Power Microwave Pulses Research Articles

Generation of powerful short microwave pulses using an amplifier on GaN transistors

Generation of powerful short microwave pulses using an amplifier on GaN transistors

Microdispersed Ti/B/N Materials Synthesized in Chain Reactions in Processes Initiated by Microwaves of a High-Power Gyrotron: Structure and Cytotoxicity

An original plasma-chemical facility has been developed at the Prokhorov General Physics Institute of the Russian Academy of Sciences based on the gyrotrons of the thermonuclear complex of the L-2 M/MIG-3 stellarator. The scope of its applications includes the synthesis of powders for new types of catalysts, the formation and doping of ceramics, and other applications. We have previously demonstrated that in specific conditions, chain oscillatory reactions can be initialized in the reactor by powerful microwave pulses of the gyrotron in mixtures of metal and dielectric powders, resulting in the formation of microdispersed materials with controllable physical and chemical properties. In such reactions, initiated in mixtures of Ti and B, BN powders in a series of particle samples with a developed surface have been obtained. The resulting materials have a heterogeneous composition and size distribution controlled by the synthesis conditions. Thus, the obtained structures exhibit repeatable characteristics attractive for numerous applications, from catalytic particle formation and reinforcement additives to biomedical materials. In order to analyze the hazardless of the materials, cytotoxicity tests were necessary. In this work, the methods for such an analysis have been applied. The study of the obtained samples for cytotoxicity against human cells (lines HEK293T, MCF7, A549, VA13) showed toxic effects only at concentrations of tens of mg/L and the absence of detectable toxic effects in bacterial system (E. coli). The low toxicity at the cellular level indicates the potential for the safe use of the proposed microstructures, but requires further testing of safety at the organism level.

Experimental Study of High Power Microwave Injection in Radar Receiving Front-end

In order to study the tolerance threshold and damage process of radar receiving front end against high power microwave pulse attack, the relationship between the damage of receiving front end and injected signal power, pulse width, and duration was obtained by injection test. The experimental results show that the damage of PIN limiter by high power microwave is a slow worsening process near the damage threshold. Based on the test results, the radar withstanding range of high-power microwave weapon attack is calculated theoretically, which can provide theoretical support for the radar receiving front-end design.

Influence of pulsed microwave on betacyanins, betaxanthins and physical properties during drying of red beetroot

This study aimed to investigate the effect of pulse ratio and microwave power during drying of red beetroot using combined intermittent microwave – hot air at low temperature (40˚C). A significant decrease in drying time was observed by increasing the microwave power from 360 to 900 W and decreasing the pulse ratio from 6 to 2. The highest Deff was obtained at a microwave power of 900 W and a pulse ratio of 6. Dried red beetroots at the microwave power of 900 W and a pulse ratio of 6 had the lowest shrinkage and the highest rehydration. Moreover, the apparent density of the dried samples decreased by increasing the microwave power and pulse ratio. The specific energy consumption was reduced by increasing the microwave power and the pulse ratio. By increasing microwave power and pulse ratio, the content of betacyanins and betaxanthins increased up to 79.47 and 44.20%, respectively. Furthermore, the samples dried at the power of 900 W and a pulse ratio of 6 showed the lowest microstructural collapse. In total, the results of this study showed that industrial dried products with good quality could be produced by considering an appropriate pulse ratio and applied power.

Effects of high power pulsed microwave on the enhanced color and flavor of aged blueberry wine.

A new method of high-power pulsed microwave (HPPM) was applied to accelerate the aging of blueberry wine. The color changes of blueberry wines during aging were investigated through Chemical Wine Age and CIE-LAB measurement. Results showed that the blueberry wines treated by HPPM at low frequencies (50 and 100Hz) exhibited improved color characteristics with L* value reaching 47.04 at 100Hz, an increased maturity of wine body, and a shortened chemical wine age from 90 days to 75 days. Moreover, the aroma changes determined by GC-MS showed that HPPM accelerated the formation of esters in blueberry wine, which were increased by 18.44% and 56.97% respectively under the conditions of 50 and 150Hz. The formation of acid substances was reduced compared with the original wine, with contents of acetic acid, caproic acid, and octanoic acid of 29.46µg/mL, 15.60µg/mL, 17.74µg/mL, respectively, displaying an enhanced wine flavor.

Two enhancements in microwave-assisted spark ignition and their causes

As a prospective ignition technique, microwave-assisted spark ignition (MAI) efficiently enhances ignition with plasma absorbing microwave energy. This paper achieves MAI through radiating a single 0.2 ms microwave pulse after the initial spark ignition, and investigates the ignition performance and the precise absorbed energy of MAI in different absorption patterns. The absorption pattern is tailored by the microwave pulse power. The results show that the enhancement of MAI can be divided into two categories based on ignition performance and absorbed energy: the glow enhancement and the incandescence enhancement. Compared to the glow enhancement, the incandescence enhancement has a greater energy absorption efficiency and thus induces more significant ignition enhancement. Additionally, the effect of gas parameters, including gas pressure and components, on these two enhancement categories is studied. Increasing pressure or decreasing methane concentration facilitates the generation of incandescence enhancement. Ultimately, the causes of both enhancements are discussed. The incandescence enhancement may be originated from the ionization of metal particles in the microwave field, whereas the glow enhancement is attributed to gas ionization. This work highlights the potential application of metal-microwave discharge on MAI, which can play a crucial role in suiting different conditions and further understanding the mechanisms of MAI.

Novel High Power Pulsed Mode Operation of Commercial Continuous-Wave Magnetron

In this article, for the first time, we proposed and studied the operation of industrial 1 kW continuous-wave (CW) S-band magnetrons in a high-power pulsed mode. It turns out that these devices in standard version have a superior pulsed performance: range of stable regulation of pulse power with high efficiency up to 8 kW, pulse duration from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3~\mu \text{s}$ </tex-math></inline-formula> to continuous mode, and repetition rate of at least 1 MHz. The possibility of forming sequences of paired pulses with an adjustable time shift from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{s}$ </tex-math></inline-formula> has been demonstrated. The parameters are provided both in the free-running and injection-locking modes. A specialized high-voltage pulse power supply (PPS) with adjustable parameters was designed for measurements. On a passive resistive load, the PPS provides output high voltage of 4.0–5.2 kV, output current up to 3 A in pulse and 0.5 A in average mode, pulse duration from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1~\mu \text{s}$ </tex-math></inline-formula> , pulse edges less than 0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> , and repetition rate up to 1 MHz. The effect of limiting the pulsed microwave power by emission current was detected for the first time. The investigated CW magnetrons in pulsed mode can be used in microwave technology, accelerator equipment, and for research purposes.

Evaluation of Viral Inactivation on Dry Surface by High Peak Power Microwave (HPPM) Exposure.

Previous research has shown that virus infectivity can be dramatically reduced by radio frequency exposure in the gigahertz (GHz) frequency range. Given the worldwide SARS-CoV-2 pandemic, which has caused over 1 million deaths and has had a profound global economic impact, there is a need for a noninvasive technology that can reduce the transmission of virus among humans. RF is a potential wide area-of-effect viral decontamination technology that could be used in hospital rooms where patients are expelling virus, in grocery and convenience stores where local populations mix, and in first responder settings where rapid medical response spans many potentially infected locations within hours. In this study, we used bovine coronavirus (BCoV) as a surrogate of SARS-CoV-2 and exposed it to high peak power microwave (HPPM) pulses at four narrowband frequencies: 2.8, 5.6, 8.5, and 9.3 GHz. Exposures consisted of 2 µs pulses delivered at 500 Hz, with pulse counts varied by decades between 1 and 10,000. The peak field intensities (i.e. the instantaneous power density of each pulse) ranged between 0.6 and 6.5 MW/m2 , depending on the microwave frequency. The HPPM exposures were delivered to plastic coverslips containing BCoV dried on the surface. Hemagglutination (HA) and cytopathic effect analyses were performed 6 days after inoculation of host cells to assess viral infectivity. No change in viral infectivity was seen with increasing dose (pulse number) across the tested frequencies. Under all conditions tested, exposure did not reduce infectivity more than 1.0 log10. For the conditions studied, high peak power pulsed RF exposures in the 2-10 GHz range appear ineffective as a virucidal approach for hard surface decontamination. © 2023 Bioelectromagnetics Society.

Combined generator–accelerator scheme for high-gradient electrons acceleration by Ka-band subnanosecond superradiant pulses

An increase in the accelerating gradient in hollow metal structures powered by an RF field is associated with the development of sources of high-power short-pulse high-frequency radiation. To date, the most powerful (multi gigawatts) nanosecond-scale microwave pulses are produced based on the effect of Cherenkov super-radiance (SR). We consider the possibility of experimental observation of high-gradient acceleration of electrons by Ka-band SR pulses in a combined generator–accelerator scheme with two coaxial electron beams formed by a single cathode. The outer tubular beam is used to generate the SR pulse in periodical slow-wave structure, while the inner one is accelerated in a “pill-box” resonator. The main parameters of the proposed scheme are determined based on full-scale particle-in-cell simulations, according to which accelerating gradient can reach 400 MV/m as some fraction of electrons passing the resonator increases energy from 250 keV to 1.85 MeV. Using the obtained data, injector of the coaxial beams and the sensor of accelerated electrons are developed and tested.

Interference effects in GaN high electron mobility transistor power amplifier induced by microwave pulses

Owing to the rapid development of wireless communication, radar and pulse power technology, the electromagnetic environment faced by electronic systems is increasingly complex and the intensity of electromagnetic field can be significant. In this study, a new interference phenomenon was observed when the microwave pulses were injected into the gallium nitride (GaN) high electron mobility transistor (HEMT) power amplifier through the output port. We investigated the relationship between the peak power of reverse injection microwave pulses and the duration or the amplitude of the interference by effect experiments. The interference duration could reach the magnitude of millisecond. Deep traps in GaN HEMT power amplifiers are proved to be the cause of this interference effects.

Particle-in-Cell Simulations of Ten-Vane Microwave-Oven Free-Running 2.45-GHz “Cooker” Magnetron: Microwave Power Increase up to 6 kW in a Pulsed Mode (3 kW With 50% Duty Cycle)

Standard operation of a conventional microwave oven 2.45-GHz “cooker” magnetron with 4.0–4.3 kV of pulsed applied voltages at 0.17–0.19-T magnetic fields results in generation of pulsed microwave power 1.8–2.8 kW, which is recalculated to an average microwave power 0.9–1.9 kW when the “cooker” magnetron operates with 50% duty cycle while driven by a “rectified” ac voltage from the wall-plug. It has been shown in many experimental studies of “cold-start” operation of a standard ten-vane 2.45-GHz “cooker” magnetron that it readily sustains, when properly conditioned, up to ~10-kV dc and up to ~14 kV of peak-to-peak ac applied voltage with just a few microamphere cold (field emission) leakage (anode) current. The latter suggests that a standard 2.45-GHz “cooker” magnetron may successfully operate in the desired, lowest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode with much more output microwave power at even higher magnetic fields when driven by up to ~10 kV of dc or quasi-dc appropriate, synchronous applied voltage. Results of improved concurrent electromagnetic particle-in-cell (ICEPIC) simulations of magnetron operation at different magnetic fields with synchronous applied voltages show that, for example, with 8.0-kV applied voltage at 0.35-T magnetic field, the 2.45-GHz “cooker” magnetron is able to generate up to 6.0 kW of pulsed microwave power with an anode current of ~0.9 A.

Evaluation of the membrane performance of ultra-smooth silicon organic coatings depending on the process energy density

Plasma-enhanced chemical vapor deposition (PECVD) can be used to apply thin layers to plastics with a wide range of customizable functionality. The selective permeation properties of the layers are particularly interesting for the application field of membrane gas separation processes. In order to be able to produce plasma polymerized membranes in an application specific manner, it is necessary to be able to correlate the plasma process parameters, such as the energy density introduced into the system, with the coating and thus separation properties. Within the scope of this work, different layers produced in a Plasma-enhanced chemical vapor deposition process were investigated with respect to their growth behavior, topographic and chemical properties as well as permeability to evaluate their performance as separation layers of a membrane. The results of the investigations show a strong dependence of the layer and separation properties on the pulsed microwave (MW) power coupled into the process. Energy input was varied over the MW power level as well as the MW pulse duration. Analysis shows the highest permeation and separation performance of the produced layers in the low energy density range of the process.

Enhanced pulsed thermoacoustic imaging by noncoherent pulse compression

Microwave-induced thermoacoustic imaging (TAI) is a hybrid imaging technique that combines electromagnetic radiation and ultrasonic waves to achieve high imaging contrast and submillimeter spatial resolution. These characteristics make TAI a good candidate to detect material anomalies that change the material electric properties without a noticeable variation in material density. Conventional pulsed TAI systems work by sending a single short pulse to the imaged target and then detecting the generated pressure signal; therefore, a very high peak power microwave pulse or data averaging is needed to produce images with a high signal-to-noise ratio (SNR). In this paper, we propose to enhance the SNR of pulsed TAI systems by using non-coherent pulse compression. In this approach, a predefined pulse coded signal is used to illuminate the imaged sample and the received pressure signal is cross correlated with a template that is related to the power profile of the excitation signal. The proposed approach can be easily deployed to pulsed TAI systems without the need for major system modifications to the RF source because it only requires a timing circuit to control the triggering time of the RF pulses. In this paper, we demonstrate experimentally that the proposed approach highly improves the SNR of TAI signals and images and can be used to reduce the acquisition time by lowering the number of data averaging or reduce the required peak power from RF sources.

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.

Experimental and numerical study of a split cathode fed relativistic magnetron

The relativistic magnetron is one of the most efficient high power microwave (HPM) sources but pulse shortening, the result of explosive cathode plasma's radial expansion toward the anode, makes it impractical because the HPM pulse terminates much earlier than the applied voltage. We present experimental results of the operation of a relativistic magnetron fed by a split cathode. A split cathode [Leopold et al., Phys. Plasmas 27, 103102 (2020)] consists of a cathode placed upstream and outside the anode, connected by an axial rod to a reflector (a transverse conducting circular plate) placed downstream from the anode. The electron charge, emitted by an annular explosive cathode emitter, accumulates in the space between the cathode and the reflector and at the same time, screens the rod from explosive plasma formation. This accumulated space charge serves as the electron source for the magnetron. The explosive plasma developing on the emitter remains outside the magnetron and does not propagate into the anode while it operates. We compare the performance of the magnetron operating with a standard explosive emitting solid carbon cathode to that with a split cathode. The experiments demonstrate that whereas for the solid cathode, the microwave pulse developing in the magnetron suffers from pulse shortening, with a split cathode, the pulse survives as long as the amplitude of the applied voltage is sufficient for the magnetron's operation. We support the experiment by particle-in-cell simulations.

Nonlinear absorption of high-power microwave pulses in a plasma filled waveguide

We observe complete absorption of an ∼1.2 GW, 0.5 ns, 25.6 GHz high power microwave pulse propagating in a plasma-filled waveguide when the plasma density dependent waveguide cutoff frequency is close to the pulse frequency. Some of the plasma electrons are ejected to the walls, leaving in the waveguide an uncompensated ion charge which forms a potential well where the remaining electrons oscillate in the pulse field. Due to the decreased group velocity of the wave, these trapped electrons have sufficient time to collide with ions, while their regular oscillatory motion becomes chaotic and thermal. Almost all the energy of the electromagnetic pulse is transferred to the kinetic energy of the electrons. This mechanism of absorption is absent when the pulse power is low, and a potential well does not form in the waveguide.

Stable Operation of a Repetitively Pulsed X-Band Relativistic Backward Wave Oscillator

This letter describes a recent activity in the development of a high-power microwave source based on a modified relativistic backward wave oscillator that is driven by an advanced version of a SINUS-family accelerator using a double-width pulse-forming line insulated with a modern synthetic oil. The relatively compact source of microwave pulses (0.6 GW, 20 ns, 9.4 GHz) can operate at a 100 pps repetition rate in a batch mode with batches of duration up to 15 s. The long-term stability of the oscillator performances during $10^{{6}}$ pulses was achieved due to the improved conditions for explosive emission of the graphite cathode and the use of a titanium slow wave structure. Both factors prevented the shortening of the microwave pulses. With a proper choice of the magnetic field strength and longitudinal distribution and of the position of the resonant reflector, the pulse-to-pulse deviation of the microwave power was reduced with sacrifice in efficiency, which decreased from a simulated maximum efficiency of 44% to 40% in the simulation and to 35 ± 4% in the experiment. At an accelerating voltage of 418 kV and a magnetic induction of 0.64 T at the cathode, the standard deviation of the microwave pulsed power could be close to the voltage deviation.

Analysis and Experimental Study of Radiative Microwave Pulses Effects on the Nonlinear Performance of a Low-Noise Amplifier

In this article, the performance of an unshielded low-noise amplifier (LNA), which is subjected to the incident high power microwave (HPM) pulse waves, is investigated analytically and experimentally. For this purpose, a time-domain algorithm is proposed, which uses the finite difference time domain (FDTD) method and a globally convergent iterative method to solve linear and nonlinear equations of the problem simultaneously. In particular, the effects of external incident electromagnetic (EM) field illumination with different types of waveforms, including HPM pulses and sinusoidal waves, on the nonlinear performance of a microwave LNA are investigated and discussed by this method. Furthermore, using a measurement setup comprised of a transverse EM (TEM) cell, the proposed method is validated by comparing with the measurement results in good agreement. The presented analysis would be useful in EM interference/compatibility (EMI/EMC) analysis, such as radiated susceptibility analysis of RF/microwave nonlinear circuits excited by the incident HPM pulse wave.

Generation of a Sequence of Powerful Ultrashort Microwave Pulses Based on the Effect of Superradiance of a Relativistic Backward-Wave Oscillator with Reflectors at the Ends of the Interaction Space

Generation of a Sequence of Powerful Ultrashort Microwave Pulses Based on the Effect of Superradiance of a Relativistic Backward-Wave Oscillator with Reflectors at the Ends of the Interaction Space

Синхронизация генераторов на ЛПД импульсного и непрерывного действия в мм-диапазоне длин волн. Часть 1. Конструкции генераторов и обобщенная модель их синхронизации внешним сигналом

Advances in the development of ultrahigh-frequency semiconductor electronics open wide opportunities for developing optimal schemes and designs of microwave power sources in the millimeter wavelength range providing high stability of the frequency and electromagnetic oscillation phase. Synchronized diode generators used in transmit/receive module for active phased array antennas, coherent low-power radar stations, etc. show great promise. The mode of external synchronization of semiconductor generators allows effectively implementing the task of creating output stages of the transmitters with high gain factor, low frequency noise and an output power level corresponding to the maximum power mode. This article presents the first of two parts of the study, which summarizes the results achieved so far in the development of synchronized oscillators based on impact ionization avalanche transit-time (IMPATT) diodes. The first part presents the electrodynamic designs of the oscillators, which are synchronized with an external source of microwave oscillations and contain a resonant oscillating system with a silicon IMPATT diode. The silicon two-drift IMPATT diode was chosen as an active element due to the fact that its use allows reaching significant levels of pulsed microwave power – an order of magnitude higher than those of the most well-known HEMT and pHEMT transistors in the millimeter wavelength range. It is shown that to reduce losses, the oscillating system should be made in the form of a radial resonator with a diode casing, which has distributed parameters. This eliminates the use of additional reactive inhomogeneities in the initial cross-section of the waveguide section of the generator. Due to the low quality factor of the resonant casing of the diode, the generalized quality factor of the microwave circuit takes the minimum value required to implement a stable generator synchronization process in the millimeter wavelength range. The second part of the work will be devoted to synchronized pulse generators with an output power of 20–150 W.