• Progress in Superconductivity and Cryogenics
• /
• v.15 no.2
• /
• pp.20-23
• /
• 2013

For sensitive measurements of micro-Tesla nuclear magnetic resonance (${\mu}T$-NMR) signal, a low-noise superconducting quantum interference device (SQUID) system is needed. We have fabricated a liquid He dewar for an SQUID having a large diameter for the pickup coil. The initial test of the SQUID system showed much higher low-frequency magnetic noise caused by the thermal magnetic noise of the aluminum plates used for the vapor-cooled thermal shield material. The frequency dependence of the noise spectrum showed that the noise increases with the decrease of frequency. This behavior could be explained from a two-layer model; one generating the thermal noise and the other one shielding the thermal noise by eddy-current shielding. And the eddy-current shielding effect is strongly dependent on the frequency through the skin-depth. To minimize the loop size for the fluctuating thermal noise current, we changed the thermal shield material into insulated thin Cu mesh. The magnetic noise of the SQUID system became flat down to 0.1 Hz with a white noise of 0.3 $fT/{\surd}Hz$, including the other noise contributions such as SQUID electronics and magnetically shielded room, etc, which is acceptable for low-noise ${\mu}T$-NMR experiments.

• Journal of the Korean Society of Safety
• /
• v.26 no.3
• /
• pp.47-51
• /
• 2011

Work platform is temporary material that many workers use in construction field, but many workers construct and use the work platform without considering safety standards, workers who have not the knowledge of safety standards construct the work platform in weakness and use the work platform in unstable, According to the statistics in 2009, 1230 people were injured at the work platform. Among them, victims by falling account for about 77% and mostly lead to fatal injuries. we have studied and survey about the safety or danger of the work platform(set limits to duble scaffold) in construction field and about how many workers observe safety standards of the work platform. According to the result of this survey, 24%~100%(average : 68%) of the work platform in survey is not observe the safety standards.

• Korean Journal of Materials Research
• /
• v.28 no.11
• /
• pp.627-632
• /
• 2018

Two dimensional(2D) crystals, composed of a single layer or a few atomic layers extracted from layered materials are attracting researchers' interest due to promising applications in the nanoelectromechanical systems. Worldwide researchers are preparing devices with suspended 2D materials to study their physical and electrical properties. However, during the fabrication process of 2D flakes on a target substrate, contamination occurs, which makes the measurement data less reliable. We propose a dry transfer method using poly-methyl methacrylate(PMMA) for the 2D flakes to transfer onto the targeted substrate. The PMMA is then removed from the device by an N-Methyl-2-pyrrolidone solution and a critical point dryer, which makes the suspended 2D flakes residue free. Our method provides a clean, reliable and controllable way of fabricating micrometer-sized suspended 2D nanosheets.

• Journal of Sensor Science and Technology
• /
• v.14 no.1
• /
• pp.22-27
• /
• 2005

A thermoelectric flow sensor for small quantity of gas flow rate was fabricated using silicon wafer semiconductor process and bulk micromachining technology. Evanohm R alloy heater and chromel-constantan thermocouples were used as a generation heat unit and sensing parts, respectively. The heater and thermocouples are thermally isolated on the $Si_{3}N_{4}/SiO_{2}/Si_{3}N_{4}$ laminated membrane. The characteristics of this sensor were observed in the flow rate range from 0.2 slm to 1.0 slm and the heater power from 0.72 mW to 5.63 mW. The results showed that the sensitivities $(({\partial}({\Delta}V)/{\partial}(\dot{q}));{\;}{\Delta}V$ : voltage difference, $\dot{q}$ : flow rate) were increased in accordance with heater power rise and decreasing of flow rate.

• Mass Spectrometry Letters
• /
• v.5 no.2
• /
• pp.57-61
• /
• 2014

A gravimetric standard addition method combined with internal standard calibration has been successfully developed for the accurate analysis of total arsenic in a laver candidate reference material. A model equation for the gravimetric standard addition approach using an internal standard was derived to determine arsenic content in samples. Handlings of samples, As standard and internal standard were carried out gravimetrically to avoid larger uncertainty and variability involved in the volumetric preparation. Germanium was selected as the internal standard because of its close mass to the arsenic to minimize mass-dependent bias in mass spectrometer. The ion signal ratios of $^{75}As^+$ to $^{72}Ge^+$ (or $^{73}Ge^+$) were measured in high resolution mode ($R{\geq}10,000$) to separate potential isobaric interferences by high resolution ICP/MS. For method validation, the developed method was applied to the analysis of arsenic content in the NMIJ 7402-a codfish certified reference material (CRM) and the result was $37.07mg{\cdot}kg^{-1}{\pm}0.45mg{\cdot}kg^{-1}$ which is in good agreement with the certified value, $36.7mg{\cdot}kg^{-1}{\pm}1.8mg{\cdot}kg^{-1}$. Finally, the certified value of the total arsenic in the candidate laver CRM was determined to be $47.15mg{\cdot}kg^{-1}{\pm}1.32mg{\cdot}kg^{-1}$ (k = 2.8 for 95% confidence level) which is an excellent result for arsenic measurement with only 2.8 % of relative expanded uncertainty.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.37 no.2
• /
• pp.99-105
• /
• 2017

Many composite materials are used in the aerospace industry because of their excellent mechanical properties. However, the nature of aviation exposes these materials to high temperature and high moisture conditions depending on climate, location, and altitude. Therefore, the molecular arrangement chemical properties, and mechanical properties of composite materials can be changed under these conditions. As a result, surface disruptions and cracks can be created. Consequently, moisture-impregnating defects can be induced due to the crack and delamination of composite materials as they are repeatedly exposed to moisture absorption moisture release, fatigue environment, temperature changes, and fluid pressure changes. This study evaluates the possibility of detecting the moisture-impregnating defects of CFRP and GFRP honeycomb structure sandwich composite materials, which are the composite materials in the aircraft structure, by using an active infrared thermography technology among non-destructive testing methods. In all experiments, it was possible to distinguish the area and a number of CFRP composite materials more clearly than those of GFRP composite material. The highest detection rate was observed in the heating duration of 50 mHz and the low detection rate was at the heating duration of over 500 mHz. The reflection method showed a higher detection rate than the transmission method.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.11
• /
• pp.1617-1620
• /
• 2013

The widely-used measurement methods for conductivity of non-magnetic metals are van der Pauw method, Two Point Probe method and Eddy Current method. Among them a more simpler and easier method is the Eddy Current method and an instrument using the method is a Conductivity Meter which can measure a conductivity by contacting its probe on a sample surface. However, conductivity standards are essentially needed to confirm the meter's performance or to calibrate it. In this study, six kinds of the standards which are made of Cu, Al-1, Al-2, brass, Zn and SUS-316 are developed and conductivity ranges for the standards are 2.27 %IACS ~ 101.6 %IACS with measurement uncertainty of less than 0.3 %.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.3-20
• /
• 2001

• Proceedings of the Korean Magnestics Society Conference
• /
• 2014.11a
• /
• pp.11-11
• /
• 2014

• Proceedings of the Korean Vacuum Society Conference
• /
• 1998.06a
• /
• pp.51-51
• /
• 1998