• Current Optics and Photonics
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• 제2권2호
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• pp.179-184
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• 2018

Terahertz (THz) wave generation by periodically poled $BaTiO_3$ (PPBT) with a quasi-phase-matching (QPM) scheme based on cascaded difference-frequency generation (DFG) is theoretically analyzed. The cascaded DFG processes comprise cascaded Stokes and anti-Stokes processes. The calculated results indicate that the cascaded Stokes processes are stronger than the cascaded anti-Stokes processes. Compared to a noncascaded Stokes process, THz intensities from $20^{th}$-order cascaded Stokes processes increase by a factor of 30. THz waves with a maximum intensity of $0.37MW/mm^2$ can be generated by $20^{th}$-order cascaded DFG processes when the optical intensity is $10MW/mm^2$, corresponding to a quantum conversion efficiency of 1033%. The high quantum conversion efficiency of 1033% exceeds the Manley-Rowe limit, which indicates that PPBT is an excellent crystal for THz wave generation via cascaded DFG.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.169-173
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• 2016

Terahertz (THz) generation by a GaP ridge waveguide with a collinear modal phase-matching scheme based on cascaded difference frequency generation (DFG) processes is theoretically analyzed. The cascaded Stokes interaction processes and the cascaded anti-Stokes interaction processes are investigated from coupled wave equations. THz intensities and quantum conversion efficiency are calculated. Compared with non-cascaded DFG processes, THz intensities from 11-order cascaded DFG processes are increased to 5.48. The quantum conversion efficiency of 177.9% in cascaded processes can be realized, exceeding the Manley-Rowe limit.

• Current Optics and Photonics
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• 제1권2호
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• pp.138-142
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• 2017

Terahertz (THz) generation by periodically-poled $KTiOPO_4$ (PPKTP) with a quasi-phase-matching scheme based on cascaded difference frequency generation (DFG) processes is theoretically analyzed. The cascaded Stokes interaction processes and the cascaded anti-Stokes interaction processes are investigated from coupled wave equations. THz intensities and quantum conversion efficiency are calculated. Compared with non-cascaded DFG processes, THz intensities from 10-order cascaded DFG processes are increased to 5.53. The quantum conversion efficiency of 479.4% in cascaded processes, which exceeds the Manley-Rowe limit, can be realized.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.45-46
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• 2013

멀티레벨 고압인버터 토폴로지 중 저압 Power Cell를 이용하여 고압을 출력하는 Cascaded 방식이 산업계에서는 널리 사용되고 이다. 최근 제품화된 Cascaded 방식은 크게 두 가지 형태로 구분할 수 있다. 저압 Power Cell에 단상 H-Bridge를 이용한 Cascaded H-Bridge 멀티레벨 인버터와 단상 NPC(Neutral Point Clamped) 토폴로지를 적용한 Cascaded NPC 멀티레벨 인버터이다. 이 중 Cascaded NPC 멀티레벨 인버터의 경우 적은 수의 셀을 사용하여 CHB와 동일한 출력 레벨을 생성할 수 있으며, NPC 방식의 고압 인버터 고유의 장점을 모두 구현할 수 있다. 반대로 CHB Type과 NPC type의 단점인 복잡한 구조의 Phase Shift Transformer와 DC_Link 중성점 전압이 변동하는 단점 또한 나타나게 된다. 본 논문에서는 Cascaded NPC 멀티레벨 인버터의 이러한 단점을 극복하기 위한 새로운 방식의 Phase Shift Transformer와 NPC Power Cell의 중성점 전압 변동을 줄일 수 있는 기법에 대해 설명하고 이 기법에 대한 타당성을 모의시험을 통해 검증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권8호
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• pp.1404-1422
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• 2011

In this paper, a new clear channel assessment (CCA) method: cascaded-CCA, is proposed. The primary motivation for the proposed approach is to integrate the respective advantages of two standard CCA mechanisms, energy detect and preamble detect, to arrive at a new dual threshold CCA family that can provide greater flexibility towards tuning MAC performance. Cascaded-CCA integrates energy efficiency of the energy detector (ED) and the reliability of the preamble detector (PD). The probability of detection/false alarm and power consumption of cascaded-CCA in the CCA modules of IEEE 802.11b are analyzed and compared with ED and PD as an example. The performance of cascaded-CCA is explored via MATLAB simulations that implement the CCA modules and medium access control (MAC) protocol for IEEE 802.11 and IEEE 802.15.4. Simulation results showed that cascaded-CCA improves the energy efficiency significantly compared to ED-only or PD-only CCA. In addition, ED, PD, and cascaded CCA are applied to a cognitive network scenario to validate the effectiveness of the proposed cascaded-CCA.

• 조명전기설비학회논문지
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• 제28권5호
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• pp.68-75
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• 2014

Cascaded applications of surge protective devices(SPDs) are required in order to reduce the stress on the electrical and electronics equipment being protected, and the energy coordination between the cascaded SPDs is very important. This paper deals with the experimental results obtained from the installation conditions of full-scale SPDs. The energy coordination between the upstream Class I SPD and the downstream Class II SPD was measured using a $10/350{\mu}s$ impulse current due to direct lightning flashes. The distances between the cascaded SPDs were 3, 10, and 50m, and the maximum test current was 12.5kA. As a result, the energy sharing between cascaded SPDs was dependent on the voltage protection level of each SPD and the distance between two SPDs. An overview of how to select SPD ratings in applications of cascaded SPDs system was discussed based on the energy coordination between the two SPDs. The proposed test results for the energy coordination between two-stage cascaded SPDs can be used in effective applications of SPDs.

• 조명전기설비학회논문지
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• 제29권6호
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• pp.70-77
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• 2015

This paper describes the experimental results obtained from various installation conditions of cascaded metal oxide varistor(MOV)-based SPDs with the objectives to analyze the coordination of the cascaded surge protective devices(SPDs) and to propose the proper selection and installation methods of the cascaded SPDs. The residual voltage, discharge current and energy sharing between the upstream and downstream SPDs in the $10/350{\mu}s$ direct lightning current wave were measured and discussed. The coordination of cascaded MOV-based SPDs is closely related to the varistor voltage and installation methods of SPDs. In cascaded SPDs without dedicated decoupling elements, the natural impedance of leads connecting two SPDs can act as a decoupler for the coordination of MOV-based SPDs. Even if the varistor voltage of the upstream SPD is higher than that of the downstream SPD at long distances between two SPDs, the energy coordination of cascaded SPDs could effectively be fulfilled in the conditions of large surge currents and the optimum voltage protection level can be achieved. Consequently, if the distance between voltage limiting type SPDs is long, the coordination of the cascaded SPDs should be determined by taking into account the decoupling effects due to the intrinsic inductance of leads connecting the upstream and downstream SPDs.

• Journal of Power Electronics
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• 제16권6호
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• pp.2099-2108
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• 2016

The cascaded multilevel converter is widely adopted to medium/high voltage and high power electronic applications due to the small harmonic components of the output voltage and the facilitation of modularity. In this paper, the operation principle of a T-type H-bridge topology is investigated in detail, and a carrier phase shifted pulse width modulation (CPS-PWM) based control method is proposed for this topology. Taking a virtual five-level waveform achieved by a unipolar double frequency CPS-PWM as the output object, PWM signals of the T-type H-bridge can be obtained by reverse derivation according to its switching modes. In addition, a control method for the T-type H-bridge based cascaded multilevel converter is introduced. Then a single-phase T-type H-bridge cascaded multilevel static var generator (SVG) prototype is built, and a repetitive controller based compound current control strategy is designed with the DC-link voltage balancing control scheme analyzed. Finally, simulation and experimental results validate the correctness and feasibility of the proposed modulation method and control strategy for T-type H-bridge based cascaded multilevel converters.

• 센서학회지
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• 제31권5호
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• pp.353-359
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• 2022

This study investigated via computational analysis the application utility of series-cascaded ring resonators based on silicon-on-insulator (SOI) slot optical waveguides in integrated optical biochemical sensors. The radii of the two rings in the series-cascaded ring resonators were 59.4 ㎛ and 77.6 ㎛ respectively, and the coupling distance was 0.5 ㎛. The series-cascaded ring resonators were computationally analyzed using FIMMProp and PICWave numerical software. The free spectral range (FSR), full width at half maximum (FWHM), sensitivity, and quality-factor (Q-factor) of the series-cascaded ring resonators were 12.2 nm, 0.134 nm, 4100 nm/RIU, and 11580, respectively, and the measurement range was calculated to be slightly smaller than 3×10^-3 RIU. Although the measurement range was smaller than that of the single ring resonator, upon considering other characteristic parameters, the series-cascaded ring resonators are found to be more effective as integrated sensors than single ring resonators.

• 대한전자공학회논문지SD
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• 제43권5호
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• pp.1-10
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• 2006

본 논문에서는, 1.8V 8-bit 500MSPS CMOS A/D 변환기를 제안한다. 8-bit 해상도, 고속의 샘플링과 입력 주파수, 그리고 저 전력을 구현하기 위하여 Cascaded-Folding Cascaded-Interpolation type으로 설계되었다. 또한 본 연구에서는 고속 동작의 문제점들을 해결하기 위하여 새로운 구조의 Digital Encoder, Reference Fluctuation을 보정하기 위한 회로, 비교기 자체의 Offset과 Feedthrough에 의한 오차를 최소화하기 위한 Averaging Resistor, SNR을 향상시키기 위한 Distributed Track & Hold를 설계하여 최종적으로 500MSPS의 A/D 변환기 출력 결과를 얻을 수가 있다. 본 연구에서는 1.8V의 공급전압을 가지는 $0.18{\mu}m$ 1-poly 5-metal N-well CMOS 공정을 사용하였고, 소비전력은 146mW로 Full Flash 변환기에 비해 낮음을 확인할 수 있었다. 실제 제작된 칩은 측정결과 500MSPS에서 SNDR은 약 43.72dB로 측정되었고, Static상태에서 INL과 DNL은 각각 ${\pm}1LSB$ 로 나타났다. 유효 칩 면적은 $1050um{\times}820um$의 면적을 갖는다.