• 한국통신학회논문지
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• 제36권2A호
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• pp.108-113
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• 2011

본 논문은 저전력 통신 변조 방식으로 새로운 QAPM(Quadrature Amplitude Position Modulation) 방식을 제안하며, 기존의 PSSK(Phase Silence Shift Keying) 변조와의 성능을 비교한다. 기존의 저전력 변조 방식의 하나인 PSSK는 PSK 변조를 기반으로 하여 PPM(Pulse Position Modulation) 변조를 결합한 방식이다. PSSK는 2개의 직교 심볼을 전송하는 방식으로 신호 주기내의 심볼 비율을 절반으로 하여 송신전력을 낮추고, 변조 심볼간의 거리를 늘림으로써 BER 성능에 향상을 가져왔다. 대역 효율은 기존의 PSK에 비해 2배 낮아졌으나 BER(Bit Error Rate) 성능은 6dB까지 향상 시켰다. 이러한 BER의 향상은 변조 레벨을 낮춤으로써 얻어지는 결과이다. 새로 제안하는 QAPM 방식은 QAM 변조를 기반으로하며, PSSK와 동일한 방식으로 심볼을 배치한다. QAM의 BER 성능은 기본적으로 PSK보다 뛰어나므로 QAPM 변조방식은 기존의 PSSK보다 더 뛰어난 BER 성능을 보여준다. 이 논문에서는 PSSK와 QAPM을 AWGN 채널에서의 BER 성능과 Throughput 성능을 비교하였다.

• Structural Engineering and Mechanics
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• 제39권1호
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• pp.1-20
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• 2011

This study investigates the feasibility of detecting structural damage using the HHT method. A damage detection index, the ratio of bandwidth (RB) is proposed. This index is highly correlated or approximately equal to the change of equivalent damping ratio for an intact structure incurring damage from strong ground motions. Based on an analysis of shaking table test data from benchmark models subjected to adjusted Kobe and El Centro earthquakes, the damage detection index is evaluated using the Hilbert-Huang Transform (HHT) and the Fast Fourier Transform (FFT) methods, respectively. Results indicate that, when the response of the structure is in the elastic region, the RB value only slightly changes in both the HHT and the FFT spectra. Additionally, RB values estimated from the HHT spectra vs. the PGA values change incrementally when the structure response is nonlinear i.e., member yielding occurs, but not in the RB curve from the FFT spectra. Moreover, the RB value of the top floor changes more than those from the other floors. Furthermore, structural damage is detected only when using the acceleration response data from the top floor. Therefore, the ratio of bandwidth RB estimated from the smoothed HHT spectra is an effective and sensitive damage index for detecting structural damage. Results of this study also demonstrate that the HHT is a powerful method in analyzing the nonlinear responses of steel structures to strong ground motions.

• 한국통신학회논문지
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• 제35권8A호
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• pp.752-759
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• 2010

WBAN의 In-body 통신 시스템은 기본적으로 낮은 소모전력이 매우 필수적이다. 기존의 PSSK(Phase-Silence-Shift-keying) 변조는 PSK 방식에서 확장된 것으로, PSK 방식보다 전력효율이 높고, FSK 방식보다 대역효율을 높은 방식이다. PSSK는 2개의 직교 심볼을 전송하는 방식으로 신호 주기내의 심볼 비율을 절반으로 하여 송신전력을 낮추고, 변조 심볼간의 거리를 늘림으로써 BER 성능에 향상을 가져왔다. 또한, FSK 방식보다 뛰어난 대역효율을 보여줌으로써 저전력특성을 유지하며 전송률을 높일 수 있었다. 본 논문에서는 이러한 PSSK의 성능을 분석하고, 새롭게 제안하는 PSPM(Phase-Shift-Position-Modulation) 방식의 BER 성능과 대역효율을 분석한다. PSPM 변조 방식은 PSK 심볼과 심볼의 위치정보를 이용하여 전력효율을 크게 향상시키는 방식이다. 이러한 PSPM 방식은 WBAN의 In-body 통신과 같이, 전력 효율이 매우 중요한 근거리 통신 시스템에 적합하여, 많은 응용이 예상된다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.296-303
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• 2004

In this study, equivalent linear damping and stiffness of a single-degree-of-freedom (SDOF) structure with a rotational friction damper are estimated using the result of experiments and compared with those obtained from non-linear time history analyses. First, the transfer function of the test model is constructed and then the equivalent stiffness and damping are calculated, using the half-power bandwidth (HPB) method. For comparative study, those properties are estimated based on stochastic theory in the time domain. Both equivalent linear systems identified from experiments and numerical analyses correspond well. Further, it is observed that there exists an optimal clamping force on the rotational friction damper from estimated equivalent damping.

• Journal of the Optical Society of Korea
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• 제18권2호
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• pp.101-109
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• 2014

In this paper, four apodization functions are proposed for silicon-on-insulator (SOI) strip waveguides with sidewall-corrugated gratings. The effects of apodization functions on the full width at half maximum (FWHM), the side-lobe level, and the reflectivity of the reflection spectrum are studied using the coupled-mode theory (CMT) and the transfer-matrix method (TMM). The results show that applying proposed apodization functions creates very good filtering characteristics. Among investigated apodized waveguides, the apodization functions of Polynomial and z-power have the best performance in reducing side-lobes, where the side-lobe oscillations are entirely removed. Four functions are also used for precise adjustment of the bandwidth. Simulation results show that the minimum and maximum values of the FWHM are 0.74 nm and 8.48 nm respectively. In some investigated functions, changing the apodization parameters decreases the reflectivity which is compensated by increasing the grating length.

• Advanced Composite Materials
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• 제17권2호
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• pp.111-124
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• 2008

The effect of temperature on natural frequency and damping is investigated in two different composite materials, Kevlar 29 fiber woven and polyethylene cloth, used especially to design ballistic armor. A damping monitoring method is used experimentally to measure the frequency response curve and it is also modeled numerically using a finite element program. The natural frequencies of a material, or a system, are a function of its elastic properties, dimensions and mass. This concept is used to calculate theoretical vibration modes of the composites. The damping properties in terms of the damping factor are determined by the half-power bandwidth technique. Numerically analyzed and experimentally measured time response curves are compared. It is seen that polymer matrix composites have temperature dependent mechanical properties. This relationship is functional and they have different effects against temperature.

• 한국군사과학기술학회지
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• 제7권1호
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• pp.47-58
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• 2004

Loss factors of A356, Mn-Cu alloy and aluminum matrix composites reinforced with $SiC_p$ and Ni-coated graphite particles at various contents have been investigated using clamped-free cantilever beam method. The loss factors of half-power bandwidth of the specimens were measured over a wide range of frequencies from 50 to 3300Hz. Among the specimens, Al-10%$SiC_p$-10%$C_p$ showed the highest loss factor at the mode I, while Mn-Cu alloy showed the highest loss factors at the modes II and III. Consequently, at the mode I the Al-10%$SiC_p$--10%$C_p$ showed the loss factor of 0.00093, which is 2.64 and 1.58 times higher than those of A356 and Mn-Cu alloy, respectively.

• 대한전자공학회논문지TC
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• 제39권5호
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• pp.251-258
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• 2002

본 논문에서는 기존외 야기-우다 안테나 배열이론을 마이크로스트립 안테나에 접목시킨 X밴드용 다이폴 급전 평면배열 안테나를 설계하고 제작하였다. 그리고 넓은 대역폭을 갖는 무선통신 시스팀에 쉽게 적용시킬수 있는 다이폴 급전 평면배열 안테나의 설계 절차에 대하여 기술하였다. 또한 FDTD 수치해석법을 이용하여 안테나의 복사특성, 반사손실과 대역폭을 개선시켰으며 제작을 통해 평면형 안테나 해석의 타당성을 입증하였다. 제작한 결과, 10GHz의 중심주파수에서 안테나의 이득은 4.9dBi이고 대역폭은 약 40%, 전후방비는 16dB, E면과 H면의 반 전력 빔폭은 각각 117°와 156°이다. VSWR<2를 기준으로 했을 때, 7.4GHz∼11.88GHZ의 주파수 범위에서 측정결과와 이론적인 결과가 비교적 잘 일치하였다.

• 전력전자학회논문지
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• 제26권3호
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• pp.214-221
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• 2021

SiC MOSFETs require a faster and more reliable short-circuit protection circuit than conventional methods due to narrow short-circuit withstand times. Therefore, this research proposes a short-circuit protection circuit using a current-sensing circuit based on Rogowski coil. The method of designing the current-sensing circuit, which is a component of the proposed circuit, is presented first. The integrator and input/output filter that compose the current-sensing circuit are designed to have a wide bandwidth for accurately measuring short-circuit currents with high di/dt. The precision of the designed sensing circuit is verified on a double pulse test (DPT). In addition, the sensing accuracy according to the bandwidth of the filters and the number of turns of the Rogowski coil is analyzed. Next, the entire short-circuit protection circuit with the current-sensing circuit is designed in consideration of the fast short-circuit shutdown time. To verify the performance of this circuit, a short-circuit test is conducted for two cases of short-circuit conditions that can occur in the half-bridge structure. Finally, the short-circuit shutdown time is measured to confirm the suitability of the proposed protection circuit for the SiC MOSFET short-circuit protection.

• KCI Concrete Journal
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• 제14권1호
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• pp.23-29
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• 2002

Recent construction activities have given rise to civil petitions associated with vibration-induced damages or nuisances. To mitigate unfavorable effects of construction activities, the measures to reduce or isolate from vibration need to be adopted. In this research, a vibration-mitigated concrete, which is one of the active measures for reducing vibration in concrete structures, was investigated. Concrete was mixed with vibration-reducing materials (i.e. latex, rubber power, plastic resin, and polystyrofoam) to reduce vibration and tested to evaluate dynamic material properties and structural characteristics. Normal and high strength concrete specimens with a certain level of damage were also tested for comparisons. In addition, recycling tires and plastic materials were added to produce a vibration-reducing concrete. A total of 32 concrete bars and eight concrete beams were tested to investigate the dynamic material properties and structural characteristics. Wave measurements on concrete bars showed that vibration-mitigated concrete has larger material damping ratio than normal or high strength concrete. Styrofoam turned out to be the most effective vibration-reducing mixture. Flexural vibration tests on eight flexural concrete beams also revealed that material damping ratio of the concrete beams is much smaller than structural damping ratio for all the cases.