Function Of Microwave Power Research Articles

Intense vanadium ion beam production for super-heavy element research experiments

Long-term production of an intense 51V13+ ion beam was imperative for synthesizing a new element (Z=119) at RIKEN. We systematically measured the beam intensity as a function of microwave power and material consumption rate for effectively producing an intense beam. Consequently, we generated a 1 emA of 51V13+ ion beam at an injected microwave power and extraction voltage of 3.5 kW and 12.6 kV, respectively.

Conversion of waste polystyrene into valuable aromatic hydrocarbons via microwave-assisted pyrolysis.

The prime objective of the current research work was to understand the role of microwave-assisted pyrolysis for the upgradation of expanded polystyrene (EPS) waste into valuable aromatic hydrocarbons. Ethyl acetate solvent was used to dissolve the EPS to enhance the homogeneous dispersion of EPS with susceptor particles. Biochar obtained from the pyrolysis was used as a susceptor. The design of experiments method was used to understand the role of microwave power (300 W, 450 W, and 600 W) and susceptor quantity (5g, 10g, and 15g) in the pyrolysis process. The pyrolysis was conducted till the temperature reached up to 600°C, and this temperature was achieved in the time interval of 14-38min based on the experimental conditions. The obtained average heating rates varied in the range of 15 to 41°C/min to attain the pyrolysis temperature. The EPS feed was converted into char (~ 2.5 wt.%), oil (51 to 60 wt.%), and gaseous (37 to 47 wt.%) products. The specific microwave energy (J/g) was calculated to know the energy requirement; it increased with an increase in susceptor quantity and microwave power, whereas specific microwave power (W/g) was a function of microwave power and increased from 15 to 30 W/g. The predicted values calculated using the model equations closely matched the actual values showing that the developed model equations via optimization had a good fit. The obtained pyrolysis oil physicochemical properties including viscosity (1 to 1.4 cP), density (990 to 1030kg/m3), heating value (39 to 42MJ/kg), and flash point (98 to 101°C) were thoroughly analyzed. The pyrolysis oil was rich in aromatic hydrocarbons and it was predominantly composed of styrene, cyclopropyl methylbenzene, and alkylbenzene derivates.

Microwave heating of graphene nanoplatelet polymer composites: Experimental and finite element study

AbstractCompared with contemporary electrofusion techniques that use embedded wires for Joule heating, microwave heating may facilitate the joining of thermoplastic polymer components, promising shortened fusion periods, superior heating uniformity, and reduced energy consumption. This study investigates the fabrication of multifunctional polylactide acid (PLA) composites with strong microwave absorption using graphene nanoplatelets (GNP). GNP/PLA nanocomposites were fabricated using a two‐step scalable manufacturing method, that is, solution blending and hot compression molding. The GNP content of the composites ranged from 0% to 8% by weight. The samples were characterized for dielectric permittivity, heat capacity, and electrical and thermal conductivity. Thermal imaging was used to investigate the efficacy of microwave heating in GNP/PLA nanocomposites as a function of microwave power and filler weight fractions. The microwave heating process in GNP composites was studied using multi‐physics finite element software. The experimental results were compared to numerical model predictions for maximum temperature and microwave energy absorbed. The produced nanocomposites were discovered to have strong microwave absorption characteristics and hence rapid heating, making this type of composite a prospective choice for gasket materials that facilitate fusion bonding for thermoplastic‐based components via localized heating.

Investigation of Josephson Contacts Pb0.6In0.4/KFe2As2 and KFe2As2/KFe2As2 and Order Parameter Symmetry Check

The characteristics of point Josephson contacts Pb0.6In0.4/KFe2As2 and KFe2As2/KFe2As2 have been studied. The temperature dependences of characteristic contact voltages VC(T) and the dependences of the first current step amplitudes in I–V characteristics on the power of 7.6-GHz electromagnetic radiation have been measured. It has been found that VC(T) curves for all contacts can be described in terms of the SIS*IS contact model (S, I, and S* stand for superconductor, insulator, and superconductor with a lower critical temperature, respectively) for superconductors with the s-symmetry of order parameter. It has been proved that the current step oscillation period as a function of microwave power can be exactly approximated with the resistive model of contact with IS = ICsin(φ). Obtained data are consistent with the normal s-symmetry of order parameter.

Enhancing Spin-Based Sensor Sensitivity by Avoiding Microwave Field Inhomogeneity of NV Defect Ensemble.

The behavior of the magnetic field sensitivity of nitrogen-vacancy (NV) centers as a function of microwave power and the inhomogeneous distribution of MW fields was systematically studied. An optimal structure for exciting spin structures by MW signals was designed using two parallel loop antennas. The volume of the homogeneous regions was approximately 42 mm3, and the associated diameter of the diamond reached up to 5.2 mm with 1016 NV sensors. Based on this structure, the detection contrast and voltage fluctuation of an optically detected magnetic resonance (ODMR) signal were optimized, and the sensitivity was improved to 5 nT/√Hz. In addition, a pulse sequence was presented to fully eliminate the MW broadening. The magnetic field sensitivity was improved by approximately one order of magnitude as the π-pulse duration was increased to its coherence time. This offers a useful way to improve the sensitivity of spin-based sensors.

Microwaves reduce water refractive index

Microwaves, long used as a convenient household appliance, have been increasingly used in industrial processes such as organic synthesis and oil processing. It has been proposed that microwaves can enhance these chemical processes via a non-thermal effect. Here we report the instantaneous effect of microwaves on the permittivity and phase velocity of light in water through the in-situ measurement of changes in refractive index. Microwave irradiation was found to reduce the water refractive index (RI) sharply. The reduction increased as a function of microwave power to a far greater extent than expected from the change in temperature. The phase velocity of light in water increases up to ~ 5% (RI of 1.27) during microwave irradiation. Upon stopping irradiation, the return to the equilibrium RI was delayed by up to 30 min. Our measurement shows that microwaves have a profound non-thermal and long-lasting effect on the properties of water. Further investigation is planned to verify if the observed RI reduction is restricted to the region near the surface or deep inside water bulk. The observation suggests a relationship between microwave-induced and the enhanced aqueous reactions.

A triple resonance (e, 1H, 13C) probehead for liquid-state DNP experiments at 9.4 Tesla

In DNP experiments, NMR signal intensity is increased by transferring the much larger electron spin polarization to nuclear spins via microwave irradiation. Here we describe the design and performance of a probehead that makes it possible to perform Overhauser DNP experiments at 1H and 13C in liquid samples with a volume of up to 100 nl. We demonstrate on a 13C-labeled sodium pyruvate sample in water that proton decoupling under DNP conditions is possible with this new triple-resonance DNP probehead. In addition, the heat dissipation from the sample has been greatly improved with our new probe design. This makes it possible to keep liquid samples at a constant temperature under irradiation with a high-frequency 263 GHz microwave gyrotron with a few watts of output power. This improved performance opens up the possibility to disentangle the role of sample temperature and applied microwave power for DNP efficiency in liquids and to obtain a quantitative determination of EPR saturation by observing the suppression of paramagnetic shift as a function of microwave power.

Stochasticity of the magnon parametron

The 'magnon parametron' is a ferromagnetic particle that is parametrically excited by microwaves in a cavity. Above a certain threshold of the microwave power, a bistable steady state emerges that forms an effective Ising spin. We calculate the dynamics of the magnon parametron as a function of microwave power, applied magnetic field and temperature for the interacting magnon system, taking into account thermal and quantum fluctuations. We predict three dynamical phases, viz. a stable Ising spin, telegraph noise of thermally activated switching, and an intermediate regime that at lower temperatures is quantum correlated with significant distillible magnon entanglement. These three regimes of operation are attractive for alternative computing schemes.

Heteronuclear DNP of 1H and 19F nuclei using BDPA as a polarizing agent.

This work explores the dynamic nuclear polarization (DNP) of 1H and 19F nuclei in a sample of 25/75 (% v/v) fluorobenzene/toluene containing the radical 1,3-bisphenylene-2-phenylallyl radical (BDPA) as a polarizing agent. Previously, heteronuclear effects in DNP were studied by analysing the shapes of DNP spectra, or by observing cross-relaxation between nuclei of different types. In this work, we report a rather specific DNP spectrum, where 1H and 19F nuclei obtain polarizations of opposite signs upon microwave (MW) irradiation. In order to explain this observation, we introduce a novel mechanism called heteronuclear thermal mixing (hn-TM). Within this mechanism the spectra of opposite signs can then be explained due to the presence of four-spin systems, involving a pair of dipolar coupled electron spins and hyperfine coupled nuclear spins of 1H and 19F, such that a condition relating their Larmor frequencies |ω1e - ω2e| ≈ ωH - ωF is satisfied. Under this condition, a strong mixing of electron and nuclear states takes place, enabling simultaneous four-spin flip-flops. Irradiation of electron spin transitions with MW followed by such four-spin flip-flops produces non-equilibrium populations of |αHβF and |βHαF states, thus leading to the enhancements of opposite signs for 1H and 19F. Signal enhancements, build-up times and DNP-spectra as a function of MW power and polarizing agent concentration, all provide additional support for assigning the observed DNP mechanism as hn-TM and distinguishing it from other possible mechanisms. We also develop a quantum mechanical model of hn-TM based on averaging of spin Hamiltonians. Simulations based on this model show very good qualitative agreement with experimental data. In addition, the system exhibits cross-relaxation between 1H and 19F induced by the presence of BDPA, which was detected by measuring the 19F signal build-up upon saturation of 1H nuclei with a train of radio-frequency pulses. We demonstrate that such cross-relaxation most likely originates due to the same electron and nuclear states mixing in the four-spin systems.

Microwave-Assisted Tunneling in Hard-Wall InAs/InP Nanowire Quantum Dots

With downscaling of electronic circuits, components based on semiconductor quantum dots are assuming increasing relevance for future technologies. Their response under external stimuli intrinsically depend on their quantum properties. Here we investigate single-electron tunneling in hard-wall InAs/InP nanowires in the presence of an off-resonant microwave drive. Our heterostructured nanowires include InAs quantum dots (QDs) and exhibit different tunnel-current regimes. In particular, for source-drain bias up to few mV Coulomb diamonds spread with increasing contrast as a function of microwave power and present multiple current polarity reversals. This behavior can be modelled in terms of voltage fluctuations induced by the microwave field and presents features that depend on the interplay of the discrete energy levels that contribute to the tunneling process.

Diffusive-like effects and possible non trivial local topology on the half-Heusler YPdBi compound

The non-ambiguous experimental identification of topological states of matter is one of the main interesting problems regarding this new quantum state of matter. In particular, the half-Heusler family RMT (R = rare-earth, T = Pd, Pt or Au and T = Bi, Sb, Pb or Sn) could be a useful platform to explore these states due to their cubic symmetry and the topological properties tunable via their unit cell volume and/or the nuclear charges of the M and T atoms. In this work, we report electron spin resonance (ESR) and complementary macroscopic measurements in the Nd3 + -doped putative topologically trivial semimetal YPdBi. Following the Nd3 + ESR lineshape as a function of microwave power, size of the particle and temperature, we have been able to observe an evolution from a Dysonian lineshape to a diffusive-like lineshape. Furthermore, the Nd3 + ESR intensity saturation is concentration dependent, which could be due to a phonon-bottleneck process. Comparing these results with the Nd3 + -doped YPtBi, we discuss a possible scenario in which the Nd3 + ions could locally tune the topological properties of the system.

Deposition of silicon oxycarbide thin films from an organosilicon source for polycarbonate glazing

To enhance the abrasion resistance of polycarbonate used to replace glass, a silicon oxycarbide thin film was deposited at <100°C using a slot antenna electron cyclotron resonance plasma enhanced chemical vapor deposition system and an organosilicon source. The thin film deposition rate, which varied as a function of microwave power and whether Ar or O2 was used to form the plasma, was above 500nm/min even at 2Pa, and reached 1μm/min as the microwave power increased. The transmittance of visible light was over 90% after thin film deposition, indicating performance similar to that of glass. The Taber abrasion test showed that the Δhazes of the thin films were under 5%, which indicates better performance than the siloxane-based wet coating sample (Momentive, AS4700) and the commercial hard plasma coating product LEXAN MR-10. Furthermore, the thin film deposited at 1.7kW exhibited similar abrasion resistance to that of glass. In addition, adhesion improved significantly when consecutive, minute-long 1.7kW Ar and O2 plasma surface treatments were performed before the depositions.

Characterization of microwave plasma in a multicusp using 2D emission based tomography: Bessel modes and wave absorption

A tomographic method based on the Fourier transform is used for characterizing a microwave plasma in a multicusp (MC), in order to obtain 2D distribution of plasma emissions, plasma (electron) density (Ne) and temperature (Te). The microwave plasma in the MC is characterized as a function of microwave power, gas pressure, and axial distance. The experimentally obtained 2D emission profiles show that the plasma emissions are generated in a circular ring shape. There are usually two bright rings, one at the plasma core and another near the boundary. The experimental results are validated using a numerical code that solves Maxwell's equations inside a waveguide filled with a plasma in a magnetic field, with collisions included. It is inferred that the dark and bright circular ring patterns are a result of superposition of Bessel modes (TE11 and TE21) of the wave electric field inside the plasma filled MC, which are in reasonable agreement with the plasma emission profiles. The tomographically obtained Ne and Te profiles indicate higher densities in the plasma core (∼1010 cm−3) and enhanced electron temperature in the ECR region (∼13 eV), which are in agreement with earlier results using a Langmuir probe and optical emission spectroscopy (OES) diagnostics.

Evaluation of Microwave Activity on Starch-Based Nanocomposites Reinforced at Different Loading Fraction Organic-to-Inorganic Nanofillers

ABSTRACTWhen subjected to microwave ageing, the microwave-induced improvement in properties is more significant for sample containing higher loading fraction of cellulose nanofiller. This is due to cellulose nanofiller has greater reactivity to microwave energy through activation of dipole–dipole interaction at the polar interface. The strengthening effects on interface were observed to magnify as a function of microwave power and irradiation time. Nevertheless, the higher montmorillonite fraction tended to inhibit such improvement effect due to the occurrence of intramolecular repulsion between montmorillonite and polysaccharides with insufficient irradiation time, facilitating the water absorption and uneven stress transfer.

Anomalous non-resonant microwave absorption in SmFeAs(O,F) polycrystalline sample

Here we present the non-resonant microwave absorption (NRMA) studies on SmFeAsO0.88F0.12 polycrystalline sample measured at 6.06K with the magnetic field swept from −250G to +250G at a frequency of 9.45GHz. It was observed that the (NRMA) line shape evolves as a function of microwave power. Again, the signal intensity increases from 22.83 µW to 0.710mW where it reaches a maximum and quite remarkably it changed from ‘normal’ absorption to ‘anomalous’ absorption at 2.247mW, then the intensity decreases with further increase of microwave power. The crossover from ‘normal’ to ‘anomalous’ NRMA absorption and its dependence on microwave power is a new phenomenon in iron pnictides superconductors and we have attributed this anomaly to come from non-hysteretic Josephson junction.

Optimization of microwave-assisted extraction of total polyphenolic compounds from chokeberries by response surface methodology and artificial neural network

Abstract Response surface methodology (RSM) and artificial neural network (ANN) were used for modeling and optimizing microwave-assisted extraction (MAE) of total polyphenolic content (TPC) from chokeberries ( Aronia melanocarpa ) as a function of microwave power (300, 450 and 600 W), ethanol concentration (25%, 50% and 75%) and extraction time (5, 10 and 15 min). The set of the optimal operational conditions, as well as the conditions which gave the maximum yield of TPC while minimizing extraction time, solvent and energy consumption, (economic conditions), were proposed. Statistical indicators such as the coefficient of determination ( R 2 ), root-mean-square error (RMSE) and mean absolute error (MAE) demonstrated the superiority of the ANN. In order to scale-up a MAE procedure of chokeberries TPC from the laboratory to the industrial scale, the following set of conditions was proposed: an ethanol concentration of 53.6%, the microwave power of 300 W and the extraction time of 5 min corresponded to a TPC yield of 420.1 mg gallic acid equivalents (GAE)/100 g of fresh plant material.

Emittance and proton fraction measurement in High current electron cyclotron resonance proton ion source

The beam characterization studies in terms of emittance and proton fraction have been carried out in the high current Electron Cyclotron Resonance (ECR) proton ion source developed for Low Energy High Intensity Proton Accelerator (LEHIPA). The beam emittance was measured using two slit emittance measurement units (EMU). The emittance was measured at three locations (1) after beam extraction at ion source end, (2) after focusing the beam using solenoid magnet and (3) after focusing and separating H+ using solenoid magnet and analyzing magnet. The beam emittance measured in all three cases was found to be less than 0.2πmm-mrad (rms-normalized). The proton fraction in the beam measured using analyzing magnet was found to be more than 90%. The variations of beam emittance and proton fraction have been studied as a function of microwave power and neutral gas pressure.

Evidence of a Nonequilibrium Distribution of Quasiparticles in the Microwave Response of a Superconducting Aluminum Resonator

In a superconductor, absorption of photons with an energy below the superconducting gap leads to redistribution of quasiparticles over energy and thus induces a strong nonequilibrium quasiparticle energy distribution. We have measured the electrodynamic response, quality factor, and resonant frequency of a superconducting aluminium microwave resonator as a function of microwave power and temperature. Below 200mK, both the quality factor and resonant frequency decrease with increasing microwave power, consistent with the creation of excess quasiparticles due to microwave absorption. Counterintuitively, above 200mK, the quality factor and resonant frequency increase with increasing power. We demonstrate that the effect can only be understood by a nonthermal quasiparticle distribution.

Microwave irradiation solvothermal technique: an optimized protocol for size‐control synthesis of Ru nanoparticles

AbstractRuthenium (III) chloride salt and Poly (N‐vinyl‐2‐pyrrolidone) (PVP as a capping agent) was dissolved in ethylene glycol, which played a dual role for synthesis, as solvent and also as reducing agent. Microwave (MW) irradiation was applied to the solvent which provided controllable thermal activation for synthesis of ruthenium nanoparticles and also restricted the agglomeration of particles in presence of excess amount of solvent, which was recovered by distillation after completion of reaction. Synthesized particle was found to be in the range of 2–20 nm with narrow size distribution and average particle size was around 14 nm. Particle size and size distribution were studied by varying different parameters e.g. reaction temperature, time, PVP/RuCl3 molar ratio and irradiation power and was characterized by Transmission electron microscopy (TEM). Mathematical model has been developed using matlab software to obtain the particle size as a function of microwave power.

Microwave Assisted Synthesis of Schiff Bases: A Green Approach

Abstract In the present study Schiff’s bases are synthesized by the conventional as well as by microwave irradiation. Excellent yield within short reaction time is obtained using microwave irradiation along with other advantages like mild reaction condition, non-hazardous and safer environmental conditions. The effects of temperature, reactant molar ratio, and microwave power variation on yield are observed. Mathematical model has been developed using matlab software to obtain the yield as a function of microwave power. Kinetic study of the reaction has also been attempted. Schiff’s bases structures are confirmed by IR, 1HNMR, Mass Spectra and elemental analysis.