Microwave Output Research Articles

A high-efficiency cross-band Cerenkov microwave generator with a resonant reflector

High efficiency and short saturation time have great significance on the practical work of high power microwave devices. A dual-band Cerenkov microwave generator with high-efficiency based on electrical tuning is presented in this paper. Two-segment slow wave structures for the C-band and X-band separately are adopted, which are isolated by a drift cavity. The collimating hole is replaced by a resonant reflector, which can effectively shorten the saturation time. Moreover, in order to realize dual-band microwave output, the electrical tuning method is used in this paper. In particle-in-cell simulation, when the guiding magnetic field is 0.7 T, the output microwaves at the X-band can be obtained with an efficiency of 38% and saturation time for nearly 20 ns; when the guiding magnetic field is 1.5 T, the output microwaves at the C-band can be obtained with an efficiency of 32% and saturation time for nearly 20 ns. Thus, microwaves at the X-band and C-band can be generated separately by modulating the guiding magnetic field, which can be realized just by altering the current in the magnetic coil. It should be mentioned that such a modulating method is much more convenient than mechanical modulation.

A long-distance high-power microwave wireless power transmission system based on asymmetrical resonant magnetron and cyclotron-wave rectifier

This paper demonstrates the analysis of a long-distance high-power microwave wireless power transmission (MWPT) system based on asymmetrical resonant magnetron and cyclotron-wave rectifier. In the system, the novel magnetron with the asymmetrical resonant cavity, the straps, and the output loop coupling circuit can effectively promote the beam–wave interaction, suppress the mode competition, and enhance the output coupling, which results in a 400 kW output microwave power with a conversion efficiency of 45%. The transceiver Cassegrain antenna system with its simple structure, high conversion efficiency, and high power capacity can attain an integral power transmission efficiency of 2.6% at 10 km distance. The cyclotron-wave rectifier with high efficiency and single-tube high power capacity can achieve 85% microwave to DC conversion efficiency. Finally, the long-distance high-power MWPT system can achieve 8.5 kW DC power with about 1% DC–DC transmission efficiency at the operating 2.45 GHz frequency and for the 10 km distance. Such a system is likely a potential and attracting solution to remotely power the fuel-free aerial vehicle from the ground, can also provide electrical power to an isolated mountain top or an island, and even an alternative to transmit the power from space solar power satellite in geostationary orbit to the ground.

Influence of drying methods on the nutrients, protein content and vitamin profile of basil leaves

In this study, basil leaves were dried using natural, microwave-, and convective-drying methods from an initial moisture content of 90.90 ± 0.1 % to a final one of 8.21 ± 0.12 %. The natural drying was done in a controlled room at a temperature of 25 ± 1 °C and relative humidity of 60 ± 5 %. The microwave-drying processes were performed using 100, 300, 500, 700, and 900 W microwave output powers, while 50 °C was used in convective-drying. The drying periods of different drying methods lasted between 16.5 and 1620 min. Consequently, the best drying method regarding drying period, energy consumption, protein amount, macronutrients (Cu, Zn, Fe, Mn and B), micronutrients (Cu, Zn, Fe, Mn and B), water-soluble vitamins (ascorbic acid, Vitamin B3 and Vitamin B6), fat-soluble vitamins (beta-carotene, Vitamin E, and Vitamin K), color parameters (L, a, b, C and α) and chlorophyll concentration was determined to be microwave-drying at 700 W.

Cultural Interference [Microwave Bytes

Examines what the author contends are the differences most frequently noted between digital and RF electronics. I have recently encountered another cultural conflict in the technological zone of optical communications— more specifically, the process of “detecting” an optical signal to obtain a microwave output. This is a world where the “RF” is light, and “intermediate frequency” (IF) is gigahertz. Despite having the electromagnetic (EM) spectrum chart and Maxwell‘s equations rammed down my throat from a relatively early age, I have always been fascinated by the “gap” that exists between where microwaves give way to light waves. It is an enormous gap, an unexplored EM ocean, comprising maybe about five orders of magnitude of wavelength.

Kinetic studies for microwave-assisted drying of Oraby date slices

This study was conducted to evaluate the effects of microwave (MW) output power on the drying kinetics and quality of ascorbic acid pretreated and untreated Oraby date slices (2, 4 and 6 mm in thickness and 24 ± 2 mm in diameter) at the end of khalal stage. The initial moisture content was 1.7397 d.b. The drying experiments were carried out using three levels of MW output power 160, 320 and 480 W. The obtained experimental data were fitted with three empirical models. The effect of MW power on drying time and drying rate were determined. Effect of drying on sugars, total phenols, tannins contents and color measurements were studied. Because of occurrence of some charring (burning) when MW drying of 4- and 6-mm slices goes beyond moisture content of 0.3678 kg[H2O].kg-1dry matter, thereafter MW drying was stopped, then drying was completed using a conventional oven at 60°C to avoid sample discoloration or burning. MW drying of 2 mm slices was completed without showing such burning. The Midilli et al. model was the best fit for the data of MW drying as well as the following convention oven drying. All sensory attributes for the dried Oraby date slices were acceptable by the panelists, however, the 2 mm slices received the highest panelists’ scores. MW shortened the time needed for drying.

A 5.8-GHz Phased Array System Using Power-Variable Phase-Controlled Magnetrons for Wireless Power Transfer

We build a phased array system with four power-variable phase-controlled magnetrons (PCMs) by applying the injection-locking method and phase-locked-loop method. To reduce the cost and ensure the durability of the phased array, a waveguide slot array antenna was designed and used for the output antenna of power-variable PCMs. The slot antenna has an expected angle deflection of 22.5°, a gain of 24.9 dBi, and the half bandwidth of the main lobe was 10°. We demonstrated the properties of microwave beamforming and wireless power transfer based on the magnetron phased array system. In horizontal directions, a beam scanning range of ±3° was obtained by adjusting the output phase of the magnetrons. Furthermore, the received dc power reaches 142 W at a distance of 5 m when the output microwave power of the magnetron phased array is 1304 W.

Spin\u2013orbit torque nano-oscillator with giant magnetoresistance readout

Spin-orbit torque nano-oscillators based on bilayers of ferromagnetic and nonmagnetic metals are ultra-compact current-controlled microwave signal sources. They are attractive for practical applications such as microwave assisted magnetic recording, neuromorphic computing, and chip-to-chip wireless communications. However, a major drawback of these devices is low output microwave power arising from the relatively small anisotropic magnetoresistance of the ferromagnetic layer. Here we experimentally show that the output power of a spin-orbit torque nano-oscillator can be significantly enhanced without compromising its structural simplicity. Addition of a ferromagnetic reference layer to the oscillator allows us to employ current-in-plane giant magnetoresistance to boost the output power of the device. This enhancement of the output power is a result of both large magnitude of giant magnetoresistance compared to that of anisotropic magnetoresistance and their different angular dependencies. Our results hold promise for practical applications of spin-orbit torque nano-oscillators.

Dispersion effects on the performance of whispering gallery mode based optoelectronic oscillators

Optoelectronic oscillators (OEOs) based on optical whispering gallery mode resonators (WGMRs) are amongst state-of-the-art technologies to generate ultra-low phase noise microwave signals. In this paper, a WGMR-based OEO is designed and effects of dispersion on its performance, such as phase noise, amplitude, and frequency of oscillation are theoretically investigated which are verified by simulations. Dispersion causes each mode existing inside a WGMR to experience a distinctive optical delay depending on its frequency. Considering the material and geometric dispersion of the WGMR used as the storage element of the OEO, we show that dispersion does not mainly affect the amplitude of oscillation while it affects the frequency of oscillation and phase noise of the output microwave signal. Indeed, through calculating the group delay and the group delay dispersion, we show that laser frequency noise (LFN) is converted into the phase noise of the generated microwave signal via the dispersion of the optical WGMR. Theoretical calculations are verified by the results obtained from two other previously published methods, i.e. the Langevin approach and the conversion matrix approach.

Preliminary experimental research of a Ka-band radial transit time oscillator.

Radial transit time oscillator (RTTO) can be relied on to generate effective coherent electromagnetic radiation in the millimeter wave domain. In this paper, the preliminary experimental research on a Ka-band RTTO is reported for the first time. In experiments, the radial electron beam emitted from the knife edge of the disk cathode is guided by the radial magnetic field. The bombardment trace on the nylon target verifies the emission and transportation uniformity of the radial e-beam. When the diode voltage is 410 kV, the beam current is 7.8 kA, and the magnetic field is 0.6 T, the RTTO can output microwaves with the power of 320 MW and the frequency of 31.35 GHz. As the diode voltage increases from 350 kV to 430 kV, the output microwave power will grow accordingly. Taking the ohmic loss into consideration, the experimental results are in agreement with the simulation ones.

A Cerenkov microwave generator with cross-band frequency hopping based on magnetic field tuning

Frequency hopping is one of the most significant technological advancements in high power microwave (HPM) sources. Mechanical alteration is generally adopted in traditional cross-band microwave generation, but it has the detriments of a complex adjustment strategy. In this paper, a cross-band frequency hopping Cerenkov microwave generator with an advantageous adjustment strategy, high beam–wave interaction efficiency, and pure output mode is developed. Two-segment slow wave structures (SWSs), which work in C and X-bands separately, are adopted. Additionally, by utilizing the cyclotron resonance absorption phenomenon reasonably, only the relative band microwave is energized under different magnetic fields, which adequately represses mode competition and realizes cross-band frequency hopping. After the electron beam passes through the first SWS section, the bunching center is consistently at the acceleration or deceleration phase of the subsequent SWS section, which a guarantees high beam–wave interaction efficiency in the two bands. The preliminary results of the particle-in-cell (PIC) simulation are as follows: when the guiding magnetic field is 0.7 T, the microwave output comprising only the X-band is obtained, with an efficiency of 42%; when the guiding magnetic field is 1.5 T, the microwave output comprising only the C-band is obtained, with an efficiency of 30%.

A Scalable Cryo-CMOS Controller for the Wideband Frequency-Multiplexed Control of Spin Qubits and Transmons

Building a large-scale quantum computer requires the co-optimization of both the quantum bits (qubits) and their control electronics. By operating the CMOS control circuits at cryogenic temperatures (cryo-CMOS), and hence in close proximity to the cryogenic solid-state qubits, a compact quantum-computing system can be achieved, thus promising scalability to the large number of qubits required in a practical application. This work presents a cryo-CMOS microwave signal generator for frequency-multiplexed control of 4 × 32 qubits (32 qubits per RF output). A digitally intensive architecture offering full programmability of phase, amplitude, and frequency of the output microwave pulses and a wideband RF front end operating from 2 to 20 GHz allow targeting both spin qubits and transmons. The controller comprises a qubit-phase-tracking direct digital synthesis (DDS) back end for coherent qubit control and a single-sideband (SSB) RF front end optimized for minimum leakage between the qubit channels. Fabricated in Intel 22-nm FinFET technology, it achieves a 48-dB SNR and 45-dB spurious-free dynamic range (SFDR) in a 1-GHz data bandwidth when operating at 3 K, thus enabling high-fidelity qubit control. By exploiting the on-chip 4096-instruction memory, the capability to translate quantum algorithms to microwave signals has been demonstrated by coherently controlling a spin qubit at both 14 and 18 GHz.

Non-uniform guiding magnetic field for efficiency enhancement of RBWO

Relativistic backward wave oscillator (RBWO) having a resonant reflector and slow wave structure (SWS) combination has been simulated for a 400 kV peak accelerating voltage and a 4.0 kA peak electron beam current. The particle in cell simulations predict an electron beam to microwave conversion efficiency of 44% at a 3.22 GHz operating frequency. Phase space plot analysis reveals that the backstreaming of electrons from the end reflector and the end part of SWS affects the device efficiency. It was demonstrated using particles in cell simulations that with non-uniform guiding magnetic field, these backstreaming electrons do not attain synchronism with the forward wave while drifting toward the anode end and eventually rebound from the anode–cathode gap. Backstreaming of electrons reduces with increasing non-uniformity in the magnetic field. These two phenomena result in a significant enhancement in the output microwave power at a 3.22 GHz frequency and device efficiency enhances to a level of 62%. With the proposed guiding magnetic field profile, RBWO retains a larger than 52% electron beam to microwave conversion efficiency with the nominal accelerating voltage anywhere in between 400 and 600 kV and an electron beam current of 3.9–7.2 kA.

Beyond linear coupling in microwave optomechanics

We explore the nonlinear dynamics of a cavity optomechanical system. Our realization consisting of a drumhead nano-electro-mechanical resonator (NEMS) coupled to a microwave cavity, allows for a nearly ideal platform to study the nonlinearities arising purely due to radiation-pressure physics. Experiments are performed under a strong microwave Stokes pumping which triggers mechanical self-sustained oscillations. We analyze the results in the framework of an extended nonlinear optomechanical theory, and demonstrate that quadratic and cubic coupling terms in the opto-mechanical Hamiltonian have to be considered. Quantitative agreement with the measurements is obtained considering only genuine geometrical nonlinearities: no thermo-optical instabilities are observed, in contrast with laser-driven systems. Based on these results, we describe a method to quantify nonlinear properties of microwave optomechanical devices. Such a technique, available now in the quantum electro-mechanics toolbox, but completely generic, is mandatory for the development of new schemes where higher-order coupling terms are proposed as a new resource, like Quantum Non-Demolition measurements, or in the search for new fundamental quantum signatures, like Quantum Gravity. We also find that the motion imprints a wide comb of extremely narrow peaks in the microwave output field, which could also be exploited in specific microwave-based measurements, potentially limited only by the quantum noise of the optical and the mechanical fields for a ground-state cooled NEMS device.

Valorization of Sweet Lime Peel for the Extraction of Essential Oil by Solvent Free Microwave Extraction Enhanced with Ultrasound Pretreatment.

Essential oils of sweet lime peel, a waste by-product in the juice industry, were extracted using the vacuum assisted solvent free microwave extraction (VASFME) method. The effects of microwave output power (500–1000 W) and extraction time (20–30 min) on the essential oils yield and antimicrobial property were investigated. Optimal conditions were observed at 797.844 W microwave output power and 30 min extraction time. The essential oils yield and antimicrobial property under these conditions were 0.792 ± 0.03% and 18.25 ± 1.45 mm, respectively, which agrees with the predicted values of 0.757% and 16.50 mm. The essential oils were extracted at optimized conditions and analyzed through GCMS for compound identification. A total of 49 compounds were identified, with limonene content (43.47%) being the highest among all sweet lime peel oil compounds. Moreover, the sweet lime peels were subjected to ultrasound pre-treatment before microwave extraction. The ultrasound pre-treatment helped to increase the essential oils yield from 0.84 to 1.06% as the treatment time increased from 30 to 90 min. The increase in yield was 37.66% more compared to VASFME at 90 min treatment time.

An improved corrugated waveguide mode purifier for TEM output in a V-band overmoded coaxial millimeter-wave oscillator

In the overmoded microwave sources, there inevitably exist multi-modes in the output microwave, so it needs to be purified to obtain the single mode output. However, due to the large longitudinal size, the traditional concave-type purifier is not suitable for coaxial devices with large overmoded ratio. The present paper proposes an improved convex-type purifier based on the coupled wave equations. With this purifier, 99.98% TEM mode can be gained effectively under the conditions of diode voltage 355 kV and beam current 3.0 kA. Compared with the traditional concave-type converter, the improved purifier has the higher coupling coefficient and its longitudinal size can be reduced by 40%.

Output microwave characteristics of a Ka-band relativistic klystron amplifier with spatially nonuniform multibeam electron emission

The effects of spatial nonuniformity of electron multibeam emission on the output characteristics of a coaxial multibeam Ka-band relativistic klystron amplifier (RKA) are investigated using particle-in-cell simulations. The spatial nonuniformity is simulated using four different electron multibeam emission models, with (1) a continuous cathode non-emission area, (2) discontinuous cathode emission areas, (3) discontinuous cathode emission areas with different electron emission current densities, and (4) cathode emission areas with different and time-varying electron emission current densities. The simulation results with the first model show that the output microwave power of the RKA decreases as the continuous non-emission area increases, but that size of the continuous non-emission area has little effect on the frequency and pulse width of the RKA. The results with the second model show that the more uniform the electron current density in the discontinuous emission areas, the greater the output microwave power. The results with the third model show that the more uniform the distribution of the Z component of the induced electromagnetic field in the discontinuous emission areas, the greater the output microwave power, and also that the output microwave power increases as this Z component increases. The results with the fourth model show that fluctuations in the electron current density in the discontinuous emission areas in the steady-state phase of RKA operation cause fluctuations in both microwave frequency and output microwave power and that these fluctuations increase as the fluctuations in electron current density become stronger and as they become more rapid.

Frequency-Tunable and Circularly Polarized Microwave Resonator for Magnetic Sensing With NV Ensembles in Diamond

A microwave (MW) resonator to provide frequency-tunable and circularly polarized MW fields is proposed. This technology enlarges the range of application in optically detected magnetic resonance (ODMR) systems based on the diamond negatively charged nitrogen-vacancy (NV) center and enable the selective excitation of its electronic spins. The characteristics of this resonator are simulated and discussed via a series of experimental studies. An adjustable MW frequency (f MW ) can be provided in the 2.5-3.1GHz range and the value of the input return loss (S11) corresponding to f MW measures <; -15 dB which mean at least 96.84% coupling efficiency between the microwave resonator and the microwave source. When f MW is equal to the resonance frequency of the NV center (f NV ) for different external magnetic fields (B), the results of the ODMR experiment indicate that the fluorescence increases upon an increase in |B|. Finally, the resonator provides a circularly polarized MW output with a purity of 97.17%. This study paves the way to novel applications and to the development of magnetic sensing devices based on the NV ensemble in diamond.

Microwave treatment of municipal sewage sludge: Evaluation of the drying performance and energy demand of a pilot-scale microwave drying system

Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L−1 (0.74 kWh L−1) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.

DRYING KINETICS AND CHANGES IN COLOR PARAMETERS WHEN DRYING GREEN PEA (Pisum Sativum l.) IN MICROWAVE

This research was conducted to determine the drying, rehydration behavior and color parameters changes of green peas when microwave drying at different temperatures. For drying, 6 drying kinetics models were applied. The values of L*, a*, b*, C* and Ho were measured to determine the effect of the microwave drying on the color parameters. The most suitable model was the parabolic model in microwave drying of green peas. Effective diffusion coefficients changed between 2.50x10-9 m2s-1 and 8.16x10-9 m2s-1. The activation energy was found as 1279.7 W/g. Equilibrium moisture contents ranged from 1.982 to 2.491 according to the Peleg Model and could not reach the initial moisture content at all microwave output powers after rehydration. L*, a* and b* color parameters were significantly influenced by microwave drying, while C* and Ho values were not the much affected.

Novel compact and lightweight coaxial C-band transit-time oscillator**Project supported by the National Natural Science Foundation of China (Grant No. 61701516).

Compactness and miniaturization have become increasingly important in the development of high-power microwave devices. Based on this rising demand, a novel C-band coaxial transit-time oscillator (TTO) with a low external guiding magnetic field is proposed and analyzed. The proposed device has the following advantages: simple structure, short axial length, high power conversion efficiency, and low external guiding magnetic field, which are of great significance for developing the compact and miniaturized high-power microwave devices. The application of a shorter axial length is made possible by the use of a transit radiation mechanism. Also, loading the opening foil symmetrically to both ends of the buncher helps reduce the external magnetic field of the proposed device. Unlike traditional foils, the proposed opening foil has a circular-hole; therefore, the electron beam will not bombard the conductive foil to generate plasma. This makes it possible to realize long pulse and high repetition rate operation of the device in future experiments. Through numerical calculation and PIC particle simulation, the stability of the intense relativistic electron beam (IREB) and the saturation time of the device are improved by using the conductive foil. The voltage and current of the diode are 548 kV and 11.4 kA, respectively. Under a 0.4-T external guiding magnetic field, a C-band output microwave with a frequency of 4.27 GHz and power of 1.88 GW can be generated. The power conversion efficiency of the proposed device is about 30%.