Microwave Output Research Articles

Squeezing microwaves by magnetostriction.

Squeezed light finds many important applications in quantum information science and quantum metrology, and has been produced in a variety of physical systems involving optical non-linear processes. Here, we show how a non-linear magnetostrictive interaction in a ferrimagnet in cavity magnomechanics can be used to reduce quantum noise of the electromagnetic field. We show optimal parameter regimes where a substantial and stationary squeezing of the microwave output field can be achieved. Realization of the scheme is within reach of current technology in cavity electromagnonics and magnomechanics. Our work provides a new and practicable approach for producing squeezed vacuum states of electromagnetic fields, and may find promising applications in quantum information processing and quantum metrology.

Research on Sub-Microsecond Compact L-Band Relativistic Cherenkov Oscillator

Prolonging the microwave pulsewidth is an important research direction to improve high-power microwaves’ energy and average power level. In this article, a sub-microsecond compact <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> -band relativistic Cherenkov oscillator (RCO) is studied. The device adopts a coaxial slow wave structure to reduce the radial size and a coaxial collector structure to improve the resonance characteristics of the slow wave structure to reduce the axial size. In particular, a coaxial outer corrugated slow wave structure is used instead of the coaxial double-corrugated slow wave structure to increase the power handling capacity (PHC) of the slow wave structure and reduce its surface electric field. Moreover, the collector structure has been improved to suppress the effects of plasma expansion. In the experiment, the device obtained a high-power microwave output with a microwave frequency of 1.496 GHz, a power of 2.0 GW, a pulsewidth of 317 ns (single pulse energy of 634 J), and a power conversion efficiency of 32%. The pulsewidth and the single pulse energy are the highest levels reported for the RCO.

Relativistic Multivircator With Two Magnetic Mirrors on Underlimit Electron Beam: Concept and PIC-Simulation Results

A relativistic magneto-isolated vircator on the underlimit electron beam is studied. It contained two serial magnetic mirrors and a coaxial output of microwave radiation. Its 2.5-D particle-in-cell (PIC)-simulation is carried out. Space and phase dynamics of electrons are calculated. The mode is found at which several virtual cathodes (VCs) exist simultaneously in an electron beam, i.e., the multivircator mode is realized in the device. Spectral and power characteristics of the multivircator generation with two magnetic mirrors are calculated. The dependence of the average output microwave radiation and wave resistance of the radiation coaxial output is also calculated. The spectrogram of microwave radiation is provided.

Influence of convective and microwave drying on Algerian blood orange slices: Drying kinetics and characteristics, modeling, and drying energetics

AbstractThis research work aims to explore for the first time the effect of two drying processes on Algerian blood oranges (Citrus sinensis [L.] Osbeck): microwave(200, 400, 600, and 800 W) and convective(40°C, 60°C, 80°C, 100°C, and 120°C), on drying characteristics. The drying time was reduced from 90 min at 120°C (rate of 2.00 × 10−2 kgH2O/kg dm.min) to 13 min at 800 W microwave output (rate of 28.86 × 10−2 kgH2O/kg dm.min). The drying data were fitted to 38 models. Sledz et al. and Midilli and Kucuk models were found to be the best fit to describe drying kinetics for microwave and convective, respectively. The effective diffusivity ranged from 2.07 × 10−9 to 15.67 × 10−9 m2/s for microwave and from 0.07 × 10−9 to 1.97 × 10−9 m2/s for convective drying. The activation energy was estimated to be 8.871 W/g and 33.7 kJ/mol for microwave and convective respectively. The highest energy consumption was obtained by convective drying (0.49 × 107 MJ/kgH2O) whereas the highest energy yield was obtained by microwave drying (36.93 × 10–2%).Practical ApplicationsDue to the great variability of drying techniques, it is difficult to design the best process for a given product. When choosing a process, several parameters must be considered including precise process control, short drying time, low energy consumption, and high energy efficiency. Blood orange is a seasonal variety, to make it available, drying is one of the most used techniques. Thus, the objective of this study was to compare two drying processes of blood orange slices (microwave, convective). The results of this research allowed to select an alternative technique (microwave) to manufacture dehydrated orange slices that could be useful to facilitate their use out off‐season in the formulation of different food products, food fortification, and pharmaceutical industry.Novelty Impact StatementTwo conventional and innovative drying methods were applied to dry blood orange slices, and in terms of kinetic results and modeling. The models of Midilli and Kucuk and Sledz were best suited for convective and microwave drying, respectively. Microwaves provide faster drying, low energy consumption, and high energy efficiency.

A low phase and amplitude noise microwave source for vapor cell atomic clocks.

A low-noise microwave source plays a key role in high-performance passive atomic clocks. Here, we propose and implement a microwave frequency synthesizer featuring a low phase and amplitude noise. With the help of a high-Q factor surface acoustic wave band-pass filter, we generate a microwave with targeted frequency by frequency multiplication of a low noise local oscillator at a radio frequency with the closest integer. At the frequency offset of 1Hz, 10Hz, 100Hz, 1kHz, and 10kHz, the absolute phase noise of the output 3.417GHz signal is -53.0, -83.3, -107.7, -119.2, and -124.0 dBc/Hz, respectively. After the microwave-to-optical conversion, the expected intermodulation effect contribution to the frequency stability of the coherent population trapping (CPT) atomic clock is 5.95 × 10-14 at an averaging time of 1s. Meanwhile, with a feature of low fluctuation of this chain's output microwave power at the level of 1.19 × 10-5W at 1s, its contribution to the frequency stability of the CPT atomic clock is 7.85 × 10-14 at the 1s integration time. Our simple and low noise microwave chain is an ideal microwave source for high-performance, compact CPT clocks and could also be applied to cold atom or ion based microwave clocks.

Suppression of Asymmetric Mode Competition in a Cross-Band Cherenkov Microwave Generator Based on Magnetic Field Tuning

A band-switching device can realize the minimization of microwave devices, saving more space than the simple combination of two devices of different bands in situations where two bands of high power microwaves (HPMs) are needed. This article presents a 3-D design and particle-in-cell (PIC) simulations of a band-switching Cherenkov microwave generator based on magnetic field tuning. Based on the cyclotron resonance absorption, the device can generate HPMs in both C- and X-bands, respectively. Mode competition is discussed and suppressed with the 3-D simulations. With the analysis of temporal growth rate in the slow wave structure (SWS), a specific method to suppress asymmetric modes is proposed. To further mimic experiment conditions, a guiding magnetic field is obtained from the magnetic coil and a voltage with a rising and falling edge is used in the simulation. In the PIC simulations, when the magnetic field is 0.67 T, an output microwave of X-band can be obtained, with a frequency of 8.4 GHz and an average power about 1.6 GW. When switching the magnetic field to 1.55 T, a C-band microwave can be obtained, with a frequency of 4.4 GHz and an average power about 1.45 GW. The simulation results indicate the device to be practical in experiments.

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.

100-MW-Level Experiments of a Gyromagnetic Nonlinear Transmission Line System

The wideband high-power microwave systems have the advantages of wide energy spectrum, electron beam independence, compactness, and low cost. The gyromagnetic nonlinear transmission line (GNLTL) has drawn much attention for its potential as a novel solid-state, frequency-agile, and compact wideband source. The working mechanism of GNLTL is different from that of the traditional electric vacuum tubes, and the strong dispersion and nonlinear characteristics make it difficult to be accurately theoretically calculated and simulated. In this article, a 100-MW-level GNLTL system based on a Tesla-type driver was designed and constructed. A series of test experiments were then carried out to investigate the effects of different configurations, including delay line length, ferrite cores’ assembly orientation, transmission line length, bias magnetic field magnitude, and excitation voltage. The changing laws of the key parameters of the output microwaves including the peak power, modulation depth, center frequency, and percentage band are summarized and the underlying physical mechanisms are analyzed. The results may be instructive for the predesign of GNLTLs, especially for the devices operating at high power. In addition, a multiple center frequency points’ phenomenon was discovered in the output signal, which may bring new application possibilities for GNLTL.

An X-band high-power and high-efficiency coaxial relativistic klystron oscillator with four-gap buncher and three-gap extractor

Because of the scaling invariance, the over-mode ratio of the coaxial resonator can be increased to increase the power handling capability. However, as the over-mode ratio increases, the characteristic impedance and external quality factor decrease, which causes the modulation of the electron beam to be weakened. Moreover, when the output microwave power increases, the double-gap output cavity will suffer from severe radio frequency breakdown. Therefore, an X-band high-power and high-efficiency coaxial relativistic klystron oscillator with a four-gap modulation cavity and a three-gap extraction cavity is proposed. First, a four-gap modulation cavity can increase the modulation depth of the electron beam to improve the beam-wave conversion efficiency. The operating mode of the modulation cavity is the 3π/4 mode of the coaxial TM01 mode. Second, a three-gap extraction cavity is adopted to enhance the microwave extraction energy and reduce the RF field strength. The simulation results show that when the diode voltage is 650 kV, the beam current is 15.4 kA, and the guiding magnetic field is 0.48 T, the device outputs a microwave power of 4.2 GW, a frequency of 8.4 GHz, and an efficiency of 42%.

A novel L-band metamaterial slow wave structure with low space charge effect and high field uniformity

A novel L-band metamaterial slow wave structure with a weak space charge effect and high field uniformity is proposed. The slow wave structure is composed of two identical all-metal resonant elements. In order to weaken the space charge effect, a long drift tube is adopted as a metal joint, connecting the front periodic unit with the rear one. Moreover, the novel metamaterial structure exhibits higher field uniformity by rotating one of the resonant elements 45° relative to the other. Electromagnetic calculation indicates that the average fluctuation in the electric field dropped from 3% to 0.5%. Based on the novel metamaterial slow wave structure, an L-band Cerenkov oscillator model is built, and a preliminary particle-in-cell simulation is carried out. Under the condition of an acceleration voltage of 500 kV, beam current of 8 kA, and magnetic field of 1 T, a 1.64 GW average output microwave power at 1.30 GHz is obtained. The corresponding conversion efficiency is 41%. The simulation results prove the advantages of the metamaterial Cerenkov oscillator, such as low magnetic field, low impedance, miniaturization, and high conversion efficiency.

Experimental research based on a C-band compact transit-time oscillator with a novel diode loading an embedded soft magnetic material and shielding structure

In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field, a novel diode with an embedded soft magnetic and shielding structure is proposed. The soft magnetic material is designed to enhance the local magnetic field in the diode region. Moreover, the diode applies a shielding structure which can reduce the radial electric field. From simulation research, it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode. Through simulation research, it is verified that the diode can increase the conversion efficiency of the transit-time oscillator (TTO) from 30% to 36.7%. In our experimental study, under the conditions of a diode voltage of 540 kV and a current of 10.5 kA, the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied. The corresponding conversion efficiency is improved from 20.0% to 26.6%, which is 6.6% higher than that of a device loaded with a conventional diode. Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field, and contribute to the miniaturization and compactness of high-power microwave devices.

Atmospheric air plasma sustainment by semiconductor microwave for hydroxyl radical production and powder metal element analysis

A semiconductor microwave device that generates a series of burst microwaves at a sub-microsecond duration has been successfully used in a breakdown plasma spectrometer in atmospheric conditions. Microwave delivery has been changed to couple the microwave with laser sparks and electric sparks which are typical plasma ignition sources in laser-induced breakdown spectroscopy (LIBS) and spark-induced breakdown spectroscopy (SIBS). A helical antenna was used for the laser spark, while a coaxial antenna was considered more appropriate for the electric spark. The weak and transient sparks in LIBS and SIBS are enlarged by the microwaves which are stably sustained in the air. The microwave's output power and pulse duration are easily controllable, resulting in tunable plasma intensity and sustained production of hydroxyl radicals (OH radicals). Even in continuous-wave operation by microwave, the low-energy system prevented the formation of high-temperature thermal plasma (>10,000 K) without any mechanical cooling system. The microwave-enhanced LIBS (MW-LIBS) and microwave-enhanced SIBS (MW-SIBS) could be applied to optical emission spectroscopy analyses. In analytical applications, MW-SIBS produces no shockwave in contrast with MW-LIBS which is a great advantage in powdered samples. The MW-SIBS successfully analyzed the direct introduction of copper metal powders.

Experimental research on a novel C-band compact transit-time oscillator with low guiding magnetic field

Compactness and miniaturization are important development directions of high-power microwave sources at present. In the previous simulation research, we proposed a compact C-band transit-time oscillator with a low external guiding magnetic field. In order to verify whether the device can be better applied to practice, we have carried out experimental research on the device. With a diode voltage of 570 kV, current of 11.5 kA, and external guiding magnetic field of 0.35 T, the output microwave pulse of 1.3 GW is obtained at 4.3 GHz. The power conversion efficiency is about 20%. By observing the fluorescent screen imaging and the far-field pattern in the experiment, it can be seen that the working mode of the device is relatively stable. The experimental results show that the device has the ability to output GW-level C-band high-power microwave under a low external guiding magnetic field.

Continuous variable quantum discord in a cavity electrooptical down-conversion quantum system

In this paper, we explore continuous variable quantum discord for the stationary microwave–optical output fields in an electrooptical system. We drive the covariance matrix of the system using the quantum Langevin equations for the intera-cavity microwave and optical modes. Employing the input–output theory, we obtained the output microwave and optical resonator variables in the Fourier frequency domain. The properties of the Gaussian quantum discord with respect to electrooptical cooperativity, the normalized cavity wave guides for microwave and optical resonators, and the thermal mean photon number for microwave and optical modes have been analyzed. Henceforth, we obtained that the Gaussian quantum discord can be enhanced by increasing the electrooptical cooperativity and microwave and optical wave guides. The thermal mean photon numbers of the microwave and optical modes have reduction effects on the Gaussian quantum discord.

Temperature control and intermittent time-set protocol optimization for minimizing tissue carbonization in microwave ablation

Purpose The charring tissue formation in the ablated lesion during the microwave ablation (MWA) of tumors would induce various unwanted inflammatory responses. This paper aimed to deliver appropriate thermal dose for effective ablations while preventing tissue carbonization by optimizing the treatment protocol during MWA with the set combinations of temperature control and pulsed microwave energy delivery. Material and methods The thermal phase transition of ex vivo porcine liver tissues were recorded by differential scanning calorimetry (DSC) to determine the temperature threshold during microwave output control. MWA was performed by an in-house built system with the ease of microwave output parameter adjustment and real-time temperature monitoring. The effects of continuous and pulsed microwave deliveries as well as various intermittent time-set of MWA were evaluated by measuring the dimensions of the coagulation zone and the carbonization zone. Results The DSC scans demonstrated that the ex vivo porcine liver tissues have been in a state of endothermic heat during the heating process, where the maximum absorbed heat occurred at the temperature of 105 °C ± 5 °C. The temperature control during MWA resulted in effective coagulative necrosis while preventing tissue carbonization, after setting 100 °C as the upper threshold temperature and 60 °C as the lower threshold. Both the numerical simulation and ex vivo experiments have shown that, upon the optimization of the time-set parameters in the periodic intermittent pulsed microwave output, the tissue carbonization was significantly diminished. Conclusion This study developed a straight-forward anti-carbonization strategy in MWA by modulating the pulsing mode and intermittent time. The programmed protocols of intermittent pulsing MWA have demonstrated its potentials toward future expansion of MWA technology in clinical application.

Study on drying kinetics of calcium oxide doped zirconia by microwave-assisted drying

Ca–ZrO2 is an essential structural and functional material, which is commonly used in refractories, electronic ceramics, and functional ceramics. The properties of Ca–ZrO2 materials are depending on the quality of Ca–ZrO2 powders. The main factors affecting the quality of powder are sintering temperature and the drying effect. This paper applied modern microwave drying technology to dry Ca–ZrO2 powder. The impact of initial mass, microwave heating power, and initial moisture content on the drying of Ca–ZrO2 were explored. The results showed that the average drying rate increased with the rise of initial mass, microwave heating power, and initial moisture content. Wang and Singh, Page, and Quadratic Model were applied to fit Ca–ZrO2 with an initial moisture content of 5.6%, mass of 30 g, and microwave output power of 400 W. The results displayed that the Page model had a better fitting effect. It was also applicable to other different initial moisture content, original mass, and microwave heating power. The diffusion coefficient calculated by Fick's second law displayed that with the increase of initial mass, initial moisture content, and microwave heating power of Ca–ZrO2, the effective diffusion coefficient increased first and then declined. When the Ca–ZrO2 of microwave heating power was 640 W, mass was 30 g, and the moisture content was 5.65%, the effective diffusion coefficients of zirconia were 1.42533 × 10−13, 2.91806 × 10−13, 5.652.2471 × 10−13 m2/s, respectively. To determine the activation energy of microwave dried zirconia, using the relationship between microwave power and activation energy, the activation energy of microwave dried zirconia was calculated to be −23.39 g/W. This paper aims to rich experimental data for the industrial application of microwaves to strengthen dried zirconia and propose a theoretical basis.

A V-Band Coaxial Relativistic Transit-Time Oscillator Operating in TM02Mode With Shallow Corrugated Output Structure

A V-band coaxial relativistic transit-time oscillator (TTO) with shallow corrugated output structure operating in TM₀₂ mode is presented. Compared with the deep corrugated output structure, the power handling capacity of the device with shallow corrugated output structure is higher. In particle-in-cell (PIC) simulation, a 403 MW output microwave at 59.10 GHz is obtained with beam voltage of 400 kV, beam current of 5.0 kA under the guiding magnetic field of 1.0 T. The maximum surface electric field in the device is 1.8 MV/cm. Compared with the maximum surface electric field in deep corrugated devices, the maximum surface electric field decreases by 38&#x0025;. In experiment, a microwave output with power of 258 MW, frequency of 59.04 GHz and pulse duration of 16.0 ns is obtained with diode voltage of 410 kV and beam current of 5.1 kA. The microwave output power and pulse width are significantly improved compared with the previous deep corrugated structure.

Experimental research on a gigawatt-class Ku-band coaxial transit-time oscillator with low guiding magnetic field

A Ku-band relativistic transit-time oscillator with a three-cavity extractor and a distance-tunable reflector was proposed in our previous work [Ling et al., Phys. Plasmas 24(1), 013103 (2017)]. Recently, a new experiment was carried out on this device with an intense relativistic electron beam generator that produces electron beams with a duration of 55 ns and voltage of 0.4–1 MV. In preliminary experiments, mode competition was found with three main frequencies of which the reasons are analyzed theoretically and experimentally. The results show that plasmas generated from the collector's surface are most likely to cause this problem. To solve this problem, the collector structure is extended axially. With an input voltage of 600 kV and a current of 11.7 kA, a microwave output power 1.9 GW with pulse width 26 ns and frequency 12.42 GHz is obtained under a 0.7 T guiding magnetic field. These experimental results effectively confirm the potential of high power capacity of this proposed Ku band transit-time oscillator.

Wide-Range Frequency-Agile Microwave Generation up to 10 GHz Based on Vanadium-Compensated 4H-SiC Photoconductive Semiconductor Switch

A frequency-agile microwave generating system is examined in this letter. Vanadium-compensated semi-insulation (VCSI) 4H-SiC photoconductive semi- conductor switch (PCSS) has been introduced to achieve wide-range frequency tuning. The output microwave frequency is tuned by adjusting the pulse width of the laser. Both the simulation and the experimental results show a tuning frequency range of 0.5 GHz to 10.0 GHz. The maximum operating output power of the system at 10 GHz is 1.13 W, equivalent to a charging voltage of 1.5 kV and a modulated light wavelength of 1064 nm. Further experiment revealed that with 355 nm laser and charging voltage of 5 kV, the output power could be increased to 86.5 kW.

High-sensitivity optical fiber sensor based on a Fourier domain mode-locked optoelectronic oscillator

We propose and experimentally demonstrate an optical fiber sensor based on a Fourier domain mode-locked optoelectronic oscillator (FDML-OEO), which is achieved by synchronizing the period of the driving current of the laser with the round-trip time of the OEO loop. Pulsed microwave output can be obtained when a narrow-band electrical filter with the central frequency located within the frequency scanning range of the FDML-OEO is employed in the cavity. Thanks to the triangle waveform of the laser driving signal, two microwave pulses can be observed in one period. The wavelength shift of the phase-shift fiber Bragg grating (PS-FBG) in the cavity will produce a shift of the frequency scanning range, resulting in the pulse interval variation of the OEO output. The experimental results indicate that the pulse interval of the generated signal has a linear relationship with the notch wavelength shift of the PS-FBG. By applying fiber axial strain to the PS-FBG, we obtained a high strain measuring sensitivity of 0.817 μs/με. The sensor reveals the advantages of highly sensitive and easy demodulation, providing great potential for practical applications.