High-power Microwave Radiation Research Articles

Investigation of the Process of Absorption of Microwave Radiation Generated by a Powerful Gyrotron in Powder Mixtures Al2O3/Pd

In this work, we investigated the energy input of high-power gyrotron microwave radiation into mixtures of Al2O3/Pd powders for various concentrations of the initial components. It was found that the absorption coefficient of microwave radiation as a result of the start of microdischarges (breakdowns) n the powder mixture depends on in the Pd concentration in the initial mixture with aluminium oxide (Al2O3) in a complex way. It is shown that the addition of a catalyst, carborane (C2H2B8), with a concentration equal to 10% of the mass of the initial Al2O3/Pd mixture increases the number of breakdown in the experimental session.

A Systematic Review of HPM Energy Absorbers for Building Applications

A modern weapon, high power microwave (HPM) pulses, can have a profound effect on the quality of functioning of society as the use of this weapon can result in damage to or destruction of electronic equipment and computer and telecommunications systems, both military and civilian. Protection against the energy of HPM pulses can be achieved in two basic ways: by using radiation-absorbent materials (RAM) or artificial electromagnetic (EM) structures. If the object to be protected is a building, protection based on RAM is used. Hence, this literature review focuses on the possibilities of using HPM energy absorbers in building products and structures. Attention is concentrated on four basic types of elements: claddings, concrete and mortar, small-sized elements (bricks, hollow masonry units), and paint coatings. In each of the categories, examples of HPM radiation absorbers having a high potential to be combined with basic construction materials are given on the basis of the literature on the subject.

Methods of Protecting Buildings against HPM Radiation—A Review of Materials Absorbing the Energy of Electromagnetic Waves

The pulsed high power microwave (HPM) technology has been developed worldwide for over 20 years. The sources of HPM pulses are a weapon of mass destruction. They pose danger especially to computer and telecommunications equipment and systems, both the military and civilian ones. This paper presents a survey of literature on electromagnetic wave radiation absorbing and shielding materials to be used in construction. Relevant protective measures should include the shielding of buildings or their parts and the absorption of radiation by building envelopes and their elements. The main focus is on the possibilities of improving the shielding and absorptive properties of common construction materials, such as concrete, mortars and synthetic resins. The survey covers the following groups of materials: carbon-based admixtures, nickel powder, iron powders, ferrites, magnetite and polymers. The final part of the survey is devoted to hybrid foam microwave absorbers in which the shape of the material’s inner structure and that of its surface play a special role.

Design and preliminary experiment of a disk-beam relativistic klystron amplifier for Ku-band long-pulse high power microwave radiation

Spatial coherent combination of multiple high power microwave (HPM) sources is considered as a promising scheme to improve the equivalent radiation power of the HPM system dramatically. Relativistic klystron amplifier (RKA) is one of the most suitable sources for the coherent power combination owing to its specific capabilities of stable microwave frequency and controllable phase. However, the RKAs operating at high frequency-band are severely limited by the problems of the intense space-charge effect and radio frequency breakdown. The radial-line HPM sources driven by the disk-shape electron beam may provide the potential to alleviate this issue due to its attractive features of the weak space-charge effect, the high power handling capacity, and the strong electron collection ability. In this paper, a disk-beam relativistic klystron amplifier (DB-RKA) is proposed and physically designed aiming to generate long-pulse HPM radiation at Ku-band. The physical idea, design principles, and simulation results are presented in detail. In a preliminary experiment, the disk-shape intense electron beam is well focused with an axial-width of 1.2 mm by an improved magnetic-excited method. Furthermore, the DB-RKA is demonstrated to be capable of generating Ku-band HPMs typically with peak power of 320 MW, pulse duration of 100 ns, and gain of 42 dB.

Spike leakage characteristic of limiter irradiated by high power microwave

In this work, the response characteristics of the microwave limiter under various high power microwave irradiation are investigated via both simulation and experiment, and the simulation results match those of the experiment well. When the input power exceeds 6 dBm, a spike leakage phenomenon is observed. As the input power increases, the rise time and pulse width of the leakage peak decrease, whereas the leakage power gradually increases. However, the leakage power of the plateau firstly linearly increases, then gradually decreases, and finally slightly increases. Moreover, the pulse width and repetition frequency have almost no influence on the characteristics of leakage pulse, and the leakage energy decreases as the injection power increases.

Preliminary investigation of a magnetically insulated relativistic backward wave oscillator operating in the C-band with low magnetic field

The design and preliminary results for a C-band relativistic backward wave oscillator (RBWO), which is magnetically well insulated, are presented. Under an external magnetic field of 0.36 T, the RBWO generated high power microwave radiation with a power of 3.3 GW and a frequency of 4.37 GHz for a diode voltage of 870 kV and a beam current of 13.5 kA. The electric field on the surface of the cathode holder was below the emission threshold, and an inlaid graphite cathode was designed to suppress the shunting current in the diode area. The device, operating with a low magnetic field and diode insulation, is a promising candidate for use as a permanent magnet package in high power microwave systems.

Mechanism of AlGaAs/InGaAs pHEMT Nonlinear Response Under High-Power Microwave Radiation

With the development of microelectronic technology, the reliability of devices in a complex electromagnetic environment has become one of the greatest challenges in the semiconductor industry. On this basis, a phenomenon of nonlinear transient response is observed in high-power microwave (HPM)-radiating AlGaAs/InGaAs pseudomorphic high-electron-mobility transistors (pHEMTs). This abnormal response is induced before the thermal failure, causing disturbances to the circuit. To understand this phenomenon, a detailed mechanism analysis is proposed. The analysis shows that the nonlinear response is initially associated with the 2DEG velocity saturation, then a breakdown process is induced by the tunneling and impact ionization combined effect. Within each radiation period, the channel current changes its direction twice under the influence of the HPM field. The nonlinear response current $I_{d}$ is derived from the theoretical analysis. TCAD simulations demonstrate the saturation and breakdown process. Corresponding experiments are performed using a Ka-band low-noise amplifier (LNA) chip. The results support the theory well.

Review of the relativistic magnetron

The cavity magnetron is the most compact, efficient source of high-power microwave (HPM) radiation. The imprint that the magnetron has had on the world is comparable to the invention of the nuclear bomb. High- and low-power magnetrons are used in many applications, such as radar systems, plasma generation for semiconductor processing, and—the most common—microwave ovens for personal and industrial use. Since the invention of the magnetron in 1921 by Hull, scientists and engineers have improved and optimized magnetron technology by altering the geometry, materials, and operating conditions, as well as by identifying applications. A major step in advancing magnetrons was the relativistic magnetron introduced by Bekefi and Orzechowski at MIT (USA, 1976), followed by the invention of the relativistic magnetron with diffraction output (MDO) by Kovalev and Fuks at the Institute of Applied Physics (Soviet Union, 1977). The performance of relativistic magnetrons did not advance significantly thereafter until researchers at the University of Michigan and University of New Mexico (UNM) independently introduced new priming techniques and new cathode topologies in the 2000s, and researchers in Japan identified a flaw in the original Soviet MDO design. Recently, the efficiency of the MDO has reached 92% with the introduction of a virtual cathode and magnetic mirror, proposed by Fuks and Schamiloglu at UNM (2018). This article presents a historical review of the progression of the magnetron from a device intended to operate as a high-voltage switch controlled by the magnetic field that Hull published in 1921, to the most compact and efficient HPM source in the twenty-first century.

A multibeam metamaterial backward wave oscillator

Microwave sources transform the kinetic energy of an electron beam into microwaves through the interaction of electrons with a periodic slow wave structure (SWS). A metamaterial (MTM) waveguide is proposed for use in a microwave oscillator instead of a conventional periodic SWS that has been used for a long time to generate high power microwave radiation. MTMs have interesting properties such as the negative refractive index, low group velocity, and below cutoff propagation, among others. In this work, we study the interaction of a multibeam cathode with a set of MTM structures inside a cylindrical waveguide. We developed a structure comprising a number of MTM metallic plates that have periodicity in the axial direction and are repeated in the azimuthal coordinate. Using eigenmode simulations, we obtained negative dispersion around the operating frequency where the group velocity is negative and extremely small. The fully electromagnetic, relativistic particle-in-cell codes MAGIC and CST Particle Studio and the fully electromagnetic software tool CST Microwave Studio were used to obtain the results in this study.

Radiation Spectra of the Plasma Relativistic Microwave Oscillator

The spectral composition of high-power microwave radiation of the plasma relativistic oscillator in the range of 1−4 GHz was studied experimentally as a function of the plasma density and the cavity length and configuration. The duration of the generated microwave pulse was in the range of 250−400 ns, and its total energy reached 15 J. The main features of the spectral composition for different cavity configurations are explained.

A GW-level Ku-band oversized coaxial relativistic Cerenkov generator with low guiding magnetic field

A novel coaxial relativistic Cerenkov generator (CRCG) operating in quasi-transverse electromagnetic mode is proposed for generating Ku-band high-power microwave radiation. It is found that using a cathode with a shielding electrode can decrease the diffusing electric field in the diode, thereby allowing a CRCG with the proposed diode structure to operate in a low guiding magnetic field. Taking advantage of the two-sectional slow wave structure, the output power and conversion efficiency are improved. Furthermore, a simple optimization rule is proposed for the length of the drift cavity and is verified by numerical simulation. In a particle-in-cell simulation, when the diode voltage and beam current are 550 kV and 4.2 kA, respectively, the microwave with an output power of 1 GW at 15.3 GHz is achieved in a guiding magnetic field of 0.35 T, yielding a conversion efficiency of 43%.

Microwave Pretreatment and Enzymolysis Optimization of the Lotus Seed Protein.

Pretreatment with a microwave was conducted before enzymolysis and shown to enhance the enzymolysis, which changed the secondary structure of the lotus seed protein. Under high-power microwave irradiation, sub bonds of the protein were broken, causing disaggregation and unfolding of the secondary structure, namely a decrease in the intermolecular aggregate structure and increase in the random coil structure, making the protein bonds susceptible to papain in the enzymolysis. On the other hand, a response surface methodology (RSM) was launched to investigate the influence of the enzymolysis process variables on the DH (degree of hydrolysis). The statistical analysis revealed that the optimized conditions were a protein substrate concentration of 15 g/L, pH of 5.5, enzymolysis temperature of 57 °C, papain amount of 0.5 g/L, and enzymolysis time of 45 min, for which the predicted value of the DH was 35.64%. The results indicated that a microwave also had better potential for applications in the enzymolysis of foods.

Feedback process study in over-sized backward wave oscillator

Internal field emission breakdown in the electro-dynamic structures of high-power microwave devices can seriously limit the devices’ output power and pulse duration. So an over-sized backward wave oscillator (BWO) is developed to increase the diameter of the electro-dynamic structure beyond the cut-off radius, and reduce these internal fields to levels, which are below critical breakdown levels. As a typical high power microwave (HPM) device, the oversized BWO is widely used and investigated. But some interaction phenomena between the beam and the microwave field in the device are not clearly understood because the beam-loaded effect is so obvious. And the physical process for the interaction is also considered to be complicated. Here as an oscillator, the feedback process is very important in the microwave device, which includes the oversized BWO. So the interaction process between the beam and the oversized BWO is explored from the feed back process instead of the field in the device. Then the physical mechanism for the feedback process in the oversized BWO is explored both in theoretical investigation and in particle-in-cell simulation. And the equivalent circuit is established for such a purpose. The mode control mechanism is explored based on the equivalent circuit. Finally an over-sized backward wave oscillator with rectangular profile corrugations is designed to produce TM<sub>01</sub> high power microwave radiation without mode-competition. An RF power of 7.9 GW at a frequency of 8.68 GHz is obtained in the particle in cell simulation driven by the beam with a beam voltage of 1 MW and a current of 20 kA, and the corresponding efficiency is 39.5%.

Shielding Effectiveness and HPM Vulnerability of Energy-Saving Windows and Window Panes

In this paper, we report results from shielding effectiveness measurements on energy-saving windows and individual, coated window panes of different generations, as well as results from high-power microwave irradiation on single panes. Shielding effectiveness was measured with two complementary methods: first, with near isotropic irradiation in nested reverberation chambers, and the other with irradiation at normal incidence in a semianechoic chamber. The measurements show that the construction of the energy conserving windows has a clear impact on how well they attenuate radio frequency signals. The more modern the window or pane, the higher is the shielding effectiveness. The high-power irradiation on coated panes showed that depending on the type of coating, hotspots can build up causing the coating to crack and, hence, deteriorate the shielding effectiveness. These results may serve as guidance when reviewing high-altitude electromagnetic pulse (EMP), high-power microwave, or intentional electromagnetic interference protection of critical infrastructures, and provide assistance in the work with reduction of compromising emanations.

Experimental study of the dynamics of microwave pyrolysis of peat

The work is devoted to the study of the effect of high-power microwave radiation on sphagnum peat. To implement the microwave pyrolysis process, a laboratory unit based on a coaxial resonator has been created. An industrial magnetron with a frequency of 2.45 GHz was used as a source of microwave radiation. Samples of gas, liquid and solid phases were obtained and analyzed. Studies of soft microwave pyrolysis in conditions of constant removal of gaseous reaction products were carried out. A comparative analysis of the products obtained in microwave pyrolysis and pyrolysis with thermal heating was performed. The aim of the research is to create highly efficient environmentally friendly technologies for processing biofuels with a high yield of combustible gases, suitable for further use in power plants, as well as the production of resinous fraction and carbon residue.

“The popcorn effect”: obtaining of the highly active ultrafine nickel hydroxide by microwave treatment of wet precipitate

Nickel hydroxide is widely used as an active material of supercapacitors. The most active are samples of Ni(OH) 2 with (α+β) layered structure synthesized in a slit diaphragm electrolyzer. However, the processes that occur during filtering and drying , negatively impact electrochemical activity. The influence of microwave treatment of different times (from 0.5 to 5 min) on the structure, surface morphology and porous structure, and also on the electrochemical properties of nickel hydroxide samples prepared in a slit diaphragm electrolyzer , has been studied. A hypothesis was proposed on the existence of the “popcorn effect”: short-term high-power microwave irradiation of the wet sample would result in water boiling and internal explosion of the sample. Treated and untreated samples were studied by means of X-ray diffraction analysis, scanning electron microscopy and BET nitrogen adsorption-desorption. Electrochemical characteristics were studied by means of galvanostatic charge-discharge cycling in the supercapacitor regime. The existence of the “popcorn effect” has been confirmed by increased sample thickness after microwave treatment by 1.94 times, specific surface area 2.13 times, pore volume by 2.66 times, and average pore diameter by 1.46 times, It was discovered , that increasing treatment duration to 2–5 min leads to microwave drying. XRD results revealed the occurrence of ageing (crystallization) processes of nickel hydroxide during thermal drying and their absence upon realization of the “popcorn effect”. This results in the formation of X-ray amorphous samples. Comparative analysis of electrochemical characteristics of treated and untreated Ni(OH) 2 samples was performed. An increase of specific capacity at high current densities (80 and 120 mA/cm 2 ) for treated samples was observed: by 10.9 % upon microwave drying, 24–42 % upon realization of the “popcorn effect”. The maximum capacity of 231.1 F/g has been observed for the sample, in which the “popcorn effect” was realized the most. However, microwave treatment resulted in lower capacities at low cycling current density. This is related to the thermal treatment of the particle surface, caused by rapid boiling of water. A magnetron of a higher power is required for avoiding this negative effect

Dynamic regimes of kinetic instabilities under conditions of double plasma resonance in mirror-confined plasma

The processes of plasma waves excitation under conditions of a double plasma resonance in a non-equilibrium plasma produced by high-power microwave radiation and confined in an open magnetic trap are studied. Two different dynamic regimes of kinetic instability have been experimentally observed: besides the generation of quasiperiodic series of short (∼50 ns) radiation pulses, a new scenario of instability in the form of generation of a single pulse of large (∼25 μs) duration with a slowly varying frequency near the second harmonic of the electron gyrofrequency in the center of the trap has been discovered. It is shown that the dynamic regimes of plasma wave generation observed in the experiment can arise when the processes of wave excitation and induced scattering compete, and the transition from quasi-continuous generation to pulse-periodic generation is determined by the ratio of the energy of non-equilibrium particles and the temperature of the background plasma. Hereinafter, the studied mechanisms will be used to explain similar phenomena in space, for example, sequences of pulses of different duration in the spectra of solar type-IV radio bursts.

Evaluation of cutting forces in granite treated with microwaves on the basis of multiple linear regression analysis

The current study is focused on the evaluation of cutting forces in granite treated with high-power (24 kW) microwave radiation based on a multiple regression analysis. As a result, dependencies of forces acting on a conical cutting pick on the irradiation time (up to 45 s), the spacing between cuts and the distance from the treated surface (in depth) were established. The values of obtained correlation coefficients are in the range from 0.90 to 0.98. The analysis of the regression models show that the noticeable reduction in cutting forces for granite used in cutting tests is achieved after its irradiation with a minimum of approximately 34 s. Cutting forces increase linearly with increasing distance from the initially irradiated surface (in depth). For an irradiation time of 45 s, the influence of cracks induced by microwaves is levelled out at the depth of 32 mm, so the treatment of the rock used in cutting tests should be repeated after cutting of some 30 mm in order to initiate a new set of cracks for subsequent layers. Representation of cutting test results in form of regression dependencies allow a more detailed analysis of the influence of irradiation and cutting parameters on the cutting forces as well as more convenient re-use of the obtained empirical data by researchers and engineers.

High power microwave plasma discharge

High-power microwave (HPM) has broad applications in scientific research, civil and military community. HPM has the character of peak power of tens of Giga-Watt and the pulse width from tens of to hundreds of nanosecond. The intense electromagnetic breakdowns in the HPM generation, transmission and radiation systems, seriously limit the HPM systematic power capacity, and become the bottle neck of the HPM technology-development and the international technical challenge. In this paper, the recent developments of intense electromagnetic breakdown at vacuum and air sides of output window and on metal surfaces are reviewed and discussed. To understand the breakdown mechanism at window, several multipactor dynamic models are developed, especially involving electron-neutral collision and ionization in the desorbed gas layer, analytically obtaining the influence of desorption gas on multipactor saturation, and space charge field and potential distribution above dielectric surface formed by multipactor and plasma. By diagnosing the time- and space-evolution optical emissions, the mechanisms of nano-second microwave-driven discharges near the dielectric/vacuum and dielectric/air interface were discussed. For breakdown at the dielectric/vacuum interface, multipactor and plasma developing in a thin layer of several millimeters above interface, revealing intense ionization concentrated in a desorbed high-pressure layer. For breakdown at the dielectric/air interface, nonlinear positive feedback of formation of a space-charge microwave sheath near the dielectric surface, accelerated by the normal components of the microwave field, significantly enhances the local-field amplitude and hence ionization near the dielectric surface. The mechanism and methods of using magnetic field satisfying specific amplitude and direction perpendicular to E rf x E dc to suppress microwave multipactor were theoretically studied and experimental demonstrated. The methods of the external resonant magnetic field have been demonstrated by proof-of principle S-band large power experiments to significantly improve the power capacity by 9 times. The Halbach-like magnets to generate the transverse homogeneous B-field in a large scale was designed to suppress multipactor, and the window breakdown threshold was significantly enhanced at multi-Giga-watt. The methods of periodic surface profiles on suppressing microwave multipactor were discussed. The three-dimensional periodic ripple profile with each unit of rotational symmetric surface is proposed and theoretically and experimentally demonstrated to suppress multipactor for arbitrary electromagnetic mode with any polarization. In theoretical aspect, basic physics courses are described qualitatively, the basic models of secondary electron multipator, gas desorption and plasma avalance are established, but lack of quantitive results and experimental diagnostic of plasma energy and density. The physical and chemical methods of periodici surface, resonant magnet, and surface fluorination are successfully used in suppressing breakdown and improving the power capacity, but there is distance away from practical application.

Rapid Heating Rate Reveal Particular Catalytic Properties of the Pt/rGO Synthesised By Microwave Assisted EG Reduction

The severe exhaustion of fossil fuels causes serious environmental pollution and the substantial research on the sustainable, environmental, abundant, and highly efficient energy systems [1]. Currently, fuel cells, such as Proton Exchange Membrane Fuel Cell (PEMFC) and Direct Methanol Fuel Cell (DMFC) are considered to be a next-generation power source for a wide range of applications in portable, stationary and transportation markets due to their high power density and relatively low temperature of operation [2]. However, the low current efficiency and poor stability of fuel cell catalyst remains one of the biggest problems for the commercialization of PEMFC and DMFC [3]. As is well-known, Pt-based catalysts play a dominant role among all the examined catalysts for fuel cell applications due to its highest activity. However, the soaring price, limited resources and low stability of Pt hinder wider use of fuel cells. Therefore, improvement of the efficiency of the catalyst by the development of Pt nanoparticles on high-surface-area carbonaceous supporting materials has been proposed as one of the most effective approaches to reduce the Pt use and continues to be an important R&D activity. To solve the aforementioned problems, it has been determined to be feasible to prepare catalysts by combining Pt with supporting material. Particularly, graphene is an attractive candidate as the supporting material, thanks to its greater abundance, relatively low cost, similar lattice constant, comparable catalytic activity with respective to Pt and they can enhance the dispersion of Pt, thereby maximizing the surface area available for the reaction and minimizing particle growth. However, because graphene basal planes are chemically inert, especially in the case of high-loading (metal content ≥40 wt.%) catalyst materials, it is necessary to apply an adequate preparation technique to ensure good dispersion of the catalyst nanoparticles on its surface with good control over the particle size and distribution. To date, several methods have been developed for the synthesis of Pt/rGO such as, impregnation, colloidal, electrodeposition impregnation reduction route, etc. As described above, the aforementioned fabrication procedures usually involve time-consuming and complicated procedures and harsh reaction conditions, which seriously limit their largescale preparation and applications in practice. Hence, it is desirable to develop a simple method for the synthesis of Pt/rGO catalyst. Microwave-assisted techniques have been widely used for the preparation of many nano materials because these offer a quick, simple, homogeneous and efficient method. The use of microwaves for material synthesis can have several advantages compared to conventional heating methods due to the uniform and volumetric nature of microwave irradiation. One of the main advantages of the high-power microwave irradiation is uniform heat transfer to the substrate, which leads to a more homogeneous nucleation and shorter crystallization time compared to the conventional heating during which unavoidable temperature gradients occur and can adversely affect the particle size distribution and yield. In addition, because microwave heating generates heat within graphene supporting materials, the graphene can act as preferred nucleation sites, consequently leading to satisfactory utilization and a uniform dispersion of the catalyst nanoparticles. Furthermore, microwave heating has a remarkable energy efficiency and can save time with respect to conventional treatments. However, although microwave irradiation provides many practical advantages over conventional heating for synthesis, it should be mentioned that it can have few potential disadvantages associated with the limitations such as batch process and the effect of temperature and heating rate on particle size of Pt and thickness of graphene sheet in synthesis process, by which the catalytic efficiency of the catalyst is affected. To the best of our knowledge, there has been no report on the use of high-power microwave as an improved synthesis technique. In the present study, we report the effect of the heating rate and the temperature for the catalytic performance by high-power microwave assisted which provides the guidance for the mass production of the high activity Pt/rGO catalyst. The nanosized materials were characterized by TEM and XRD and their electrocatalytic behavior was evaluated using cyclic voltammetry and in situ infrared studies. Physical and chemical measurements were conducted to elucidate the better performance that the rapid heating rate (heating to 120℃ in 17s) of the prepared Pt/rGO have the electrochemically active surface area which superior to the commercial Pt/C. References Nano Lett. 15 (2015) 7616−7620.Journal of Power Sources 61 (1996) 113–124.Journal of Power Sources 184 (2008) 104–119.Ceramics International 37(2011) 505–512. Figure 1