共查询到20条相似文献,搜索用时 171 毫秒
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基于压电器件的等效电路模型,利用导纳圆理论图测量压电器件阻抗特性参数及过零检测相位差测量原理,构建了一套完整的压电器件性能参数阻抗测试系统。通过单片机控制信号产生幅值固定、频率可变的正弦信号,经功率放大后驱动压电器件产生超声高频振动,并采集压电器件两端的电压、电流及相位差信号,通过串口传给上位机。上位机采用基于Labview人机交互界面,实现压电器件阻抗特性参数计算和图形显示。实验结果表明,本测试系统能测量压电器件各主要相关参数,并动态显示阻抗特性曲线,可用于压电器件的参数测试与性能评估。 相似文献
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基于压电器件的等效电路模型,利用导纳圆理论图测量压电器件阻抗特性参数及过零检测相位差测量原理,构建了一套完整的压电器件性能参数阻抗测试系统。通过单片机控制信号产生幅值固定、频率可变的正弦信号,经功率放大后驱动压电器件产生超声高频振动,并采集压电器件两端的电压、电流及相位差信号,通过串口传给上位机。上位机采用基于Labview人机交互界面,实现压电器件阻抗特性参数计算和图形显示。实验结果表明,本测试系统能测量压电器件各主要相关参数,并动态显示阻抗特性曲线,可用于压电器件的参数测试与性能评估。 相似文献
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基于全息光学原理,提出并设计了一种加载相位调制的毫米波圆极化全息天线,天线由电小尺寸的人工阻抗单元按表面阻抗分布参数排列而成。利用横向谐振技术分析了标量人工阻抗单元表面阻抗的计算方法,建立了单元尺寸与表面阻抗之间的数据库。给出了干涉表面的阻抗分布参数计算方法,通过加载相位调制,实现了全息天线的圆极化。利用Matlab-HFSS联合建模仿真,建立了毫米波圆极化全息天线的基本模型,仿真结果表明,天线工作于35 GHz,波束沿法向偏转35°,中心的轴比小于1.5 d B。 相似文献
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On artificial magnetodielectric loading for improving the impedance bandwidth properties of microstrip antennas 总被引:1,自引:0,他引:1
Ikonen P.M.T. Maslovski S.I. Simovski C.R. Tretyakov S.A. 《Antennas and Propagation, IEEE Transactions on》2006,54(6):1654-1662
The effect of artificial magnetodielectric substrates on the impedance bandwidth properties of microstrip antennas is discussed. We review the results found in the literature and then focus on practically realizable artificial magnetic media operating in the microwave regime. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model. It is shown that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magnetodielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated. 相似文献
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A simple analytical transmission line model of a split-coaxial balun is proposed and tested. It is based on the coupled symmetric transmission line approach. The model leads to a closed-form analytical expression for the termination impedance/transfer function of the complete antenna system that includes antenna, balun, and a non-splitted coaxial line of certain length. It accepts the impedance of a center-fed symmetric antenna as input parameter. The model is in excellent agreement with full wave simulations and is confirmed by a series of prototype measurements. It can be applied to a linearly-polarized radiator or to a broadband circularly-polarized turnstile, where the phase quadrature is created by two complex-conjugate impedances. The present model only describes the impedance matching properties of the balun but is not capable of predicting the balance quality of baluns. 相似文献
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In the last years Waver Level LED Packages (WLP-LEDs) were developed. They are thin film flip chips where the sapphire substrate remains attached on top of the epitaxial light emitting layer (EPI) which can be assembled directly on a printed circuit board. The thermal resistance and the thermal path of WLP-LED packages are measured by transient thermal analysis and transient finite element simulation. This study investigates the impact of the upstream thermal masses, i.e. the sapphire (SP), phosphor layer (PL) and the side coating (SC) on the transient thermal impedance curve and the cumulative structure function. It is shown that the standard approach to extract thermal properties by features (steps) within the structure function is misleading for thermal networks with upstream thermal load and distributed heat source (EPI and PL) because they influence the shape of the structure function. By transient thermal measurements and finite element (FE) simulation the transient thermal measurements are analysed to extract information about the thermal parameters and the thermal path. Starting from the analysis of the blue flip chip LED (FC-LED, no PL and no SC) the FE-model is set up. Stepwise the FE model is extended and the influence of the PL and the SC on the transient thermal measurement is investigated. A FE model is validated and calibrated which allows simulating the transient thermal curves of these modern LEDs. Using the model the impact of structural changes in the LED package on the transient thermal curves can be identified for reliability analysis. 相似文献
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Aberg P Nicander I Hansson J Geladi P Holmgren U Ollmar S 《IEEE transactions on bio-medical engineering》2004,51(12):2097-2102
Electrical bio-impedance can be used to assess skin cancers and other cutaneous lesions. The aim of this study was to distinguish skin cancer from benign nevi using multifrequency impedance spectra. Electrical impedance spectra of about 100 skin cancers and 511 benign nevi were measured. Impedance of reference skin was measured ipsi-laterally to the lesions. The impedance relation between lesion and reference skin was used to distinguish the cancers from the nevi. It was found that it is possible to separate malignant melanoma from benign nevi with 75% specificity at 100% sensitivity, and to distinguish nonmelanoma skin cancer from benign nevi with 87% specificity at 100% sensitivity. The power of skin cancer detection using electrical impedance is as good as, or better than, conventional visual screening made by general practitioners. 相似文献
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Dua R Beetner DG Stoecker WV Wunsch DC 《IEEE transactions on bio-medical engineering》2004,51(1):66-71
Variations in electrical impedance over frequency might be used to distinguish basal cell carcinoma (BCC) from benign skin lesions, although the patterns that separate the two are nonobvious. Artificial neural networks (ANNs) may be good pattern classifiers for this application. A preliminary study to show the potential of neural networks to distinguish benign from malignant skin lesions using electrical impedance is presented. Electrical impedance was measured in vivo from 1 kHz to 1 MHz at five virtual depths on 18 BCC and 16 benign or premalignant lesions. A feed-forward neural network was trained using back propagation to classify these lesions. Two methods of preprocessing were used to account for the impedance of normal skin and the size of the lesion, one based on estimating the impedance of the lesion relative to adjacent normal skin and one based on estimating the impedance of the lesion independent of size or surrounding normal skin. Neural networks were able to classify measurements in a test set with 100% accuracy for the first preprocessing technique and 85% accuracy for the second. These results indicate electrical impedance may be a promising clinical diagnostic tool for basal cell carcinoma or other forms of skin cancer. 相似文献
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A special anisotropic model for the Earth subsurface is adopted in which the horizontally directed conductivities may be different from one another. Allowance is also made for contrasts in the magnetic permeability in the horizontal directions. It is shown that the surface impedance will depend on the lateral variations of the exciting field. It is also found that the dependence is more complicated than for a laterally isotropic half-space 相似文献
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A new technique is proposed which enables the transformation of a large class of switched-capacitor (SC) networks into equivalent time-continuous (analogue) circuits to analyse them by use of standard, general-purpose circuit simulation programs such as SPICE It is based on a block partitioning, i.e. a total SC network is divided into small building blocks. It is shown how basic SC building blocks like integrators and summers can be modelled by equivalent two-ports containing only resistors, lossless transmission lines and current-controlled voltage sources. Furthermore, some new offset-free SC integrator schemes based on multi-step integration algorithms are also described. 相似文献
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The finite-difference technique is used to calculate the electromagnetic field within the diode chip based on a solution of Maxwell's equations. The skin effect, charge carrier inertia, and dielectric relaxation are shown to greatly increase the series impedance at high frequencies. The finite difference technique is accurate for diode structures that incorporate an epitaxial layer of different doping than the substrate and a nonideal ohmic contact on the bottom of the chip. An important feature of this analysis is an impedance calculation based on power considerations, rather than the electrostatic potential. The analysis is used to investigate the series impedance as a function of epilayer doping density, anode diameter, chip thickness and ohmic contact resistivity. It is shown that a proposed membrane diode, whose thickness is less than one skin depth, will have a series impedance 30% less than that of a comparable standard diode, provided that the ohmic contact has a specific contact resistivity of 10-8 Ω-cm 2 or less 相似文献
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CC1010芯片在无线传感器网络节点设计中的应用 总被引:10,自引:2,他引:8
无线传感器网络,可以在一些特殊的场合实现信号的采集、处理和发送.在简要介绍无线传感器网络节点结构的基础上,对Chipcon公司开发的CC1010射频芯片的功能特点进行了研究,结合其工作原理与应用电路,阐述了它在无线传感器网络节点硬件设计中的应用. 相似文献
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It is commonly considered that the sensitivity of a microsensor increases with its increasing surface-to-volume ratio. However, it is not exactly clear how the surface-to-volume ratio affects the sensitivity of a conducting polymer microsensor. The change in any of the three geometrical dimensions (i.e., length, width and thickness) of a microsensor changes the surface-to-volume ratio. In designing a microsensor of desired sensitivity, it is important to know the effect of each dimension on the sensitivity for properly defining the sizes and shapes of the microsensor. As such, in this work, we have investigated the effects of each individual dimension on the sensitivity of a conducting polymer microwire sensor. Polypyrrole (PPy) and Poly (3,4-dimethlydioxythiophene) poly(styrenesulfonate) (PEDOT-PSS) microwire sensors of different dimensions were fabricated using an intermediate-layer lithography (ILL) method. They were further employed to detect methanol and acetone vapors at concentrations in the range of 0.6-7.1 parts per thousand (ppt). The corresponding three relationships between the three geometrical dimensions and the sensitivities were found using a statistical program, SAS. From the point view of surface-to-volume ratio, the thickness should affect the sensitivity much more than the other two dimensions. However, the three relationships indicate that the effects of the three geometrical dimensions on the sensitivity of a microwire sensor vary with the conducting polymer materials and the targets to detect. In other words, which dimension has more effects on sensitivity is case-dependent. Results presented in this work can be potentially used to aid in the design of conducting polymer microwire sensors of high sensitivity. 相似文献