• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.11
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• pp.1-8
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• 2011

One of the most important parameters that limit maximum output power of transistor is breakdown. InAlAs/InGaAs/GaAs Metamorphic HEMTs (MHEMTs) have some advantages, especially for cost, compared with InP-based ones. However, GaAs-based MHEMTs and InP-based HEMTs are limited by lower breakdown voltage for output power even though they have good microwave and millimeter-wave frequency performance with lower minimum noise figure. In this paper, InAlAs/$In_xGa_{1-x}As$/GaAs MHEMTs are simulated and analyzed for breakdown. The parameters affecting breakdown are investigated in the fabricated 0.1-${\mu}m$ ${\Gamma}$-gate MHEMT device having the modulation-doped $In_{0.52}Al_{0.48}As/In_{0.53}Ga_{0.47}As$ heterostructure on the GaAs wafer using the hydrodynamic transport model of a 2D commercial device simulator. The impact ionization and gate field effect in the fabricated device including deep-level traps are analyzed for breakdown. In addition, Indium mole-fraction-dependent impact ionization rates are proposed empirically for $In_{0.52}Al_{0.48}As/In_xGa_{1-x}As$/GaAs MHEMTs.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.1
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• pp.1-6
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• 2008

Thermoelectric properties of calcium cobalt layer structure oxide system, $Ca_3Co_2O_6$ and $Ca_3Co_4O_9$ were investigated at the temperature range of 300 to 1000K for the application of thermoelectric generation. In the composition, the Ca site was partially substituted with Bi, Sr, La, K and the Co site was partially substituted with Mn, Fe, Ni, Cu, Zn. The thermoelectric properties of Bi substituted $Ca_3Co_4O_9$. $Ca_{2.7}Bi_{0.3}Co_4O_9$ for electrical conductivity, Seebeck coefficient and power factor were $85.4({\Omega}$cm)^{-l}, $176.2{\mu}V/K$ and $265.2{\mu}W/K^m$, respectively. The unit thermoelectric couple was fabricated with the p-type of $Ca_{2.7}Bi_{0.3}Co_4O_9$ and n-type ($Zn_{0.98}Al_{0.02}$)O thermoelectrics whose figure-of-merit(Z) were $0.87{\times}10^{-4}/K$ and $0.41{\times}10^4/K$, respectively. The generated thermoelectric power was about 30mV at the temperature difference of 120K in the unit thermoelectric couple.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.2
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• pp.34-45
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• 2007

Digital decimation filter is inevitable in oversampled sigma-delta A/D converters for the sake of reducing the oversampled rate to Nyquist rate. This paper presented a Verilog-HDL design and implementation of an area-efficient digital decimation filter that provides time-to-market advantage for sigma-delta analog-to-digital converters. The digital decimation filter consists of CIC(cascaded integrator-comb) filter and two cascaded half-band FIR filters. A CSD(canonical signed digit) representation of filter coefficients is used to minimize area and reduce in hardware complexity of multiplication arithmetic. Coefficient multiplications are implemented by using shifters and adders. This three-stage decimation filter is fabricated in $0.25-{\mu}m$ CMOS technology and incorporates $1.36mm^2$ of active area, shows 4.4 mW power consumption at clock rate of 2.8224 MHz. Measured results show that this digital decimation filter is suitable for digital audio decimation filters.

• The Journal of the Acoustical Society of Korea
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• v.29 no.5
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• pp.314-324
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• 2010

In waveguide structures, waves may be partially reflected by local non-uniformities. The effects of local non-uniformities has been previously investigated by means of a combined spectral element and finite element (SE/FE) method at relatively low frequencies. However, since the SE is formulated based on a beam theory, the SE/FE method is not appropriated for analysis at higher frequencies where complex deformation of the waveguide occurs. So it is necessary to extend this approach for high frequencies. For the wave propagation at higher frequencies, a combined spectral super element and finite element (SSE/FE) method is introduced in this paper. As an example of the application of this method, wave reflection and transmission due to a local defect in a rail are simulated at frequencies between 20kHz and 30kHz. Also numerical errors are evaluated by means of the conservation of the incident power.

• Korean Journal of Remote Sensing
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• v.30 no.2
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• pp.185-205
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• 2014

SAR ground moving target indicator (GMTI) has long been an important issue for SAR advanced applications. As spatial resolution of space-borne SAR system has been significantly improved recently, the GMTI becomes a very useful tool. Various GMTI techniques have been developed particularly using multi-channel SAR systems. It is, however, still problematic to detect ground moving targets within single channel SAR images while it is not practical to access high resolution multi-channel space-borne SAR systems. Once a ground moving target is detected, it is possible to retrieve twodimensional velocities of the target from single channel space-borne SAR with an accuracy of about 5 % if moving faster than 3 m/s. This paper presents a quick-and-dirty method for detecting ground moving targets from single channel SAR single-look complex (SLC) images by differentiation. Since the signal powers of derivatives present Doppler centroid and rate, it is very efficient and effective for detection of non-stationary targets. The derivatives correlate well with velocities retrieved by a precise method with a correlation coefficient $R^2$ of 0.62, which is well enough to detect the ground moving targets. While the approach is theoretically straightforward, it is necessary to remove the effects of residual Doppler rate before finalizing the ground moving target candidates. The confidence level of results largely depends on the efficiency and effectiveness of the residual Doppler rate removal method. Application results using TerraSAR-X and truck-mounted corner reflectors validated the efficiency of the method. While the derivatives of moving targets remain easily detectable, the signal energy of stationary corner reflectors was suppressed by about 18.5 dB. It results in an easy detection of ground targets moving faster than 8.8 km/h. The proposed method is applicable to any high resolution single channel SAR systems including KOMPSAT-5.

• Journal of Korean Home Economics Education Association
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• v.35 no.3
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• pp.67-96
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• 2023

The purpose of this study was to develop and validate a scale that can grasp the reality of the three systems of action for middle and high school students in home economics. For this purpose, a total of 105 questions, 35 questions for each systems of action, were developed as a 5-point Likert scale in order to measure technical action, communicative action, and emancipative action as preliminary questions by reviewing domestic and international literature related to the three systems of action. The procedure for revising and supplementing the developed preliminary questions by reviewing the content validity of the home economics education expert was executed twice. A preliminary survey was conducted on middle and high school students with 70 developed preliminary questions, and 166 copies were collected. As a result of exploratory factor analysis of the collected questionnaires to test the validity of the scale, it was found that 38 questions 7 factors were appropriate. After constructing this survey based on the results of exploratory factor analysis, this survey was conducted on middle and high school students, and 548 copies were collected and a confirmatory factor analysis was performed. A total of 38 questions were finally selected through confirmatory factor analysis, including basic living ability 5 questions, self-management ability 4 questions, information processing ability 4 questions, communication/interpersonal ability 12 questions, critical thinking ability 3 questions, decision-making ability 7 questions, empowerment 3 questions. The Model Fit was χ²=1846.741(p<.001), CFI=0.865, TLI=0.853, RMSEA=0.058, and the Standardized Regression Weights for each question was more than 0.5, so it can be seen as a suitable measurement instrument for measuring the status of the three systems of action of middle and high school students in home economics. The three systems of action scales were found to have significant correlations with self-acceptance, future planning, intimacy, uniqueness, which are sub-factors of the self-identity scale, and social participation scales therefore confirmed that they have recognized concurrent validity.