Microwave Reflection Method Research Articles

Defect Detection of Cable Termination Based on the Microwave Reflection Method

Defect Detection of Cable Termination Based on the Microwave Reflection Method

Quantitative evaluation of dislocation density in SUS316L utilizing non-contact microwave reflection method

Quantitative evaluation of dislocation density in SUS316L utilizing non-contact microwave reflection method

Simulation Study of Composite Insulator Material Defects Based on Microwave Detection

Glass Fiber Reinforced Polymer (GFRP) is a kind of raw material used in the manufacture of composite insulator mandrels. If crack defects occur in the composite insulator mandrel, it will eventually lead to brittle fractures, which will cause extremely serious accidents. Aiming at detecting the internal defects of GFRP materials by the microwave reflection method, we carried out a numerical modeling analysis adopting the electromagnetic simulation method. Samples with different depths of defects are used for sweep frequency calculation, and the frequency range is from 18 to 26.5 GHz. A simple method for judging defective GFRP boards and non-defective GFRP boards is obtained. In addition, as the depth of the defect increases, the valley value of the S11 signal increases, and at the same time, the absolute value of the phase change of the signal decreases. The simulation results show that the microwave reflection method is feasible for detecting the defects of composite insulator materials.

Method of diagnosing broadband microwave reflection of plasma sheath

<sec>During the re-entry process of the aircraft, a layer of plasma sheath wrapping its surface will be generated, which will lead the communication quality to deteriorate and even interrupt, resulting in the phenomenon of “radio blackout”. The “radio blackout” problem has plagued the aerospace industry for many years. One of the very important reasons is the lack of awareness of the communication transmission environment caused by the limitations of plasma sheath measurements. Therefore, the realization of in-situ measurement of sheath parameters is the key to the research of the “radio blackout” problem of hypersonic vehicles.</sec><sec>In this work, a broadband microwave reflection method is presented and developed for diagnosing the reentry plasma sheath .The relationship between broadband microwave reflection data and plasma parameters is derived theoretically, and effective diagnostic frequency points are selected. Then, the plasma parameters are obtained by inversely using the reflection data of the selected effective frequency points to realize the simultaneous diagnosis and measurement of electron density and collision frequency.</sec><sec>This method makes up for the deficiency that the traditional reflectometer cannot diagnose high collision frequency plasma, and it can diagnose the parameter of the plasma sheath of the hypersonic vehicle in a complex environment.</sec><sec>A simulation model and an experimental platform are established, and the simulation analysis and ground experiment are carried out to verify the method. The electron density of the plasma is diagnosed by transmission diagnostics to provide a control for reflection experiments. The experimental results show that the difference between the two diagnostic results is small, which verifies the effectiveness of the method.</sec><sec>The method can realize the real-time diagnosis of plasma sheaths of re-entry vehicles or hypersonic vehicles under various flight conditions, and accumulate a large number of first-hand measurement data, which is of great scientific value in recognizing the characteristics of plasma sheaths comprehensively, objectively and accurately. It can also be used for the parameter input link of the adaptive measurement and control system environment. In addition, this method can also be used for real-time measurement of environment parameters of ground plasma jet and real-time monitoring of changes of plasma jet parameters without changing the jet shape.</sec>

Critical Review of the Methods to Measure the Condensed Systems Transient Regression Rate

Accurate knowledge of steady state and transient burning rate of solid fuels and energetic materials is very important for evaluating the performance of different propulsion and/or gas generator systems. The practical demands imply accuracy of available burning rate data on the level of 1% or better and proper temporal resolution. Unfortunately, existing theoretical models do not allow predicting the magnitude of the burning (regression) rate with needed accuracy. Therefore, numerous burning rate measurement methods have been developed by various research groups over the world in the past decades. This paper presents a critical review of existing techniques, including basic physical principles utilized for burning rate determination, an estimate of the temporal and spatial resolutions of the methods as well as their specific merits and limitations. There are known the methods for measuring linear regression rate via high speed cinematography, X-ray radiography and ultrasonic wave reflection technique. Actually, none of those methods could satisfy the practical demands. As an alternative is the microwave reflection method, which potentially possesses high spatial and temporal resolutions and may solve the measurement problem. In addition, there exist methods for measuring transient mass or weight of the burning material. They are based on recording the frequency of oscillations of elastic element with attached specimen or a cantilevered rod with a strain gauge pasted to the base. Practically, these methods could not provide needed accuracy. Much better parameters can be obtained when using the recoil force or microwave resonator techniques. Recommendations for special applications of certain methods are formulated.

Influencing factors of moisture measurement when using microwave reflection method

Using microwave reflection for detecting moisture content in building materials is a known method. By combining sensor heads with different microwave penetration depths make it possible to generate 3D moisture content maps. This is a problematic and not easy task because several problems exist: interference between waves reflected from different layers, calibration accuracy, inhomogeneity of the material under the test etc. To interpret real measuring results several artificial moisture content distributions for measurements were built up. We describe rules to catch information about moisture distribution in depth of material from data measured with sensors with different sensing depths.

Magnetic-field tunability of the vortex translational mode in micron-sized permalloy ellipses: Experiment and micromagnetic modeling

A microwave reflection method has been used to measure the spin excitations corresponding to the translational mode of magnetic vortices in samples containing either one or two vortices. Experimental findings are complemented by micromagnetic simulations. One-vortex systems are investigated in micron-sized circular and elliptical cylinders. For ellipses, the resonance frequency can effectively be tuned by applying static magnetic fields and the field dependence of the frequency is significant for fields applied along the short axes but negligible when applied along the long axes of the ellipses. This is contrary to the circular case, where virtually no field dependence was found. This can be understood by considering the shape of the vortex potential well. Further, it is found that the resonance frequency is independent on the direction of the excitation field for the one-vortex systems. Ellipses containing two interacting vortices are also investigated. It is shown that the relative vortex core polarizations dominate the vortex translational mode and cause, in the case of opposite polarizations, a dependence on the excitation field direction. For parallel core polarizations, no dependence on the excitation field direction is found. The dependence of the resonance frequencies on applied static fields along the long and short axes are also experimentally mapped out and compared with micromagnetic simulations, where the possible eigenmodes are determined. Another section of the thesis introduces the dawning of a device based on patterned magnetic elliptical elements for the manipulation and movement of magnetic particles on a surface. The controlled movement and separation of individual particles are successfully demonstrated. Contributions to micromagnetic standard problems and simulations on magnetization switching in nanoscale particles have also been performed. The standard problems highlight some important aspects of choosing the discretization cell sizes and the finite temperature simulations show that thermal fluctuations can alter the magnetization reversal paths.

Minority-carrier lifetime in indium-doped n-type Hg0.78Cd0.22Te liquid-phase-epitaxial films

The recombination mechanisms of the minority-carrier lifetime in n-type indium-doped Hg0.78Cd0.22Te liquid-phase-epitaxial films have been studied. Its temperature dependence was measured from 78 to 200 K using standard photoconductivity decay method. The dependence on doping concentration from 1×1014 to 2×1015 cm−3 was measured using a contactless microwave reflection method at 77 K. From best fits to the experimental temperature dependence data, it was found that lifetimes at temperatures higher than 130 K were dominated by Auger recombination with a value of 0.15 for the overlap integral of Bloch functions. For most films with a doping concentration below 1×1015 cm−3, Shockley–Read–Hall recombination via an acceptor-like deep level at about 40 meV below the conduction band affected lifetimes below 120 K. It was also found that the recombination parameters determined from fitting the lifetime versus temperature curves were adequate to analyze and understand the lifetime versus doping concentration curve, which comprised data from over 100 films.

Conductivity of the solid electrolyte RbAg 4I 5 in the microwave region

The high frequency ionic conductivity of RbAg 4I 5 single crystals was measured in the range from 0.1 MHz to 8 GHz using a microwave reflection method. In the whole temperature region studied (30°C to 135°C) the bulk conductivity was found to be frequency independent and to coincide with the latest published values for the static conductivity. This result is in contradiction with values reported formerly in literature but agrees very well with recent measurements on the structurally similar solid electrolyte AgI.

Microwave Reflection from a Plasma Column in a Rectangular Waveguide

The paper concerns the microwave reflection method suitable for the diagnostics of a plasma column placed transversely across a rectangular waveguide for a TE10 wave. VSWR and phase measurement results are presented regarding the complex reflection coefficient of a discharge Neon diode Philips K50A used as a positive column in the 2–11 Gc/s band. A reflection coefficient theory of cylindrical dielectric post having two coaxial layers of different dielectric permittivity, has also been presented and checked with measurements on calibrated dielectric rods. A numerical calculation of the complex coefficient of reflection performed in the 2–11 Gc/s band is presented for conventional plasma parameters along with a radial electron density distribution depending on a paraboloidal function. The computed values fit the measurement results within the experimental errors.

The relaxation phenomena in an ionized shock front

We have investigated the ionization process in the shock front structure in argon using various experimental techniques: 10 GHz microwave reflection method, 70 GHz mm wave interferometer, laser light scattering, spectroscopy, electric probes. To drive high speed shock waves, the electromagnetically driven (EM) shock tube and pressure driven shock tube with two diaphragms were used.

Scattering of Microwaves from a Plasma Column in Rectangular Waveguide

The microwave reflection method for the measurement of various parameters of cold plasma is examined. The exact solutions are obtained for the waves scattered by a plasma column inserted in the duct. The probing electric field of TE10 mode is parallel to the axis of the column. The emphasis is placed on the fact that inhomogeneous electron density distribution is fully taken into account. The electron density in the column is assumed to be n(r)=n0(1-r2/ρ2), where ρ is the radius of the column and n0 is the electron density on the axis of the column. The electric permeability is then locally defined with use of n(r). Numerical calculations of reflection coefficients are carried out with the electronic computer OKITAC–5090 and their results are tabulated for such parameters as ωp/ω, ν/ω, ka, and kρ for practical convenience. The electron densities in a positive column determined by the microwave reflection method with use of the tables are compared with those determined by the Langmuir probe method. The comparison is found in satisfactory agreement.

Microwave Reflection Measurements of Electron Densities in Electromagnetically Driven Shock-Produced Plasmas

The electron densities from 1013 to 1017 cm−3 in plasmas produced by electromagnetically driven, propagating, or reflected shock waves are measured by a microwave reflection method. The Mach number of the shock waves is varied from 9 to 25 in argon, air, and helium at initial pressures from 0.4 to 2.0 Torr. A 35-GHz microwave reflection probe is inserted into a T-type shock tube perpendicular to its axis, or is placed at the tube end parallel with the axis. Despite some perturbation on the gas flow by the inserted probe, surprisingly good agreements are found between the microwave and spectroscopic measurements. The measured electron densities are compared with predicted values calculated from the Rankine-Hugoniot and Saha equations. For Mach numbers higher than 20, the maximum values of the electron densities measured behind the shock fronts agree well with the theoretically predicted values. For low Mach numbers, however, the measured maximum electron densities are lower than the theoretically predicted values. Reasons for the discrepancy between the theoretical and experimental values in low Mach numbers are discussed. In addition, radial and axial density distributions behind the shock fronts are measured for various Mach numbers.

Microwave Reflection by Plasma With Density Gradient

In order to extend the applicability of the microwave reflection method for measuring electron densities which are higher than critical, reflections by a boundary layer with density gradient and also by an inhomogeneaus plasma are examined. Approximate expressions for reflection coefficient are derived for the respective cases.

Microwave Study of Plasmas Produced by Electromagnetically Driven Shock Waves

A microwave reflection method is applied to the measurement of very high electron densities in plasmas produced by shock waves. The electron density can be determined from the phase angle of a reflection coefficient at the shap boundary of the plasma which exists at the end of the shock tube. The electron densities measured by an X -band frequency (9000 Mc) range from 10 13 to 10 15 cm -3 . The plasma is produced by shock waves of Mach number 8 to 15 in argon at a pressure of 0.1 mm Hg. The electron densities are compared with values predicted by theoretical calculations under thermal equilibrium. The maximum density detectable reaches 1×10 16 cm -3 . The afterglow plasma which continues after the shock wave has passed is investigated. The loss mechanism of electrons during a few hundred microseconds seems not to depend on diffusion but on recombination. The temperature of electrons which are almost in thermal equilibrium with ions and neutral atoms in this afterglow plasma is sustained for a relatively l...