• 한국정보통신학회논문지
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• 제20권3호
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• pp.457-463
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• 2016

본 논문에서는 변형된 내장형 밸런을 사용하여 이중 다이폴 준-야기 안테나(double-dipole quasi-Yagi antenna; DDQYA)의 대역폭을 향상하는 방법에 대하여 연구하였다. 변형된 내장형 밸런은 동일면 스트립 선로의 중앙으로 삽입된 마이크로스트립 선로로 구성되며, 마이크로스트립 선로의 끝은 급전점에서 단락 핀으로 동일면 스트립 선로와 연결되어 있다. 변형된 내장형 밸런의 구조는 DDQYA의 대역폭을 향상시키기 위해 조정하였다. 또한, 제안된 밸런의 back-to-back 구조에서의 성능을 기존 밸런과 비교하였다. 최적화된 변형된 내장형 밸런을 가진 DDQYA 안테나를 FR4 기판 상에 제작하고 특성을 실험한 결과 전압 정재파비(voltage standing wave ratio; VSWR) < 2 이하인 대역은 1.56-3.04 GHz(64.4%)이고, 대역폭이 기존의 밸런을 가진 DDQYA에 비해 증가함을 확인하였다.

• 전력전자학회논문지
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• 제9권5호
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• pp.457-466
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• 2004

본 논문에서는 태양광 컨버터로서 변형된 벅-부스트 컨버터를 제안하고 분석하며, 출력을 증가시키고 출력전압의 리플을 저감하기 위한 새로운 병렬 구동 기법을 제안한다. 변형된 컨버터의 입ㆍ출력 관계는 기존의 승압형 컨버터인 부스트 컨버터와 동일하지만, 출력단자의 구성을 변형시켜 출력 콘덴서의 동작전압과 커패시턴스 용량을 저감시킬 수 있는 장점을 가진다. 또한 변형된 컨버터와 전류 제어 기법을 이용하는 제안된 병렬구동 기법은 기존병렬 구동 방식의 전류 분배에 대한 불평등 문제를 해결할 수 있으며, 부가적인 스위칭 손실의 증가 없이 등가 스위칭 주파수를 증가 시킬 수 있어 출력전압 리플 저감에 효과적이다. 제안된 병렬 구동 기법의 타당성을 컴퓨터 시뮬레이션과 실험을 통하여 입증한다.

• Journal of electromagnetic engineering and science
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• 제5권2호
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• pp.49-60
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• 2005

In this paper, an efficient performance enhancement scheme for an adaptive antenna array under the flat and the frequency-selective Rayleigh fadings is proposed. The proposed signal enhancement scheme is the modified linear signal estimator which combines the rank N approximation by reducing noise eigenvalues(RANE) and Toeplitz matrix approximation(TMA) methods into the linear signal estimator. The proposed performance enhancement scheme is performed by not only reducing the noise component from the signal-plus-noise subspace using RANE but also having the theoretical property of noise-free signal using TMA. Consequently, the key idea of the proposed performance enhancement scheme is to greatly enhance the performance of an adaptive antenna array by removing all undesired noise effects from the post-correlation received signal. The proposed performance enhancement scheme applies at the Wiener maximal ratio combining(MRC) method which has been widely used as the conventional adaptive antenna array. It is shown through several simulation results that the performance of an adaptive antenna array using the proposed signal enhancement scheme is much superior to that of a system using the conventional method under several environments, i.e., a flat Rayleigh fading, a fast frequency-selective Rayleigh fading, a perfect/imperfect power control, a single cell, and a multicell.

• 대한기계학회논문집A
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• 제33권5호
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• pp.489-495
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• 2009

A novel technique to measuret of viscoelastic properties of polymers is proposed to investigate complex Poisson's ratio as a function of frequency. The forced vibration responses for the samples under the normal and the shear deformation are to be measured with varying load masses. The measured data were used to obtain the viscoelastic properties of the material based on an accurate 2D numerical deformation model of the sample. The 2D model enabled us to exclude data correction by the empirical form factor used in 1D model. Comprehensive measurements of viscoelastic properties of two slightly varied silicone RTV rubber ($Silastic^{(R)}$ S2) compositions were performed. Standard composition (90% PDMS polymer + 10% catalyst) and modified composition (92.5% polymer + 7.5% catalyst) were tested in temperature range from $30^{\circ}C$ to $70^{\circ}C$. Shear modulus, modulus of elasticity, loss factor, and both the real and the imaginary parts of the Poisson's ratio were determined for frequencies from 50 to 400Hz in the linear deformation regime (at relative deformations $10^{-4}{\sim}10^{-3}$).

• Advances in Energy Research
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• 제3권2호
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• pp.81-95
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• 2015

Microgrid, which can be considered as an integration of various dispersed resources (DRs), is characterized by number of DRs interfaced through the power electronics converters. The microgrid comprising these DRs is often operated in an islanded mode. To minimize the cost, reduce complexity and increase reliability, it is preferred to avoid any communication channel between them. Consequently, the droop control method is traditionally adopted to distribute active and reactive power among the DRs operating in parallel. However, the accuracy of distribution of active and reactive power among the DRs controlled by the conventional droop control approach is highly dependent on the value of line impedance, R/X i.e., resistance to reactance ratio of the line, voltage setting of inverters etc. The limitations of the conventional droop control approach are demonstrated and a modified droop control approach to reduce the effect of impedance mis-match and improve the time response is proposed. The error in reactive power sharing is minimized by inserting virtual impedance in line with the inverters to remove the mis-match in impedance. The improved time response is achieved by modifying the real-power frequency droop using arctan function. Simulations results are presented to validate the effectiveness of the control approach.

• Korean Journal of Acupuncture
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• 제32권1호
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• pp.20-29
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• 2015

Objectives : The objectives of this study is to compare the effects of electroacupuncture(EA), warm needling(WN) and Radio Frequency warm needling(RFWN) stimulations on the acupoints at the artificially damaged ankles of Sprague-Dawley rats, which could be classified as the Grade 3. Methods : The foot weight bearing force ratio(FWBFR) of ankle sprain was measured first at 24 hours after without any other stimulations. Pain Recovery Index(PRI) represents the analgesic level, and modified Pain Recovery Index(mPRI) shows the accumulated recovery level. PRI was measured at 2 hours after each stimulus on GB34, GB39 and GB42, and mPRI was during 7 days. Results : EA stimulation of GB34 and GB39 acupoint in grade 3 ankle sprain showed a marked analgesic and recovery effect. RFWN of GB42 exhibited significant analgesic and pain recovery effect. RFWN of GB34 resulted in pain recovery effect but not analgesic effects, and RFWN of GB39 resulted in analgesic effect 2 hours after but not pain recovery. However, WN did not affect the pain recovery among three acupoints at all. Conclusions : In the Grade 3 ankle sprain model, the difference of analgesic effects were explained by the acupoints and the stimulation methods according to the accumulated recovery effects during 7 days. It is insufficient to determine that a certain acupoint has a specific analgesic effect depending on the stimulation method by the results of this study. Therefore, the effects of each stimulation on the acupoints in any other meridians at the sprained ankle should be compared and analyzed.

• 한국통신학회논문지
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• 제36권3C호
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• pp.163-169
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• 2011

Partial transmit sequence (PTS) algorithm is known as one of the most efficient ways to reduce the peak-to-average power ratio (PAPR) in the orthogonal frequency division multiplexing (OFDM) system. The PTS algorithm, however, requires large numbers of computation to implement. Thus there has been a trade-off between performance of PAPR reduction and computational complexity. In this paper, the performance of PAPR reduction and computation complexity of PTS algorithms are analyzed and compared through computer simulations. Subsequently, a new PTS algorithm is proposed which can be a reasonable method to reduce the PAPR of OFDM when both the performance of PAPR reduction and computational complexity are considered simultaneously.

• 전기학회논문지
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• 제59권2호
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• pp.333-337
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• 2010

In this paper, an advanced torque control scheme of Switched Reluctance Motor(SRM) using modified non-linear logical TSF (Torque Sharing Function) with PWM is presented. In the proposed control scheme, a simple calculation of PWM duty ratio and switching rules from DITC(Direct Instantaneous Torque Control) can reduce the torque ripple with fixed switching frequency. The proposed control scheme is verified by the computer simulations and experimental results.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.472-474
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• 2004

본 연구에서는 변형된 Folded 다이폴 안테나의 특성을 모멘트법을 이용하여 조사하였다. 안테나의 중심주파수는 200MHz, 도선의 반지름은 0.5mm이고 두 개의 선형 다이폴 사이의 간격은 2cm이다. 시뮬레이션 결과 18cm 정도의 내부 sub 변화와 4.5cm 정도의 외부 stub 변화는 SWR 기준으로 3 미만을 유지한다. 이는 변형된 Folded 다이폴 안테나가 추가적인 정합회로 없이 광대역 특성을 보이는 것을 의미한다.

• Investigative Magnetic Resonance Imaging
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• 제20권1호
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• pp.53-60
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• 2016

Purpose: To develop a technique for quantifying the $^{13}C$-metabolites by performing frequency-selective hyperpolarized $^{13}C$ magnetic resonance spectroscopy (MRS) in vitro which combines simple spectrally-selective excitation with spectrally interleaved acquisition. Methods: Numerical simulations were performed with varying noise level and $K_p$ values to compare the quantification accuracies of the proposed and the conventional methods. For in vitro experiments, a spectrally-selective excitation scheme was enabled by narrow-band radiofrequency (RF) excitation pulse implemented into a free-induction decay chemical shift imaging (FIDCSI) sequence. Experiments with LDH / NADH enzyme mixture were performed to validate the effectiveness of the proposed acquisition method. Also, a modified two-site exchange model was formulated for metabolism kinetics quantification with the proposed method. Results: From the simulation results, significant increase of the lactate peak signal to noise ratio (PSNR) was observed. Also, the quantified $K_p$ value from the dynamic curves were more accurate in the case of the proposed acquisition method compared to the conventional non-selective excitation scheme. In vitro experiment results were in good agreement with the simulation results, also displaying increased PSNR for lactate. Fitting results using the modified two-site exchange model also showed expected results in agreement with the simulations. Conclusion: A method for accurate quantification of hyperpolarized pyruvate and the downstream product focused on in vitro experiment was described. By using a narrow-band RF excitation pulse with alternating acquisition, different resonances were selectively excited with a different flip angle for increased PSNR while the hyperpolarized magnetization of the substrate can be minimally perturbed with a low flip angle. Baseline signals from neighboring resonances can be effectively suppressed to accurately quantify the metabolism kinetics.