• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.487-493
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• 2004

This study was conducted to develope a capacitive micromachined ultrasonic transducer (cMUT) which enable to high efficient non-contact transmit and receive the ultrasonic wave in air. Theoretical analysis and finite element analysis of the behavior of membrane (such as resonance frequency, membrane deflection, collapse deflection and collapse voltage) of the cMUT were performed. The design parameters of the cMUT such as the dimension and thickness of membrane, thickness of sacrificial layer, thickness and size of electrode were estimated. The resonance frequency of the membrane increased as the thickness of the membrane increased but decreased as the diameter of the membrane increased. The deflection of the membrane increased as d-c bias voltage increased. The collapse voltage of the membrane was analyzed.

• Progress in Superconductivity
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• v.11 no.2
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• pp.152-157
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• 2010

We have fabricated the low noise liquid helium(LHe) dewar with a different shape of thermal shield to apply the 64-channel SQUID(Superconducting Quantum Interference Device) gradiometer. The first shape of thermal shield was made of an aluminum plate with a wide width of 100 mm slit and the other shape was modified with a narrow width of 20 mm slit. The two types of dewars were estimated by comparing the thermal noise and the signal-to-noise ratio(SNR) of magnetocardiography(MCG) using the $1^{st}$ order SQUID gradiometer system cooled each dewar. The white noise was different as a point of the dewar. The noise was increased as close as the edge of dewar, and also increased at the thermal shield with the more wide width slit. The white noise of the dewar with thermal shield of 100 mm slit was 6.5 fT/$Hz^{1/2}$ at the center of dewar and 25 fT/$Hz^{1/2}$ at the edge, and the white noise of the other one was 3.5 - 7 fT/$Hz^{1/2}$. We measured the MCG using 64-channel SQUID gradiometer cooled at each LHe dewar and compared the SNR of MCG signal. The SNR was improved of 10 times at the LHe dewar with a modified thermal shield.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.6
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• pp.581-589
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• 2004

In this study, the capacitive micromachined ultrasonic transducer(cMUT) was developed based on the previous research results. The cross sectional image of the developed cMUT was characterized. To measure the membrane displacement of the cMUT, the Michelson phase modulation fiber interferometer was constructed. The measured membrane displacement was in good agreement with the result of the finite element analysis. To estimate the ultrasonic wave generated by the cMUT, an ultrasonic system including a pulser, receiver and charge amplifier was used. The cMUT developed in this study shows a good performance and hence will be widely used in the non-contact ultrasonic applications.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.806-808
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• 1999

An automatic measurement system of high value resistance standards($10M{\Omega}$ and $1G{\Omega}$) was developed. A system has been assembled with programmable do calibrators in two of the arms. An electrometer is used to measure the difference in currents flowing through the remaining two arms of the bridge consisting of unknown and standard resistors. Type A standard uncertainty was 2ppm in the $10M{\Omega}$, 1 ppm in the $1G{\Omega}$.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.5
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• pp.275-281
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• 2001

To improve the reliability of hardness test results, Rockwell hardness round robin test was carried out for 10 laboratories. The test condition was the same with the ISO(International Standards Organization) standards. Korea Research Institute of Standards and Science(KRISS) supplied the hardness standard blocks and an indenter to laboratories for the measurement. The participating laboratories measured hardness of the specified areas on the blocks for 6 times with their own indenter as well as common indenter, respectively, and reported the results to KRISS. The result showed that quite large amount of the differences came from the indenter and it is necessary to change indenter with better quality for improved reliability in hardness measurement.

• Journal of Korean Society for Quality Management
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• v.40 no.3
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• pp.295-305
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• 2012

Purpose: This study identified the standardization activities from the early stage of acquisition to disposal during the materiel life cycle and proposed the improvement of standardization process. Methods: Through improvement of duplicated deliberation for the revision of military specification, unification of technical change proposal reception organization, and resolution between the conflicting parts of laws and regulations, simplifying the standardization procedure and strengthening linkages between the civilian standards were gained. Results: We have redefined the concept of the standards and standardization in the field of defense and proposed the standards-driven documentary standards as a measurement standards and reference standards to expand the activities. Conclusion: Through a standardization survey, we came to conclusion that we need to change the concept of standardization in the field of national defense from making the specification to using the means of efficient management of military resources.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.11a
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• pp.249-249
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• 2004

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.482-483
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• 2007

For measurement of dielectric constants, the commercial parallel plate electrodes system with guard-ring electrode have been widely used up to now. The capacitance derived from the parallel plate electrodes capacitor with guard-ring electrode is calculated by the equation of ($C={\epsilon}\;{\cdot}\;\frac{area\;of\;electrod}{distance\;between\;electrodes}$). Therefore, in parallel plate electrode capacitor, the diameter of the guarded electrode, the gap size between guarded electrode and guard ring, and distance between two active electrode should be measured precisely to calculate dielectric constants from the measured capacitance. Consequently their mechanical measurement uncertainties are directly contributed. Especially the air-gap between the electrodes and dielectric specimen at the system must be existed and the measurement error derived from the air-gap is impossible to evaluate as measurement uncertainties. In this study, we analyze the uncertainty of the commercial dielectric constant test cell using 3 kinds CRMs.

• Journal of Sensor Science and Technology
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• v.32 no.6
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• pp.447-454
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• 2023

The Korea Laboratory Accreditation Scheme (KOLAS) operates accreditation programs for ensuring measurement traceability with the International System (SI) of Units - the highest calibration standard that measurements can be tested against. As of September 2023, there are 70 KOLAS-accredited laboratories in the Republic of Korea that specialize in humidity calibration. Among them, 32 KOLAS laboratories, along with one laboratory not affiliated with KOLAS, participated in the proficiency test (PM 2023-11) for relative humidity transducers in 2023. This proficiency test was conducted within a relative humidity range of 20-90% at a temperature of approximately 20 ℃, taking into consideration the calibration and measurement capability (CMC) of the participating laboratories. The primary objective of the proficiency test was to establish the measurement equivalence between each participating laboratory and the reference laboratory, by calculating the number of equivalence (En). When |En| was less than 1, the measurements from the participating and reference laboratory were equivalent. Out of the 33 participating laboratories, 32 successfully met this criterion and passed the proficiency test.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.18-18
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• 2010

Methods of the characteristics evaluation of turbo-molecular pumps (TMP) are well-defined in the international measurement standards such as ISO, PNEUROP, DIN, JIS, and AVS. The Vacuum Center in the Korea Research Institute of Standards and Science has recently designed, constructed, and established the integrated characteristics evaluation system of TMPs based on the international documents by continuously pursuing and acquiring the reliable international credibility through measurement perfection. The measurement of TMP pumping speed is normally performed with the throughput and orifice methods dependent on the mass flow regions. However, in the UHV range of the molecular flow region, the high uncertainties of the gauges, mass flow rates, and conductance are too critical to precisely accumulate reliable data. With UHV gauges of uncertainties less than 15% and a calculated conductance of the orifice, about 35% of pumping speed uncertainties are experimentally derived in the pressure range of less than $10^{-6}$ mbar. In order to solve the uncertainty problems of pumping speeds in the UHV range, we introduced an SRG with 1% accuracy and a constant volume flow meter (CVFM) to measure the finite mass flow rates down to $10^{-3}$ mbar-L/s with 3% uncertainty for the throughput method. In this way we have performed the measurement of pumping speed down to less than $10^{-6}$ mbar with an uncertainty of 6% for a 1000 L/s TMP. In this article we suggest that the CVFM has an ability to measure the conductance of the orifice experimentally with flowing the known mass through the orifice chambers, so that we may overcome the discontinuity problem encountering during introducing two measurement methods in one pumping speed evaluation sequence.