• Journal of Biomedical Engineering Research
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• v.28 no.1
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• pp.66-74
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• 2007

We have developed a multi-channel, multi-frequency EIT system with operating frequency of 10Hz to 500KHz. The number of digital voltmeters using phase-sensitive demodulation can be varied from 8 to 64 and we found that 16 and 32-channels are most practical. This paper describes the design, implementation, and construction of 16 and 32-channel systems. The performance of the system was thoroughly tested and we found that CMRR of the developed voltmeter is about 85dB with $100{\Omega}$ unbalancing series resistor. The SNR is greater than 99.6dB and the output impedance of the constant current source is $1{\Omega}W$ at least for all frequencies. Imaging experiments using a banana with frequency-dependent conductivity and permittivity show that frequency-difference imaging is possible using the developed system. Future works of animal and human experiments are discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.109-112
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• 1995

CuInS$_2$thin film was prepared by heat treatment at vacuum 10$\^$-3/ Torr of S/In/Cu stacked layer which was deposited by sequential. And so, the polycrystalline CuInS$_2$with chalcopyrite structure was well made at heat treatment temperature of 250$^{\circ}C$ and heat treatment time of 60 min. Single phase of CuInS$_2$was formed from Cu/In composition ratio of 0.84 to 1.3. p conduction type of CuInS$_2$thin film was appeared from Cu/In competition ratio of 0.99. The highest resistivity of CuInS$_2$with p type was 1.608${\times}$10$^2$$\Omega$cm at Cu/In composition ratio of 0.99 and The lowest resistivity was 5.587${\times}$10$\^$-2/$\Omega$cm at Cu/In composition ratio of 1.3.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.242-246
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• 1999

For the fabrication of fault current limiting device using HTSC thick film, YBa$_2Cu_3O_x$ superconducting thick film was formed by surface diffusion process of the Y$_2BaCUO_5$ and the mixed compound of (3BaCuO$_2$+2CuO) expected to be liquid phase above the peritectic temperature of YBa$_2Cu_3O_x$. For the surface diffusion, the compounds of 3BaCuO$_2$+2CuO mixed with binder material was patterned on Y$_2BaCUO_5$ substrate by the screen printing method. After proper sintering, the characteristics of current limit on thick film fabricated was measured. The thick film was able to limit the current from 2.8213 mA$_{rms}$nu to 4.2034 mA$_{rms}$ with 500${\omega}$ load resistance, and from 4.1831 mA$_{rms}$ to 4.2150 mA$_{rms}$ with 10${\omega}$ load resistance.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.443-448
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• 1997

Titanium carbonitride (Ti(CxN1-x)) ceramics were prepared by hot pressing of the mixture of TiN and graphite. Hot pressing was performed in a graphite mold at 198$0^{\circ}C$ for 40 min under 44 MPa in N2 atmosphere. The effect of graphite addition on sinterability and the mechanical properties of titanium carbonitride were investigated. In this study, the solubility limit of graphite in Ti(CxN1-x) was slightly below 10 wt% based on the results of XRD analysis. Within the solubility limit, graphite dissolved completely into titanium nitride and formed the single phase Ti(CxN1-x) solid solution. Peak relative density of 99% and hardness of 16 GPa were observed for Ti(CxN1-x) ceramics with 7 wt% graphite while maximum flexural strength of 500 MPa and fracture toughness of 4.0 MPa.m1/2 were observed for Ti(CxN1-x) ceramics with 10 wt% graphite. The electrical resistivities of the ceramics with 7 wt% and 10 wt% graphite were observed 40 {{{{ mu OMEGA }}cm and 50 {{{{ mu OMEGA }}cm respectively.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.383-389
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• 2003

Clay minerals show a distinct induced-polarization phenomenon, which is one of the most important factors for predicting groundwater flow and contaminant transport. This paper presents a step-by-step process to estimate Cole-Cole parameters from spectral induced-polarization (IP) data measured on the surface of three-dimensional earth. First, the inversion of low-frequency resistivity survey data is made to identify the dc resistivity ${\rho}_dc$ of a volume having IP effects. The other parameters, chargeability m, time constant $\tau$, and frequency dependence c, are sought for the polarizable volume. Next, using multi-frequency data, c can be obtained as high or low asymptotes of the slope of log phase vs. log frequency. Further, for low m, intrinsic $\tau$ is approximated by apparent one, ${\tau}_a$, which is derived from the relation ${{\omega}{\tau}}_a$=1 at an angular frequency $\omega$, where the imaginary component of spectral IP data has an extreme value. Finally, to obtain intrinsic m a two-step linearized procedure has been derived. For a body of given $\tau$ and c, forward modeling with a progression of m values yields a plot of observed vs. intrinsic imaginary components for a frequency. Since this plot is essentially linear, to extract the intrinsic imaginary component is quite simple with an observed value. Using the plot of intrinsic imaginary component vs. m, intrinsic m is determined. We present a synthetic example to illustrate that the Cole-Cole parameters can be recovered from spectral IP data.

• Journal of the Korean Ceramic Society
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• v.28 no.11
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• pp.935-941
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• 1991

Effects of calcination process and ZrO2 addition on the electrical properties of [(Ba0.82Sr0.08Ca0.1)O]m(Ti1-$\chi$Zr$\chi$)O2 ceramics have been investigated. With the variation of A/B-site ratio m of the dielectric formulations, sintering behavior and the resistivity after sintering in a reducing atmosphere have been affected by the calcination process. When the dielectric formulations of m=1.01 were sintered in a reducing atmosphere, the room-temperature resitivity of 109 {{{{ OMEGA }}.cm was obtained for samples processed with two-step calcination, which was much lower than 1012 {{{{ OMEGA }}.cm of samples calcined once. It was confirmed that high resistivity of Ca-doped BaTiO3 ceramics, after sintering in a reducing atmosphere, is maintained by acceptor-like behavior of CaTi" which is formed by Ca substitution to Ti-site. It was also found out that the critical amount of B-site Ca substitution for reduction inhibition of BaTiO3 is around 0.005 mol. With the increasing amount of ZrO2 addition to dielectric formulations, Curie peak was depressed and Curie temperature was lowered due to the enhanced diffuse phase transition.tion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.9
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• pp.1710-1718
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• 1994

In this paper, a broadband tunable YIG(Yittrium Iron Garnet) oscillator is designed and fabricated. To design an YTO(YIG Tuned Oscillator), a suitable YIG resonator is selected according to the design oscillation range and its equivalent R, L, C resonant circuit parameters are obtained through the measurement of its resonance characteristic. Using the equivalent circuit, the wideband topology which suppresses the parasitic oscillation is selected and implemented. The designed circuit is simulated by HBT(Harmoic Balance Technique) using EEsof's jOMEGA. The YTO thus fabricated has the wide oscillation range from 1.4 GHz to 4 GHz, and its linearity is 0.5% in the oscillation range. The phase noise is below 105dBc at 100kHz offset.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.11
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• pp.555-561
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• 2001

In this paper, the low power (1.5 W) solenoid-type magnetic thin-film transformers utilizing a $Ni_{81}Fe_{19)$ core material were designed and fabricated for 5 MHz-drive DC-DC converter application. The $20\mum$ thick copper films were used as the coils. The transformers fabricated in this work have the sizes of $3.08 mm\times25.5 mm\; and\; 6.15 mm\times12.75 mm.$ The optimum design of solenoid-type magnetic thin film transformers was performed utilizing the conventional equations, a Maxwell computer simulator (Ansoft HFSS V7.0 for PC), and parameters obtained from the magnetic properties of NiFe magnetic core materials. frequency characteristics of inductance, dc resistance (R), coupling factor (k) and gain of developed transformers were measured using HP4194A impedance and gain-phase analyzer. The fabricated transformers with the size of $6.15 mm\time12.75 mm$ exhibit the inductance of $0.83 \muH$, the dc resistance of $2.3\Omega$$\Omega$, the k of 0.91 and the gain of -1 dB at 5 MHz, which show the comparable results to those reported in the recent literatures. The measured high-frequency characteristics for the fabricated transformers agreed well with those obtained by theoretical calculations .

• Journal of Biosystems Engineering
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• v.23 no.2
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• pp.135-146
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• 1998

The equation to predict the soil temprature of Pusan and Chinju city as a function of time and soil depth for the geothermal energy utilization system and agriculture was devised. The equation was $T(x,t)\;=\;Tm\;-\;To{\cdot}ExP(-{\xi}){\cdot}cos{{\omega}{\cdot}[t-to-x/(2{\cdot}{\alpha}{\cdot}{\omega})^{0.5}]}$ with the soil thermal diffusivity, ${\alpha},\;of\;0.4\;\textrm{m}^2/day,\;0.0375\;\textrm{m}^2/day$ and phase zero point, to, of 24 days, 22.4 days in Pusan and Chinju city, respectively, during ten years from 1987 to 1996. The predicted and measured soil temperatures agreed well with the coefficient of determination of 0.95 at the soil depth of 0.0, 0.5, 1.0, 3.0, 5.0 m. The maximum and minimum temperature in Pusan 3.7, $30.1^{\circ}C$ at soil surface and 14.3, $18.0^{\circ}C$ at the depth of 5.0 m. The total mean temperature of soil in Pusan and Chinju city was about 16.3, $16.0^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.120-125
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• 2003

A low melting borosilicate glass frit was used as an adhesion promoter, which enables $MnWO_4$to be sintered with in a reasonable sintering temperature range ($800∼1000^{\circ}C$). The glass was evaluated for glass transition temperature ($Τ_{g}$ X) and thermal expansion coefficient($\alpha$). Mechanical property (Vickers hardness), grain growth, the comparison of lattice parameter and pore distribution of sintered $MnWO_4$ with the frit were methodically discussed. As sintering temperature increased, a typical liquid phase sintering showed the rapid grain growth and high densification of X$MnWO_4$grain, improvement of hardness (until $920^{\circ}C$) and different pore size distribution. Resistance of sintered $MnWO_4$varied from 450k$\Omega$ to 8.8M$\Omega$ under the measuring humidify ranging from 30 to 90%. Thus, the results will contribute to the application of glass frit containing sensor materials and their future use.