Su-Yong Kwon

Accurate dew-point measurement over a wide temperature range using a quartz crystal microbalance dew-point sensor

Quartz crystal microbalance (QCM) dew-point sensors are based on frequency measurement, and so have fast response time, high sensitivity and high accuracy. Recently, we have reported that they have the very convenient attribute of being able to distinguish between supercooled dew and frost from a single scan through the resonant frequency of the quartz resonator as a function of the temperature. In addition to these advantages, by using three different types of heat sinks, we have developed a QCM dew/frost-point sensor with a very wide working temperature range (−90 °C to 15 °C). The temperature of the quartz surface can be obtained effectively by measuring the temperature of the quartz crystal holder and using temperature compensation curves (which showed a high level of repeatability and reproducibility). The measured dew/frost points showed very good agreement with reference values and were within ±0.1 °C over the whole temperature range.

Long-term stability of CdSe/CdZnS quantum dot encapsulated in a multi-lamellar microcapsule

We developed a novel and easy encapsulation method for quantum dots (QDs) using a partially oxidized semi-crystalline polymeric material which forms a micron-sized granule with a multi-lamellar structure from a dilute solution. The QDs were highly dispersed in the granule in such a way that they were adsorbed on the lamella with ∼12 nm spacing followed by lamellar stacking. The QDs were heavily loaded into the granule to 16.7 wt% without aggregation, a process which took only a few minutes. We found that the quantum yield of the QDs was not degraded after the encapsulation. The encapsulated QD-silicone composite exhibited excellent long-term photo- and thermal stability with its initial photoluminescence intensity maintained after blue LED light radiation for 67 days and storage at 85 °C and 85% relative humidity for 119 days.

Recognition of supercooled dew in a quartz crystal microbalance dew-point sensor by slip phenomena

Distinguishing between a supercooled dew and frost below 0 °C in dew/frost-point measurements is an important and challenging problem that has not yet been completely solved. This study presents a new method for the recognition of a supercooled dew in a dew/frost-point sensor. A quartz crystal microbalance (QCM) sensor was used as a dew/frost-point sensor to detect a dew and a supercooled dew as well as frost. The slip phenomenon occurring at an interface between the water droplet and the surface of the quartz crystal resonator of the QCM sensor gives a simple and accurate way of distinguishing between a supercooled dew and frost below 0 °C. This method can give a highly accurate measurement of the dew or the frost point without misreading in the dew-point sensor at temperatures below 0 °C.

Micromachined thin-film multijunction thermal converters developed at KRISS

Micromachined thin-film multijunction thermal converters (MJTCs) suitable as high performance ac-dc transfer standards have been fabricated and studied at KRISS. This paper describes their thermal design and the materials chosen to improve performance. And finally performance data are given over a wide range of frequencies and conditions.

Surge-Resistant Nanocomposite Enameled Wire Using Silica Nanoparticles with Binary Chemical Compositions on the Surface

We developed polyesterimide (PEI) nanocomposite enameled wires using surface-modified silica nanoparticles with binary chemical compositions on the surface. The modification was done using silanes assisted by ultrasound, which facilitated high density modification. Two different trimethoxysilanes were chosen for the modification on the basis of resemblance of chemical compositions on the silica surface to PEI varnish. The surface-modified silica was well dispersed in PEI varnish, which was confirmed by optical observation and viscosity measurement. The glass transition temperature of the silica-PEI nanocomposite increased with the silica content. The silica-dispersed PEI varnish was then used for enameled wire fabrication. The silica-PEI nanocomposite enameled wire exhibited a much longer lifetime compared to that of neat PEI enameled wire in partial discharge conditions.

Development of QCM dew point sensor and its sensing characteristics study

This paper represents development of quartz crystal microbalance (QCM) and usage as a dew point sensor. The temperature of a quartz resonator was controlled precisely from to with the ramping rate of by using a custom-made crystal holder housing the quartz resonator associated with a thermoelectric cooler (Peltier cooler), which results in the working range from to based on an accurate holder temperature compensation and temperature effect compensation process. The developed QCM dew point sensor and analysis techniques show very good sensing characteristics at measurement of moist air with the relative humidity from 10 %R.H. to 90 %R.H. generated by a divided-type humidity generator and the dew point temperatures were determined with an accuracy of less than , which also showed good agreement with reference values in their error range.

Development of a hygroscopic polymer-coated QCM humidity sensor and its characteristics

A highly stable quartz crystal microbalance (QCM) that showed a stability of frequencies and exhibited a very low noise level has been developed. The long-term drift was RH. Comparing the characteristics of the QCM sensor with those of other types of humidity sensors employing PMMA film as a hygroscopic layer, and with other QCM sensors employing other hygroscopic layers is represented.

Performance Improving of KRISS Micromachined Multijuntion Thermal Converter

Thin-film multijunction thermal converters (MJTCs) with chromel-constantan thermocouples and an Evanohm R alloy heater were fabricated using semiconductor process and bulk micromachining. The voltage sensitivity and the ac-dc voltage transfer differences were evaluated. And the ac-dc transfer differences seem to be stabilized below the value of 1 ppm in the frequency range from 1 kHz to 500 kHz