Power Microwave Pulses Research Articles

Wideband Resistive Sensors for Double-Ridged Waveguides

Two types of resistive sensors with flat frequency response for WRD840 and WRD250 double-ridged waveguides were developed. The first type of sensors is optimized for microwave power measurements inside the waveguide. The second type of sensors is connected to the particular horn antenna and optimized for microwave pulse power density (or electric field strength) measurements in free space. The flat frequency response of the sensors was designed by changing the parameters of the sensing element. Proposed sensors can measure high-power microwave pulses covering frequency ranges 0.84-2.0 GHz and 2.6-7.8 GHz.

Wakefield in a waveguide

The feasibility of an experiment which is being set up in our plasma laboratory to study the effect of a wakefield formed by an ultra-short (≤10−9 s) high-power (∼1 GW) microwave (10 GHz) pulse propagating in a cylindrical waveguide filled with an under-dense [(2–5) × 1010 cm−3] plasma is modeled theoretically and simulated by a particle in cell code. It is shown that the radial ponderomotive force plays a circular key role in the wakefield formation by the TM mode waveguide. The model and the simulations show that powerful microwave pulses produce a wakefield at lower plasma density and electric field gradients but larger space and time scales compared to the laser produced wakefield in plasmas, thus providing a more accessible platform for the experimental study.

Repetitive ${ {X}}$ -Band Relativistic Traveling Wave Oscillator

This paper presents the results of an experimental study of a relativistic traveling wave oscillator with a tubular electron beam of enlarged cross section. Repetitively pulsed (30 Hz) generation of 10.1-GHz, 80-ns microwave pulses in 1-s batches is realized. The microwave pulse power a level of quasi-steady-state oscillation was 220 ± 44 MW. The driving electron beam (370-keV, 2.4-kA, 107-ns pulsewidth) was transported along the interaction space by a quasi-constant (few seconds in duration) external magnetic field with an induction of 0.6 T. The power efficiency of the generator is 25% ± 5%. The energy in a single microwave pulse is about 15 J as measured with an aperture calorimeter.

Generation of trains of ultrashort microwave pulses by two coupled helical gyro-TWTs operating in regimes of amplification and nonlinear absorption

Based on a time-domain model, we demonstrate that a periodic train of powerful ultrashort microwave pulses can be generated in an electron oscillator consisting of two coupled helically corrugated gyrotron travelling wave tubes (gyro-TWTs) operating in regimes of amplification and saturable absorption, respectively. The mechanism of pulse formation in such an oscillator is based on the effect of passive mode-locking widely used in laser physics. Saturable absorption can be implemented in a gyro-TWT in the Kompfner dip regime by a proper matching of the guiding magnetic field. According to simulations with the parameters of an experimentally realized Ka-band gyro-TWT, the peak power of generated pulses with a duration of 200 ps can achieve 400 kW.

Control of high power microwave radiation by electromagnetic band gap structures

A plasma control of powerful microwave propagation through the 1D and 2D EBG structures is investigated. Pulsed discharges in argon (or helium) at atmospheric pressure are applied as the plasma inhomogeneities. Temporal behavior of electron concentration in discharge is determined. The timedependent transmission spectra of 1D EBG structure formed solely by plasma in the X-waveguide are measured. The amplitudes of short (∼200 ns) powerful (50 kW) microwave pulses at frequency of 9.15 GHz are strongly suppressed (more than 40 dB) when they fall in the time interval of plasma structure existing. The propagation of these powerful microwave pulses through the triangle metallic 2D EBG structure with the plasma control elements is investigated too: when plasma acts as a compensator of defect in the front row of EBG structure the transmission in direction of 45 o quickly ceases (during a few tenth of nanoseconds), or one quickly arises, when plasma is as an additional defect.

Generation of single and periodically repeated powerful ultrashort microwave pulses

Generation of single and periodically repeated powerful ultrashort microwave pulses

Real time measurement system for high power microwave hot carrier detector

A real time measurement system without synchronised triggering was developed for the hot carrier detector. This system can measure the power and waveform of the high power microwave pulse. Based on the buck converter and the Wilson current mirror, it was composed of the voltage stabilising module and the constant current module. Unlike the original bias power supply which works in the pulse mode, a constant current about 20 mA can be continuously provided with the sensor. The system was tested by a X band hot carrier detector and a magnetron amplifier microwave source. With this measurement system, the microwave pulse of 50 ns–1 μs, 0.1–90 kW can be accurately measured. The output voltage of the hot carrier detector reaches 2 V while the input power equals 90 kW.

Theoretical analysis of transmembrane potential of cells exposed to nanosecond pulsed electric field

Purpose: Intracellular electroporation occurs when the cells are exposed to nanosecond pulsed electric field (nsPEF). It is believed the electroporation (formation and extension of pores on the membrane induced by external electric field) is affected significantly by the transmembrane potential. This paper analyzed transmembrane potential induced by nsPEF in the term of pulse frequency spectrum, aiming to provide a theoretical explanation to intracellular bio-effects.Methods: Based on the double-shelled spherical cell model, the frequency dependence of transmembrane potential was obtained by solving Laplace’s equation, while the time course of transmembrane potential was obtained by a method combined with discrete Fourier transform and Laplace transform. First-order Debye equation was used to describe the dielectric relaxation of the cell medium.Results: Frequency-domain analysis showed that when the electric field frequency was higher than 105 Hz, the transmembrane potential on the organelle membrane (ΔΦo) was increasing to exceed the transmembrane potential on the cellular membrane (ΔΦc). In the time-domain analysis, transmembrane potentials induced by four nsPEF (short trapezoid, long trapezoid, bipolar and sine shapes) with the same field strength were compared with each other. It showed that ΔΦo is obviously larger than ΔΦc if the curve of the normalized frequency spectrum of the pulse is more similar with the curve of normalized ΔΦo in frequency domain. Pulses with major frequency components higher than 108 Hz lead to both small ΔΦo and ΔΦc. This may explain why high power pulsed microwave lead to unobvious bio-effects of cells than nsPEF with trapezoid form.Conclusion: Through the pulse frequency spectrum it is clearer to understand the relationship between nsPEF and the transmembrane potential.

Spectroscopic and probe measurements of the electron temperature in the plasma of a pulse-periodic microwave discharge in argon

A pulse-periodic 2.45-GHz electron-cyclotron resonance plasma source on the basis of a permanent- magnet mirror trap has been constructed and tested. Variations in the discharge parameters and the electron temperature of argon plasma have been investigated in the argon pressure range of 1 × 10–4 to 4 × 10–3 Torr at a net pulsed input microwave power of up to 600 W. The plasma electron temperature in the above ranges of gas pressures and input powers has been measured by a Langmuir probe and determined using optical emission spectroscopy (OES) from the intensity ratios of spectral lines. The OES results agree qualitatively and quantitatively with the data obtained using the double probe.

Generation of “gigantic” ultra-short microwave pulses based on passive mode-locking effect in electron oscillators with saturable absorber in the feedback loop

A periodic train of powerful ultrashort microwave pulses can be generated in electron oscillators with a non-linear saturable absorber installed in the feedback loop. This method of pulse formation resembles the passive mode-locking widely used in laser physics. Nevertheless, there is a specific feature in the mechanism of pulse amplification when consecutive energy extraction from different fractions of a stationary electron beam takes place due to pulse slippage over the beam caused by the difference between the wave group velocity and the electron axial velocity. As a result, the peak power of generated “gigantic” pulses can exceed not only the level of steady-state generation but also, in the optimal case, the power of the driving electron beam.

Cellular effects of acute exposure to high peak power microwave systems: Morphology and toxicology.

Electric fields produced by advanced pulsed microwave transmitter technology now readily exceed the Institute of Electrical and Electronic Engineers (IEEE) C.95.1 peak E-field limit of 100 kV/m, highlighting a need for scientific validation of such a specific limit. Toward this goal, we exposed Jurkat Clone E-6 human lymphocyte preparations to 20 high peak power microwave (HPPM) pulses (120 ns duration) with a mean peak amplitude of 2.3 MV/m and standard deviation of 0.1 with the electric field at cells predicted to range from 0.46 to 2.7 MV/m, well in excess of current standard limit. We observed that membrane integrity and cell morphology remained unchanged 4 h after exposure and cell survival 24 h after exposure was not statistically different from sham exposure or control samples. Using flow cytometry to analyze membrane disruption and morphological changes per exposed cell, no changes were observed in HPPM-exposed samples. Current IEEE C95.1-2005 standards for pulsed radiofrequency exposure limits peak electric field to 100 kV/m for pulses shorter than 100 ms [IEEE (1995) PC95.1-Standard for Safety Levels with Respect to Human Exposure to Electric, Magnetic and Electromagnetic Fields, 0 Hz to 300 GHz, Institute of Electrical and Electronic Engineers: Piscataway, NJ, USA]. This may impose large exclusion zones that limit HPPM technology use. In this study, we offer evidence that maximum permissible exposure of 100 kV/m for peak electric field may be unnecessarily restrictive for HPPM devices. Bioelectromagnetics. 37:141-151, 2016. © 2016 Wiley Periodicals, Inc.

A megawatt solid-state modulator for high repetition rate pulse generation.

A novel solid-state modulator capable of generating rapid consecutive power pulses is constructed to facilitate experiments on plasma interaction with high power microwave pulses. The modulator is designed to output a 100 kHz tone burst, which consists of up to 10 pulses, each with 1 μs duration and 1 MW peak power. The pulses are formed by discharging a total of 480 μF capacitors through 24 synchronized MOSFETs and 6 step-up transformers. The highly modular design, as a replacement of an old single-pulse version used in earlier experiments which employs a pulse forming network, brings great flexibility and wide potential to its application. A systematic cost-effectiveness analysis is also presented.

Multichannel Systems of Resonant Microwave Pulse Compression

Different designs of multichannel resonant microwave pulse compression systems operating in $X$ - and $S$ -bands are described. The output pulsed microwave power of these systems is expected to be severalfold greater than that of compression systems with a single output channel. These compression systems can be used as compact sources of high-power nanosecond-duration microwave pulses, sources of synchronized sequences of microwave pulses, and sources for development of phased arrays of compressed microwave pulses. In particular, the authors describe the characteristics of a two-channel $S$ -band resonant microwave pulse compression system with nanosecond-duration output pulse and an output pulsed microwave power of 1 GW. The operation of a four-channel $X$ -band compression system with a possible eightfold output pulsed microwave power increase, relatively to the microwave power in the cavity, is also described. The design of an eight-channel system with a 16-fold output pulsed microwave power increase is reviewed. The parameters of an $X$ -band compression system with multichannel output unit formed as a set of interference microwave switches extracting the energy in synchronism are presented.

The Effect of Pulsed Microwave Power on Transesterification of Chlorella sp. for Biodiesel Production

Pulsed microwave technique was employed for the production of biodiesel from Chlorellasp. via transesterification. Real-time microwave power and temperature profiles were used for the evaluation of efficiency of biodiesel production. The effect of power setting was determined in the range of 100–1000 W at the fixed reaction time (10 min) and temperature (60°C). In this work, the highest yield of biodiesel per unit energy consumption observed was 0.53% by weight of crude lipid per kilo joule at 250 W. From the results in this study, the efficiency of biodiesel production was correlated to the uniform pulse intensity and pulse frequency during the reaction process provided at the power setting of 250 W.

Perturbative harmonic modulation of longitudinal electron-spin magnetization for short [formula omitted] determination

Longitudinally detected T1 measurement scheme (LOD-T1) is studied in detail. In contrast to the original work on LOD-T1, using high power microwave pulses, this work deals with general and practically frequent cases in which perfect inversion of the electron-spin magnetization is not feasible due to the effect of relaxation during microwave pulses. Theoretical studies, numerical simulations, and experiments reveal a pair of separate contributions of the dynamics of the longitudinal magnetization to the LOD signal, namely, the periodic modulation and the relaxation contributions. The latter alone which is of interest can be extracted to give relaxation curves. In addition, it is shown that T1 information can be obtained even when the available microwave power is so low that the electron magnetization can only be perturbatively modulated, at the cost of reduced sensitivity. To overcome this, a modified pulse sequence is proposed. In this new method, the pulse excitations are repeated during half a period of the resonance of the longitudinal detection circuit. The method is called the perturbative harmonic modulation method for longitudinally detected T1 measurement (HM-LOD-T1). HM-LOD-T1 experiments are demonstrated in 2,2-diphenyl-1-picrylhydrazyl (DPPH).

Electron heating and density production in microwave-assisted helicon plasmas

Microwaves are injected into argon and helium helicon plasmas at 6 to 20 mTorr neutral pressure, 1.2 kW pulsed microwave power, up to 500 W continuous RF power, and up to 1 kG magnetic fields, with the objective of heating the tail of the electron energy distribution function (EEDF) and populating ion metastable states. Langmuir probes are used to measure the EEDF and optical emission spectroscopy is used to monitor ion emission. The injection of microwave power in argon helicon plasmas is shown to heat the high energy tail of the EEDF without increasing the plasma density. Argon ion emission is shown to increase by a factor of 4. Injection of microwaves into a helium helicon plasma is shown to cool the bulk of the of the EEDF and increase the plasma density. Previously absent helium ion emission lines are observed with the injection of microwaves. All the microwave results are shown to be independent of RF power within the limits of the system.

A microwave coaxial switch

Microwave coaxial switch on p-i-n-diodes is described. The device is a section of a coaxial line with a broken external conductor. The control p-i-n-diodes are embedded into the break (annular gap) of the conductor. A toroidal resonator, the gap of which is in line with the break of the external conductor of the coaxial line, is axially aligned to the line. The device is made in versions with working frequencies of 2450 and 2856 MHz; maximal pulse microwave power of 3 (2A520A p-i-n-diodes), 1 (2A507A), and 0.2 kW (2A509A); and leading edge of microwave pulses of no more than 200, 50, and 30 ns, respectively.

Development of method for synchronous spark excitation of ultra-wideband antenna array elements

To test the effectiveness of screening facilities and equipment to ensure information security simple compact generators of electromagnetic radiation is needed. For this purpose it is proposed to use spark generators-radiators of powerful ultra-wideband microwave pulses. A new method to synchronize the array of spark generators-radiators is offered. This method allows to simplify the synchronization of the antenna array. The analysis of dependence an array factor on switching time of fuses and voltage distribution on the plates of strip radiators at the time of fuses breakdown is conducted. The results of mathematical modeling parameters of the linear array of spark strip radiators are confirmed by experimental results. During the experiment the effect of coherent addition of pulses generated at the breakdown time of the spark gaps of strip radiators has been observed. As a result generator radiation directivity and power has increased.

A high power microwave triggered RF opening switch.

A 4-port S-band waveguide structure was designed and fabricated such that a signal of any amplitude (less than 1 MW) can be switched from a normally closed state, <0.5 dB insertion loss (IL), to an open state >30 dB IL by initiating plasma in a gas cell situated at the junction of this waveguide and one propagating a megawatt level magnetron pulse. The 90/10 switching time is as low as 20 ns with a delay of ∼30 ns between the onset of the high power microwave pulse and the initial drop of the signal. Two ports of this device are for the high power triggering pulse while the other two ports are for the triggered signal in a Moreno-like coupler configuration. In order to maintain high isolation, these two sets of waveguides are rotated 90° from each other with a TE111 resonator/plasma cell located at the intersection. This manuscript describes the design and optimization of this structure using COMSOL 4.4 at the design frequency of 2.85 GHz, comparison of simulated scattering parameters with measured "cold tests" (testing without plasma), and finally the temporal waveforms of this device being used to successfully switch a low power CW signal from 2 W to <5 mW on a sub-microsecond timescale.

3-D Printed All-Dielectric Frequency Selective Surface With Large Bandwidth and Field of View

In this paper, an all-dielectric frequency selective surface (ADFSS) was developed using genetic algorithms and fast Fourier transforms (FFTs) to generate random geometries. This device showed a stop-band fractional bandwidth (FBW) of 54% and a field of view of 16°. The optimized FSS was manufactured by three-dimensional (3-D) printing and the frequency response was measured in the laboratory. This device was also tested in the pass band at a high pulsed microwave power of 45.26 MW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and no damage was observed. This is the first known demonstration of a 3-D printed ADFSS.