Input Microwave Power Research Articles

Dual mode microwave deflection cavities for ultrafast electron microscopy

This paper presents the experimental realization of an ultrafast electron microscope operating at a repetition rate of 75 MHz based on a single compact resonant microwave cavity operating in a dual mode. This elliptical cavity supports two orthogonal TM110 modes with different resonance frequencies that are driven independently. The microwave signals used to drive the two cavity modes are generated from higher harmonics of the same Ti:Sapphire laser oscillator. Therefore, the modes are accurately phase-locked, resulting in periodic transverse deflection of electrons described by a Lissajous pattern. By sending the periodically deflected beam through an aperture, ultrashort electron pulses are created at a repetition rate of 75 MHz. Electron pulses with τ = (750 ± 10) fs pulse duration are created with only (2.4 ± 0.1) W of microwave input power; with normalized rms emittances of ϵn,x = (2.1 ± 0.2) pm rad and ϵn,y = (1.3 ± 0.2) pm rad for a peak current of Ip = (0.4 ± 0.1) nA. This corresponds to an rms normalized peak brightness of Bnp,rms=(7±1)×106 A/m2 sr V, equal to previous measurements for the continuous beam. In addition, the FWHM energy spread of ΔU = (0.90 ± 0.05) eV is also unaffected by the dual mode cavity. This allows for ultrafast pump-probe experiments at the same spatial resolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be used for exciting the sample. Moreover, the dual mode cavity can be used as a streak camera or time-of-flight electron energy loss spectroscopy detector with a dynamic range >104.

Circularly polarized antenna for coherent manipulation of NV-centers in diamond

Dielectric resonator antenna with circular polarization of microwave magnetic field for efficient, coherent and uniform spin manipulation at nitrogen-vacancy centers in diamond is discussed. The results of numerical simulations of the microwave magnetic field generated by the antenna are reported and analyzed. The uniform magnetic field with circular polarization is obtained inside the antenna. Using the simulated amplitude of the magnetic field inside the antenna the Rabi frequency is estimated. The Rabi frequency of 41 MHz with inhomogeneity less then 1 % for the diamond volume of 3 mm3 is demonstrated under 10 W of input microwave power.

Microwave heating characteristics of bulk metallic materials and role of oxides

In the present work, microwave heating characteristics of a few selected bulk metallic materials were studied in the ambient environment using 1400 W input microwave power at 2.45 GHz. Interactions of microwaves with the three target metallic materials—aluminum, copper and stainless steel and their effects were elucidated using the time–temperature profiles monitored during microwave hybrid heating. Metal oxides formed at different stages of the exposure were characterized using scanning electron microscopy and other X-ray-based techniques; role of the oxides in the heating behavior has been explained. The results revealed that heating of the target materials get influenced by the metallic oxides formed on the exposed surfaces of the metallic materials. The oxide layer reduces heat transfer between the susceptor and metallic material at initial stages of heating; however, it assists microwave absorption in the metallic materials depending upon its electromagnetic properties at elevated temperatures during irradiation. The oxide particles act as tiny susceptors initially, which, however, turn into secondary sources of conventional heating in the target material during hybrid heating.

A numerical investigation of microwave ablation on porous liver tissue

The understanding of heat transport in biological tissues is important for enhanced insight on the physiological mechanisms and thermoregulatory mechanisms. This article presents a numerical simulation of microwave (MW) ablation using a single-slot MW antenna on two layers of porous liver tissue. The two layers are of tumor and normal tissue. A porous media approach is proposed for mathematical model of MW ablation. Three coupled models which include transient momentum equations and a transient energy equation coupled with an electromagnetic wave propagation (EWP) equation are analyzed. This article focuses on the influences of the tumor diameter, tumor porosity, and input MW power on the specific absorption rate (SAR) profile, temperature profile, and blood velocity profile within the porous liver tissue. The results obtained from the calculation of porous media model are examined and compared with the one of bioheat model along with the experimental results from previous work. The results indicated that all parameters have a significant effect on the SAR profile, temperature profile, and blood velocity profile in the porous liver tissue. The advanced results in this research can be used in applications such as it provides guidance on the practical treatment and can be developed medically for therapeutic.

Direct Thrust Measurement of an Electron Cyclotron Resonance Plasma Thruster

Direct thrust measurements of an electron cyclotron resonance plasma thruster are performed with a thrust balance. The thruster performances are deduced, and the influence of power and mass-flow rate is studied. The measured thrust is around 1 mN for 50 W of microwave power input and of xenon, corresponding to 1000 s of specific impulse and 11% of total efficiency. It is found that the thrust is increased by 25% when the walls of the plasma source are covered with a dielectric layer. Comparisons are made between the direct thrust measurements and the indirect thrust measurements obtained with electrostatic probes in the plasma beam.

Impact of hydrocolloid addition and microwave processing condition on drying behavior of foamed raspberry puree

In this study, foamed raspberry puree was dried by microwave-assisted freeze drying (MWFD). The combined use of microwaves and a foamed structure was intended to accelerate the drying process, while creating an innovative product structure with intense aroma impact for consumption as a snack. The influence of potato protein as foaming agent, maltodextrin as foam stabilizer and microwave (MW) power on the drying characteristics of raspberry foams during MWFD was investigated. Conventional freeze drying (FD) experiments were performed as a reference. MD concentration was shown to significantly influence product temperature. As higher MD concentrations yielded smaller bubbles and a more uniform bubble size distribution, lower drying temperatures were needed to reach the same final moisture content.Varying MW power did not significantly influence the drying time. MWFD at 1.0 W g−1 yielded a 3–4-fold decrease in total drying time as compared to FD. The addition of 10% protein led to the most gentle drying at high MW power input due to structural changes enabling a lower resistance against water vapor mass transfer. There was a high correlation between the foam characteristics and the drying behavior. An overrun above 450% led to gentle drying at all tested microwave power input levels. Foam bubble size and bubble size distribution correlated well with drying velocity. Overall, MWFD was shown to be a much faster and more gentle alternative to FD for the production of fruit foams.

Microwave heating behaviors of used mercury-containing catalysts

Heating characteristics of two types of used mercury-containing catalysts with different mercury content in microwave field were studied. Spent mercury catalysts were proved to be good microwave receptors. Heating curves were analyzed using heat transfer equation. With microwave heating, the sample temperature increased linearly, then increased gradually with considering heat loss, and finally reached an equilibrium value. Effects of material mass, microwave input power and particle size on heating behaviors were investigated. A proper material mass fitted with microwave power can lead to higher average heating rate and equilibrium temperature. Sample temperature increased with increasing input power at a constant material mass. Average heating rate was linearly related to input power. A good linear fitting relation between equilibrium temperature and input power was observed especially for catalyst support activated carbon and used low-level mercury catalysts.

Direct Thrust Measurements of an 8-GHz Microwave Electrothermal Thruster

Direct thrust measurements of an 8-GHz microwave electrothermal thruster were performed. Experimental work involved the redesign of the thruster cavity to minimize its weight and the construction of a vertical thrust stand. Thrust measurements were made using ammonia and simulated hydrazine (50% and 100% decomposed) as propellants. Testing was performed over a range of 100–250 W of microwave power input into the thruster. For all three propellants, the thrust increased with the increasing mass flow at higher microwave power levels able to sustain plasma at higher flow rates. Ammonia specific impulse increased with increasing cavity input power, reaching 264 s at 250 W. The 50% and 100% simulated decomposed hydrazine exhibited an initial increase in specific impulse with increasing power; however, further increases in power did not result in increased specific impulse. Higher levels of thrust and specific impulse at the same microwave input power were measured for the 100% decomposed simulated hydrazine compared to the 50% decomposed due to the absence of ammonia in the 100% decomposed hydrazine.

Systematic research on the performance of self-designed microwave plasma reactor for CVD high quality diamond

Abstract Optical grade diamond, in particular, high-end products, are mainly used for aerospace and defense purposes. How to manufacture them with higher quality and lower cost was critical technology. Systematic research on the performance of Self-designed plasma reactor with higher power for synthesizing diamond film was carried out. Microwave input power can reach up to 10 kW, the plasma reactor has good adaptability for the deviation of microwave frequency f at 2.45 GHz ± 20 MHz. The secondary plasma could be eliminated by adjusting the working gas pressure and the cylinder adjustment structure, it is helpful to improve the deposition rate with less energy loss. The concentrated and steady plasma could be obtained device with higher gas pressure and relative lower microwave input power. Gas supply modes and inlet gas flow rate were optimized, which would be beneficial to synthesize the film with good quality.

On-site SiH4 generator using hydrogen plasma generated in slit-type narrow gap

We have been developing an on-site silane (SiH4) generator based on use of the chemical etching reaction between solid silicon (Si) and the high-density H atoms that are generated in high-pressure H2 plasma. In this study, we have developed a slit-type plasma source for high-efficiency SiH4 generation. High-density H2 plasma was generated in a narrow slit-type discharge gap using a 2.45 GHz microwave power supply. The plasma’s optical emission intensity distribution along the slit was measured and the resulting distribution was reflected by both the electric power distribution and the hydrogen gas flow. Because the Si etching rate strongly affects the SiH4 generation rate, the Si etching behavior was investigated with respect to variations in the experimental parameters. The weight etch rate increased monotonically with increasing input microwave power. However, the weight etch rate decreased with increasing H2 pressure and an increasing plasma gap. This reduction in the etch rate appears to be related to shrinkage of the plasma generation area because increased input power is required to maintain a constant plasma area with increasing H2 pressure and the increasing plasma gap. Additionally, the weight etch rate also increases with increasing H2 flow rate. The SiH4 generation rate of the slit-type plasma source was also evaluated using gas-phase Fourier transform infrared absorption spectroscopy and the material utilization efficiencies of both Si and the H2 gas for SiH4 gas formation were discussed. The main etch product was determined to be SiH4 and the developed plasma source achieved a SiH4 generation rate of 10 sccm (standard cubic centimeters per minute) at an input power of 900 W. In addition, the Si utilization efficiency exceeded 60%.

Microwave-freeze drying of lactic acid bacteria: Influence of process parameters on drying behavior and viability

Abstract Microwave-freeze drying was investigated as an alternative to conventional lyophilization to preserve the lactic acid bacteria Lactobacillus paracasei ssp. paracasei F19 (Lb. paracasei) and Bifidobacterium animalis ssp. lactis INL1 (B. lactis). The process parameters microwave power input (1.5–3 W∗g−1) and chamber pressure (0.6, 1, 2 mbar) were varied. Drying kinetics, overall drying time, process stability and energy demand were assessed. Survival rate and cell membrane integrity were evaluated. Survival rate and membrane integrity after microwave-freeze drying were comparable to the standard lyophilization process for both cultures. For Lb. paracasei, survival could almost be maintained at all microwave-freeze drying process conditions. Best results in terms of process stability were achieved at 1 mbar and 1.5 W∗g−1. For B. lactis, the highest survival of more than 90% was measured at 0.6 mbar and 1.5 W∗g−1 microwave input. These conditions led to a drying time of 5 h, whereas conventional freeze drying lasted 24 h. A potential reduction of drying time compared to freeze drying of bacterial cultures of up to 80% renders microwave-freeze drying an alternative with comparable survival rates but higher efficiency.

Superconducting membrane mechanical oscillator based on vacuum-gap capacitor**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0301801), the National Natural Science Foundation of China (Grant Nos. 11474154 and 61521001), and the Priority Academic Development Program of Jiangsu Higher Education Institutions and Dengfeng Project B of Nanjing University, China.

Using the diluted S1813 UV photoresist as a sacrificial layer, we successfully fabricate a superconducting suspended parallel-plate capacitor, in which the top layer of aluminum film acts as a membrane mechanical resonator. Together with a superconducting octagonal spiral inductor, this parallel-plate capacitor constitutes a superconducting microwave resonator. At mK temperature, the transmission characteristic and spectrum of the microwave resonator are measured. Sideband frequencies caused by the vibration of the membrane mechanical resonator are clearly demonstrated. By down-converting with a mixer, the dependence of fundamental frequency and its harmonics on the input microwave power are clearly demonstrated, which is consistent with the numerical simulation.

Optimization of Biodiesel Production using a Stirred Packed-bed Reactor

The use of waste cooking oil (WCO) as feedstock and in microwave heating technology helps to reduce the cost of biodiesel. In this study, a continuous flow transesterification of waste cooking oil (WCO) by microwave irradiation for biodiesel production using calcium oxide (CaO) as aheterogeneous catalyst, calcined from cockle shells, is used. The catalyst was packed inside a plastic perforated container mounted on a stirrer shaft and inserted inside the reactor. The thermocouple inside the reactor was connected to a temperature controller and microwave power input to maintain the temperature. Response surface methodology (RSM) was employed to study the relationships between power input, stirrer speed and liquid hourly space velocity (LHSV) on the WCO methyl ester (WCOME) conversion at a fixed molar ratio of methanol to oil of 9 and a reaction temperature set at 65°C. The experiments were developed using the Box-Behnken design (BBD) for optimum conditions. The transesterification of the WCO was produced at 72.5% maximum WCOME conversion at an optimum power input of 445 W, stirrer speed of 380 rpm and LHSV of 71.5 h-1. The energy consumption in a steady state condition was 0.594 kWh for the production of 1 litre WCOME, for this heterogeneous catalyst is much faster than conventional heating.

CO2 neutral fuels

CO2 is a valuable resource, life on Earth depends on it. Rather than wasting it to the atmosphere, or burying it underground, CO2 can be combined with water and turned into valuable chemicals and fuels, the process being powered by renewable electricity. Renewable electricity generated by wind and photovoltaics (PV) is making big strides, but is limited by ill-matched supply and demand. In addition, electricity only makes up 20% to 30% of total energy demand. Domestic heating, high temperature/pressure Industrial processes and mobility/transportation gobble up the rest. Mobility and transportation prove particularly difficult to decarbonise. Aviation is a case in point. Battery-powered aircraft are unlikely to become feasible by 2050. Hydrogen has too low an energy density and is haunted by safety issues. Current policy, therefore, is directed at bio fuels. One problem, there is not enough of it. The Fuel vs. Food vs. Flora trilemma of bio-based fuel is unlikely to gain public acceptance. By converting renewable electricity into fuel, power to molecules (P2M), two birds are killed with one stone: providing fuel for long haul transportation and enabling long-term, large-scale energy storage to cover the seasonal mismatch between supply and demand of renewable electricity. Feedstock consists of air-captured carbon or nitrogen and water. Chemically combined, it creates a liquid fuel with greatly enhanced energy density, such as kerosene or ammonia, or gaseous fuel like methane which can replace natural gas in the existing gas network. Direct air capture of CO2 is currently being commercialised. The conversion technology of water and CO2 by electrolysis has recently been extended to novel plasma technology, the sub ject of this paper. For CO2 splitting by plasmolysis, the reduced electric field has been identified as the key parameter explaining and improving the energy efficiency. Energy efficiency by plasmolysis is similar to that of electrolysis, but offers advantages in energy density, upscaling and switching in response to intermittent power with no use of scarce material. A simple model explains the inverse relation between energy efficiency and particle conversion and relates input microwave power to CO2 gas density, plasma dimension and ionisation degree, allowing design parameters for a 100 kW pilot reactor to be specified. Recycling CO2 in combination with P2M is a game-changing technology to meet overall CO2 emission reduction targets. It takes advantage of existing, inexpensive infrastructure for energy storage, transport and distribution. Existing internal combustion engine technology can be maintained where necessary. Close coupled to a remote solar array or an off-shore wind farm it offers a solution to decentralised renewable fuel production at the renewable electricity source.

Temperature-controlled microwave-vacuum drying of lactic acid bacteria: Impact of drying conditions on process and product characteristics

An efficient drying process for high-value products such as bacterial cultures is characterized by high retention of viability or activity, but low energy demand. Microwave-vacuum drying was tested in this work as a new technique for the preservation of probiotics and starter cultures, which has the potential to fulfill all of these requirements. The impact of chamber pressure (7, 15, 30 mbar), microwave power (1–5 W g−1) and maximum product temperature (30–50 °C) on drying time, drying rate, efficiency of microwave input and survival rate of the model strain Lactobacillus paracasei ssp. paracasei F19 (L. paracasei F19) was studied. Microwave drying time ranged from 50 to 240 min with microwave power as main influencing factor on drying behavior and efficiency. The maximum product temperature and vacuum pressure did not affect the drying time, absorbed energy and thus microwave efficiency significantly, but both parameters had a great impact on survival rate. The combination of 3 W g−1 microwave power input and 35 °C maximum temperature at a low chamber pressure of 7 mbar resulted in a very short drying time of 64 min, a high level of energy efficiency (27%) and also the best product quality in terms of survival rate (33%). Thus, a microwave-vacuum drying process is a potential alternative to conventional freeze or vacuum drying.

Characteristics of a KA-band third-harmonic peniotron driven by a high-quality linear axis-encircling electron beam

We employ a high-quality linear axis-encircling electron beam generated by a Cuccia coupler to drive a Ka-band third-harmonic peniotron and develop a self-consistent nonlinear calculation code to numerically analyze the characteristics of the designed peniotron. It is demonstrated that through a Cuccia coupler, a 6 kV, 0.5 A pencil beam and an input microwave power of 16 kW at 10 GHz can generate a 37 kV, 0.5 A linear axis-encircling beam, and it is characterized by a very low velocity spread. Moreover, the electron beam guiding center deviation can be adjusted easily. Driven by such a beam, a 30 GHz, Ka-band third-harmonic peniotron is predicted to achieve a conversion efficiency of 51.0% and a microwave output power of 9.44 kW; the results are in good agreement with the Magic3D simulation. Using this code, we studied the factors influencing the peniotron performance, and it can provide some guidelines for the design of a Ka-band third-harmonic peniotron driven by a linear electron beam and can promote the application of high-harmonic peniotrons in practice.

Electron cyclotron resonance plasma reactor for production of carbon stripper foil

A graphite antenna for the production of carbon-containing hydrogen plasmas is being developed to prepare impurity-free charge exchange foils for high-energy synchrotrons. Microwave power at 2.45 GHz frequency drives a coaxial structure antenna with a 12-mm-diameter central graphite cylinder and a tapered surrounding cylinder serving as the ground electrode. The antenna was placed in a linear magnetic field to investigate how it performs under an electron cyclotron resonance (ECR) condition. A clear resonance phenomenon was observed in plasma luminosity, microwave power absorption, and microwave power reflection when the induction current used to produce a linear magnetic field was changed. The antenna realized the best microwave coupling to the plasma with the ECR zone formed 5 mm from the end of the center electrode. The antenna realized stable operation for more than 5 h with 100 W input microwave power and with operating hydrogen pressure from 0.5 to 50 Pa.

Nonlinear spin waves in dynamic magnonic crystals created by surface acoustic waves in yttrium iron garnet films

Experimental results on the influence of the intensity of surface magnetostatic spin wave (SMSW) on its propagation in the dynamic magnonic crystals (MCs) created by surface acoustic waves (SAW) propagating in yttrium iron garnet (YIG) film on the gallium gadolinium garnet (GGG) substrate are presented. The shift of the resonant frequency of the SMSW reflections (frequency of the magnonic gap) and widening of the resonant reflection curves (increasing the width of the magnonic band gap) from their former meanings (3730 MHz and 5.25 MHz, respectively) were observed at 20 MHz SAW of 20 mW in biasing magnetic field of 640 Oe at input microwave power exceeding the threshold value of −5 dBm. At the input power of 10 dBm, the deviations of the magnonic gap frequency and of the width of the SMSW resonant reflected curves reach the values of 5 MHz and 2 MHz, respectively. At a frequency of 3730 MHz, a decrease in the reflection coefficient of the SMSW was observed at the input powers above the threshold. These results may be useful in investigations of MC and for creating new nonlinear signal processing devices.

Deposition of large area uniform diamond films by microwave plasma CVD

Diamond films with 70 mm in diameter were deposited on silicon substrates with Ar/CH4/H2 gas mixture, using microwave plasma chemical vapor deposition (MPCVD) technique. One designed water-cooling substrate stage was used to improve the uniformity of the surface temperature across the substrate. An uniform substrate surface temperature was obtained at the pressure of 10 kPa when the input microwave power was 5500 W. The condition of the plasma was diagnosed by optical emission spectrum (OES) and the grown diamond films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that higher microwave power can further improve the uniformity of the temperature distribution across the substrate which in turn increases the uniformity of diamond film. And introducing more H2 into Ar/CH4/H2 gas mixture at high microwave power is effective on the improvement of the quality and the decrease of the stress in the deposited diamond films. The diamond films with low average intrinsic stress of 0.32 GPa were finally deposited with introducing 100 sccm H2 into Ar/CH4/H2 gas mixture at 5500 W.

Controllable optical bistability in an optomechanical system assisted by microwave

We theoretically investigate bistable behaviour of the mean intracavity photon number in an optomechanical system, where a cavity mode and microwave field are coupled to a common mechanical resonator. The results of the numerical simulation demonstrate that by tuning the signal of microwave field, optical bistability can be controlled. More importantly, we found that by tuning the microwave input power or pump laser-exciton detuning, the optical bistability can be obviously modulated. These results can be used to find potential applications in optical switch in the quantum information processing.