共查询到20条相似文献,搜索用时 31 毫秒
1.
High-Temperature Dielectric Response and Multiscale Mechanism of SiO2/Si3N4 Nanocomposites 下载免费PDF全文
The high-temperature dielectric properties of SiO2/Si3N4 nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300°C at 9.0GHz are measured by the resonant cavity method. The SiO2/Si3N4 nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO2/Si3N4 on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures. 相似文献
2.
Design of a TE10-TE30 Rectangular Mode Converter for 4.6GHz LHCD Launcher in the Experimental Advanced Superconducting Tokamak 下载免费PDF全文
A compact rectangular TE10-TE30 mode converter is developed for the lower hybrid current drive (LHCD) launcher on the Experimental Advanced Superconducting Tokamak (EAST) at 4.6 GHz. The converter with periodic width perturbation aims to divide the microwave power into three sub-waveguides in the poloidal direction. We present the design and numerical calculation of the mode converter. Calculations are performed on the ripple wall converter by codes based on numerical solving the coupled-mode differential equations and on the simulation of the High Frequency Structure Simulator (HFSS) package. The resulting conversion efficiency from TE10 mode to TE30 mode exceeds 95% within the bandwidth from 4.56 GHz to 4.64 GHz, and the return loss of the oversized transducer can be considerably decreased to 0.068% by means of a capacitive button embedded in the E-plane of the waveguide. 相似文献
3.
We present an improved structure of the tapered magnetically insulated transmission fine oscillator (MILO). Simulation results show that this structure can obtain more microwave power with higher efficiency. Studies indicate that the distance between the load support legs and the last vane can affect the operation characteristics of this device. In the experiments, we obtain microwave with peak power of 2 GW, frequency of 2.63 GHz, and mode TMol. The beam to microwave power efficiency is 11%. 相似文献
4.
M. Lorenz H. Hochmuth D. Natusch K. Kreher 《Applied Physics A: Materials Science & Processing》1999,69(7):S905-S911
Large-area pulsed laser deposition (PLD) producing high-quality YBa2Cu3O7-x (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave stripline filters for satellite and mobile communication systems. A relatively simple PLD arrangement with fixed laser plume and rotating substrate, with an offset between the laser plume and the center of the substrate is employed to deposit laterally homogeneous 3-inch-diameter Ag-doped YBCO thin films. The YBCO:Ag films are about 250 nm thick and have laterally homogeneous critical current densities of more than 3.5 MA/cm2 at 77 K and homogeneous maps of microwave surface resistance Rs of about 40 m Q at 145 GHz and 77 K. The Rs at 8.5 GHz and 77 K, determined in the center position of the YBCO:Ag films, remains constant at about 370 7 Q up to a microwave surface magnetic field of about 10 mT. After experience with more than 700 double-sided 3-inch-diameter films, a high degree of homogeneity and reproducibility of jc and Rs is reached. The PLD-YBCO:Ag films are suitable for microwave applications envisaged for future communication systems. 相似文献
5.
With the combined use of the drift-diffusion (DD) model, experiment measured parameters and small-signal sinusoidM steady-state analysis, we extract the Y-parameters for 4H-SiC buried-channel metal oxide semicon- ductor field effect transistors (BCMOSFETs). Output short-circuit current gain G and Mason's invariant U are cMculated for extrapolating unity current gain frequency in the common-source configuration fT and the maximum frequency of oscillation fmax, respectively. Here fT = 800 MHz and fmax= 5 GHz are extracted for the 4H-SiC BCMOSFETs, while the field effect mobility reaches its peak value 87cm2/Vs when VGs = 4.5 V. Simulation results clearly show that the characteristic frequency of 4H-SiC BCMOSFETs and field effect mobility are superior, due to the novel structure, compared with conventional MOSFETs. 相似文献
6.
SiNx and SiCx films were grown on Si(001) and Si(111) using pulsed reactive crossed-beam laser ablation of Si with N2 and CH4. The scattering processes in the ablation plasma and the reactive gas pulse were investigated using time-of-flight quadrupole mass spectroscopy. The film crystallinity was determined by FTIR spectroscopy, X-ray diffraction, and reflection high-energy electron diffraction, while the stoichiometry and chemistry were investigated using XPS. SiNx was amorphous over the investigated temperature range of 25-850 °C, and x increased monotonically with temperature from 0.67 to 0.94. SiCx films grown at 850 °C consisted of oriented large #-SiC crystallites embedded in a Si matrix. 相似文献
7.
Quantitative investigations are made for the laser-duration dependence of the emission properties of high-order harmonic generation (HHG). HHG emission properties produced by few-cycle lasers show some useful characteristics. The cutoff energy is less than that by laser for infinite duration. The single energy distribution pulse decreases much faster than its duration as the laser duration grows. A two-cycle laser with carrier-envelope phase of 0° can produce a single distribution pulse peaked at the laser carrier phase 1.22 rad and spanned 1.18 rad with the cutoff energy 2.9Up + Ip and a bandwidth 0.63Up, where Up is the ponderomotive potential of the laser field and Ip is the atomic ionization potential. 相似文献
8.
Investigation of SOI Substrates Incorporated with Buried MoSi2 for High Frequency SiGe HBTs 下载免费PDF全文
Highly arsenic-doped Si-on-insulator (SOI) substrate incorporated with buried MoSi2 layers is fabricated aiming at decreasing the collector series resistance of SiGe heterojunction bipolar transistors (HBTs) on SOI, thereby enhancing cutoff frequency (fT) performance and increasing the maximum value of fT (fTMAX ). The .fT performance at medium current is enhanced and current required for fT = 15 GHz is reduced by half The value of fTMAX is improved by 30%. 相似文献
9.
This paper investigates the mechanical properties at the interface of the coating-substrate system, which comprises the electroless nickel-phosphorus (Ni-P) coating and the aluminum matrix composite substrate reinforced by the silicon carbide particles (SiCp/Al), and is used for the space mirror. To estimate the adhesion of Ni-P coating on SiCp/Al substrate, the scratch adhesion testing has been performed by drawing a spherically tipped diamond indenter with a radius of 200 μm over the coated surface. The influence of the coating thickness on the interfacial stress induced by the inertial accelerations, temperature gradients and thermal soaks has been evaluated by simulation analysis based on the finite element method. The results of the scratch testing indicate that the adhesion strength of Ni-P coating to SiCp/Al composite is more than 3.0 GPa. Compared the maximum value of the interfacial stress obtained by simulation analysis with results of the scratch testing, it is can be seen that the mirror has enough safety margin. Furthermore, the most significant conclusion that can be drawn from this work is that the coating thickness should not exceed 45 μm in order to ensure the performance and reliability of Ni-P coating and SiCp/Al substrate system for space applications. 相似文献
10.
W.J. Kim W. Chang S.B. Qadri H.D. Wu J.M. Pond S.W. Kirchoefer H.S. Newman D.B. Chrisey J.S. Horwitz 《Applied Physics A: Materials Science & Processing》2000,71(1):7-10
Ferroelectric (Ba0.6Sr0.4)TiO3 (BST) thin films have been deposited by pulsed laser deposition onto single-crystal Y3Fe5O12 (YIG) substrates with/without a MgO buffer layer. The structure and microwave properties of the BST films have been investigated as a function of substrate orientation and O2 deposition pressures (50-800 mTorr). The crystallographic orientation of BST film varies with the deposition conditions. The dielectric properties of the ferroelectric were measured using interdigitated capacitors deposited on top of the BST film. BST films exhibit high tunability (20-40%) and high dielectric Q=1/cos' (30-50) with a dc bias field of 67 kV/cm at 10 GHz. A coplanar waveguide transmission line was fabricated from a (001)-oriented BST film on (111)YIG which exhibited a 17° differential phase shift with an applied dc bias field of 21 kV/cm (10 GHz). An equivalent differential phase shift was achieved with a magnetic field of 160 Gauss. 相似文献
11.
With an effective bianisotropy picture, high-frequency behaviours of different magnetic materials can be reconciled, and the higher permeability and higher resonance frequencies are achieved even in the GHz range. The validity of the bianisotropy picture is quantitatively verified by the in-plane anisotropic Fe34Co55Zr11 thin films. A prolate elliptical precession of the magnetization about its equilibrium direction is the key point, which can be induced by an artificial or an intrinsic bianisotropy system. 相似文献
12.
Adjustable microwave absorption properties of flake shaped (Ni0.5Zn0.5)Fe2O4/Co nanocomposites with stress induced orientation 总被引:1,自引:0,他引:1
Flake shaped (Ni0.5Zn0.5)Fe2O4/Co nanocomposites were successfully fabricated by co-precipitating of Ni-Zn ferrite on the surface of cobalt nanoflakes. The electromagnetic characteristics of the samples were studied at the frequency of 0.1–14 GHz. The results showed that the cobalt nanoflakes in compacted nanocomposites were well orientated, and the nanocomposites were characterized with low optimal reflection loss (RL) of −33.8 dB at 11.5 GHz and broad RL bandwidth for <−20 dB in the frequency range of 7.6–12.1 GHz. At the same time, the position of the absorptive band can be adjusted by changing the mass ratio of ferrite to cobalt in the nanocomposites. It is proposed that the excellent microwave absorption properties are related to the combination of strong shape anisotropy of cobalt nanoflakes and adjustable dielectric loss. 相似文献
13.
Carrier-Envelope-Phase Dependence of Emission Properties of High-Order Harmonic Generation 下载免费PDF全文
The carrler-envelope-phase (CEP) dependence of the emission properties of high-order harmonic generation (HHG) are quantitatively investigated. Calculation shows that a two-cycle laser with CEP of 15° can produce a single energy distribution pulse peaked at 0.94 radian (tad) and spanned 1.29 tad with the cutoff energy 2.9Up + Ip and a bandwidth 0.86Up (where Up is the ponderomotive potential of the laser field and Ip is the atomic ionization potential). The CEP dependence of the energy and temporal localizations of the single distribution pulse show interesting 180° periodic structures. These characteristics may be useful in optimizing attosecond x-ray sources and measurements. 相似文献
14.
The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range. The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy, and can be further enhanced by using a rotational orientation method. The complex permeability can be considered as the superposition of two types of magnetic resonance. The resonance peak at high frequency is attributed to the natural resonance, while the peak at low frequency is attributed to the domain-wall resonance. The simulated results of the microwave reflectivity show that the matching thickness, peak frequency, permeability, and permittivity are closely related to the quarter wavelength matching condition. The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band (1-2 GHz). 相似文献
15.
A hypothesis is brought forward that the materials with low propagation loss in both optical and microwave band may exhibit good performance in terahertz (THz) band because THz wave band interspaces those two wave bands. For the purpose-of exploring a kind of low-loss material for THz waveguide, Lu2.1Bi0.9Fe5O12(LuBiIG) garnet films are prepared by liquid phase epitaxy (LPE) method on a gadolinium gallium garnet (GGG) substrate from lead-free flux because of the good properties in both optical and microwave bands. In microwave band, the ferromagnetic resonance (FMR) linewidth of the film 2△H = 2.8-5.1Oe; in optical band, the optical absorption coefficient is 600cm^-1 at visible range and about 100-170cm^-1 when the wavelength is longer than 800nm. In THz range, our hypothesis is well confirmed by a THz-TDS measurement which shows that the absorbance of the film for THz wave is 0.05-0.3 cm 1 and the minimum value appears at 2.3 THz. This artificial ferromagnetic material holds a great promise for magnetic field tunable THz devices such as waveguide, modulator or switch. 相似文献
16.
By introducing an adjustment waveguide besides the incident waveguide, zero-dispersion slow light with wide bandwidth can be realized due to anticrossing of the incident waveguide mode and the adjustment waveguide mode. The width of the adjustment waveguide (W2) and the hole radii of the coupling region (r') will change the dispersion of incident waveguide mode. Theoretical investigation reveals that zero dispersion at various low group velocity vg in incident waveguide can be achieved. In particular, proper W2 and r' can lead to the lowest vg of 0.0085c at 1550 nm with wide bandwidth of 202 GHz for zero dispersion. 相似文献
17.
Well-dispersed Fe3O4 nanoparticles are synthesized via an oxidization method with NANO2 as oxidant. The microwave magnetic properties of the composites are studied with different volume fractions of fe3O4 nanoparticles. It is found that a lower volume fraction corresponds to a higher magnetic resonance frequency. This could be ascribed to the enhancement of exchange interaction with a weakened dipolar interaction when the volume fraction decreases. 相似文献
18.
19.
20.
The optical properties—reflectivity, real part of the refractive index, absorption coefficient as well as the thermal and electrical conductivity of AlSi-alloy/SiCp composite were measured. The optical parameters and both conductivities decreased with the increase of SiCp particles volume in AlSi-alloy matrix. This decrease was almost linear for the volume fraction of SiCp particle up to 10 vol% of the total mass of the composite. For the 15 vol% of SiCp particles, the departure from linearity is connected with the presence of additional phases in AlSi-alloy/SiCp composite materials. The measured temperature dependencies of optical reflectivity and electrical conductivity for AlSi-alloy/SiCp 15 vol% are of metallic character. Modelling of the interaction of the CO2 laser radiation with AlSi-alloy/SiCp 15 vol% composite should allow to estimate the initiation time at which the surface composite reaches melting temperature. 相似文献