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A high frequency transmission line periodically loaded with varactor diodes is presented to study nonlinear wave propagation.
The nonlinearity and dispersion characteristics are experimentally and theoretically analysed. Experimental results on shock
wave formation and harmonic frequency generation are found to be in good agreement with theoretical predictions. The influence
of dispersion on second-harmonic frequency generation is particularly discussed yielding large values of the efficiency. 相似文献
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A.W. Bett F. Dimroth G. Stollwerck O.V. Sulima 《Applied Physics A: Materials Science & Processing》1999,69(2):119-129
Research activities in the field of III-V solar cells are reviewed. III-V compound semiconductors are used for space solar
cells, concentrator solar cells, and in thermophotovoltaic generators. The epitaxial growth of ternary and quaternary material
by MOVPE and LPE allows us to realize various band gaps. Multi-junction solar cells with different band gaps are necessary
to obtain efficiencies larger than 30%. Recent results of the III-V solar cell research at the Fraunhofer ISE are presented.
A mechanically stacked GaAs/GaSb tandem concentrator solar cell achieved an efficiency of 31.1% under 100×AM1.5d. An efficiency
of 23% for a two-terminal concentrator module (486 cm2) with Fresnel lenses has been measured under realistic outdoor conditions.
Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999 相似文献
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The computer-aided design of finlines and suspended-substrate microstrip lines are investigated. The numerical results of this paper show good agreement with those computed by other techniques for unilateral finlines and open suspended microstrip lines. The approach of this paper may be used to the computer-aided design of many other kinds of transmission lines and circuits for millimeter wave applications. 相似文献
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The capacitance and voltage (C-V) characteristics of metal, oxide, and semiconductors (MOS) capacitors passivated by SrF2-B2O3-GeO2-SiO2 glasses with various water and fluoride contents were investigated. As the OH– absorption coefficient of a glass increased, adverse effects on the recovery of shifts of the hysteresisC-V curve have been observed. The water content of ions is closely related to the fluoride content in the SrF2-B2O3-GeO2-SiO2 glass. The viscous-flow transition point of glass was lowered with increasing degree of ionic character obtained from Hannay's equation. 相似文献
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《Comptes Rendus Physique》2017,18(2):107-117
This paper reports a multiband rectenna (rectifier + antenna) suitable for the electromagnetic energy harvesting of the spill-over loss of microwave antennas placed on board of geostationary satellites. Such rectenna is used for powering autonomous wireless sensors for satellite health monitoring. The topology of the rectenna is presented. The experimental results demonstrate that the proposed compact rectenna can harvest efficiently the incident electromagnetic energy at three different frequencies that are close to the resonant frequencies of the cross-dipoles implemented in the antenna array. 相似文献
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Strong interests are recently emerging for development of integrated high-performance chemical sensor chips. In this paper, the present status of understanding and controlling the current transport in the GaN and AlGaN Schottky diodes is discussed from the viewpoint of chemical sensor applications. For this purpose, a series of works recently carried out by our group are reviewed in addition to a general discussion. First, current transport in GaN and AlGaN Schottky barriers is discussed, introducing the thin surface barrier (TSB) model to explain the anomalously large leakage currents. Following this, attempts to reduce the leakage currents are presented and discussed. Then, as an example of gas-phase sensors using Schottky barriers, a Pd/AlGaN/GaN Schottky diode hydrogen sensor developed recently by our group is presented with a discussion on the sensing mechanism and related current transport. On the other hand, in liquid-phase sensors, contact is made between liquid and semiconductor which is regarded as a kind of Schottky barrier by electrochemists. As one of such liquid-phase sensors, open-gate AlGaN/GaN heterostructure field effect transistor (HFET) pH sensor developed recently by our group is presented. Finally, a brief summary is given together with some remarks for future research. 相似文献
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We study both theoretically and experimentally the possibilities of detecting malignant tumor inside a human body using near-field microwave probing. Our theoretical analysis is based on the developed theory of near-field diagnostics of plane-layered media. We verified this theory experimentally under controlled conditions of water-medium probing. Model calculations of recorded tumor contrast as a function of the size and depth of the tumor are performed. Two-dimensional images of an object imitating the tumor are obtained for different depths of object immersion in water. 相似文献
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用于宽带高功率微波辐射的双层贴片天线特性 总被引:2,自引:3,他引:2
研究了用于宽带高功率微波辐射的双层贴片微带天线输入阻抗带宽和辐射特性,提出一种适合于高功率微波辐射的圆锥传输线馈电结构以减小传统馈电探针的引线感抗,使天线的功率容量提高到百MW级,同时作为同轴线到径向传输线的过渡变换,使反射系数降低近50%。通过数值计算分析了不同的介质基底厚度组合和贴片尺寸对天线带宽的影响,优化参数后的天线带宽达到了34.9%(电压驻波比小于3),带内平均增益高于6.5 dB,最大增益8.3 dB,主辐射方向上的远场辐射因子与馈入宽带脉冲幅度比值大于1.3。分析了天线的功率容量,模拟计算表明该天线可用于辐射幅值300 kV的宽带高功率微波。 相似文献
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A. Müller D. Neculoiu D. Vasilache D. Dascalu G. Konstantinidis A. Kosopoulos A. Adikimenakis A. Georgakilas K. Mutamba C. Sydlo H.L. Hartnagel A. Dadgar 《Superlattices and Microstructures》2006,40(4-6):426
This paper presents the manufacturing of GaN membrane supported F-BAR structures. The 2.2 μm thick GaN layer was grown using MOCVD techniques on a high-resistivity 111-oriented silicon substrate. Conventional contact lithography, electron-gun Ti/Au evaporation and lift-off techniques were used to define top-side metallization of the the FBAR structures. Bulk micromachining techniques were used for the release of the GaN membrane. The bottom-side metallization of the micromachined structure was obtained by means of sputtered gold. S-parameter measurements have shown a pronounced resonance around 1.2 GHz. The extracted value of acoustic velocity is in good agreement with those reported by other authors on materials fabricated by other methods. The demonstrated FBAR function in epitaxially grown GaN layers opens new avenues for a low-cost monolithic integration with GaN-based electronics and sensing devices. 相似文献
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A closed-form model for electrostatic potential distribution in the direction normal to the channel for double-gate (DG) MOSFETs is presented. The effects of doping (NA for nMOS) and minority carriers both are taken into account for the first time, in solving Poisson's equation analytically. Excellent agreement between model-predicted results and numerical device simulation is achieved for a wide range of body thickness, light or high channeldoping, under various bias conditions. This complete closed form for position-dependent potential distribution has wide applications for MOS compact modelling and device design. 相似文献
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Conclusion The coupling effects for multiconductor microstrip on semiconductor substrate are analyzed by full-wave spectral domain approach. It is believed that the contribution aforementioned will facilitate successful design of MMIC modules in millimeter wave band and very high-speed digital integrated circuits. 相似文献
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An experimental study is described of barrier heights at the junction between (111) faces of semiconductingn-type bulk GaAs and alloyed In−Ge−Ag metal contacts. It is observed that strong corrugation of the semiconducting surface
causes the barrier height to be higher than that of flat surfaces. 相似文献
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A. Ioachim M.G. Banciu L. Nedelcu H.V. Alexandru A. Dutu 《Applied Surface Science》2006,253(1):335-338
The (Zr0.8Sn0.2)TiO4 material (ZST), has been prepared by solid state reaction and characterized. The samples were sintered in the temperature range of 1260-1320 °C for 2 h. The effects of sintering parameters like sintering temperature (Ts) and MgO addition (0.2 wt.%) on structural and dielectric properties were investigated. Bulk density increases from 4900 to 5050 kg/m3 with the increase of sintering temperature. The effect of MgO addition is to lower the sintering temperature in order to obtain well sintered samples with high value of bulk density. The material exhibits a dielectric constant ?r ∼ 37 and high values of the Q × f product, greater than 45,000, at microwave frequencies. The dielectric properties make the ZST material very attractive for microwave applications such as dielectric resonators, filters, dielectric antennas, substrates for hybrid microwave integrated circuits, etc. 相似文献
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Humberto César Chaves Fernandes Idalmir de Souza Queiroz Júnior 《International Journal of Infrared and Millimeter Waves》1996,17(8):1391-1402
The Transverse Transmission Line (TTL) is used in the theory of the overlay shielded microstrip lines considering the superconductor strip on two semiconductor regions. The superconductor effect is included with the boundary condition of the surface impedance, that is related to the complex conductivity of the material, calculated from the advanced two-fluid model. Applying the moment method the complex propagation constant of the structure, including the phase constant and the attenuation constant, is obtained. Results are presented for the complex propagation constant, versus the frequency and the temperature, of this overlay superconducting microstrip lines. 相似文献
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C. Ghezzi 《Applied Physics A: Materials Science & Processing》1981,26(3):191-202
The space charge analysis within depletion layers in semiconductors containing deep trap levels is reconsidered. A simple approach to the frequency dependence of the admittance ofp
+/n junctions is properly generalized in order to deal with the effect of interface states at heterojunctions and Schottky barriers, as well as with a special case for the space distribution of the trap density. The density of interface states atp-Ge/CdS heterojunctions is so derived. Approximate analytical solutions accounting for a spatially distributed time constant are obtained for the admittance ofp
+/n junctions with a single trap state. A comparison with experimental data is given and discussed. 相似文献