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Via exploring the spin dynamics and transport properties at interfaces of magnetic material/non-magnetic metal bilayers, spintronics advanced many techniques on generation, detection, and manipulation of spin currents, which laid down a foundation for designing spintronic devices. New ideas and methods for manipulating spin are required in the spintronics community. Merging with cavity quantum electrodynamics, magnetic resonance in ferromagnets inside of a microwave cavity, realizes a strong magnon-microwave coupling at room temperature, opening an avenue to manipulate spin and spin current for the spintronics community. Spin-microwave coupling strength was significantly improved by replacing a few spins in a paramagnetic spin system with magnetization in ferromagnetic materials. Thus, a strongly coupled magnon-microwave system offers a hybrid quantum platform with many measures to tune the coupled system, such as an exchange magnetic field, an anisotropy field, controlled coupling strength, controlled damping parameters, and so on. Many devices were proposed and demonstrated with potential applications. In this review, we briefly introduce the concept and mechanism of magnon-microwave coupling, a classical electrodynamical coupling model for the coupling, spin currents produced by the coupled magnon, and manipulation of the spin current via the strong coupling. In ferromagnets, magnons can couple to a microwave mode as a magnon-polariton propagating in the materials. The strongly coupled magnon-microwave system is a magnon-polariton in a cavity where the microwave was confined as a resonance mode with a high quality factor. Using the Landau-Lifshitz-Gilbert equation and Maxwell equations, we introduce the classical electrodynamical coupling model and reveal that the magnon is driven by a torque produced by the microwave magnetic field on the magnetization and the microwave is feedback via Faraday’s law. Therefore, the coupling strength of the magnon-microwave system can be controlled by changing the torque. Magnon-microwave coupling is experimentally studied using many techniques, such as microwave transmission, Brillouin light scattering, Faraday rotation measurement, and spin pumping electrical detection. Spin pumping is well explored in the spintronics community as a spin current produced by magnon and detected as a voltage via inverse spin Hall effect in a novel metal. Combining with microwave transmission of the coupled microwave subsystem, spin pumping electrical detection by directly detecting the spin current produced by the magnon subsystem in the coupled system, illustrates a more complete profile of the coupled magnon-microwave system. In addition, the strongly coupled magnon-microwave system offers a new technique to manipulate spin currents. We experimentally demonstrate that spin currents produced by the strongly coupled system are correlated with each other mediated by the microwave cavity, and can be manipulated remotely. Two almost identical magnet samples are used to couple to a cavity and the coupling strengths between each magnet and the cavity are tunable individually. By using electrical detection to locally detect each magnet sample respectively, we find that the spin currents produced by two magnet samples are coherently correlated. By tuning the coupling strength of one magnet sample to the cavity, the spin current produced by the second magnet sample is manipulated distantly over a few centimeters, which is far longer than the distance of spin-orbit interaction or exchange interaction. This distant control is only limited by the coherence length of the microwave and the dimension of the cavity. This flexibility opens the door to improve spin current generation and manipulation for cavity spintronic devices.

A hybrid Microwave-assisted Chemical Vapor Infiltration (MW-CVI) pilot plant to produce silicon carbide-based Ceramic Matrix Composites was designed, built and setup, as a part of the European project HELM. Being different from the existing lab-scale MW-CVI equipment, this pilot plant was designed with the idea of a further industrial scale-up. In order to enable the infiltration of the large samples of interest in industrial applications, the reactor was designed with the internal microwave cavity acting as an overmoded resonator at the frequencies of interest. The designed pilot plant allowed proper microwave heating of cylindrical samples of diameter doubled with respect to typical lab-scale preforms, with reproducible operating conditions in terms of transmitted/reflected power. First infiltration trials resulted in an average reaction efficiency of 25 % with the desired inside-out silicon carbide infiltration. The main steps of the design and the results of the first infiltration tests are discussed in this paper.

We describe the observation of a previously unreported resonance phenomenon in UWB SAR imaging and its application in a novel scheme for the retrieval of thickness and dielectric properties of scene features. The resonance was observed in a 14–50 GHz laboratory study of very high resolution SAR imagery. It presented as a periodic fluctuation in the backscatter of a scene feature in response to changes in the radar measurement frequency. The complimentary static reflectivity measurements of a range of dielectric materials showed the phenomenon could be understood as a material behaving as a resonant microwave cavity. Modeling simulations were able to accurately reproduce the observed nulling characteristics for visually homogeneous materials (acrylic, MDF, and plasterboard) and which displayed a regular frequency spacing between nulls. Those with inhomogeneous structures (chipboard and plywood) showed much more irregular nulling patterns. The spacing of the backscatter nulls is set by the product of the permittivity and thickness of the material. By exploiting diversity in viewing geometry, the two terms can be separated and measured. The scheme offers a new opportunity in the SAR surveillance and monitoring of man-made structures.

In this study, the main focus is laid on the design of an optoelectronic converter as a part of the quantum radar to enhance the entanglement between retained and returned modes at high temperatures. The electro-opto-mechanical converter has been widely studied, and the results showed that the operation at high temperature is so crucial to generate and preserve the entanglement between modes. The main problem arises because the mechanical part operating at a low frequency leads to a large number of thermally excited photons, and eventually, the entanglement between modes becomes lost. To solve the problem, we replace the mechanical part with the optoelectronic components. The optical cavity is coupled to the microwave cavity in the newly designed system through a Varactor diode excited by a photodetector. As the main goal, to improve the entanglement sustainability, the effect of the coupling factor of the microwave cavity to photodetector is investigated. The results show that the mentioned factor creates some degrees of freedom to enhance the entanglement at high temperatures compared to the electro-opto-mechanical converter. At some specific values of the coupling factor, the retained and returned fields remained completely entangled up to 5.5 K and partially entangled around 50 K.

Analytic solution of semiclassical dynamics equations of the Dicke model in a superradiant state is presented. The time dependences of the amplitudes of superradiant photonic condensate and coherent population of two-level atomic array in the microwave cavity prove to be expressed via Jacobi elliptic functions of real time and manifest existence of an adiabatic invariant of motion in the strongly coupled system. The periodic beatings of the photonic and atomic coherent state amplitudes are shifted in time revealing an effect of “bound luminosity,” when energy stored in the two-level system during “darkness” in the cavity is suddenly converted into photonic condensate that “illuminates” the cavity for half a period, before it plunges into “darkness” again.

The electron density of the nonstationary atmospheric pressure discharge in a helium flow is estimated using microwave cavity resonance spectroscopy. For this, a measurement scheme was developed based on a spectrum analyzer and a cylindrical resonator with the first three transverse electric (TE) eigenmodes in the range of 1–1.5 GHz. The main working mode was the TE TE112 mode, which made it possible to place the high-frequency measuring and discharge power supply circuits in the most optimal geometry. By measuring the eigenfrequency shift of this mode and its $Q$ factor, gas-discharge plasma parameters were calculated using the well-known perturbation theory. The results are in good agreement with the known data from the literature. This method was additionally tested on a glass rod and a thin low-pressure gas discharge tube.

Overcoming poor readout is an increasingly urgent challenge for devices based on solid-state spin defects, particularly given their rapid adoption in quantum sensing, quantum information, and tests of fundamental physics. However, in spite of experimental progress in specific systems, solid-state spin sensors still lack a universal, high-fidelity readout technique. Here we demonstrate high-fidelity, room-temperature readout of an ensemble of nitrogen-vacancy centers via strong coupling to a dielectric microwave cavity, building on similar techniques commonly applied in cryogenic circuit cavity quantum electrodynamics. This strong collective interaction allows the spin ensemble’s microwave transition to be probed directly, thereby overcoming the optical photon shot noise limitations of conventional fluorescence readout. Applying this technique to magnetometry, we show magnetic sensitivity approaching the Johnson–Nyquist noise limit of the system. Our results pave a clear path to achieve unity readout fidelity of solid-state spin sensors through increased ensemble size, reduced spin-resonance linewidth, or improved cavity quality factor., Conventional optical readout limits the sensitivity of solid state spin sensors due to photon shot noise and poor contrast. Here, the authors demonstrate room-temperature microwave detection of an ensemble of NV centers embedded in a microwave cavity, which offers high-fidelity readout without time overhead.

Background: Nowadays the disposal or recycling of polyethylene terephthalate (PET) material is a real-world problem. The European Union’s DEM3TO project aims at recycling PET to return it to the main chemical components with which it was produced. In a specific reactor, microwave radiation is used to quickly depolymerise the initial polymer. At the end of the de-polymerization process, a filtering and drying process through an agitated Nutsche filter (ANF) is necessary. Methods: This study aims to design and develop a High Frequency (HF) cavity inside the ANF (plugin “HF-ANF”) to speed up and improve the drying process. The effects studied are the efficiency of the HF cavity as a function of the heating process, the evaporation/drying process, and the mechanical mixing (due to the blades) of the mixture. Results: During these studies it was possible to improve the efficiency of the HF plugin and allowing to absorb more than the 95% of the microwave energy into the mixture to increase the drying speed and the drying homogeneity of the ANF. In addition, the mixture was characterised to obtain the dielectric proprieties as a function of the temperature of the ANF and the concentration of the residual water. Conclusions: The study allowed us to develop some important methodology that usually cannot to be simulated in a non-multi physics simulator. The careful modelling of certain aspects that are not normally available in EM (Electro-Magnetic) simulators, like variable geometries, mixed material, heating effect and the dielectrics characterization process are difficult and critical process but are very important steps to be undertaken in order to obtain results that can be compared with real measurements.

We present an experimental characterisation of the electrical properties of 3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant microwave cavity resonator. The resonator was cooled to temperatures below the critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while measuring the quality factors of the electromagnetic resonances. This was then compared with finite element analysis of the cavity and a measurement of the same cavity with an Aluminium post of similar dimensions and frequency, to extract the surface resistance of the Niobium post. The 3D-printed Niobium exhibited a transition to the superconducting state at a similar temperature to the regular Niobium, as well as a surface resistance of $3.1\times10^{-4}$ $\Omega$. This value was comparable to many samples of traditionally machined Niobium previously studied without specialised surface treatment. Furthermore, this study demonstrates a simple new method for characterizing the material properties of a relatively small and geometrically simple sample of superconductor, which could be easily applied to other materials, particularly 3D-printed materials. Further research and development in additive manufacturing may see the application of 3D-printed Niobium in not only superconducting cavity designs, but in the innovative technology of the future., Comment: 5 pages, 4 figures

Sample preparation is one of the most time-consuming steps in diagnostic assays, particularly those involving biological samples. In this paper we report the results of finite-difference time-domain (FDTD) simulations and thermographic imaging experiments carried out with the intent of designing a microplate for rapid, high-throughput sample preparation to aid diagnostic assays. This work is based on devices known as microwave lysing triangles (MLTs) that have been proven capable of rapid sample preparation when irradiated in a standard microwave cavity. FDTD software was used to model a microplate platform as a polystyrene substrate with an array of various passive scattering elements (PSEs) of different sizes, shapes, and interelement spacings in a 2.45 GHz field identical to that of a common microwave oven. Based on the FDTD modeling, several PSE arrays were fabricated by cutting PSEs out of aluminum foil and adhering them to the bottom of regular polystyrene microplates to make prototypes. Each prototype microplate was then irradiated in a microwave cavity for a range of different times, powers, and source angles and the heating effects were observed via a forward looking infrared (FLIR) camera. Based on the results, two prototype microplate platforms have been shown to demonstrate electromagnetic and thermal enhancements similar to those seen with MLTs as well as tunable thermal responses to radio frequency (RF) irradiation.

The accurate measurement of the internal dimensions of closed cavities with conducting walls without the access of measuring tools inside the cavities is relevant when measuring the parameters of radio materials and the dimensions of metal vessels with limited access to them, when clarifying the Boltzmann constant, and when conducting gas thermometry and other tasks. This article presents the results of measuring the internal dimensions of cavities, namely, microwave cavity resonators, by considering the range of their resonant frequencies. The differences between the eigenfrequency and resonant frequency in a resonator with perfectly conducting walls and those in a real resonator with impedance walls are clarified. The types of functions suitable for describing the resonant amplitude-frequency characteristics of real resonators are analyzed. This article also presents the results of measuring the inner diameter and length (height) of microwave resonators from the State Primary Standard for the units of complex dielectric permeability (GET 110-2012) with frequencies ranging from 1 to 178.4 GHz.

Utilizing 3D printing to create custom microwave filters has promising aspects such as light weight and low cost, most importantly including the fact that complicated structures can be printed quickly and inexpensively. Some SLA resins have very high Coefficient of Thermal Expansion (CTE) compared to metal, so SLA 3D printed microwave filters can have frequency responses that are strongly dependent on temperature-a serious problem for narrow band filters. The presented technique overcomes this limitation, and in fact yields an SLA 3D printed filter with better temperature stability than an uncompensated metal 3D printed or a conventionally machined metal filter. Two 3D printed, temperature compensated microwave cavity notch filters have been fabricated using stereolithography (SLA) resins. Both use two different values of CTE for compensation. The 3D printed plastic parts are electroplated with copper. One filter consists of a resonant cavity with the TE011 mode coupled to a TE10 waveguide. The other is a TE101 resonant cavity coupled to TE10 waveguide. As temperature increases, the side walls of the cavities grow, lowering the resonant frequency. At the same time, for the TE011 cavity, an end-wall tuning plunger made of stereolithography resin with a higher CTE than the cavity walls expands at a faster rate. The end wall expansion increases the resonant frequency. In the case of the TE101 cavity, a metallic plunger expands much more slowly than the cavity and effectively withdraws as temperature increases, which increases the resonant frequency.

In this article, an attractive resonant technique is devised for calculating the dielectric properties of arbitrary length material under test (ALMUT), which is partially filled inside a waveguide cavity sensor. The proposed technique exempts two major assumptions viz. the depolarization effect and the theory of images, which were neglected in earlier cavity perturbation methods. A numerical model of the depolarizing factor, which precisely considers the impact of the relative permittivity and the sinusoidal variation of the electric field, is also formulated. First, the technical modification and the numerical analysis are provided and after that, a new set of formulas for characterizing the complex permittivity of ALMUT is developed. The numerical results suggest the accuracy and validity of the scheme for a broad range of dielectric samples, including the typical case, i.e., the full-length dielectric sample. The novelty of the presented technique can be ascertained from the fact that it provides higher accuracy irrespective of the actual sample length when compared with standard cavity techniques. A few standard dielectric samples with the partially filled arrangement are measured using the WR90 cavity, and the results are compared with their corresponding values obtained using the earlier reported conventional and modified techniques. It is found that the results evaluated using the devised scheme are consistent and independent of the actual dimensions of ALMUT. On the other hand, error in estimated complex permittivity using the earlier reported approaches shows substantial dependence on the sample size.

Many simulations employed in microwave heating simplify the geometric model of the microwave cavity to reduce the complexity of the model. Some detailed design features of the cavity, such as magne...

The article studies the attenuation of vacuum Rabi oscillations for a system of two superconducting solid-state qubits placed in a high-Q microwave cavity. Two different cases are considered in which: 1) the first qubit is excited at the initial time and 2) the initial state comprises an entangled symmetric and antisymmetric pair of states. The dependence of the attenuation on various parameters, primarily on the coupling constant between qubits and the field and on the distance between qubits, is studied in detail. It is shown that, for some parameters, the relaxation time of the excited state of a qubit in such a system is significantly longer than that of a single qubit in the cavity.

The opto-electro-mechanical system as a quantum interface between electronic information and optical information plays an important role in quantum information processing. Ground-state cooling of the macroscopic mechanical oscillator is a crucial requirement for this system in order to eliminate the effect of thermal fluctuations on transmission of information. Here, we propose a scheme of ground-state cooling for a mechanical oscillator which is coupled to an optical cavity through radiation pressure force and simultaneously coupled to a superconducting microwave cavity through an effective capacitance. Meanwhile, the periodical frequency modulations are applied to the optical mode, microwave cavity, and mechanical mode, respectively. The cooling efficiency is analyzed and cooling dynamics is simulated numerically by means of covariance matrix. The results show that the Stokes heating processes can be suppressed effectively by means of frequency modulations, and the mechanical oscillator can be cooled to near its ground-state with a higher efficiency than that of a standard optomechanical system due to the double cooling channel. Moreover, a complementary cooling effect is found between these two cooling channels, i.e., a high cooling efficiency can be achieved by cooperation between a good optical cavity and a bad microwave cavity, or vice versa. This cooperative cooling of the double channel breaks the limitation of resolved-sideband regime.

[EN] This paper reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house single-port vectorial reflectometer and a resonant coaxial bi-reentrant microwave cavity where the material under test is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semi-solids, powders and granular materials. The relation between the dielectric properties of the involved materials and the cavity resonance has been solved by numerical methods based on mode-matching and circuit analysis. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is de-embedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other well-established instruments and methods. Errors lower than 2% in the dielectric constant, and 5% in the loss factor, are found. This simple, portable, affordable and robust device could help non-specialized personnel to accurately measure dielectric properties of materials used in a wide range of microwave applications., This paper has been financially supported through the grant reference BES-2016-077296 of the call Convocatoria de las ayudas para contratos predoctorales para la formacion de doctores de 2016 by Ministerio de Economia y Competitividad (MINECO) and by European Social Funds (ESF) of European Union and the project SEDMICRON TEC2015-70272-R (MINECO/FEDER) supported by Ministerio de Economia y Competitividad (MINECO) and by European Regional Development Funds (ERDF) of European Union. The Associate Editor coordinating the review process was Samir Trabelsi.

Dielectric measurements offer the possibility of highly sensitive detection of physical cell properties, and are of interest for clinical applications due to their non-destructive nature and the lack of need for cell labelling. Here we report sensitive measurements on single, living, free-flowing cells (not electrostatically or dielectrophoretically trapped, cultured or fixed directly on sensing elements) in aqueous medium at ∼9.8 GHz taken using a coupled dielectric-split ring resonator assembly. Inductive coupling between the two resonators enabled separation of microfluidic chips from RF connectors and allowed for time-resolved continuous-wave measurements on flowing single cells via the coaxial ports of a dielectric-loaded microwave cavity. Analysis via an equivalent circuit model showed that the novel resonator assembly maintained the permittivity-dependent sensitivity of a split ring resonator while operating at quality factors >1000 with lossy aqueous media (typically ∼1900). Using a microfluidic channel with a 300 × 300 μm cross section, at a water-loaded resonant amplitude of ∼−22 dB at 0 dBm input power level, shifts in amplitude due to individual cells passing through the sensing region of up to −0.0015 dB were observed. Correlations between averaged amplitude shifts and cell size as well as material properties demonstrate the diagnostic potential of this technique.

The coupled 3D and transient form of heat and Maxwell’s equations were solved to determine the temperature distribution within a carrot slice in the microwave cavity during pasteurization as a clean and energy saving process. To precisely simulate the turning of the sample, the dissipated thermal energy was applied to the carrot as a rotating heat source field. The temperature evolution pattern through time was determined for various power levels and compared to measured experimental data to validate the simulation. Additionally, an inactivation modeling for Enterococcus faecalis, Bacillus cereus, Staphylococcus aureus and Shigella flexneri based on the cumulative exposure time to the elevated temperatures was proposed. According to the results, it was shown that due to the temperature variation profiles, three inactivation phases (heating process; holding temperature; microwave turn off phase) can be introduced. The most inactivation was occurred through the first and second phases for 600 W and also the temperature level was not sufficiently high to produce a major inactivation for 200 W during the last phase. Additionally, the 400 W microwave power created the highest inactivation of bacteria through the last phase. Based on the obtained results the energy demand of the microwave thermal treatment was 52.3% lower than conventional steam surface pasteurization and also it can be used as a clean process in pasteurization of carrots instead of chemical pasteurization.

In this study, plasmonic opto-mechanical tripartite system is proposed to improve the performance of the traditional tripartite opto-mechanical system. In the new design, significantly, optical cavity and microwave cavity modes are directly coupled to each other. The originality of this work consists in embedding a microsphere in the optical cavity where the plasmon-plasmon interaction between the metal plates generates a plasmon mode inside the optical cavity and changes the electric field distribution. The plasmonic property influences the microsphere electrical properties and interacts with the photonic mode inside the optical cavity by which the microwave cavity properties are also affected through coupling to the optical cavity. Microsphere introduces a capacitor as a function of plasmonic properties that can strongly influence the microwave cavity resonance frequency. That is the feature that we want to utilize to enhance the performance of the system at high temperature. The results show that the optical cavity and microwave cavity modes remain entangled at high temperature. It is contributed to the plasmonic-based capacitor induced by the microsphere which is not affected by the thermally induced photons (noise). It is worth mentioning that the induced noise strongly restricts the traditional tripartite system operated with a wide bandwidth.

We report a high-performance pulsed optically pumped (POP) Rb clock based on a novel magnetron-type microwave cavity. The cavity has a volume of 30 mL, enabling a highly homogenous microwave field distribution. With the laser frequency tuning to the ground-state hyperfine level ${F}= {2}$ of the ${D}_{{2}}$ line, we observe a Ramsey fringe contrast of 52% in terms of optical absorption detection. The resultant shot noise limit is estimated to be ${1.6} \,\times \, {10}^{-{14}}{\tau }^{-\text {1/2}}$ . The clock frequency stability is measured as ${2.3}\,\times \, {10}^{-{13}}\tau ^{-\text {1/2}}$ (1–100 s), which is limited by the relative intensity noise of the light.

We investigated a chemically modified rhodamine B dye as a sensor of local water content in dye-modified epoxy resins, where these measurements were combined with dielectric measurements to estimate the dye-water association ratio in the material. In particular, the water-sensitive fluorogenic dye was covalently attached to the epoxy resin backbone. This dye becomes fluorescent only upon photoactivation by ultraviolet light and its protonation in the presence of water. High-resolution noncontact microwave cavity dielectric measurements on these materials indicate a decrease of the dielectric permittivity upon photoactivation. We utilize this effect to determine the average extent of hydration of the activated dye molecules. Our results suggest that fluorogenic dyes are promising for the quantification of the local water content in polymer materials, such as the technologically important problem of interfacial water in epoxy materials.

In this article, Au/As2Se3/Ag/As2Se3/Yb Schottky barriers are formed and characterized. The devices prepared by the thermal evaporation technique under vacuum pressure of 10−5 mbar are observed to exhibit metal-induced crystallization process when coated onto Au substrates. Electrically, the arsenic selenide-based Schottky devices exhibited typical metal-oxide-semiconductor (MOS) characteristics with a built-in potential of 0.17 eV. The device shows resonance–antiresonance switching, negative capacitance (NC) effect, and high to low conductance switching features in the frequency domain of 10–1800 MHz. In addition, measurement of the impedance, amplitude of reflection coefficient, return loss ( ${L}_{r}$ ), and voltage standing wave ratio (VSWR) spectra in the same domain have shown that the Au/As2Se3/Ag/As2Se3/Yb Schottky barriers display band stop features at 1180 MHz. The ${L}_{r}$ and VSWR values at this critical frequency are 29.1 dB and 1.1, respectively. The electrical characterizations of the Au/As2Se3/Ag/As2Se3/Yb MOS devices have confirmed their suitability for use as parasitic capacitance cancellers, noise reducers, and as switching clock with selective switching time scales of switching delay time less than 0.40 ns.

A versatile, modular in situ high-intensity monochromatic illumination set-up installed on a standard Q-band ESR spectrometer equipped with a cryostat and probe head for measurements at cryogenic temperatures, which can be easily assembled from commercially available optical components is presented. Using as monochromatic light sources pig-tailed laser diodes (LDs) or fiber-coupled light-emitting diodes (LEDs), a high efficiency of the light transfer (more than 95%) through an optical guide inserted in the sample holder is achieved in the sample area of the microwave cavity. With various LEDs and LDs, one can perform ESR in situ illumination experiments from UV to far-IR, in both cw and pulse mode. Its operation is illustrated with an experiment revealing the presence of certain ESR silent defects in oxygen-doped floating-zone ultrapure Si samples irradiated at room temperature with high-energy–high-fluence electron beams and pulse annealed up to 300 °C. New information is obtained by comparing the ESR spectra recorded at T = 120 K, without and with 1.06 µm across-the-gap in situ illumination.

Knowing the advantages of microwave processing on different materials, it has established a good base for the sintering process. Although it has similar advantages for other processes, still other fields are not much established for industrial use. Microwave casting is one of the emerging fields which are yet to be studied in detail. In this paper, a literature review is carried out for the microwave casting of different materials such as metals, metal matrix composites (MCC), etc. Microwave casting is processed under an apparatus that involves microwave hybrid heating (MHH) where heat is transferred to charge using susceptor material. Further depending upon the designed apparatus, microwave casting is divided as in-situ and ex-situ casting processes. If molten material is allowed to solidify inside the microwave cavity is termed as “in-situ” casting while if molten material is allowed to solidify outside the microwave cavity it is termed as “ex-situ” casting. From the review, it can be concluded that the microwave casted materials produce better properties as compared to conventional casting processes in terms of homogeneity and mechanical properties. But most of the research is reported for low melting point materials like Aluminum and their alloys. With the implementation of a new design setup, microwave casting can be used for the materials that are having a melting point above 1000 °C.

In this paper we will describe the characterisation of a rf detection chain based on a travelling wave parametric amplifier (TWPA). The detection chain is meant to be used for dark matter axion searches and thus it is mounted coupled to a high Q microwave resonant cavity. A system noise temperature $T_{\rm sys} = (3.3 \pm 0.1$) K has been measured at a frequency of 10.77 GHz, using a novel scheme allowing measurement of $T_{\rm sys} $ exactly at the cavity output port., Comment: 8 pages

In this paper, we present the design and implementation methods of quarter-wavelength resonators accommodating Beltrami standing waves with parallel electric and magnetic (E‖H) fields. The resonator is bounded by the quarter-wavelength longitudinal electromagnetic conductor (LEMC), the circumferential electromagnetic conductor (CMEC), and the radial electromagnetic conductor (REMC). The LEMC, CEMC, and REMC boundaries are artificially implemented by the circumferentially aligned corrugation, concentrically aligned circular fins, and axisymmetrically aligned radial fins, respectively. The coupling control methods by introducing slots in the CEMC and REMC with the external TM01 and TE01 circular waveguides are presented. We design the quarter-wavelength resonators with the implemented LEMC, CEMC, and REMC boundaries with controlled external couplings and numerically demonstrate their E‖H properties, which confirms the validity of the proposed design method.

This article reports a comparative study of experimental results obtained during the drying of Castilla-variety coffee beans from Santander, Colombia. They were performed by two means: thermal and electromagnetic radiation. Twenty experiments were carried out, ten tests in a microwave cavity at 2,450 MHz-1,080W, and ten tests using a conventional electric oven with temperature controlled at 50 ± 2°C. Experiments were made using samples of coffee beans with parchment, without parchment, and of the only-parchment. For each sample, dimensionless moisture ratio and diffusion coefficients were determined, according to the second law of Fick. We found that the diffusion coefficient of the samples dried in a microwave cavity was twenty-two times higher than the diffusion coefficient of samples dried with thermal radiation. Likewise, it was observed that samples in conventional oven showed a uniform temperature, in contrast with those heated by microwave radiation. Such results are useful for designing hybrid systems for drying coffee beans. RESUMEN El presente artículo reporta los resultados de una investigación experimental, obtenidos en el secado de granos de café variedad Castilla, originarios de Santander, Colombia. Los experimentos fueron llevados a cabo a través de dos técnicas: radiación térmica y radiación electromagnética. Veinte experimentos fueron realizados, 10 en un horno microondas a 2.450 MHz-1.080W, y 10 en un horno eléctrico convencional con temperatura controlada a 50 ± 2°C. Las pruebas fueron hechas a muestras de grano con cascarilla, sin cascarilla y a la sola cascarilla. En cada experimento se determinó la relación de humedad adimensional del proceso de secado, y su coeficiente de difusión, de acuerdo con la segunda ley de Fick. Se encontró que el coeficiente de difusión de las muestras secadas en horno microondas fue veintidós veces mayor que el respectivo coeficiente de las muestras secadas en horno eléctrico. Las muestras secadas por radiación térmica mantuvieron una temperatura uniforme, en contraste con las muestras secadas por microondas. Los resultados son de gran utilidad para el posterior estudio de sistemas híbridos de secado de granos de café.

The aim of this work was to study the spectrum of LF and HF oscillations generated by plasma bunches created and confined in the volume of a microwave cavity immersed in the magnetic field of a mirror trap. The registration of electrostatic oscillations in the plasma was carried out using two flat electrodes mounted diametrically opposite in the central part of the cavity close to its wall. This diagnostic showed the presence of low-frequency oscillations with frequencies of 130 kHz and 450 kHz. The oscillation spectrum in the microwave range was recorded at the minimum of the magnetic trap using a real-time spectrometer and a loosely coupled loop antenna. The registration of the spectra in the 40 MHz band revealed a regular change in the frequency of the fundamental oscillation mode of the cavity and the presence of two harmonics of the synchrotron radiation of the plasma bunch at frequencies of 2.25 GHz and 4.52 GHz, respectively. According to the obtained data, the parameters of the formed bunch (density, shape, volume, energy spectra of plasma components) can be restored.