• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.39-42
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• 2018

In this paper, a low-power MPPT interface circuit for vibration energy harvesting sources is presented. The designed circuit rectifies the harvested ac type energy to the dc type energy required to drive the system, and periodically samples and holds the open circuit voltage (Voc) through the MPPT controller, and transfers the harvested power to the load while maintaining the input voltage at 1/2 of the maximum available power point. All circuits have been designed using a 0.35-um CMOS technology, and the operation has been verified through simulation. Simulation results show that the designed circuit consumes 98nA of current at 3V input voltage and the maximum power efficiency is 99.21%. The designed chip occupies $1.281mm{\times}1.236mm$.

• Geomechanics and Engineering
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• v.6 no.3
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• pp.293-320
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• 2014

In this study, in order to evaluate adequacy of considering local site effect, excluding soil-structure interaction (SSI) effects in inelastic dynamic analysis and design of mid-rise moment resisting building frames, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with two soil types with the shear wave velocities less than 600 m/s, representing soil classes $D_e$ and $E_e$ according to the classification of AS1170.4-2007 (Earthquake actions in Australia) having 30 m bedrock depth. Structural sections of the selected frames were designed according to AS3600:2009 (Australian Standard for Concrete Structures) after undertaking inelastic dynamic analysis under the influence of four different earthquake ground motions. Then the above mentioned frames were analysed under three different boundary conditions: (i) fixed base under direct influence of earthquake records; (ii) fixed base considering local site effect modifying the earthquake record only; and (iii) flexible-base (considering full soil-structure interaction). The results of the analyses in terms of base shears and structural drifts for the above mentioned boundary conditions are compared and discussed. It is concluded that the conventional inelastic design procedure by only including the local site effect excluding SSI cannot adequately guarantee the structural safety for mid-rise moment resisting buildings higher than 5 storeys resting on soft soil deposits.

• Earthquakes and Structures
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• v.14 no.6
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• pp.577-587
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• 2018

The quantitative assessment of the seismic collapse risk of a structure requires the usage of an optimal intensity measure (IM) which can adequately characterise the severity of the ground motion. Research suggests that the average spectral acceleration ($Sa_{avg}$) may be an efficient and sufficient alternate IM as compared to the more traditional first mode spectral acceleration, $Sa(T_1)$, particularly during seismic collapse risk estimation. This study primarily presents a comparative evaluation of the sufficiency of the average spectral acceleration with respect to ground motion duration, and secondarily assesses the impact of ground motion duration on collapse risk estimation. By assembling a suite of 100 historical ground motions, incremental dynamic analysis of 60 different inelastic single-degree-of-freedom (SDF) oscillators with varying periods and ductility capacities were analysed, and collapse risk estimates obtained. Linear regression models are used to comparatively quantify the sufficiency of $Sa_{avg}$ and $Sa(T_1)$ using four significant duration metrics. Results suggests that an improved sufficiency may exist for $Sa_{avg}$ when the period of the SDF system increases, particularly beyond 0.5, as compare to $Sa(T_1)$. In reference to the ground motion duration measures, results indicated that the sufficiency of $Sa_{avg}$ is more sensitive to significant duration definitions that consider almost the full wave train of an accelerogram ($SD_{a5-95}$ and $SD_{v5-95}$). In order to obtain a reduced variability of the collapse risk estimate, the 5-95% significant duration metric defined using the Arias integral ($SD_{a5-95}$) should be used for seismic collapse risk estimation in conjunction with $Sa_{avg}$.

• Journal of the Korean Magnetics Society
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• v.19 no.3
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• pp.81-84
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• 2009

We examine the effect of U term (U = 3 eV) describing the Coulomb interactions between electrons on the results of electronic band structure calculations carried out for bcc Fe bulk, monolayer, and chain. We investigated the properties of the three Fe structures by using the all-electron total-energy full-potential linearized augmented plane wave method. The U term was included in the exchange - correlation functionals constructed on the basis of local density approximation (LDA) and general gradient approximation (GGA). We found that in the case of bcc Fe bulk structure inclusion of the U term leads to the overestimated values of magnetic moment on Fe atom. The values of magnetic moment calculated for Fe in monolayer and chain are in accordance with calculations in which the U term was not included. In general, for each system the calculated values of magnetic moment on Fe sites were larger when the U term was incorporated in the energy functional. In Fe bulk, the value of magnetic moment $2.54{\mu}_B$ for LDA+U larger than $2.25{\mu}_B$ for LDA.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.11
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• pp.101-106
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• 2014

This paper presents a wide dynamic range radio-frequency (RF) root-mean-square (RMS) power detector using an automatic gain control (AGC) loop. The AGC loop consists of a variable gain amplifier (VGA), RMS conversion block and gain control block. The VGA exploits dB-linear gain characteristic of the cascade VGA. The proposed circuit utilizes full-wave squaring and generates a DC voltage proportional to the RMS of an input RF signal. The proposed RMS power detector operates from 500MHz to 5GHz. The detecting input signal range is from 0 dBm to -70 dBm or more with a conversion gain of -4.53 mV/dBm. The proposed RMS power detector is designed in a 65-nm 1.2-V CMOS process, and dissipates a power of 5 mW. The total active area is $0.0097mm^2$.

• Journal of the Korean Magnetics Society
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• v.16 no.2
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• pp.111-114
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• 2006

We investigated the magnetism and electronic structures for the layered structures consisting of (110) layers of zinc-blende CrAs and MnAs. We calculated the electronic structures for $(CrAs)_3(MnAs)_3(110)$ superlattice consisted of alternating three layers of CrAs(110) and MnAs(110) by the full-potential linearized augmented plane wave (FLAPW) method. The calculated magnetic moment of Cr in interface layer ($3.07\;\mu_B$) was slightly larger than that of Cr atom in center layer ($3.06\;\mu_B$), while that of interface Mn atom ($3.74\;\mu_B$) was slightly smaller than the value of Mn atom in center layer ($3.76\;\mu_B$). The electronic structure and half-metallicity in this superlattice were discussed using the calculated density of states.

• Smart Structures and Systems
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• v.17 no.1
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• pp.91-105
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• 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.8A
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• pp.620-625
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• 2003

The coplanar waveguide bandpass filter using folded-line stepped-impedance resonators(SIRs) is proposed. The folded-line SIR has about λ/8 length using the short-circuited end on coplanar waveguide. It make that the bandpass filter has the half size in comparison with general λ/4 SIR filter. In this paper, we derive the equivalent circuit and design the bandpass filter by using that. We design and fabricate the bandpass filter which has 5 GHz center frequency and 3 % fractional bandwidth. The measurement results fur 4-pole folded SIR bandpass filter agreed well with full-wave simulation and equivalent circuit results. The fabricated bandpass filter has a good spurious characteristic, which the harmonic frequency appeared at 2.5f$\_$0/). The proposed folded-line SIR bandpass filter are applicable for MMIC and High-Tc superconducting filters. bandwidth.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.1
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• pp.37-47
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• 1995

In this paper, the slot coupled stacked microstrip antenna, which has wide bandwidth characteristics because of the double tuning effects from the interactions between two patches and feeding slot and improves distortions of radiation patterns due to spurious radiation from feeder, is analyzed. For the analy- sis Green function in the spectrum domain and Galerkin method is applied with an accurate analysis mode for slot coupled feeding structure using the scattering analysis method. The basis functions are 3 EB modes for patches and 5 PWS modes for feeder. The slot coupled stacked microstrip antennas are designed and fabricated with the center frequency of 11.5 Ghz and 12.0 GHz. The experimental results show the wide bandwidth characteristics of 1.9 ~ 2.2 GHz and agree well with the simulation results which have 15~20% bandwidth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.3
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• pp.245-252
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• 2010

This paper proposes an improved filter synthesis method for dual-band filters based on coupled lines loaded with shunt stubs. The conventional design method relies on equality of the response of the conventional single-band filter and its dual-band counterpart at two frequencies. On the other hand, the proposed method is based on equivalence of the propagation constants and the image impedances of the two filters. Therefore, the proposed method does not suffer from bandwidth reduction phenomena, which requires complex compensating process in the conventional method. Also, the alternative design parameters provided by the demonstrated method enable to construct dual-band filters with more flexibility. For experimental verification, a Chebyshev type dual-band filter with center frequencies at 1 GHz and 3.5 GHz is designed and fabricated. The measured results are in excellent agreement with the full-wave simulated results.