Power Microwave Pulses Research Articles

High-power relativistic microwave sources based on the backward wave oscillator with a modulating resonant reflector

Results of theoretical and experimental investigations into a relativistic backward wave oscillator with a modulating resonant reflector are generalized. The modulating resonant reflector is used to reflect a counter propagating wave and guide it toward an electron collector. It is shown that premodulation of the electron beam near the reflector may have a significant effect on the starting conditions of oscillation; selective properties of the oscillator; and its efficiency, which may reach 40% when a high-current beam is transported by a strong magnetic field. In the reduced magnetic fields that were employed in the pulsed-periodic regime and were 1.5–2.0 times lower than those at which cyclotron resonance with the counter propagating wave is observed, the oscillator efficiency (30–35% at a wavelength of 8 mm) is limited by position and velocity spreads of particles. Mechanical pulsewise frequency tuning within about 10% at a repetition rate of 1–50 Hz and a multigigawatt microwave power, as well as a rise in the power and energy of microwave pulses via an increase in the cross-sectional dimensions of the slow-wave structure, are demonstrated to be feasible.

High power microwave switching utilizing a waveguide spark gap

A reduction in the rise time of a 2.85 GHz high power microwave (HPM) pulse is achieved by implementing an overvoltaged spark gap inside a waveguide structure. The spark gap is oriented such that when triggered, the major electric field component of the dominant TE(10) mode is shorted. The transition from a transmissive to a highly reflective microwave structure in a relatively short period of time (tens of nanoseconds) creates a means to switch multimegawatt power levels on a much faster timescale than mechanical switches. An experimental arrangement composed of the waveguide spark gap and a high power circulator is used to reduce the effective rise time of a HPM pulse from a U.S. Air Force AW/PFS-6 radar set from 600 ns down to 50 ns. The resulting HPM pulse exhibits a much more desirable excitation profile when investigating microwave induced dielectric window flashover. Since most theoretical discussions on microwave breakdown assume an ideal step excitation, achieving a "squarelike" pulse is needed if substantial comparison between experiment and theory is sought. An overview of the experimental setup is given along with relevant performance data and comparison with computer modeling of the structure.

Influence of electromagnetic radiation on raf kinase inhibitor protein and its related proteins of hippocampus

To study the development of changes for Raf kinase inhibitor protein (RKIP) and its mRNA in rats hippocampus after electromagnetic radiation. Rats were exposed to X-band high power microwave (X-HPM), S-band high power microwave (S-HPM) and electromagnetic pulse (EMP) radiation source respectively. The animal model of electromagnetic radiation was established. Western blot was used to detect the expression of RKIP, and RT-PCR was applied to detect the expression of RKIP mRNA. The interaction of RKIP and Raf-1 was measured with co-immunoprecipitation method, and the expression of cerebral choline acetyltransferase (CHAT) was measured by immunohistochemistry. The expression of RKIP significantly down-regulated at 6 h after radiation, and recovered at 1 d in group EMP, but the down-regulation continued during 1 approximately 7 d after radiation in the two microwave groups. The expression of RKIP mRNA changed wavily during 6 h approximately 7 d after radiation, which showed down-regulation at 6 h, and up-regulation at 3 d. The interaction of RKIP and Raf-1 decreased during 6 h approximately 7 d after radiation, most significantly at 7 d, and the two microwave groups were more significant. The expression of CHAT decreased continuously during 6 h approximately 7 d after radiation, and generally recovered on 14 d. The down-regulation of RKIP and its related proteins of hippocampus is induced by electromagnetic radiation.

Manipulating Electromagnetic Waves in Magnetized Plasmas: Compression, Frequency Shifting, and Release

A new approach to manipulating the duration and frequency of microwave pulses using magnetized plasmas is demonstrated. The plasma accomplishes two functions: (i) slowing down and spatially compressing the incident wave, and (ii) modifying the propagation properties (group velocity and frequency) of the wave in the plasma during a uniform in space adiabatic in time variation of the magnitude and/or direction of the magnetic field. The increase in the group velocity results in the shortening of the temporal pulse duration. Depending on the plasma parameters, the frequency of the outgoing compressed pulse can either change or remain unchanged. Such dynamic manipulation of radiation in plasma opens new avenues for manipulating high power microwave pulses.

Study on proton fraction of beams extracted from electron cyclotron resonance ion source

A permanent magnet electron cyclotron resonance ion source PMECR II is used to generate proton ions for radio frequency quadrupole (RFQ) injection at Peking University (PKU). The proton fractions of the extracted beam were measured at the positions both after extraction system of ion source and the end of low energy beam transport line (LEBT). Experiments show that the proton fraction has a rise time within a beam pulse, and its value varies with pulse width and microwave power. The proton fractions measured at different positions are comparable.

Nanosecond High Voltage Pulse Generator Using Water Gap Switch for Compact High Power Pulsed Microwave Generator

Nanosecond and sub-nanosecond high voltage pulses can provide new applications. A cancer treatment by an ultra-short pulse high electric field is one of them. High power pulsed microwave has been proposed to apply the high electric field for that treatment. This work focuses on the design of a compact high power pulsed microwave generator using a nanosecond pulse power generator for the cancer treatment. To obtain fast rise time of voltage and current for nanosecond pulses, a switch has to have low inductance. Water gap switches have this property. Since water has a dielectric strength exceeding 1 MV/cm, gap distances for switching can be reduced to several hundreds of micrometers, and still allow switching of tens of kV. The narrow gaps allow us to reduce the switch inductance. In this study, the water gap switch was built in a Blumlein pulse forming line. The Blumlein line was designed to provide a pulse of 1 ns and to match an impedance to 16 Omega of an antenna. By using the water gap switch in the Blumlein line, the voltage rise time obtained approximately 750 ps at 13 kV of a peak pulse voltage. An electromagnetic wave was radiated underwater by the loop antenna. A measuring antenna at 0.15 m and 0.4 m from the radiating antenna caught electric field intensities of 116 kV/m and 32 kV/m, respectively. A frequency element of 250 MHz had higher intensity.

Microwave-Triggered Surface Plasmon Coupled Chemiluminescence

We describe a high sensitivity and rapid sensing technology for the detection and determination of surface-bound proteins/enzymes and potentially even DNA/RNA. Low power microwave pulses are used to “trigger” chemiluminescence “on demand” at the tips of planar triangular structures. When the triangles are deposited on 40 nm thick continuous silver films with a spacer layer, the intense pulsed chemiluminescence photon bursts become highly polarized and directional through the back of the film, as compared to traditional weak free-space isotropic emissions. Subsequently, microwave-triggered surface plasmon coupled chemiluminescence (MT-SPCC) appears to be a significant improvement over traditional chemiluminescence “slow glow” for surface assays, as well as other surface plasmon coupled fluorescence based assay technologies, such as surface plasmon coupled emission (SPCE) and surface plasmon coupled fluorescence (SPCF). Mw − Microwave pulses to locally “trigger” chemiluminescence, No Mw − No Microwave pulses, i.e. traditional chemiluminescence “slow glow”.

Microwave-Triggered Chemiluminescence with Planar Geometrical Aluminum Substrates: Theory, Simulation and Experiment

Previously we combined common practices in protein detection with chemiluminescence, microwave technology, and metal-enhanced chemiluminescence to demonstrate that we can use low power microwaves to substantially increase enzymatic chemiluminescent reaction rates on particulate silvered substrates. We now describe the applicability of continuous aluminum metal substrates to potentially further enhance or "trigger" enzymatic chemiluminescence reactions. Furthermore, our results suggest that the extent of chemiluminescence enhancement for surface and solution based enzyme reactions critically depends on the surface geometry of the aluminum film. In addition, we also use FDTD simulations to model the interactions of the incident microwave radiation with the aluminum geometries used. We demonstrate that the extent of microwave field enhancement for solution and surface based chemiluminescent reactions can be ascribed to "lightning rod" effects that give rise to different electric field distributions for microwaves incident on planar aluminum geometries. With these results, we believe that we can spatially and temporally control the extent of triggered chemiluminescence with low power microwave (Mw) pulses and maximize localized microwave triggered metal-enhanced chemiluminescence (MT-MEC) with optimized planar aluminum geometries. Thus we can potentially further improve the sensitivity of immunoassays with significantly enhanced signal-to-noise ratios.

Interference Effects of a Powerful Pulsed Microwave Field on Microphone Devices

Results of experimental investigations of interference effects by powerful short microwave pulses on typical electromagnetic and electret microphones of radio-electronic communication and control facilities are presented. The parameters (shape, duration, amplitude) of spurious pulses induced on a microphone are studied as a function of parameters of the pulsed microwave field and the irradiation angle.

Microwave-Triggered Metal-Enhanced Chemiluminescence (MT-MEC): Application to Ultra-fast and Ultra-sensitive Clinical Assays

In this rapid communication we describe a new approach to protein detection with chemiluminescence. By combining common practices in protein detection with chemiluminescence, microwave technology, and metal-enhanced chemiluminescence, we show that we can use low power microwaves to substantially increase enzymatic chemiluminescent reaction rates on metal substrates. As a result, we have found that we can in essence trigger chemiluminescence with low power microwave (Mw) pulses and ultimately, perform on-demand protein detection assays. Using microwave triggered metal-enhanced chemiluminescence (MT-MEC), we not only improve the sensitivity of immunoassays with enhanced signal-to-noise ratios, but we also show that we can accurately quantify protein concentrations by integrating the photon flux for discrete time intervals.

Numerical investigation of resonances within the X-band waveguide type

In this letter, we report on the numerical investigation of resonances within waveguide type resistive sensors used for measuring high power microwave pulse radiation in the X-band. We have applied a finite-difference time-domain method to determine the dependencies of the average electric field and its distribution on frequency for several sets of dimensions and specific resistances of the sample.

An experimental study of high power microwave pulsed discharge in nitrogen

We investigated a plasma excited by high power pulsed microwaves (MWs) (pulse duration 2.5 µs, repetition rate 400 Hz, peak power 105 W, frequency 9.4 GHz) in nitrogen at reduced pressure (pressure range 10–2000 Pa) with the aim of a better understanding of such types of discharge. The construction of the experimental device suppresses the plasma–wall interactions and therefore the volume processes are predominant. To obtain the temporal evolution of the electron density we used two MW interferometers at frequencies of 15 and 35 GHz with dielectric rod waveguides which gives them the capability of localized measurements. We estimated the effective collision frequency from the absorption of a measurement beam. Time resolved optical emission spectroscopy of the 1st negative system and the 2nd positive system was carried out, too. Due to a high power input the discharge dynamics was fast and the steady state was typically reached in 1 µs. We found that the effective collision frequency has the same temporal behaviour as the 2nd positive system of N2, including a characteristic maximum at the beginning of the pulse.

CMOS and post-CMOS on-chip microwave pulse power detectors

Schottky diode microwave pulse power detectors were fabricated by both a CMOS process and a post-CMOS process. Focused ion beam (FIB) milling and ion-induced deposition were used for the post-CMOS fabrication. Fabricated detectors were tested under RF direct injection and RF radiation. CMOS fabricated Schotty diode power detectors had 820 ns pulse response time, 36 dBm dynamic range, and began to detect −21 dBm injected input power level. FIB fabricated Schottky diode power detectors with large contact area had 6 μs pulse response time, 25 dBm dynamic range, and began to detect −15 dBm injected input power level, and Schottky diode with small contact area had 100 ns pulse response time, 16 dBm dynamic range, and began to detect −1 dBm injected input power level. The main factor determining pulse response time and dynamic range was the area of the Schottky contact of diodes.

Photon-induced magnetization changes in single-molecule magnets (invited)

Microwave radiation applied to single-molecule magnets can induce large magnetization changes when the radiation is resonant with transitions between spin levels. These changes are interpreted as due to resonant heating of the sample by the microwaves. Pulsed-radiation studies show that the magnetization continues to decrease after the radiation has been turned off with a rate that is consistent with the spin’s characteristic relaxation rate. The measured rate increases with pulse duration and microwave power, indicating that greater absorbed radiation energy results in a higher sample temperature. We also performed numerical simulations that qualitatively reproduce many of the experimental results. Our results indicate that experiments aimed at measuring the magnetization dynamics between two levels resonant with the radiation must be done much faster than the ⩾20μs time scales probed in these experiments.

Lack of direct DNA damage in human blood leukocytes and lymphocytes after in vitro exposure to high power microwave pulses

Currently, the potential genotoxicity of high power microwave pulses (HPMP) is not clear. Using the alkaline single cell gel electrophoresis assay, also known as the alkaline comet assay, we studied the effects of HPMP (8.8 GHz, 180 ns pulse width, peak power 65 kW, pulse repetition frequency 50 Hz) on DNA of human whole-blood leukocytes and isolated lymphocytes. The cell suspensions were exposed to HPMP for 40 min in a rectangular waveguide. The average SAR calculated from the temperature kinetics was about 1.6 kW/kg (peak SAR was about 300 MW/kg). The steady-state temperature rise in the 50 microl samples exposed to HPMP was 3.5 +/- 0.1 degrees C. In independent experiments, we did not find any statistically significant DNA damage manifested immediately after in vitro HPMP exposure of human blood leukocytes or lymphocytes or after HPMP exposure of leukocytes subsequently incubated at 37 degrees C for 30 min. Our results indicate that HPMP under the given exposure conditions did not induce DNA strand breaks, alkali-labile sites, and incomplete excision repair sites, which could be detected by the alkaline comet assay.

Investigating microwave assisted rock breakage for possible space mining applications

An optimal combination of mechanical means and microwave energy to break rock material could prove beneficial for space applications in terms of large scale production drilling or rock removal processes. In the present paper, application of low power microwave pulses was used to induce thermal cracks in rock samples, before use of mechanical breakage methods. The present investigation is conducted with the scope of possible space bound and terrestrial applications. Experimental studies were carried out to assess the low power (∼150 W) microwave susceptibility of terrestrial basaltic rock samples (chosen for its close chemical similarity to lunar and Martian rocks). Point load tests were carried out on the microwaved rock samples in order to determine their strength before and after exposure to microwaves. The preliminary experimental results showed that the basalt rock samples used were quite susceptible to the exposure of low power microwaves. From the point load test results, a decreasing trend is observed in terms of strength of the rock samples with microwave exposure duration. Some rock samples even presented visible macro cracking and even splitting for the longest exposure duration used in this experimental program.

Design, Numerical Analysis and Test of HF Absorber

The paper presents numerical analysis of the microwave absorber design. It is possible to use modifled concept of the absorber. There were used novel numerical methods (flnite element method (FEM)) for thin layers modelling with sandwich non-isotropic electromagnetic materials. Modifled absorber has appropriate properties and it is possible to use it in non- re∞ecting chamber construction. The non-re∞ecting chamber will be used for open space testing of relativistic microwave pulse generator; Pmax = 500MW, tp = 10i100ns. An experimental testing of the proposed pyramidal absorbers was done in the laboratories at University of Defence Brno, Czech Republic. DOI: 10.2529/PIERS060901094301 Figure 2: The shielded laboratory. The calorimetric sensor has disc design. The carbon with changed crystal lattice is used as one of the thin layers. Combined calorimetric sensors was designed for microwave vircator with output power Pmax = 500MW, length of pulse tp 2 ns. Usually, two types of the absorber materials (non-re∞ecting) are used. The polyurethane foam impregnated by graphite is used in high frequency range (more than 1GHz) | the foam employs heat losses in material. The ferrite absorber is used in low frequency range | the ferrite absorber employs magnetic losses. The mentioned materials are used to prevent re∞ection of the electromag- netic waves inside the laboratory. The idea is to rebuild the laboratory in Fig. 2 to the shielded non-re∞ecting chamber for measurements and experiments with power microwave pulse generators iPmax = 500MW, length of pulse tp 2 ns. 2. SHIELDING OF THE WALLS It is possible to deflne an electromagnetic shielding by help of shielding coe-cient ?. It represents the ratio of the electrical fleld Et (magnetic fleld Ht) in the given place of the chamber to the electrical fleld Ei (magnetic fleld Hi) incoming at the absorber. ? = Et

Multifrequency microwave sounding of nonlinear objects

Numerical modelling process of nonlinear dispersion of powerful microwave pulses on the objects containing semi-conductor components is realized. The attention is given to an irradiation by ultrashort pulses on various carrier frequencies. Numerical modelling is based on the integrated equations for the induced current. Possibility of multifrequency nonlinear dispersion use with allocation both summed, and difference frequencies is shown.

Computation of the Averaged Electric Field in the Semiconductor Obstacle Placed in the Coaxial Line

In this paper we present computed results of the averaged electric field in the semiconductor obstacle placed in the coaxial line. Such layout might be used as a sensor for the measurement of microwave pulse power transmitted through the coaxialline. FDTD (finite different time domain) method was applied for the theoretical investigation. The dependences of the averaged electric field in the obstacle on the microwave frequency, as well as on the dimensions and specific resistance of the obstacle are considered. Both layouts with the obstacle placed on the inner and on the outer conductor of the coaxial line were investigated. Calculations were performed for the 50 Ω impedance coaxial line filled with air and obstacle made from Si.

Generation of acoustic waves by power microwave pulses with the use of thin metal films

We study the features of excitation of acoustic waves by high-power microwave pulses in thin metal films bordering on liquid. Aluminum films with thicknesses 1–10 nm deposited onto a quartz substrate were used in experiments. It is shown theoretically that the absorption coefficient of microwaves is maximum for film thickness from 2 to 3 nm and the value of this maximum is determined by the dielectric permittivity of the bordering liquid. Theoretical calculations and experiments are performed for water and ethyl alcohol. The sound generation in a layered system quartz-aluminum film-liquid is analyzed with the help of the step-by-step approach. At the first step, microwave energy is absorbed in the film and heat is released. Then heat almost instantly diffuses into a liquid whose thermal expansion creates an acoustic signal. Profiles of acoustic signals excited in aluminum films by microwave pulses with a 5-ns duration and an energy of up to 1 mJ are experimentally detected. The most efficient transduction was observed for an aluminum film 3.5 nm thick.