Fabrication-tolerant active-passive integration scheme for vertically coupled microring resonator

The large-scale photonic integration of microring resonators in three dimensions made possible by recent developments in vertical coupling and wafer bonding technology is shown to be sensitive to lateral mask misalignment for the ring and bus waveguides introduced during the fabrication process. For a typical 20-/spl mu/m radius, vertically coupled microring calculations reveal a linear relationship between deviation in the coupling coefficient and lateral misalignment. A coupling coefficient reduction of 50% is predicted for a lateral misalignment of 0.3 /spl mu/m, which is typical for an alignment accuracy limited by the current state-of-the-art mask alignment process. The use of a wide multimode bus waveguide is proposed to ameliorate this alignment sensitivity. The mode-expanded bus waveguide, together with its physically wider structure, reduces the dependence of modal overlap and coupling length on precise alignment, resulting in significantly relaxed fabrication tolerance. Deviation of coupling coefficient decreases by an order of magnitude for the new ring coupler geometry, where a sole reduction of 5% is obtained for the same amount of misalignment. The implications of the proposed structure are subsequently investigated for microring laser performance. The differential slope efficiency is shown to be at least five times less sensitive to lateral misalignment for the proposed structure within a small misalignment regime. This readily adaptable coupler geometry based on existing vertical coupling architectures is transferable to any fabrication scheme with multiple waveguide layers coupled vertically, and is of particular importance to microring resonators with small radii.     

General synthesis techniques for coupled resonator networks

This article presented general techniques for the synthesis and design of coupled resonator filters. The synthesis of the prototype circuit focuses on the compatibility between the coupling topology and the filtering function to be realized, providing some guidelines to select a proper coupling topology and to solve the coupling matrix synthesis problem. The dimensioning of the distributed filter is centered on parameter extraction techniques.     

Fabrication and characterization of PZT (lead zirconate titanate) bridge-shaped resonator for mass sensing application

Our research, based on executing theoretical modeling depending on the dimensions of PZT (lead zirconate titanate) thin film, was applied to two different bridge-shaped resonators. The critical point of having two different types of resonators is that it is a way of releasing the bridge. The first type of bridge-shaped resonator is released through use of an isotropic etching method using XeF₂ gas, while the second type of bridge-shaped resonator is released by a wet etching method that uses a KOH solution. The bridge-shaped resonators are anticipated to have accurate mass detecting sensors based on high mass sensitivity compared to the other shapes, such as diaphragms and cantilevers. The feasibility of a bridge-shaped PZT resonator as a mass sensor has been researched through studying the resonant frequency shift of a bridge-shaped resonator. The actual resonant properties of bridge-shaped resonators were determined by measuring resonant frequency and Q-factor measurements using an LDV (Laser Doppler Vibrometer). The resonant frequency appears in the ranges of 378.4?C419.8, 144.0?C180.3, and 107.8?C123.4?kHz for dimensions of 50???m?×?250???m, 100???m?×?500???m, and 150???m?×?750???m, respectively. Finally, four different thicknesses of Titanium (Ti) were loaded on the bridge-shaped resonator to confirm its variation and mass sensitivity. Significantly, mass sensitivities with dimensions of 50???m?×?250???m, 100???m?×?500???m, and 150???m?×?750???m were 2.02?Hz/pg, 330.42?Hz/ng, and 43.67?Hz/ng, respectively. Thus, the bridge-shaped resonator with dimensions of 50???m?×?250???m was able to detect the picogram-level of a mass.     

钢管组合大跨越输电塔导地线耦合效应研究

利用ANSYS软件建立了跨越珠江铁桩水道的220kV钢管组合大跨越输电塔线体系的空间数值分析模型。通过对实际工程进行环境振动测试,识别出输电塔耦合导地线的振动模态,验证了输电塔线体系有限元模型和理论计算的正确性。从动力特性和地震反应方面研究了单塔和塔线体系的动力特性和地震响应特点,分析得到关于输电塔导地线耦合效应的初步认识,进一步揭示了导地线对输电塔的耦合作用规律。研究表明,悬挂的导地线不仅具有质量效应,同时在线路的纵向和侧向还施加了一定的刚度效应。地震反应分析中可知导地线对输电塔具有一定的减震效应,并指出导地线的减震效应是否具有普遍性,还需要进一步研究。上述研究对类似输电塔的抗震、抗风设计有一定参考意义。     

Graphene-based four-port circulator with an elliptical resonator for THz applications

Journal of Computational Electronics - We suggest a new graphene-based four-port circulator for THz applications that consists of two parallel graphene waveguides coupled to an elliptical graphene...     

Opportunities for harmonic cancellation with carrier-based PWM fora two-level and multilevel cascaded inverters

Pulsewidth modulation (PWM) strategies have been the subject of many years of research effort, and the merits of the various alternatives investigated have been argued extensively. In general, it is now accepted that natural or asymmetrical regular sampled PWM with a third harmonic injected or a space-vector centered reference waveform gives the best harmonic performance, with discontinuous modulation having some advantages for higher modulation ratios. This paper uses a general analytical solution for carrier-based PWM to mathematically identify the harmonic cancellation that occurs in various PWM implementations and converter topologies. This solution provides a formal justification for the superiority of natural and asymmetrical regular sampling techniques in eliminating half of their sideband harmonics simply by virtue of their phase leg switching. Then, the use of fundamental reference phase shifting between phase legs to create single- and three-phase 1-1 output voltages is reviewed, and the harmonic cancellation that occurs is identified. One significant result from this analysis is the realization that an odd/triplen carrier/fundamental ratio has no intrinsic harmonic benefit, contrary to the generally accepted wisdom. Finally, opportunities for harmonic elimination in multilevel cascaded inverter systems by carrier phase shifting are investigated, and the optimum phase shift is identified     

A passivity-based multilevel active rectifier with adaptive compensation for traction applications

The control of a single-phase multilevel H-bridge rectifier suitable for traction applications is considered. Such a converter often presents instability problems making difficult its design and uncertain its behavior. In this paper the use of a passivity-based controller is experimentally investigated. Such a controller achieves stability, unity power factor, good balancing between the two DC links, and satisfactory behavior even in the presence of load changes. A right choice of the damping parameters allows the fulfilling of system requirements in terms of DC-link voltage error and grid current distortion.     

两种混合多电平变换器拓扑结构控制策略的分析

提出了一种以是否共享中间直流电压源为依据的新的多电平拓扑结构分类,并给出了两种相应的拓扑结构.这两种拓扑结构结合了GTO耐压值高和IGBT开关频率快的优点,并对它们分别采用工频调制和PWM调制策略,既可以减小系统开关损耗,降低EMI,又可以提高电压等级.其中不同电压比的混合拓扑结构还可以在相同直流电压源的情况下,增加输出电压电平数量.最后对这两种拓扑结构和控制策略进行了比较和分析,同时给出了一些在实际设计中应该注意的问题.     

Modeling and controller synthesis for the cascaded H-bridge multilevel active power filter with ADALINE-based identifiers

This paper presents the averaged state-space modeling and controller synthesis methodology for the cascaded H-bridge multilevel active power filters (CHB-APFs). The accurate harmonic current compensation and dc-link stabilization among the individual H-bridge modules are crucial problems for the CHB-APF, which is the prerequisite for the global stability of the system. In this study, a novel voltage balancing algorithm is devised by splitting the dc-link control task into two parts, namely, the average voltage control and the voltage balancing control, where the sine and cosine functions of the phase angle of the fundamental grid voltage are used, respectively. To ensure accurate phase tracking, a novel phase-locked loop algorithm is proposed by using the adaptive linear neural network (ADALINE). Moreover, a separate ADALINE identifier is applied for reference current generation, and the proportional-resonant controller is used for current tracking. The simulation results obtained from the Alternative Transient Program (ATP/EMTP) are provided under dynamic reactive power compensation and active filtering scenarios. The experimental results from the prototype system are also presented, which verifies the effectiveness of the devised algorithms.     

Application of differential evolution for cascaded multilevel VSI with harmonics elimination PWM switching

Harmonic elimination pulse width modulation (HEPWM) method has been widely applied to multilevel voltage source inverter (MVSI) to remove low frequency harmonics from its output voltage. However, the computation of the HEPWM switching angles for MVSI is very challenging due to several constraints, namely angle sequencing, very tight angular spacing and the numerous possibilities of angles distribution ratio. Realizing the potential of Differential Evolution (DE) to handle complex problems, this work proposes its application to solve the HEPWM problem for cascaded MVSI. Its emphasis is on improving the availability of HEPWM for higher output voltage by extending the maximum range of modulation index (M). It also removes the discontinuities in the switching angles and reduces the number of distribution ratio required to obtain the required solution. Compared to the most advanced (similar) work, i.e., 7-level MVSI with seventeen switching angles, DE covers a wider range of M; the maximum achievable M is 2.80. Furthermore, it exhibits very low second order distortion factor (DF₂): for the worst case, the value of DF₂ is 0.0014%. To verify the viability of the proposed algorithm, simulation is carried out and hardware prototype is constructed. Both results show very good agreement with the theoretical prediction.     

单元串联多电平中压变频器的研制综述

介绍一种最近研制成功的单元串联多电平中压变频器 ,详细阐述了该装置的原理、结构、控制策略、技术性能以及试验结果 ,介绍了高速浮点型DSP在中压变频调速装置中的软硬件设计思想。试验结果验证了设计方案的正确性和可行性。     

提高能源效率的主要技术与途径

与1978年相比,2008年我国电力工业通过降低供电煤耗及线损节约了3．8亿tce,减少二氧化碳排放约9．2亿t,减少二氧化硫排放约320万t,为我国节能减排作出了巨大贡献。但未来我国电力工业将随着中国经济的发展而持续增长,其能源消耗量以及二氧化碳、二氧化硫的排放量将呈不断增加的趋势。这将对电力工业的能效提出严峻的挑战。研究提高发电、输电、配电及用电的能效将具有重要的现实意义。介绍了美国发电、输电、配电及用电方面提高能效的先进技术,结合我国发布的行业标准,探讨提高我国发输配用电效率的途径。     

广东电网运行关键技术问题及应对措施

介绍广东电网的现状和结构特点,从电网安全稳定控制、安全防御系统建设、抑制短路电流过快增长、把握交直流混联电网运行规律、解决区域互联电网低频振荡问题、建设用地紧张及输电瓶颈现象、自然灾害频发使电网运行风险加大等方面,阐述目前广东电网运行中存在的关键技术问题,同时提出具体应对措施或防御对策.指出建设现代化大电网必须高度重视影响电网快速发展的关键技术问题,及时化解电网运行风险,提高安全稳定控制水平.     

KPFM导电探针的制备及应用

开尔文探针力显微镜(KPFM)可以测量样品与探针之间的接触电势差(CPD),从而可以测得样品表面电势.为了更好地测量样品表面电势的微小变化,需要制备新型导电探针.金属铱稳定的化学性质与高导电率等特性能够稳定地测量尖端样品之间的电势差.实验使用物理气相沉积(PVD)的方法修饰硅探针,使针尖镀上一层厚度为纳米级的金属铱薄膜...     

混流式水轮机转轮工地加工的新工艺

<正>随着水轮发电机组单机容量不断增大,大型混流式水轮机转轮的制造尺寸和制造重量不断增加,目前世界上制造的最大的混流式水轮机转轮名义直径已经超过10m。尺寸如此巨大的转轮,如果不具备水运码头,是无法完成内陆运输的。为便于运输,一般采用分瓣式制造、工地组装的方案,     

新能源汽车超级电容器电极的制备研究

通过气相沉积法成功地原位合成了膨胀石墨/碳纳米管复合材料,利用扫描电镜、拉曼光谱和X射线衍射仪确定得到碳纳米管插层的膨胀石墨三维多孔复合结构,并通过循环伏安法、交流阻抗法和恒流充放电等对其电化学性能进行测试。结果表明,膨胀石墨/碳纳米管在1 m V/s扫速速率下的比电容达到149.5 F/g,且倍率性能表现出色;同时1 000次充放电后比电容仍保持94%,具有很好的循环寿命,并能保持96%~99%的高充放电效率,功率性能高。     

异种钢焊接转轮的制造与应用

叙述国内外异种钢焊接转轮的制造工艺和应用情况,并对此类转轮接头的开裂原因进行分析与探讨,结合国外实际经济,对今后如何制造和应用异种钢焊接转轮提出了见解。     

国产碳纤维纸合成PEMFC气体扩散层

以国产碳纤维纸为基体、酚醛树脂为粘接剂,采用液相浸渍法对碳纤维纸进行导电碳黑填充,合成了适合质子交换膜燃料电池扩散层使用的碳纤维纸。采用Pt载量为0．6mg／cm^2的MEA,在70℃H2／O2常压条件下对碳纤维纸组装的单体电池进行了性能测试,测试结果表明：电池输出性能良好,在0．55V时输出功率为520mW／cm^2。     

硅纳米颗粒的制备及其在太阳能电池中的应用

利用HF和AgNO3混合液刻蚀制备出n型硅纳米颗粒,并将其应用到纳米薄膜太阳能电池。结果表明,随着酸刻蚀时间的延长,硅纳米颗粒的尺寸不断减小,当刻蚀时间为35min时,其尺寸平均值为80nm。将n型硅纳米颗粒作为太阳能电池的窗口材料制备出纳米薄膜太阳能电池器件,发现19型硅纳米颗粒尺寸对太阳能电池的光电转换性能也有明显的影响,随着n型硅纳米颗粒尺寸的减小,太阳能电池的光电转化效率不断提高。