共查询到20条相似文献，搜索用时 531 毫秒
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新型人工电磁材料是指具有自然界中不存在的奇异电磁特性的人造材料.获得其基本的电磁特性参数,如介电常数、磁导率,折射率和波阻抗等,是新型人工电磁材料在电磁场工程中有效应用的前提和关键.应用Ansoft公司的三维全波有限元电磁仿真软件HFSS,以金属丝和金属开口谐振环所组成的左手材料单元为例,详细介绍提取新型人工电磁材料电磁特性参数的基本原理及操作步骤和要点,这种仿真和分析方法可以有效应用于其它周期排列形成的人工电磁材料. 相似文献
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论文基于无板灯电子镇流器的简化电路,详细探讨了无极灯电子镇流嚣谐振环的频域特性,以及基于频域特性的谐振环设计思路,并比较了有极灯和无板灯电子镇流器在主要频域特性之间的差别和内在联系. 相似文献
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设计了一种小功率强磁耦合全谐振无线电能传输系统,系统由高频逆变电路、谐振耦合模块、高频整流滤波等组成。发射线圈和接收线圈在1MHz固定频率下自谐振,可以对间距70 cm范围内的负载提供能量。通过实验分析了电磁耦合谐振无线电能传输主要参数包括两谐振线圈间的系统能量随时间变化情况、发射线圈与接收线圈在水平错位时对传输效率的影响、谐振线圈空间距离D对功率、效率的影响。 相似文献
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《科技通报》2017,(7)
在工业半导体制造业中,伴随微电子器件尺寸不断缩小及集成程度的提高,对制作电子器件的半导体材料性质的检测是不可或缺的。因此文中提出在不同调制频率下对半导体载流子输运特性进行分析并研究它与时域曲线的关系。首先,利用自由载流子吸收检测技术,根据半导体原料中的自由载流子对光吸收的性质获取吸收系数,并通过该系数得到载流子浓度比例,运用调制激励光改变载流子浓度,依据载流子吸收光的特性再次调制探测光明确载流子输运参数;其次,运用调制载流子对光的吸收作用获取的输入参数,通过仿真实验利用输入参数中的载流子寿命、扩散系数和表面复合速度等因素,在不同频率下分析载流子输运特性与时域曲线的关系。实验证明,利用该技术能够较好地分析载流子输运特性对时域曲线的影响。 相似文献
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Armin Saeedi Vahdat 《Journal of The Franklin Institute》2011,348(4):622-639
This paper deals with effects of residual and axial stresses on thermoelastic damping (TED) in micro-beam resonators. Equations of coupled thermoelastic case for a capacitive micro-beam resonator have been governed using two dimensional non-Fourier heat conduction model based on continuum theory frame. A Galerkin based finite element formulation has been used to analyze TED for the first mode of vibration of the micro-beam resonator with both ends clamped and isothermal. Effect of axial stresses owing to stretching of the micro-beam on the TED ratio has been investigated. As results illustrate, this effect gets importance only when the resonator is vibrating about a large static deflection due to a bias DC voltage close to the pull-in voltage of the resonator, otherwise it can be neglected in calculations. Effect of compressive and tensile residual stresses has been also studied. The results show that compressive (tensile) residual stresses increase (decrease) the TED ratio considerably. The residual stresses effect has been also studied for various values of the micro-beam thicknesses. The results illustrate that the effect of residual stress on the TED ratio decreases by increasing the thickness of the micro-beam. The results show that, applying DC voltages near the pull-in voltage increases energy dissipation due to the TED considerably, therefore, there is a limitation for applied DC voltage for resonators, since residual stresses change the pull-in voltage of the resonator, hence, existing residual stresses can change the interval of the applied voltage limitation. 相似文献
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以2000-2008年国家高新区数据为依据, 构建了国家高新区强弱综合指数,在此基础上,运用极化指数测量了国家高新区的极化水平及其空间方向。研究结果表明:近9年间国家高新区整体极化趋势呈现"M"型特征,并在南方-北方表现为增强,而在发达城市-次发达城市、沿海-内陆方向上稍微减弱;就平均极化水平而言,发达城市-次发达城市方向>沿海-内陆方向>南方-北方方向。最后根据实证结果,相应地推导出我国国家高新区均衡政策的选择域:北京、西安、天津、武汉、成都、大连、长春、沈阳,并相应地提出了一些建议。 相似文献
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《Journal of The Franklin Institute》2019,356(14):7731-7753
Since being postulated more than a decade ago, inerters have been successfully employed to enhance the dynamic performance of mechanical systems in several applications. Their ability to lend a high dynamic mass presence to systems that employ them with only a relatively small static device mass makes them unique among mechanical elements. This study explores the mechanical wave manipulation characteristics of nonlinear inertant acoustic metamaterial (NLIAM) configurations using analysis and simulations for their one-dimensional discrete element lattice representations. Firstly, based on notional concepts for nonlinear inertant devices, potential frequency-dependent and acceleration-dependent nonlinear inertant models are identified. Using an effective mass model for the NLIAM with frequency-dependent inertance in the local resonator attachment, the dispersion characteristics of inverse square law and power law inertance models are examined and contrasted with those for an acoustic metamaterial with frequency invariant inertance. While a tuned inverse square law inertance model ensures the existence of a band gap over almost the entire frequency bandwidth of interest even encompassing the extremely low frequency regime, the low and high frequency limits for this inertance law would not be realizable in practice. A potentially more practical power law approximation is proposed and shown to deliver a widening of the band gap by more than 100% towards frequencies below the lower bound of the band gap for the acoustic metamaterial with frequency invariant inertance. Further, drawing inspiration from the Duffing-type stiffness, an acceleration-dependent cubically nonlinear inertance model is proposed. First order corrections to the dispersion characteristics are obtained for an NLIAM with acceleration-dependent inertance using a perturbation approach. For weakly nonlinear cases, excitation amplitude-activated shifts in the dispersion curves are found to enable this NLIAM to act as a passive adaptive filter for mechanical waves based solely on their excitation amplitude. Practical manifestations of such NLIAM could therefore provide a means to realize extraordinary wave manipulation capabilities especially suitable for low frequency structural dynamic applications. 相似文献
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变频空调应用高新的变频技术,增强了空气调节功能,在家用空调当中占有较大的优势。着重介绍变频技术如何应用于家用空调中,并通过与普通家用空调相比较,总结出变频空调的特点。 相似文献
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文章主要介绍了运用双频道激发极化法在河南省西南部伏牛山东段找矿工作中发现矿体的过程及在野外施工过程中应注意的几个问题.经过研究认为,该工作区内所发现的高阻高极化双频激电异常多由石英脉型金属硫化物所引起.通过该实例来说明,利用双频道激发极化法在豫西南地区寻找中深部石英脉型金属硫化物矿体具有良好的效果. 相似文献
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Annie Ruimi Yueming Liang Robert M. McMeeking 《Journal of The Franklin Institute》2012,349(7):2294-2312
The performance of a microscale aluminum nitride piezoelectric resonator in the shape of a trampoline is analyzed using three-dimensional finite element simulations. The air-suspended resonator is supported by beams and is designed to respond to longitudinal through-thickness vibrations. The device is targeted to operate at UHF frequencies (3 GHz) suitable for wireless filtering applications. Energy loss due to material damping is accounted for in the model. Other sources of damping are considered. We analyze if and how the material thickness, number of beams and beam length affect the resonator performance. This is intended to provide useful information at the design stages and eliminate the high costs associated with manufacturing a filter with poor performance. Performance is evaluated by means of the electromechanical coupling coefficient (K2) and the quality factor (Q) calculated from the electrical impedance frequency response plots. The results indicate that (i) K2 is insensitive to geometry (K2～6.5%), (ii) Q increases linearly with the AlN thickness attaining Q～1900 for a 1.7 μm thick resonator and (iii) a trampoline resonator with three beams has a better performance capability than the resonator with four or eight beams with a figure of merit K2Q～120 and resonating at a higher frequency value than its counterparts resonators, peaking at 3.21 GHz. The performance figures agree well with those predicted by a one dimensional theory. The value of K2 also agrees well with test data but that of Q is higher than the one recorded in the lab. 相似文献
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本文针对异步电动机变频调速原理,结合变频调速矢量控制策略,基于Matlab/Simulink工具箱,建立了异步电动机矢量控制变频调速系统仿真模型,对异步电动机的矢量控制特性进行研究。设置了多种电机运行状态,对电机的空载、加载、加速、减速等动态特性进行仿真研究,验证了所建立的仿真模型的正确性和可行性。 相似文献
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合成孔径雷达土壤水分反演研究进展 总被引：1，自引：0，他引：1
土壤水分作为地表水存储的重要组成部分,直接影响着陆地和大气间的物质和能量交换,成为水文、气象、农业和生态环境等领域的研究热点之一。合成孔径雷达(Synthetic Aperture Radar,SAR)由于其数据的极化特征、后向散射强度及相位特性对土壤水分的敏感性而成为高空间分辨率土壤水分监测中最有效的方法之一。本文首先对可用于土壤水分反演的SAR传感器进行总结;然后,分别对裸露地表和植被覆盖地表的微波散射模型进行介绍;在讨论影响土壤水分监测因素的基础上,分析主要影响因素的校正方法,并探讨当前合成孔径雷达反演土壤水分的主要方法;最后总结土壤水分反演中存在的问题,同时对未来的发展方向进行展望。 相似文献
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Si-Yuan Yu Cheng He Xiao-Chen Sun Hong-Fei Wang Ji-Qian Wang Zi-Dong Zhang Bi-Ye Xie Yuan Tian Ming-Hui Lu Yan-Feng Chen 《国家科学评论(英文版)》2021,8(2)
Waveguides and resonators are core components in the large-scale integration of electronics, photonics and phononics, both in existing and future scenarios. In certain situations, there is critical coupling of the two components; i.e. no energy passes through the waveguide after the incoming wave couples into the resonator. The transmission spectral characteristics resulting from this phenomenon are highly advantageous for signal filtering, switching, multiplexing and sensing. In the present study, adopting an elastic-wave platform, we introduce topological insulator (TI), a remarkable achievement in condensed matter physics over the past decade, into a classical waveguide-ring-resonator configuration. Along with basic similarities with classical systems, a TI system has important differences and advantages, mostly owing to the spin-momentum locked transmission states at the TI boundaries. As an example, a two-port TI waveguide resonator can fundamentally eliminate upstream reflections while completely retaining useful transmission spectral characteristics, and maximize the energy in the resonator, with possible applications being novel signal processing, gyro/sensing, lasering, energy harvesting and intense wave–matter interactions, using phonons, photons or even electrons. The present work further enhances confidence in using topological protection for practical device performance and functionalities, especially considering the crucial advantage of introducing (pseudo)spins to existing conventional configurations. More in-depth research on advancing phononics/photonics, especially on-chip, is foreseen. 相似文献
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We propose an alternate fabrication technique of microchannel resonators based on an assembly method of three separate parts to form a microchannel resonator on a chip. The capability of the assembled microchannel resonator to detect mass is confirmed by injecting two liquids with different densities. The experimental and theoretical values of the resonator frequency shift are in agreement with each other, which confirms the consistency of the device. The noise level of the device is estimated from the Allan variance plot, so the minimum detectable mass of 230 fg after 16 s of operation is expected. By considering the time of the practical application of 1 ms, it is found that a detectable mass of around 8.51 pg is estimated, which is applicable for detecting flowing microparticles. The sub-pico to a few picogram levels of detection will be applicable for the mass analysis of flowing microparticles such as single cells and will be greatly beneficial for many fields such as chemistry, medicine, biology, and single-cell analysis. 相似文献