120 Hz under 3.4 g((1 g = $9.8m/sec^2$). The wireless sensor node could work as the electric power generated by the developed piezoelectric harvester.

• Elastomers and Composites
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• 제47권4호
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• pp.318-328
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• 2012

본 연구에서는 blocked isocyanate와 하이브리드 기술을 이용해서 1액 경화형 폴리우레탄 탄성체를 제조하였다. 1액 경화형 하이브리드 폴리우레탄의 제조를 위해서 hydroxyl group을 포함하는 실리카 하이브리드를 합성하고 입자크기, 형태 및 탄성체 내의 하이브리드 입자분포를 확인하였다. 또한, 열해리특성, 기계적 물성, 성형특성을 조사하였다. 1액 경화형 폴리우레탄 탄성체의 열해리 특성을 평가한 결과 온도가 높을수록, 열처리 시간이 길어질수록 blocking된 isocyanate의 해리가 더 잘 진행되었다. 합성된 실리카 하이브리드는 직경이 23~27 nm이고 구형이었으며 하이브리드 폴리우레탄의 단면을 FE-SEM과 EDS를 사용해서 분석한 결과 하이브리드 입자가 폴리우레탄 분자구조 내에 잘 분산되어있는 것을 확인하였다. 하이브리드 폴리우레탄의 경우에는 하이브리드를 포함하지 않는 폴리우레탄 탄성체에 비해 기계적물성, 내마모성 및 열적특성이 향상되었으며 가소제를 사용하는 경우에는 물성의 변화가 거의 없는 것으로 확인되었다.

• 자원리싸이클링
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• 제18권6호
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• pp.10-17
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• 2009

과열 증기를 이용하여 생활 폐기물내 유기성 성분의 분해를 수행하고 폐기물의 특성 및 반응 시간이 폐기물의 분해율에 미치는 영향을 살펴보았다. 과열 증기를 이용한 분해 후 음식 및 폐지와 같은 생분해성 유기 성분은 쉽게 분해되었고 생분해성 유기 성분중 나무와 석유계 유기성 성분인 플라스틱, 금속과 같은 무기성 성분이 분해되지 않은 상태로 남아 쉽게 분리가 가능한 상태를 형성하였다. 입자의 크기 변화를 살펴본 결과 폐기물 내 생분해성 유기 성분이 적을수록 짧은 반응 시간에도 높은 입자 크기 감소를 보였으며 반응 시간이 60분 이상에서 최대 90% 이상의 입도 감소를 나타내었다.

• 센서학회지
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• 제26권2호
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• pp.141-147
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• 2017

A pressure sensor in pulse measurement system is a core component for precisely measuring the pulse waveform of radial artery. A pulse sensor signal that measures the pulse wave in contact with the skin is affected by the temperature difference between the ambient temperature and skin surface. In this study, we found experimentally that the signal changes of the pressure sensors and a temperature sensor were caused by the temperature of the wrist surface while the pressure sensor was contacted on the skin surface for measuring pulse wave. To observe the signal change of the pulse sensor caused by temperature increase on sensor surface, Peltier device that can be kept at a set temperature was used. As the temperature of Peltier device was kept at $35^{\circ}C$ (the maximum wrist temperature), the device was put on the pulse sensor surface. The temperature and pressure signals were obtained simultaneously from a temperature sensor and six pressure sensors embedded in the pulse sensor. As a result of signal analysis, the sensor pressure was decreased during temperature increase of pulse sensor surface. In addition, the signal difference ratio of pressure and temperature sensors with respect to thickness of cover layer in pulse sensor was increased exponentially. Therefore, the signal of pressure sensor was modified by the compensation equation derived by the temperature sensor signal. We suggested that the thickness of cover layer in pulse sensor should be designed considering the skin surface temperature.

• 한국결정성장학회지
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• 제14권6호
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• pp.281-289
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• 2004

The temperature hump is found to be most efficient in suppressing parasitic nucleation. With the temperature humps, there are found to be observed in undersaturations along the transport path for convective-diffusive processes ranging from $D_{AB}$ = 0.0584 $\textrm{cm}^2$/s to 0.584 $\textrm{cm}^2$/s, axial positions from 0 to 7.5 cm. With decreasing Ar = 5 to 3.5, the temperature difference is increased because of the imposed nonlinear temperature profile but the rate is decreased. For 2 $\leq$ Ar $\leq$ 3.5, the rate is increased with the aspect ratio as well as the temperature difference. Such an occurrence of a critical aspect ratio is likely to be due to the effect of sidewall and much small temperature difference. The rate is decreased exponentially with the aspect ratio for 2 $\leq$ Ar $\leq$ 10. Also, the rate is exponentially decreased with partial pressure of component B, P for 1 $\leq$ P $\leq$ 100 Torr.$ B/ $\leq$ 100 Torr.

• 한국세라믹학회지
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• 제46권3호
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• pp.253-262
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• 2009

The purpose of this study is to find out optimum conditions for zinc crystalline glaze under variables of firing: maximum firing temperature, crystal growth temperature, temperature increasing speed, annealing speed, holding time at maximum temperature and holding time at crystal growth temperature. Ferro Frit3110, ZnO and Quartz were used as starting materials and tested by three component system. The best result of test was selected and extended to its vicinity as five glaze formulas. And then the specimens were experimented by variable firing conditions and analyzed by crystal appearance observation, XRD, FT-IR and Raman spectroscopy. In result, main crystal was willemite in the zinc glazes. Some gahnite was detected in specimens which were fired at $1230^{\circ}C$, $1250^{\circ}C$ and $1270^{\circ}C$, however gahnite was not identified at $1300^{\circ}C$. Optimum zinc crystalline glaze was gained by following firing condition: temperature increasing speed $5^{\circ}C$/min, holding 1 h at $1270^{\circ}C$, annealing speed $3^{\circ}C$/min till $1170^{\circ}C$, holding 2 h at $1170^{\circ}C$ then naturally annealed.

• 한국생산제조학회지
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• 제26권4호
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• pp.378-386
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• 2017

Friction stir welding was performed using six welding conditions to evaluate the mechanical properties and microstructure of the welded zone based on its temperature change in the extruded plate of magnesium alloy AZ61. The welded zone temperature was measured using a thermocouple, and the maximum temperature ranges for the advancing and retreating sides were approximately $210-315^{\circ}C$ and $254-339^{\circ}C$, respectively. Depending on the welding conditions, a temperature difference of more than $100^{\circ}C$ was observed. In addition, the maximum yield strength and maximum tensile strength of the welded component was 84.4% and 96.9%, respectively, of those of the base material. For the temperatures exceeding $300^{\circ}C$, oxidation defects occurred in the weld zone, which decreased the mechanical strength of the weld zone. The microstructure and texture confirmed that fracture occurred because of the grain size deviation of the welding tool and the severe anisotropy of the texture of the welded joints.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1078-1083
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• 2002

Ceramics are significantly used in many industrial applications due to their excellent mechanical and thermal properties such as high temperature strength, low density, high hardness, low thermal expansion, and good corrosion resistive properties, while their disadvantages are brittleness, poor formability and high manufacturing cost. To combine advantages of ceramics with those of metals, they are often used together as one composite component, which necessiates reliable joining methods between metal and ceramic. Direct brazing using an active filler metal has been found to be a reliable and simple technique, producing strong and reliable joints. In this study, the fracture characteristics of Si$_3$N$_4$ ceramic joined to ANSI 304L stainless steel with a Ti-Ag-Cu filler and a Cu (0.25-0.3 mm) interlayer are investigated as a function of strain rate and temperature. In order to evaluate a local strain a couple of strain gages are pasted at the ceramic and metal sides near joint interface. As a result the 4-point bending strength and the deflection of interlayer increased at room temperature with increasing strain rate. However bending strength decreased with temperature while deflection of interlayer was almost same. The fracture shapes were classified into three groups ; cracks grow into the metal-brazing filler line, the ceramic-brazing filler line or the ceramic inside.

• International Journal of Automotive Technology
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• 제5권3호
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• pp.155-164
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• 2004

The direct injection gasoline spray-wall interaction was characterized inside a heated pressurized chamber using various visualization techniques, including high-speed laser-sheet macroscopic and microscopic movies up to 25,000 frames per second, shadowgraph, and double-spark particle image velocimetry. Two hollow cone high-pressure swirl injectors having different cone angles were used to inject gasoline onto a heated plate at two different impingement angles. Based on the visualization results, the overall transient spray impingement structure, fuel film formation, and preliminary droplet size and velocity were analyzed. The results show that upward spray vortex inside the spray is more obvious at elevated temperature condition, particularly for the wide-cone-angle injector, due to the vaporization of small droplets and decreased air density. Film build-up on the surface is clearly observed at both ambient and elevated temperature, especially for narrow cone spray. Vapor phase appears at both ambient and elevated temperature conditions, particularly in the toroidal vortex and impingement plume. More rapid impingement and faster horizontal spread after impingement are observed for elevated temperature conditions. Droplet rebounding and film break-up are clearly observed. Post-impingement droplets are significantly smaller than pre-impingement droplets with a more horizontal velocity component regardless of the wall temperature and impingement angle condition.

• Journal of the Korean Wood Science and Technology
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• 제39권2호
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• pp.117-124
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• 2011

The possibility of using the properties of an ultrasonic wave as a means for monitoring the moisture content of a board during drying was investigated. The ultrasonic wave signals are influenced by moisture content and other factors such as temperature, moisture gradient and coupling area. The effect of temperature was examined by measuring the transit times, amplitudes and velocities of ultrasonic waves transmitted through air, a metal bar and a board at various temperatures. The effect of a moisture gradient was studied using a model specimen composing five wood pieces of various moisture contents. The velocity and amplitude of the ultrasonic waves transmitted through air increase with temperature, while those through a metal bar and a board decrease. It was confirmed that the temperature effect is partially attributed to the change of transducer's properties. The effect of a moisture gradient on the velocity of an ultrasonic wave varies with the average moisture content of a board. As the dimension of the end face of a board increases the velocity of an ultrasonic wave increases and low frequency components more dominates than high frequency components. The transit times of ultrasonic waves transmitted through a board during kiln drying reflect the temperature steps in the drying schedule and the transducer temperatures.