Cylindrical Microwave Cavity Research Articles

Physics package based on intracavity laser cooling 87Rb atoms for space cold atom microwave clock

Abstract This article proposes a new physics package to enhance the frequency stability of the space cold atom clock with the advantages of a microgravity environment. Clock working processes, including atom cooling, atomic state preparation, microwave interrogation, and transition probability detection, are integrated into the cylindrical microwave cavity to achieve a high-performance and compact physics package for the space cold atom clock. We present the detailed design and ground-test results of the cold atom clock physics package in this article, which demonstrates a frequency stability of 1.2 × 10−12 τ −1/2 with a Ramsey linewidth of 12.5 Hz, and a better performance is predicted with a 1 Hz or a narrower Ramsey linewidth in microgravity environment. The miniaturized cold atom clock based on intracavity cooling has great potential for achieving space high-precision time-frequency reference in the future.

Dual-mode rectangular microwave cavity for precision spectroscopy of hyperfine structure in muonium

Precision microwave spectroscopy of the ground-state hyperfine structure in muonium provides a stringent test of the Standard Model in particle physics. The MuSEUM collaboration is preparing for such a measurement, aiming for precision down to ≈1ppb, utilizing the world’s most intense pulsed muon beam at J-PARC. The measurement of the Zeeman-split structure with an external magnetic field of 1.7T also precisely determines the muon’s magnetic moment (≈10ppb). In the future, improved precision of the magnetic moment can be potentially obtained by measurements with different magnetic field strengths, however, it entails upgrading current cylindrical microwave cavities to rectangular ones. As the first step for the upgrade, we have developed a dual-mode rectangular cavity for the measurement with 2.9T field. The electromagnetic design and production have been established, and frequency sweeping with two desired modes has been successfully demonstrated. Moreover, the overall performance of the measurement at 2.9T field was evaluated with Monte Carlo simulations. These studies pave the way for a further extension of the MuSEUM experiment at various strengths of the magnetic fields.

Dielectric Properties of Carbons in Blast Furnace Dust

This study has presented the cavity perturbation theory applied to measurements of the dielectric properties of carbon materials contained in the blast furnace dust (BFD) at single frequency of around 2.5 GHz using a cylindrical microwave cavity at TM010 mode. In addition, the study shows that multimode microwave cavity system at different TM modes can be used to measure the microwave complex permittivity of these materials in the frequency range of 2 to 8 GHz.

High-volume biological sample processing using microwaves

This paper describes the design and optimization of a 10 ml cartridge for patient sample processing using a 3.5 GHz (empty resonant frequency) TM010 cylindrical microwave cavity. The cartridge has been designed to augment a novel approach for the rapid diagnosis of M. tuberculosis (the causative agent of Ttuberculosis), which uses the direct application of microwaves to a bacteria-containing sample to release pathogen-specific DNA. The target bacterial DNA is then captured and recovered using magnetic nanoparticles coated with pathogen-specific DNA probes. Excitation parameters were optimized using three surrogates for M. tuberculosis, namely, M. smegmatis, M. abscessus, and M. bovis suspended in water and simulated sputum. The paper also explores the mechanism of microwave-mediated DNA release from bacteria using scanning electron microscopy. Examination of bacteria exposed to microwaves at power levels known to mediate the release of DNA reveals no obvious signs of permanent cell disruption, suggesting that a more subtle interaction is taking place. Finally, the presence of microwave-liberated M. bovis DNA was able to be detected at a level of sensitivity comparable to that achieved using microscopy.

Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Introduction. Technologies related to the use of low-temperature atmospheric plasmas are developing at a rapid pace. Creation of new low-temperature plasma sources for specific applications requires monitoring of dynamic processes in such discharges with a high time resolution. Electron concentration is one the most important plasma characteristics, which can be very low for a low-temperature atmospheric pressure plasma. However, the methods currently available for diagnostics of gas-discharge plasmas are either characterized by insufficient sensitivity or unable to monitor dynamic processes in non-stationary discharges. In this regard, the development of new diagnostic approaches to low-temperature atmospheric plasma seems to be a relevant research direction.Aim. To develop a diagnostic method for an atmospheric plasma with a low gas temperature and a low electron concentration in a cylindrical microwave resonator.Materials and methods. The proposed diagnostic method is based on the well-known principle of measuring the frequency shift and the Q-factor of the eigenmodes of the microwave resonator, inside which the plasma under study is located.Results. Measurements of the atmospheric barrier discharge plasma jets in a helium and argon stream in a cylindrical microwave resonator were performed. The proposed geometry made it possible to significantly increase the sensitivity of measurements. It became possible to exclude the effect of polarization degeneracy in a round cylindrical resonator. The developed system was also tested on test objects with a known value of permittivity.Conclusion. A method for microwave diagnostics of stationary and non-stationary cold atmospheric plasma jets in a cylindrical resonator, inside which transmitting and receiving antennas are installed, as well as an orthogonal thin conductor preventing the excitation of undesirable modes, was developed.

Microwave Cylindrical Cavity Resonator Sensor for Detection and Characterization of Contaminants in Lubricating Oil

Accurate monitoring of contaminants, such as wear particles in lubricating oil, is critical for the efficient maintenance of engines. Here, a TE011-mode cylindrical cavity resonator-based sensor system is presented. In the measurement, a glass test tube was used to contain the oil sample under test and placed in the center of the cavity. Particles in oil change the dielectric properties and perturb the resonance parameters, thereby achieving sensing. Sensitivity to both the presence of conductive and nonconductive powders is demonstrated. Linear relationships between the powder weight and the quality factor are established. Hence, the degree of contamination can be better evaluated compared with existing microwave sensors. Powder differentiation can be achieved using the resonance frequency and quality factor. In addition, analytical modeling of the sensing system incorporating field analysis is proposed, and the effective permittivity of the mixture can be determined. The sensor developed is compact, portable, easy to implement, complementary to other approaches for liquid evaluation, and has the potential for high-throughput online measurement.

Machine Learning to Predict Quasi TE₀₁₁ Mode Resonances in Double-Stacked Dielectric Cavities

We have applied machine learning in a neural network to calculate the quasi TE₀₁₁ mode of a cylindrical microwave cavity with two symmetrically stacked dielectric resonators (DRs) inside, with aspect ratios of the overall cavity being limited to the range of 0.25&#x2013;4. The neural network was trained with 99 970 samples and evaluated using 9564 samples from a holdout dataset. The samples were created using a supercomputer to solve random cavity configurations via finite-element method (FEM) programming. The trained neural network predicts the resonant frequency of the quasi TE₀₁₁ mode and expresses the mode in terms of expansion coefficients of empty cavity TE<inline-formula> <tex-math notation="LaTeX">$_{\mathrm {0\,np}}$ </tex-math></inline-formula> modes, from which plots of the electric and magnetic fields can be made. The predictions are extremely quick, taking &#x007E;0.05&#x2013;0.2 s running on a typical personal computer, and are very accurate when judged against the FEM results: the overall median error in the frequency neural network is 0.2&#x0025;, and the overall median error of the expansion coefficients neural network is 0.003&#x0025;. This should allow designers to much more rapidly determine optimal cavity and DR dimensions and other parameters in order to achieve the frequency and mode they desire, with a speedup of approximately <inline-formula> <tex-math notation="LaTeX">$10\,\,000\times $ </tex-math></inline-formula> compared with FEM calculations alone. A link to the Python implementation of our FEM code and our trained neural network code is provided.

Detection and analysis of metallic contaminants in dry foods using a microwave resonator sensor

Current systems for metal detection in dry food processing are limited by relatively large foreign objects and high-cost implementation. These issues are resolved here using a non-contact, cylindrical microwave cavity resonator sensor where food passes through the cavity and metallic objects are detected by a shift in the resonant frequency. Classic perturbation theory is applied to the basic set-up and numerical simulations are used to verify the design of the sensor. A cavity sensor was fabricated with a quartz tube symmetrically located for dry food flow and metal detection. Good performance is demonstrated for a range of foods such as spaghetti, noodles, rice, wheat flour and soy milk powder. It is shown that the resonance frequency shift becomes larger when the foreign body gets closer to the cavity centre. The frequency variation is directly related to the volume of the object, and it is estimated that the minimum diameter of a detectable ball can be lower than 2 mm. For completeness it is also observed that the set-up can be used to detect dielectric objects. A graphical user interface is developed for practical applications. The method proposed is low-cost, convenient, scalable and complementary to other metallic contaminant detection approaches. • A new microwave sensor is developed for metal contamination detection in dry foods. • The presence of a metallic object causes a resonance frequency shift. • Effects of the position, volume and shape of the object are thoroughly studied.

A computational study for the effects of sample movement and cavity geometry in industrial scale continuous microwave systems during heating and thawing processes

Microwave (MW) applications in food processing are used to reduce process time and increase process efficiency. While 915 MHz frequency is dominant for industrial processes, 2450 MHz systems are also observed. Attained temperature uniformity is specific concern with significant effect of the non-uniform electromagnetic field distribution due to the cavity geometry and design. Therefore, the objective of this study was to determine the cavity geometry effect with applied frequency and to present industrial scale continuous process system with a computational approach. A computational model was developed for heating and thawing processes, and experimental validation was completed in a cylindrical MW cavity. Sample rotational movement and cavity geometry effects (conventional rectangular versus cylindrical, ellipsoidal and triangular) were determined, and industrial scale system designs were presented with frequency effect. Temperature change and electromagnetic field distribution were also introduced for improved design. The results demonstrated improved designs for industrial processes.

Compact cyclotron resonance high-power accelerator for electrons

Exact numerical solutions for the single particle equations of motion have revealed conditions for highly nonlinear rapid acceleration near cyclotron resonance for electrons injected into a ${\mathrm{TE}}_{111}$-rotating-mode cylindrical microwave cavity immersed in a uniform axial magnetic field. We dub this the eCRA interaction. Magnitudes of acceleration energy in eCRA are shown to exceed to a large degree the limits for the related cyclotron autoresonance acceleration (CARA) interaction, wherein autoresonance acceleration is sustained for traveling rotating ${\mathrm{TE}}_{11}$-mode waves in a cylindrical waveguide. As with CARA, all injected electrons in an idealized eCRA enjoy equal energy gain without bunching. Injection of high currents that involve heavy beam loading allow acceleration in eCRA to multi-MeV levels for beams with average powers of hundreds of kW and rf-to-beam power efficiencies that exceed 80%. It is shown, to cite one example, that an effective acceleration gradient of over $90\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ can be sustained with a maximum cavity surface field of only $40\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, when producing a 4.5 MeV, 300 kW average power electron beam, with an rf-to-beam efficiency of about 86%. In that example, the cavity operates at 2.856 GHz, and the cavity's average surface heating rate is $100\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$. Other examples are given for beams with over one MW levels of average power and energies up to about 20 MeV. This paper's goal is only to elucidate and give examples of the basic mechanism for the strongly nonlinear acceleration that is predicted to occur in eCRA, rather than to present a particular engineered design. Still, the predicted parameters for an idealized eCRA suggest that practical realizations could emerge to satisfy a range of needs for efficient, compact accelerators for industrial, commercial, and national security applications.

Upconversion Loop Oscillator Axion Detection Experiment: A Precision Frequency Interferometric Axion Dark Matter Search with a Cylindrical Microwave Cavity

First experimental results from a room-temperature tabletop phase-sensitive axion haloscope experiment are presented. The technique exploits the axion-photon coupling between two photonic resonator oscillators excited in a single cavity, allowing low-mass axions to be upconverted to microwave frequencies, acting as a source of frequency modulation on the microwave carriers. This new pathway to axion detection has certain advantages over the traditional haloscope method, particularly in targeting axions below 1 μeV (240MHz) in energy. At the heart of the dual-mode oscillator, a tunable cylindrical microwave cavity supports a pair of orthogonally polarized modes (TM_{0,2,0} and TE_{0,1,1}), which, in general, enables simultaneous sensitivity to axions with masses corresponding to the sum and difference of the microwave frequencies. However, in the reported experiment, the configuration was such that the sum frequency sensitivity was suppressed, while the difference frequency sensitivity was enhanced. The results place axion exclusion limits between 7.44-19.38neV, excluding a minimal coupling strength above 5×10^{-7} 1/GeV, after a measurement period of two and a half hours. We show that a state-of-the-art frequency-stabilized cryogenic implementation of this technique, ambitious but realizable, may achieve the best limits in a vast range of axion space.

Characterisation and analysis of alcohol in baijiu with a microwave cavity resonator

The world's most consumed liquor-baijiu is characterised by measuring the perturbation in the resonance condition of a cylindrical microwave cavity as a function of alcohol content. Compared with other methods, the microwave sensor described here is compact, portable, low-cost and need of a small sample size (<0.1 mL) of liquid. The dielectric properties are obtained from the shift of the resonance frequency and changes in the quality factor. The measurement accuracy is validated by comparison with standard liquid samples, where high estimation accuracy (better than 6%) is achieved. The resonant responses and permittivity of baijiu samples are evaluated, where the alcohol content has a significant effect. Six other types of alcoholic drinks and ethanol-water mixtures were also measured for comparison purposes. From all the experimental results, it is demonstrated that the alcohol by volume can be readily deduced from the regressed functions obtained. In addition, the principal component analysis is successfully applied to the classification of liquids with varied alcohol contents.

Increased flow rate of hyperpolarized aqueous solution for dynamic nuclear polarization-enhanced magnetic resonance imaging achieved by an open Fabry-Pérot type microwave resonator.

A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized state of water protons can be achieved by flowing aqueous liquid through a microwave resonator placed directly in the bore of a 1.5 T MRI magnet. Here we describe a new open Fabry-Pérot resonator as DNP polarizer, which exhibits a larger microwave exposure volume for the flowing liquid in comparison with a cylindrical TE microwave cavity. The Fabry-Pérot resonator geometry was designed using quasi-optical theory and simulated by CST software. Performance of the new polarizer was tested by MRI DNP experiments on a TEMPOL aqueous solution using a blood-vessel phantom. The Fabry-Pérot resonator revealed a 2-fold larger DNP enhancement with a 4-fold increased flow rate compared to the cylindrical microwave resonator. This increased yield of hyperpolarized liquid allows MRI applications on larger target objects.

Characterisation of water in honey using a microwave cylindrical cavity resonator sensor

A low-cost microwave cavity resonator sensor is developed for the assessment of honey. When a liquid sample is placed in the cavity, the resonant responses are significantly changed caused by the material perturbation. From the measurement of standard liquid samples with known permittivity, it is well demonstrated that the electric permittivity can be accurately determined. For the honey-water mixtures with the added water content from 10% to 50% w/w, it is found that the resonance frequency decreases with increasing added water content, and its change conforms to the law of mixture. In addition, there is a linear relationship between the added water content and the real part of the permittivity, and a quadratic relationship is found between the real and imaginary parts of the permittivity. These findings agree well with the results of the mixtures with added water contents below 10%. Hence, both the resonant responses of the cavity and the permittivity obtained can be employed for the indication of adulteration and accurate evaluation of the water content. Further, it is shown that the full penetration of the liquid sample can be achieved. The microwave sensor presented here provides an alternative tool for rapid food evaluation.

Avoided Mode Crossings in Cylindrical Microwave Cavities

Axion haloscope detectors require high-$Q$ cavities with tunable TM$_{010}$ modes whose resonant electric field occupies as much of the full volume of the cavity as possible. An analytical study of the effects of longitudinal symmetry breaking within microwave cavities was conducted to better understand the mode structure. The study revealed longitudinal symmetry breaking of the cavities was the mechanism for avoided mode crossings (AMC) in cylindrical microwave cavities. The results showed the size of the gaps in the search frequency spectrum due to an AMC was roughly proportional to the magnitude of symmetry breaking for small perturbations.

Level attraction and level repulsion of magnon coupled with a cavity anti-resonance

We report on coherent and dissipative coupling between a magnon mode and an anti-resonance of transmission in a cylindrical microwave cavity. By effectively suppressing coherent coupling, we observe the hybridized dispersion to change from level repulsion to level attraction. A careful examination reveals distinct differences in the line shape and phase evolution of transmission spectra between these coupling behaviors. For a quantitative understanding of the interactions between the magnon mode and the cavity anti-resonance, we develop a model which precisely describes our experimental observations, particularly, the signature in the line shape and phase of the microwave transmission. Our work sets a foundation for understanding strong coupling between magnon modes and cavity anti-resonances. In addition, it also confirms the ubiquity of level attraction in coupled magnon-photon systems, which may be helpful to develop future magnon-based hybrid quantum systems.

Measurement of Axially Inhomogeneous Permittivity Distributions in Resonant Microwave Cavities

The cavity perturbation method is a standard technique for material parameter estimation. It typically assumes that the sample consisting of the material under test (MUT) is small. This and other assumptions are violated in in-process measurement scenarios that involve big and inhomogeneous samples. We analyze the limitations of the classical perturbation method and present a new approach toward the measurement of spatially varying material parameters associated with a large sample in a rectangular or a circular cylindrical microwave cavity. The method is based on the measurement of multiple resonance frequencies and quality factors and is validated by numerical and laboratory experiments. It is demonstrated that relative permittivities and conductivities may be measured with typical accuracies on the order of 1%.

Dielectric characterizations and heating behavior of siderite in microwave field

Microwave absorption capabilities of siderite, Fe3O4 and Fe2O3 were investigated by measuring the dielectric characterization (dielectric constant, loss factor and loss tangent) from room temperature to 900 °C using the microwave cylindrical resonant cavity technique at 2450 MHz. There was little change in the microwave absorption capabilities of siderite before 600 °C. As the temperature increasing, the microwave absorption capabilities of siderite increased sharply due to the generation of Fe3O4. However, the microwave absorption capabilities of siderite decreased when temperature higher than 900 °C, which was attributed to the formation of Fe2O3 by the oxidation of Fe3O4. The microwave heating behavior of siderite was studied and the result showed that the heating rate of siderite became slower when temperature higher than 550 °C, this was because amount of decomposition reaction of siderite occurred in this stage which consuming large amounts of heat.

Phase-matching of multiple-cavity detectors for dark matter axion search

Conventional axion dark matter search experiments employ cylindrical microwave cavities immersed in a solenoidal magnetic field. Exploring higher frequency regions requires smaller size cavities as the TM010 resonant frequencies scale inversely with cavity radius. One intuitive way to make efficient use of a given magnet volume, and thereby to increase the experimental sensitivity, is to bundle multiple cavities together and combine their individual outputs, ensuring a phase-matching of the coherent axion signal. We perform an extensive study for realistic design of a phase-matching mechanism for multiple-cavity systems and demonstrate its experimental feasibility using a double-cavity system.

Magnetoresistance in copper at high frequency and high magnetic fields

In halo dark matter axion search experiments, cylindrical microwave cavities are typically employed to detect signals from the axion-photon conversion. To enhance the conversion power and reduce the noise level, cavities are placed in strong solenoid magnetic fields at sufficiently low temperatures. Exploring high mass regions in cavity-based axion search experiments requires high frequency microwave cavities and thus understanding cavity properties at high frequencies in extreme conditions is deemed necessary. We present a study of the magnetoresistance of copper using a cavity with a resonant frequency of 12.9 GHz at the liquid helium temperature in magnetic fields up to 15 T utilizing a second generation high temperature superconducting magnet. The observations are interpreted to be consistent with the anomalous skin effect and size effect. This is the first measurement of magnetoresistance at a high frequency (>10 GHz) in high magnetic fields (>10 T).