Microwave Resonant Cavity Research Articles

The measurement of a single-mode thermal field with a microwave cavity parametric amplifier

In this paper, we present the experimental study of a single-mode thermal field carried out using a microwave parametric amplifier tuned at 1.5 GHz and working at room temperature. The parametric amplifier is based on a variable capacitance diode placed inside a microwave resonant cavity. The measured distribution of the thermal photons inside the resonator follows the expected Bose–Einstein distribution probability.

Anion dynamics in the first 10 milliseconds of an argon–acetylene radio-frequency plasma

The time evolution of the smallest anions (C2H− and H2CC−), just after plasma ignition, is studied by means of microwave cavity resonance spectroscopy (MCRS) in concert with laser-induced photodetachment under varying gas pressure and temperature in an argon–acetylene radio-frequency (13.56 MHz) plasma. These anions act as an initiator for spontaneous dust particle formation in these plasmas. With an intense 355 nm Nd : YAG laser pulse directed through the discharge, electrons are detached only from these anions present in the laser path. This results in a sudden increase in the electron density in the plasma, which can accurately and with sub-microsecond time resolution be measured with MCRS. By adjusting the time after plasma ignition at which the laser is fired through the discharge, the time evolution of the anion density can be studied. We have operated in the linear regime: the photodetachment signal is proportional to the laser intensity. This allowed us to study the trends of the photodetachment signal as a function of the operational parameters of the plasma. The density of the smallest anions steadily increases in the first few milliseconds after plasma ignition, after which it reaches a steady state. While keeping the gas density constant, increasing the gas temperature in the range 30–120 °C limits the number of smallest anions and saturates at a temperature of about 90 °C. A reaction pathway is proposed to explain the observed trends.

Towards particle creation in a microwave cylindrical cavity

We present for the first time numerical results for the particle (photon) creation rate of Dynamical Casimir effect (DCE) radiation in a resonant cylindrical microwave cavity. Based on recent experimental proposals, we model an irradiated semiconducting diaphragm (SCD) using a time dependent 'plasma sheet' where we show that the number of photons created for the TM_{011} mode is considerably enhanced even for low laser powers (of microjoule order). Conversely to the moving mirror case, we also show that the fundamental TM mode (TM_{010}) is not excited for an irradiated plasma sheet. We show that polarization (arising due to the back reaction of pair created photons with the plasma SCD) implies losses for TM, but not TE modes. However, we argue that these losses can be reduced by lowering the laser power and shortening the relaxation time. The results presented here lead support to the idea that TE and, in particular, TM modes are well suited to the detection of DCE radiation in a cylindrical cavity.

Innovative production of nuclear fuel by microwave internal gelation: Heat transfer model of falling droplets

Based on closed packed microspheres produced by internal gelation, the Sphere-pac concept provides a safer and cleaner process and better remote production capability compared to the traditional production of nuclear fuels. Whereas classical reactor fuel rods are fed with UO2 pellets, this advanced concept is suggested for minor actinide bearing fuels.This paper focuses on the thermal analysis of the microspheres during their preparation by microwave-assisted internal gelation (MIG). Internal gelation is a sol-gel process initiated by a temperature shift within aqueous droplets. Alternatively this critical temperature increase takes place by contact heat transfer from a hot silicon-oil bath. Microwave heating of the droplets during their free fall provides a simpler and cleaner process, where the experimental parameters have to be carefully optimized.A matlab model is developed to study the thermal behaviour of a droplet during processing inside a microwave resonant cavity. This finite elements model takes into account the most relevant parameters (size of droplet, thermal properties of the solution, heat and mass transfer …) and calculates the temperature profile inside the droplet. The model is validated with experimental data from literature. The influence of each parameter on the temperature profile is investigated and the optimal microwave power can then be determined and applied to the production unit.

Application Study on Microwave Resonance Cavity for Non-Electrical Quantity Detection

In order to detect the humidity and the density of cigarette, we designed a type of microwave resonance cavity sensor which is called repeating-entry model. We used TM010 resonance model to the real-time detection of cigarette humidity and density. Under two conditions: vacuum resonance and cigarette in existence, through the swept technique we obtain resonance frequency，peak powerand half power point bandwidth from amplitude-frequency peculiarity (Figure I). According to mathematical formulas (6) and (7), we get cigarette humidity and density respectively. The detection technique has many advantages such as speediness, continuation, high resolution rate, non-pollution, safe and convenient operation, etc. And it is applicable to industrial survey on the spot.

Application Study on Microwave Resonance Cavity for Non-Electrical Quantity Detection

In order to detect the humidity and the density of cigarette, we designed a type of microwave resonance cavity sensor which is called repeating-entry model. We used TM010 resonance model to the real-time detection of cigarette humidity and density. Under two conditions: vacuum resonance and cigarette in existence, through the swept technique we obtain resonance frequency，peak powerand half power point bandwidth from amplitude-frequency peculiarity (Figure I). According to mathematical formulas (6) and (7), we get cigarette humidity and density respectively. The detection technique has many advantages such as speediness, continuation, high resolution rate, non-pollution, safe and convenient operation, etc. And it is applicable to industrial survey on the spot.

Small-Conductive-Particle Detection with a Microwave Resonant Cavity

SUMMARY The recent miniaturization and increased complexity of electrical devices have increased the influence of impurities on device performance, especially the influence of small conductive particles with a size on the order of micrometers. Therefore, the inspection of devices during the manufacturing process has become important. In this study, changes in the resonance properties of a microwave cavity were used to detect a metal particle. The decrease in the resonant frequency for a 100-µm stainless steel sphere was about 0.1 MHz, which was less than 1 ppm of the resonant frequency used. This frequency change is too small to detect directly in the output of a particle detector. Transmission measurements (the scattering parameter S21) at a frequency that was a few megahertz higher than the resonant frequency where the S21 changes sharply were used to magnify signal changes resulting from the introduction of a small conductive particle. A resonant frequency of 13.3 GHz and a frequency 3 MHz higher were chosen for obtaining measurements in the present study. By applying a filtering technique, it was shown that the minimum detectable sphere size is around 50 µm. This sensitivity was experimentally shown to be uneven along the long axis of the cavity. The unevenness was related to the electrical field strength of the standing wave at the resonant frequency. For practical industrial inspection of devices, multiple frequencies should be employed in view of the present discussion. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(2): 61–67, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22490

Influence of Additives on Cokemaking from a Semi-soft Coking Coal during Microwave Heating

Coke was produced from a Waterberg semi-soft coking coal using microwave heating and selected microwave susceptors. Waterberg semi-soft coking coal is poorly susceptible to microwave heating, especially below 500°C, and therefore requires microwave susceptors. Susceptors were selected from ferroalloy fines and their respective ores.Various batch experiments were performed on compressed discs utilizing a resonant microwave cavity at a constant 915 MHz frequency to heat a batch of about 5 to 7 kg of the semi-soft coking coal (sscc) to obtain coke. Materials were characterized using Inductive Coupled Plasma (ICP) analysis and coke strength tests.Dielectric property results showed that chrome and manganese ores, as well as their respective high carbon ferrochrome and ferromanganese alloys, are suitable microwave susceptors to enable rapid coke formation during microwave heating. Coke formation was completed within 2 to 3 hours up to 1100°C compared to 21 hours for a commercial plant since microwave heating reduces the “cold centre” in a coke oven. Obtained coke strengths were slightly lower than for a commercial coke but still of a high quality. It was also shown that the admixture of chrome ore resulted in its partial reduction which will be advantageous to the ferrochrome industry since this method allows for recycling of fines without additional pelletisation. The results also showed that microwave energy has the potential to be employed during commercial coke formation, either on its own or as a hybrid technology.

The Design of Microwave Cavity Resonator Used for Measuring the Moisture Content in Plant Leaves

This paper designs the cavity parameters of rectangular microwave cavity resonator, mainly including the design of cavity size, coupled diaphragm radius, and the position to place leaf, to make the largest power of resonant cavity and most significant impact on S11 parameters when the dielectric constant changes. Then conducts optimized analysis with finite element analysis software HFSS, gains the relation between dielectric constant and resonator parameters within the 3.2GHz-3.8GHz swept frequency range, and analyzes the simulation results. Finally, concludes the application sphere of cavity resonator designed in this paper according to the multiformity of plant leaves measured, and makes a simple introduction to the improvement methods.

Measurements of electromagnetic wave absorption properties of carbon nanotube–epoxy composites at microwave frequencies around 8.43 GHz

Microwave (8.43 GHz) absorption properties have been measured for multiwalled carbon nanotube (MWCNT)–epoxy composites. A microwave resonant cavity technique was utilized as a probe. Six groups of MWCNT–epoxy composite samples with different MWCNT outside diameters were fabricated and tested. The weight percentages of MWCNTs in each sample group were in the range of 1%–10%. The amplitudes of the absorption profiles, the linewidths at half-power maxima, and the shifts in resonant frequencies under load for the six groups of MWCNT–epoxy composite samples were compared. Similar to our previous results measured at 9.968 GHz [Z. Ye et al., J. Appl. Phys. 108, 054315 (2010)], the microwave absorption properties of our samples strongly rely on two parameters: the number of nanotubes and the density of nanotube bundles. It was found that the measured microwave absorption properties of the samples around 8.43 GHz showed a more sensitive response to the magnetic component of the microwave field rather than the electric component.

Determination of Activated Carbon Residual Life using a Microwave Cavity Resonator

This paper presents the continuation of work conducted jointly between Dstl and LJMU. This unique body of work has been, largely, concerned with detecting the residual life of high performance filter materials using electromagnetic (EM) waves within a resonant cavity. Past work has considered both HEPA [1] and ASZM-TEDA[2] activated carbon filter materials. This paper continues the later work, considering the response of ASZM-TEDA activated carbon through the co-ageing of two distinct batches of the material. The paper briefly introduces activated carbon, discusses theory relevant to the work and the methodology used for investigation. A comprehensive set of results is included which seek to validate this technique for determining the residual lifespan of activated carbon.

Chemical vapour deposition enhanced by atmospheric microwave plasmas: a large-scale industrial process or the next nanomanufacturing tool?

This paper describes several specific aspects of atmospheric plasma deposition carried out with a microwave resonant cavity. Deposition over a wide substrate is first studied. We show that high deposition rates (several hundreds of μm h−1) are due to localization of fluxes on the substrate by convection when slightly turbulent flows are used. Next, we describe possible routes to localize deposition over a nanometre-sized area. Scaling down atmospheric plasma deposition is possible and two strategies to reach nanometre scales are described. Finally, we study self-organization of SiO2 nanodots deposited by chemical vapour deposition at atmospheric pressure enhanced by an Ar–O2 micro-afterglow operating at high temperature (>1200 K). When the film being deposited is thin enough (∼500 nm) nanodots are obtained and they can be assembled into threads to create patterned surfaces. When the coating becomes thicker (∼1 µm), and for relatively high content in HMDSO, SiO2 walls forming hexagonal cells are obtained.

High-rate deposition by microwave RPECVD at atmospheric pressure

The post-discharge of a microwave resonant cavity working at atmospheric pressure is used to enhance deposition of SiO x thin films from HMDSO by chemical vapor deposition. Maximum static deposition rates are close to 150 μm h − 1 for low power consumption per unit of coated width (~ 100 W/cm). Dynamic deposition rates are close to 3.5 nm m s − 1 . The distribution of the coating thickness is heterogeneous over an area of 150 × 90 mm 2. The influence of the main parameters of the process is systematically studied to show how the key reactions, i.e. gas phase synthesis of powders and surface deposition, are correlated.

Combination of Wirebound and Microwave Measurements for In Situ Characterization of Automotive Three-Way Catalysts

Recently, a novel approach for the characterization of the state of automotive catalysts has been proposed, viz., the direct electrical characterization of the catalyst material itself. This direct approach has the potential to do away with the complex models needed by indirect measurement methods to infer the catalyst state, for instance from the oxygen partial pressure outside of the catalyst determined by lambda probes. In this work, we compare two ways of directly observing the catalyst state. Firstly, the electrical conductivity of the catalyst material is determined by wirebound sensors mounted inside of the catalyst and fabricated from catalyst-formulation coated planar interdigital electrodes. Secondly, we employ a contactless method based on the perturbation of the partially filled microwave cavity resonator formed by the catalyst and its metallic housing. For a better understanding of the observed effects, the data obtained at microwave frequencies from engine tests are compared with the local electrical conductivity measurements. It is shown that both methods give a coherent picture of the oxygen loading state of an automotive three-way catalyst and that both methods enable one to follow the progress of reaction fronts inside the catalyst. Furthermore, it is demonstrated that the resonance frequency is strongly correlated with the oxygen load.

Dynamic microwave-assisted extraction coupled on-line with clean-up for determination of caffeine in tea

A rapid method based on dynamic microwave-assisted extraction (DMAE) coupled on-line with clean-up was developed for the determination of caffeine in tea samples. A TM 010 microwave resonance cavity was applied to concentrate the microwave energy. An extraction vessel was placed in microwave irradiation zone of the TM 010 microwave resonance cavity. A silica gel column connected with the extraction vessel was used to remove chlorophyll in tea. The extraction and clean-up procedures were carried out simultaneously in a single step. The DMAE parameters were optimized by the Box–Behnken design. The maximum extraction efficiency was achieved using 70 W of microwave power, 3.5 mL of extraction solvent and 1.0 mL min −1 of extraction solvent flow rate. The limit of detection obtained is 0.012 mg g −1. The RSDs of intra- and inter-day of eight kinds of tea samples are 2.7%–5.4% and 5.1%–7.3%, respectively. The recovery of caffeine in the tea samples is in the range of 88.2%–99.3%.The proposed method has selectivity and sensitivity and considerably less labor and time for determination of caffeine in tea compared with conventional extraction methods, such assoxhlet extractionand liquid–liquid extraction.

変調された電場による電極を用いない有機材料中の伝導度測定の原理と応用

Recently a variety of supra-molecular architectures have been successfully reported based on the strong non-covalent interactions of conjugated molecules, and their feasibility for practical electric materials has been investigated vigorously. The most important parameter determining the performance of electronic devices based on the conjugated supra-molecular architectures is the mobility of charge carriers, however the non-covalent architectures exhibit extremely wide variety of the stacking structures of the component molecules, leading to the several orders of magnitude difference in the value of mobility. The non-covalent interactions to promote supra-molecular architectures are intrinsically anisotropic, thus the value along each axis of a structure gives important insights into not only highly conducting pathways in the materials but also design strategies of the architectures for the optimized electric properties. Conventional techniques of mobility measurements, however, have not been suitable to reveal the anisotropic conductivity because of the difficulty of the electrode fabrication onto the architectures along a variety of axes. The non-contact measurement technique of electric conductivity using a microwave resonant cavity (TRMC) system has been developed, and successfully applied to estimate the value of mobility along each axis of solid supra-molecular architectures. In the present paper, we report the anisotropic nature of electric conduction in several supra-molecular architectures, as well as the direct observation of space-resolved nm-scaled mobility in the bulk solids and interfaces of conjugated molecular materials.

Cavity QED with an ultracold ensemble on a chip: Prospects for strong magnetic coupling at finite temperatures

We study the nonlinear dynamics of an ensemble of cold trapped atoms with a hyperfine transition magnetically coupled to a resonant microwave cavity mode. Despite the minute single atom coupling one obtains strong coupling between collective hyperfine qubits and microwave photons enabling coherent transfer of an excitation between the long lived atomic qubit state and the mode. Evidence of strong coupling can be obtained from the cavity transmission spectrum even at finite thermal photon number. The system makes it possible to study further prominent collective phenomena such as superradiant decay of an inverted ensemble or the building of a narrowband stripline micromaser locked to an atomic hyperfine transition.

Electromagnetic wave absorption properties of carbon nanotubes-epoxy composites at microwave frequencies

This paper focuses on the absorption properties of electromagnetic waves, both electric and magnetic, from multiwalled carbon nanotubes (MWCNTs)-epoxy composites. A microwave resonant cavity was utilized as a probe. Six groups of MWCNT-epoxy composite samples with different MWCNT outside diameters (ODs) were fabricated and tested. The weight percentages of MWCNTs in each sample group were in the range of 1%–10%. The line widths at half-power-maxima, the shifts in resonant frequency under load, and the amplitudes of the absorption profiles for the six groups of composite samples were compared. In general, the MWCNTs with smaller ODs had higher microwave absorption efficiency at 9.968 GHz than the large diameter ones. However, the sample group M5 (OD<8 nm) showed unusual results, a lower microwave absorption than other sample groups, even though the OD of the MWCNTs in the sample group M5 was smaller than those of other groups. The scanning electron microscope analysis and microwave absorption measurements showed that the microwave absorption efficiency of the CNTs was strongly affected by the morphologies of MWCNTs in individual bundles. It was found that a higher density of MWCNTs in the CNT bundles results in relatively lower efficiency in absorbing the microwave fields at the central frequency of 9.968 GHz.

High-$Q$ Tunable Microwave Cavity Resonators and Filters Using SOI-Based RF MEMS Tuners

This paper presents the modeling, design, fabrication, and measurement of microelectromechanical systems-enabled continuously tunable evanescent-mode electromagnetic cavity resonators and filters with very high unloaded quality factors (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ). Integrated electrostatically actuated thin diaphragms are used, for the first time, for tuning the frequency of the resonators/filters. An example tunable resonator with 2.6:1 (5.0-1.9 GHz) tuning ratio and Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> of 300-650 is presented. A continuously tunable two-pole filter from 3.04 to 4.71 GHz with 0.7% bandwidth and insertion loss of 3.55-2.38 dB is also shown as a technology demonstrator. Mechanical stability measurements show that the tunable resonators/filters exhibit very low frequency drift (less than 0.5% for 3 h) under constant bias voltage. This paper significantly expands upon previously reported tunable resonators.

Waveguide effects on quasispherical microwave cavity resonators

The perturbing effect of a waveguide on the boundary of a quasispherical cavity resonator is investigated both theoretically and experimentally. Expressions for the frequency perturbation to the triply degenerate TM1mn and TE1mn modes are derived using cavity perturbation theory. The fields in and around the waveguide are calculated in the static limit using finite-element software. Experiments performed using quasispherical and cylindrical cavity resonators confirm the accuracy and generality of the approach. The impact of this study on attempts to re-determine the Boltzmann constant (kB) by an acoustic resonance technique is briefly considered.