Microwave Reflection Technique Research Articles

Multiple Frequencies Five-Port Reflectometer (FPR) for Pure and Adulterated Honeys

Honey adulteration is one of the major health concerns among honey consumers, it is essential to inspect the quality of honey. One of the methods is to characterize the honey by using the microwave reflection technique. A Five-Port Reflectometer (FPR) is proposed in this work. The microstrip Five-Port ring junction circuit was designed for multiple frequencies of 0.60 GHz, 2.28 GHz, and 3.47 GHz. The fabricated circuit works with an analogue-digital converter, open-ended coaxial sensor, diode detectors and computer to form a complete FPR measurement system. The reflection measurements were conducted on Honey Gold and Trigona Honey for multiple frequencies. The performance of the FPR in s-parameter measurement was verified by Vector Network Analyzer (VNA). This study shown that the performance of FPR in term of reflection measurement has promising accuracy which is comparable with VNA. The FPR can be used as an alternative instrumentation system for characterizing pure and adulterated honey.

Evaluation of Road Pavement Density Using Ground Penetrating Radar

This study describes an analysis of Ground Penetrating Radar (GPR) measurements at frequency range of 1.7-2.6 GHz to get a relationship between attenuation and density for nine road pavements slabs with different densities. There are about four different frequencies had been tested. The method is simple, fast, non-destructive and accurate way to determine the density of road pavement. Density is a one of the important parameter in order to determine the compressive strength of road pavement for road user safety. In laboratory, the measurement system consists of a signal generator (250 kHz-3 GHz) as a source, spectrum analyzer (100 Hz-8 GHz), directional coupler with adapter and horn antenna. The first part of the measurement system setup is to determine the amplitude of transmitted wave (received signal strength). A few of received signal strength and attenuation for nine road pavement slab samples were taken at four different frequencies. An instantaneous method for measuring the density of road pavement was developed by using microwave reflection technique and free space method. The MATLAB software is used to analyze the measurement data and also for the graphs comparisons. At the end of this study, it is found that density plays an important factor in causing a major in the recorded signal strength as well as the differences of attenuation of the GPR signal.

On the Impact of Metal Impurities on the Carrier Lifetime in N-type Germanium

AbstractThe impact of metallic impurities on the carrier lifetime in n-Ge is studied using microwave reflection and absorption techniques. Co, Fe, Ti, Ni and Cr are introduced by ion implantation followed by a thermal anneal and quenching to room temperature. Excess carrier decay transients are examined by microwave reflection and absorption probing after pulsed light excitation. A detailed analysis allows to evaluate the ratio of the capture cross-sections for minority and majority carriers revealing an acceptor-like character of the metal induced traps. Cross-sectional lifetime measurements show an U-shaped depth distribution with the lowest lifetimes in the bulk of the wafer. The lifetime results are correlated with those of deep level transient spectroscopy in order to clarify the properties of the dominant metal related recombination centres. Fe and Co are the most effective lifetime killers in n-Ge while Cr has the least influence.

Vortex dynamics in patterned ferromagnetic ellipses

The dynamics of individual magnetic vortices and vortex pairs confined in lithographically defined ferromagnetic ellipses were measured using a microwave reflection technique. Resonance frequencies were detected in the subgigahertz range for Ni80Fe20 (Permalloy) ellipses ranging in size from 3 by 1.5μm to 1 by 0.5μm, 40nm in thickness. Micromagnetic simulations indicate that the single mode observed for one vortex is a translational mode and that the two eigenmodes associated with a vortex pair correspond to coupled translational modes of vortices with parallel or antiparallel core polarizations. The single-vortex resonance scales inversely with the ellipse size, in agreement with the simulations and analytical theory.

Soliton-pair dynamics in patterned ferromagnetic ellipses

Confinement alters the energy landscape of nanoscale magnets, leading to the appearance of unusual magnetic states, such as vortices, for example. Many basic questions concerning dynamical and interaction effects remain unanswered, and nanomagnets are convenient model systems for studying these fundamental physical phenomena. A single vortex in restricted geometry, also known as a non-localized soliton, possesses a characteristic translational excitation mode that corresponds to spiral-like motion of the vortex core around its equilibrium position. Here, we investigate, by a microwave reflection technique, the dynamics of magnetic soliton pairs confined in lithographically defined, ferromagnetic Permalloy ellipses. Through a comparison with micromagnetic simulations, the observed strong resonances in the subgigahertz frequency range can be assigned to the translational modes of vortex pairs with parallel or antiparallel core polarizations. Vortex polarizations play a negligible role in the static interaction between two vortices, but their effect dominates the dynamics.

Water detection in fuel tanks using the microwave reflection technique

Water is often present in fuel tanks due to night and day temperature changes,resulting in a build-up of condensed water within the inner surface of the tank. Theexpectancy of water infiltration in fuel tanks is even higher in flooding proneareas. Water settlement at the bottom of the tank causes internal corrosion. Inthis work, a simple, low cost and accurate microwave reflection type system fordetection of water in fuel tanks has been developed. A module consisting of amicrowave generator and a detecting diode is used to measure the microwavereflection coefficient at various positions through the fuel tank. In the course ofthe study, a motion control and data acquisition system has been developed.Software written using the LabVIEW programming language is used to control themovement of the sensor and for the data acquisition. Theoretical and experimentalresults show the ability of the system to detect the presence of a water level downto approximately 1 mm. A simple theoretical model for power prediction of thereflected signal at various positions of the sensor in the tank is also presented.

Surface damage threshold of Si and SiO2 in electron-cyclotron-resonance plasmas

Damage thresholds of Si and SiO2 during reactive ion etching (RIE) were measured in an electron cyclotron resonance plasma reactor equipped with an energy-analyzed mass spectrometer, Faraday cup, and in situ ellipsometer. Si damage was monitored by the minority-carrier lifetime measured by the noncontact microwave reflection technique. The threshold ion energy of displacement damage is very low near 20 eV but the RIE damage threshold for Si devices is found to be about 100 eV. This means that a RIE process with the bias voltage lower than 100 Vdc can fabricate Si devices with no serious damage effect as long as surface contamination by reactive radicals is carefully avoided. In a SF6 plasma, the threshold energy of SiO2 RIE is 15 (±2) eV, independent of a substrate temperature, while the physical sputtering threshold is roughly 40 eV in Ar plasmas.

Bulk and surface components of recombination lifetime based on a two-laser microwave reflection technique

An algorithm for separating the bulk and surface components of recombination lifetime, tailored for contactless measurement techniques with laser excitation, is presented in the paper. In order to analyze the carrier decays and subtract the surface recombination term, two lasers operating at 910 and 830 nm are applied. A separation of carrier decay resulting from the different contribution of surface and bulk components due to difference in the light absorption is observed for such a case. This separation is a function of surface recombination velocity S. An experimental verification of the analysis is presented using microwave absorption/reflection measurements.

Experimental requirements for the measurement of excess carrier lifetime in semiconductors using microwave techniques

Experimental requirements for an accurate evaluation of the excess carriers lifetime in semiconductors using nondestructive microwave reflection techniques are presented. A relationship between the observed exponential decay time constant and the excess carrier lifetime is derived. It is shown that the microwave transient decay time constant could be either the lifetime or half of the lifetime depending on the arrangement of the measurement setup. The theory of the lifetime measurement has been corroborated by the microwave measurements taken on silicon and semiinsulating gallium arsenide (Si-GaAs) wafers and by an independent photovoltage decay method on silicon solar cells.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrical Properties of Sipos Films Deposited on Crystalline Silicon

AbstractTransport and trapping effects on undoped and phosphorus-doped SIPOS films on n-type and p-type Si have been characterized by C-V-ω, I-V, DLTS and photo-induced microwave reflection techniques. Our C-V and DLTS data on undoped SIPOS indicate that interface traps with a density of 2 × 1012cm−2 eV−1 and a response time between 1 and 10 μsec exist near the midgap of the SIPOS. Photo-induced microwave reflection transient-waveforms show an order of magnitude increase in photoconductivity decay time with doped SIPOS films. Our data shows that trapping effects exist in doped SIPOS and that these traps could reduce the cutoff frequency of SIPOS emitter transistors.

Photoconductivity lifetime measurements on HgCdTe using a contactless microwave technique

Photoconductivity lifetime measurements on narrow band-gap HgCdTe thin films and bulk slices using a contactless microwave reflection technique have been demonstrated for the first time. A horn antenna was used to allow cooling of samples to 77 K outside the waveguide and testings of large-size samples. A good agreement was established between lifetime results from the contactless microwave reflection technique and the standard photoconductivity decay method using two ohmic contacts. The feasibility of lifetime mapping by moving the pulsed light beam to different locations on the samples was also demonstrated.

Measurement of magnetization of YIG films on gadolinium-gallium garnet substrates from ferrimagnetic resonance and ferrimagnetic antiresonance

The radio-frequency magnetic properties of (111) oriented YIG films epitaxially grown on gadolinium-gallium garnet substrates have been investigated using microwave transmission and reflection techniques. Measurement of the microwave frequency and applied magnetic field at ferrimagnetic resonance indicate that the g-factor is 1.997±0.003 and 4πM−2Ku/M+4K1/3M = 1700 G. In addition to FMR, a broad feature ∼100 G wide, observed in both transmission and reflection, is argued to be associated with the zero of the real part of the permeability (ferrimagnetic antiresonance, FMAR). The YIG magnetization is directly proportional to the separation in magnetic field between FMR and FMAR and is in the range 1560–1660 G for these films. The measurement of both FMR and FMAR is a new method of determining the magnetization of as-grown nonconducting, ferrimagnetic films. The uniaxial anisotropy does not complicate the determination of the magnetization. This method is applicable to any film for which the magnetization is significantly larger than the FMR linewidth and/or the magnetostatic mode spectrum excited.

Nonlinear skin effect of high-power microwaves and a density-rarefaction wave in a collisionless magnetoplasma

Experimental results are presented which verify the nonlinear skin effect of high-power microwaves incident on a collisionless, uniform plasma having a sharp boundary. The skin depth, observed by microwave reflection techniques, increases with the incident microwave power. The results are compared with the theoretical analysis in which the radiation pressure due to the electromagnetic field is taken into account. It is also found that a density-rarefaction wave caused by an incident microwave propagates through an over-dense plasma at a velocity closer to that of the ion acoustic wave.

Nonlinear Skin Effect of High-Power Microwaves Incident on a Collisionless Magnetized Plasma

Experimental results are presented which verify a nonlinear skin effect of high-power microwaves incident on a collisionless, uniform plasma having a sharp boundary. The skin depth, observed by microwave reflection techniques, increases with the incident microwave power.

Recombination Lifetimes in Gold-Doped p-Type Silicon

Transient recombination lifetimes have been measured in gold-doped p-type silicon from 30°K to room temperature. Photoconductive decay curves and quiescent electrical conductivity have been obtained with the microwave reflection technique. The presence of a controlled amount of gold permits unambiguous determination of attractive and neutral capture cross sections which are compared with theoretical values obtained by Lax and with other experimental values. An unusual feature of the data is a dramatic drop in excess conductivity at temperatures below 50°K. The observed variations of lifetimes with temperature and the drop in excess conductivity are explained using a transient analysis similar to that of Sandiford and Wertheim.

Ionization measurement in reactive shock and detonation waves using microwave techniques

The use of microwave cavity techniques in the study of ionization in detonation waves and shock waves in reactive gas mixtures is discussed. Absorption measurements were conducted using a cavity oscillating in the TM010 mode at S band frequency and the shift in resonant frequency of a TE011 mode cavity, operating at X band frequency, was obtained by repetitively sweeping the frequency through the cavity resonance and displaying the response by means of a raster scan generator. The results are compared with microwave free-propagation experiments obtained at X and Q band frequencies in which both the microwave power absorbed by the ionized medium and the power transmitted through and reflected from the medium are monitored. Some results obtained by dc probes are also included for comparison.Equilibrium conductivities measured for the oxyhydrogen and oxyacetylene detonation waves are in reasonable accord with theoretical values. For the reactive shocks, however, the results obtained from the microwave reflection techniques yield far higher values of electron density than those obtained by the absorption methods; this is attributed to the inhomogeneous nature of the ionized medium.

Application of Microwave Reflection Technique to the Measurement of Transient and Quiescent Electrical Conductivity of Silicon

A microwave reflection technique for measuring both the transient and quiescent electrical conductivity of semiconductors in a temperature range from 4.2 to 450 K is described. This technique eliminates the difficulties due to non-Ohmic contacts when making electrical measurements on semiconductors, particularly silicon.

Electron-Ion Recombinations in a Dense Hydrogen Plasma

Measurements are carried out of electron densities and temperatures in a plasma produced behind an electromagnetically driven, reflected shock wave in a T -tube filled with hydrogen at an initial pressure of 1.0 Torr. The ranges of the measured electron densities and temperatures are respectively from 10 17 to 10 15 cm -3 and from 2.5×10 4 to 10 4 °K. The electron densities are determined by the 35-GHz microwave reflection technique. These measured values are in good agreement with those determined from Stark broadening of the H β line. The electron temperatures are determined from the ratio of the total spectral line to continuum intensity, and from the measured collision frequency and electron density. The observed plasma decay is interpreted in terms of the collisional-radiative electron-ion recombination theoretically calculated by Bates, Kingston and McWhirter, who take account of the effect of the ionization.

Recombination Lifetimes in High-Purity Silicon at Low Temperatures

Transient recombination lifetimes have been measured in high-purity, n-type, float-zone silicon from 4.2°K to room temperature. Photoconductivity decay curves and quiescent electrical conductivity values have been obtained by a microwave reflection technique which does not require electrical contacts to the sample. Experiments were performed at low injection levels on unirradiated samples and after irradiation with 30-MeV electrons. An unusual feature of the data is a pronounced increase in lifetime with decreasing temperature below 45°K, similar to a trapping effect. This variation of lifetime with temperature has been explained using the two-lifetime transient analyses of Sandiford and Wertheim. The temperature dependences of the capture cross sections are calculated and compared with the theoretical predictions of Lax and with other experimental results.

Ion density and current distributions in a propagating current sheet, determined by microwave reflection technique

Electron and ion density distributions and the problem of electron/ion current partitioning are studied in a large radius Z-pinch in argon. Radial scans of the electron density and temperature proffles in the propagating sheet are obtained with a multi-purpose microwave interferometer which measures the complex refiexion coefficient from the plasma. At 70 GHz the probe resolves densities up to 1017 cm−3 over dimensions of ˜ 4 mm. Proffles of the electric and magnetic field components are obtained using standard probe techniques, and these data are used to calculate ion and electron current components in the sheet.Within the approximations of MHD theory, calculations show that the overall axial current pattern is built up of four interior zones alternately dominated by electron or ion current. This structure is observed to be closely correlated with variations of the Hall parameter, Wb/vc, about the value of unity through the sheet, which suggests that this parameter might be used as a guide to the relative importance of ion conduction in pinch discharge current sheets.