Microwave Intensity Research Articles

Ultrahigh pressure filtration dewatering of municipal sludge based on microwave pretreatment

Municipal sludge is difficult to treat and dispose of because of its high moisture content (MC) and volume. In this study, a novel dewatering method that utilizes ultrahigh pressure filtration (UHPF) and thin-cake-press (TCP) coupled with microwave pretreatment was proposed to reduce the MC of sludge cake. The influence of microwave contact time (MCT), microwave intensity (MI), initial MC of sludge, dewatering time, applied pressure and sludge weight (Ws) on the MC of a sludge cake was investigated by the single-factor experiment. Moreover, a water discharge path model was developed to understand the dewatering mechanism and explain the relationship between thickness and MC of the cake. The key factors affecting the MC of the cake were explored by the orthogonal experiment. The experimental results showed that microwave irradiation could effectively improve the dewatering performance and reduce the MC of the sludge cake. The MC of the cake reached its lowest value of 28% at MCT of 120 s and MI of 400 W, which is much lower than the value obtained by the traditional dewatering method. Among the parameters mentioned above, Ws has the most significant influence on MC because a large amount of sludge leads to a thicker cake, which seriously hampers the flow of filtrate and inevitably increases the MC of the cake.

Discharge in a Subthreshold Microwave Beam as an Effective Means for Mercaptan Decomposition

A subthreshold microwave discharge in atmospheric-pressure air is used to process mixtures of mercaptans (thiols) with air and with air and methane. It is found that, at microwave intensities of ~10 kW/cm2 and pulse durations of 1–3 ms, the mercaptan concentration decreases 100-fold in mixtures with air and 20-fold in mixtures with air and methane. It is shown that, at an average specific energy deposition in a single discharge of ~0.4 J/cm3, the specific microwave energy spent on mercaptan decomposition is ~10 J/cm3. It is concluded that the active zone of the discharge with high specific energy deposition occupies less than 5% of the microwave beam volume.

Carrier Lifetime Measurements in Semiconductors through the Microwave Photoconductivity Decay Method.

This work presents a protocol employing the microwave photoconductivity decay (μ-PCD) for measurement of the carrier lifetime in semiconductor materials, especially SiC. In principle, excess carriers in the semiconductor generated via excitation recombine with time and, subsequently, return to the equilibrium state. The time constant of this recombination is known as the carrier lifetime, an important parameter in semiconductor materials and devices that requires a noncontact and nondestructive measurement ideally achieved by the μ-PCD. During irradiation of a sample, a part of the microwave is reflected by the semiconductor sample. Microwave reflectance depends on the sample conductivity, which is attributed to the carriers. Therefore, the time decay of excess carriers can be observed through detection of the reflected microwave intensity, whose decay curve can be analyzed for estimation of the carrier lifetime. Results confirm the suitability of the μ-PCD protocol in measuring the carrier lifetime in semiconductor materials and devices.

Improvement of cooking quality of germinated brown rice attributed to the fissures caused by microwave drying

Germinated brown rice (GBR) contains rich bio-active components, but has poor edible quality. To improve the cooking quality of GBR, fissure generation in kernels caused by microwave drying were investigated considering cooking properties, microstructure and textural attributes. The microwave intensity had significant effects on the fissure percentage of GBR, and microwave intensity of 3-4W/g may be suitable for the microwave drying of GBR based on the distribution of fissure percentage for the GBR. The fissures of GBR caused by microwave drying provided the suitable penetration routes of water into GBR kernel. Appropriate fissure amount in range of 3-4 in GBR kernels were conducive to increase its cooking quality and rice taste due to the moderate water absorption and starch gelatinization. The results present a new viewpoint from the perspective of fissures inside grain kernels to evaluate the drying quality of cereal materials such as GBR.

Effects of different microwave intensity on the extraction yield and physicochemical properties of pectin from dragon fruit (Hylocereus polyrhizus) peels

In this experiment, microwave-assisted extraction (MAE) was applied at different intensity of 300, 450, 600, and 800 W to extract pectin from dragon fruit peels. The microwave-assisted extraction was optimized using a central composite experimental design. The optimal extraction condition was established to be pH 2.07, extraction time of 65 s, and solid-to-liquid ratio of 66.57. The maxima extraction yields at 300, 450, 600, and 800 W were 11.8, 14.9, 17.2 and 18.5%, respectively. Experimental and predicted extraction yields obtained at the different microwave power levels were fitted to second-order response surface model. Microwave-assisted extraction process is effective in obtaining high-quality dragon fruit peel pectin, i.e. GalA content: 59.73–69.68%, DE value: 45.82–46.95%, crystallinity: 15.32–21.22%.

Microwave-enhanced quantum heat engines via electromagnetically induced transparency

Quantum heat engines based on electromagnetically induced transparency first proposed by Harris [S. E. Harris, Phys. Rev. A 94, 053859 (2016)] have been recently demonstrated in experiment. Here we present an improved version of such a heat engine by adding a microwave field in the $\mathrm{\ensuremath{\Lambda}}$-type atomic system to modify the cross sections for absorption and emission. We find that this microwave-assisted atomic system behaves as a heat engine only when (i) all three laser or microwave fields resonate with their corresponding transitions and (ii) the relative phase between these fields is $n\ensuremath{\pi}$ with $n=0,\ifmmode\pm\else\textpm\fi{}1,\ifmmode\pm\else\textpm\fi{}2,\ensuremath{\cdots}$. In particular, below the threshold of lasing without inversion, the engine's output field exhibits a brightness increasing with the microwave's intensity, and the brightness in the presence of a weak microwave field can be tens of (or even larger) that in the absence of a microwave field. We also note that the microwave field has the equivalent effect of increasing (decreasing) the hot (cold) reservoir's temperature.

Enhanced catalytic activity of templated-double perovskite with 3D network structure for salicylic acid degradation under microwave irradiation: Insight into the catalytic mechanism

Salicylic acid (SA) is considered as a priority pollutant due to its physiological toxicity and pseudo-persistence in the environment. In this study, a new catalytic degradation technology using microwave (MW) induced templated-double perovskite was proposed and applied in the treatment of SA in aqueous solution. A series of LaCo1-xCuxO3@PMMA (X = 0, 0.3, 0.5, 0.7, 1) perovskite-type catalysts with three-dimensionally porous network structure were synthesized by polymethylmethacrylate (PMMA) templating method, and characterized by scanning electron microscopy (SEM), N2 adsorption-desorption analysis (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and microwave network analysis. The results showed that the addition of PMMA template and substitution with Cu (x = 0.5) were beneficial to the generation of LaCo0.5Cu0.5O3@PMMA with high catalytic activity, which possessed unique 3D porous network structure, smaller particle size distribution, better microwave absorbing performance and higher ratios of Co3+/Co2+ and Oads/Olatt. The SA removal fit pseudo-first-order model, and its degradation efficiency increased firstly and then decreased with the increase of MW intensity, solution pH and catalyst dosage, while decreased as initial SA concentration increasing. The LaCo0.5Cu0.5O3@PMMA catalyst presented favorable recycling and stability in the repeated experiment. The excellent catalytic activity was attributed to both active species and MW “hot spots”, among which OH and hvb+ played main roles in the catalytic process, and MW “hot spots” effect had a small contribution to the degradation. Hence, LaCo0.5Cu0.5O3@PMMA/MW technology with rapid degradation and negligible secondary pollution provides a potential way for treating salicylic acid in water.

Estimation of Tropical Cyclone Intensity in the North Atlantic and Northeastern Pacific Basins Using TRMM Satellite Passive Microwave Observations

AbstractA statistical passive microwave intensity estimation (PMW-IE) algorithm for estimating the intensity of tropical cyclones (TCs) in the North Atlantic and northeastern and central Pacific basins is developed and tested. The algorithm is derived from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) 85-GHz brightness temperatures and near-surface rain-rate retrievals to provide objective estimates of current maximum sustained surface winds (Vmax) and 6-h future Vmax of TCs. The full record of TRMM data (1998–2013) including 2326 TMI overpasses of 503 TCs is separated into dependent samples (1998–2010) for model development and independent samples (2011–13) for model verification. The best track intensities are used as dependent variables in a stepwise multiple-regression approach. Separately for each basin, three regression models are derived using selected 1) 85-GHz-only variables, 2) rain-rate-only variables, and 3) combined 85-GHz and rain variables. The algorithms are evaluated using independent samples and those with contemporaneous aircraft-reconnaissance measurements. Rain-only and combined models perform better than the 85-GHz-only model. Lower errors are found for estimating the 6-h future Vmax than estimating the current Vmax using all three models. This suggests that it is optimal to use passive-microwave-retrieved rain variables observed a few hours earlier to estimate TC intensity. The MAE (RMSE) of 6-h future Vmax is 9 (12) kt (1 kt ≈ 0.51 m s−1) when testing the combined models with ATL and EPA independent samples. Aircraft-reconnaissance-based independent samples yields a MAE of 9.6 kt and RMSE of 12.6 kt for estimating 6-h future Vmax.

Effect of laser intensity on microwave radiation generated in nanosecond laser-plasma interactions

Microwave radiation in several gigahertz frequency band is a common phenomenon in laser-plasma interactions. It can last hundreds of nanoseconds and cause huge electromagnetic pulse disturbances to electrical devices in experiments. It has been found that the microwave radiation might originate from the oscillation of charged chambers, the return current on target holders, the dipole radiation, the quadrupole radiation, and the electron bunch emitted from the plasma to the vacuum. The microwave radiation waveform, frequency spectrum, and intensity depend on many factors such as laser pulse, target, and chamber parameter. To distinguish the microwave radiation mechanisms, the influence of the experimental parameters on the radiation characteristics should be investigated systematically. In this paper we investigate the microwave radiation influenced by the laser intensity in nanosecond laser-plasma interactions. It is found that the microwave radiation intensity varies nonmonotonically with the laser intensity. For the lower laser intensity, the radiation intensity first increases and then decreases with laser intensity increasing, the radiation field continuously oscillates in tens of nanoseconds, and the radiation spectrum contains two components below and above 0.3 GHz, respectively. For the higher laser intensity, the radiation intensity increases with the laser intensity increasing, the radiation field has a unipolar radiation lasting tens of nanoseconds, and the radiation spectrum mainly includes the component below 0.3 GHz. The waveform and spectrum analysis show that these phenomena are due to the difference of the radiation mechanisms at different laser intensities. The frequency component below and above 0.3 GHz are induced by the electron bunch emitted from the plasma to the vacuum and the dipole radiation respectively. At low laser intensity, both the dipole radiation and the electron bunch emitted from the plasma contribute to the microwave radiation. At high laser intensity, the microwave radiation is mainly produced by the electron beam emitted from the plasma to the vacuum. This work is significant for understanding the microwave radiation mechanisms in nanosecond laser-plasma interactions, and implies the potential to provide a reference to the diagnosing of the escape electrons and the sheath field on the target surface by the microwave radiation in laser-plasma interaction.

Effect of high power microwave injection on ozone balance

High power microwave (HPM) injection into the troposphere to block the chain of chlorofluorocarbons (CFCs) or injection into the stratosphere to promote ozone generation are two feasible methods to artificially affect the ozone number concentration. Based on Maxwell’s equations and current density control equations, this study adopts the finite difference time domain (FDTD) method to quantitatively analyze the process of HPM injection into different heights of atmosphere. By taking consideration of the main atmospheric components and the major chemical reactions in the atmospheric, the decomposition of CFCs and the change of the ozone number density is also quantitatively simulated in response to the injection of single pulse microwaves. The numerical simulation results show that under the injection of high power microwaves, the number density of electrons increased exponentially with time, reaching a maximum value of 1017cm-3, and it increased considerably with the pulse time of injected high power microwaves and finally saturates when the state of atmospheric breakdown occurs. The decomposition of CFCs mainly occurs in the electron relaxation process, and the decomposition rate can reach 6% according to the simulation result. Before the atmosphere breaks down occurs, increase of microwave intensity or pulse width facilitates the production of more free electrons, which can consequently lead to a considerable increase in the ozone number density in ozone layer for a prolonged period.

Detection of the efficiency of microwave-oxidation process for meat industry wastewater by dielectric measurement.

Our experimental work focused on the applicability of a quite novel process for wastewater treatment, i.e. a microwave (MW) irradiation-enhanced Fenton-like method. The aim of our research was to detect and evaluate the efficiency of this oxidation process, during the treatment of meat industry wastewater containing a high concentration of organic material. The efficiency was defined by the measurement of the change in COD (chemical oxygen demand, with an initial COD value of 1,568 mg L-1), and with the determination of dielectric parameters during the process. It can be summarized that MW irradiation could assist in a Fenton-like oxidation process to achieve higher organic matter removal. Furthermore, our experimental results and statistical analysis show that there can be found a correlation between the effects of applied MW energy and the dosage of H2O2/FeSO4. If the intensity of MW irradiation and the amount of FeSO4 were set higher, the decrease of COD and the increase of tanδ (the dielectric loss tangent) were definitely more significant. With the application of 60 kJ MWE and a 0.14 mgFe2+/mgCOD dosage, the COD removal efficiency was more than 40%, and the increment of tanδ was nearly threefold. Considering the effects of MW-specific process parameters, it can be concluded that the power intensity of MW-oxidation treatment has a significant effect on COD decrease, if the irradiated MW energy was set at lower (30-45 kJ) levels.

Discharge in a Subthreshold Microwave Beam as an Unusual Type of Ionization Wave

Ionization−overheating instability of a non-self-sustained discharge in air in a subthreshold microwave field creates a self-sustained discharge with a fine cellular structure, whose UV radiation, in turn, generates a new non-self-sustained discharge on the microwave beam path, where ionization−overheating instability arises again. It is shown that, at microwave intensities in the range of 3–18 kW/cm2, the propagation velocity of the ionization wave, including the region of the self-sustained discharge and the forward region of the non-self-sustained discharge developing in its UV halo, is proportional to the third power of the microwave field strength, while the maximum temperature in the discharge is inversely proportional to the microwave field strength.

Theoretical and Experimental Study of Multipactor Discharge on a Dielectric

A review of theoretical and experimental studies of secondary electron emission microwave discharge (multipactor) on a dielectric is presented. The coefficient of microwave power absorption by a single-surface multipactor on a dielectric is found as a function of the incident microwave power and secondary electron emission properties of the dielectric. Results of experimental studies of a single-surface multipactor on a lithium fluoride (LiF) single crystal in a rectangular waveguide are presented and compared with theoretical results. The dependence of the micowave power absorbed by a single-surface multipactor on the incidence angle of microwave radiation is studied numerically and analytically. The influence of the metal waveguide walls on a single-surface multipactor in a parallel-plate waveguide is analyzed. It is shown that, at a sufficiently high microwave intensity, a combined single + double-surface multipactor develops in the region adjacent to the dielectric window.

Electromagnetic interference attenuation and shielding effect of quaternary Epoxy-PPy/Fe3O4-ZnO nanocomposite as a broad band microwave-absorber

An increase in the electromagnetic wave pollution generated from wireless telecommunication devices has devoted to a great request for exploiting microwave absorbing materials for themselves. The combination of inherently conducting polymers such as polypyrrole (PPy) with metal oxides has led to design ideal microwave absorbing materials which benefit both advantage effects of ICPs and metal oxide nanoparticles. Herein, the quaternary nanocomposite of Epoxy-PPy/Fe3O4-ZnO was prepared and tested for the absorption of X-band microwaves. Simultaneous application of metal oxides and conducting polypyrrole in the epoxy matrix was evaluated in order to increase the absorption intensity and broadness of microwaves in X-band region. The morphology, microstructure, and phase structure of Fe3O4, ZnO, and PPy, as well as quaternary nanocomposite were characterized and studied using FTIR, XRD, FESEM and TEM techniques. The presence of nanoparticles in the quaternary nanocomposite was confirmed by EDS. The magnetization of iron oxide was studied by VSM. The synergetic effect of iron oxide and zinc oxide nanoparticles in different weight ratios (Fe3O4/ZnO) on the electromagnetic wave absorption was evaluated. The electromagnetic parameters have been evaluated by the vector network analyzer in the frequency range of 8.2–12.4 GHz which is named as X-band region and is adequate for radar applications. The electromagnetic wave absorbing outcomes indicated that Epoxy-PPy/Fe3O4-ZnO quaternary nanocomposite has wide absorption area and high attenuation, which is believed to be due to dielectric loss properties related to the polypyrrole, magnetic loss factor of Fe3O4, and synergetic effects of components. The maximum reflection loss reached to −32.53 dB at 9.96 GHz with a nanocomposite thickness of 2 mm which is dedicated to the Epoxy-PPy/Fe3O4-ZnO with iron oxide to zinc oxide ratio of 2:1. The absorption bandwidth with the reflection loss lower than −10 dB (90% attenuation) was up to 4.2 GHz that covering a frequency range of 8.2–12.4 GHz. Results showed that absorber having %15 (w/w) polypyrrole/epoxy resin in Epoxy-PPy/Fe3O4-ZnO nanocomposite with iron oxide to zinc oxide ratio of 2:1 displays the best reflection loss properties. The loss curves illustrated the values of dielectric loss tangent and magnetic loss tangent of prepared nanocomposites which are in the range of 0.25–0.7 and −0.08 to 0.09 respectively. Therefore, microwave absorption mechanism is probably attributed to dielectric loss.

Mathematical modeling of packed bed and microwave drying of enriched couscous

In this study, the drying kinetics and modeling of enriched couscous with two different compositions (A and B) were carried out by using packed bed (60 and 80 °C) and microwave (180 and 360 W) drying techniques. Seven drying models were used to determine the best fitting of experimental data. Moreover, the effects of drying methods and parameters on color, yield and sensory attributes of enriched couscous were evaluated. It was found that microwave intensity increment is more effective on drying rate and drying time in contrast to the increment of drying air temperature in the packed bed drying. The free moisture contents of the enriched couscous decreased with time. The effective moisture diffusivities of enriched couscous produced with composition A and B were between 0.93 × 10−8 to 1.68 × 10−8 and 0.86 × 10−8 to 1.42 × 10−8 m2 s−1, respectively. Midilli and others model for the packed bed and microwave drying was observed to be the most suitable for the experimental data with the highest values of R2, and the lowest values of RMSE, χ2 and RSS.

Coherent Microwave-to-Optical Conversion via Six-Wave Mixing in Rydberg Atoms

We present an experimental demonstration of converting a microwave field to an optical field via frequency mixing in a cloud of cold ^{87}Rb atoms, where the microwave field strongly couples to an electric dipole transition between Rydberg states. We show that the conversion allows the phase information of the microwave field to be coherently transferred to the optical field. With the current energy level scheme and experimental geometry, we achieve a photon-conversion efficiency of ∼0.3% at low microwave intensities and a broad conversion bandwidth of more than 4MHz. Theoretical simulations agree well with the experimental data, and they indicate that near-unit efficiency is possible in future experiments.

Effect of microwave heating on ph and termite resistance of Pinus roxburghii wood

This study investigated the effect of microwave treatment on wood pH and termite resistance. Pinus roxburghii heartwood was exposed to four different microwave intensities at 2450 MHz frequency for 5 minutes. Preservative impregnation, pH variation and termite resistance of microwave-treated and control specimens were studied. Wood pH decreased from 4.6 (C1) to 3.9 (T4) and preservative uptake increased (i.e., 10.41 to 21.61 kgm-3) with increasing microwave treatment intensities. However, microwave treatment had little effect on termite resistance.

Dynamic generation and coherent control of beating stationary light pulses by a microwave coupling field in five-level cold atoms

We propose an efficient scheme for generating and controlling beating stationary light pulses in a five-level atomic sample driven into electromagnetically induced transparency condition. This scheme relies on an asymmetrical procedure of light storage and retrieval tuned by two counter-propagating control fields where an additional coupling field, such as the microwave field, is introduced in the retrieval stage. A quantum probe field, incident upon such an atomic sample, is first transformed into spin coherence excitation of the atoms and then retrieved as beating stationary light pulses exhibiting a series of maxima and minima in intensity due to the alternative constructive and destructive interference. It is convenient to control the beating stationary light pulses just by manipulating the intensity and detuning of the additional microwave field. This interesting phenomenon involves in fact the coherent manipulation of dark-state polaritons and could be explored to achieve the efficient temporal splitting of stationary light pulses and accurate measurement of the microwave intensity.

Photon‐Induced Distant Pseudospin Interaction Between Graphene Sheets Inserted Into a Cavity

The pseudospin interaction between graphene sheets inserted into a microwave cavity is studied, and a pseudospin radiation driven by the pseudospin interaction is presented. It is found that a circularly polarized photon can induce a distant pseudospin interaction and a pseudospin radiation. An interference effect of pseudospins from two graphene sheets results in an oscillation distribution of this interaction with the distance between two graphene sheets. Both the pseudospin interaction and pseudospin radiation can be enhanced by increasing microwave intensity and decreasing the microwave frequency. The acting range of this pseudospin interaction may reach the order of magnitude of the cavity length. This makes the distant interaction of pseudospins in two graphene sheets become possible if the distance between the two reflectors in the cavity is far enough. The graphene vibration around the positions of some antinodes of standing microwaves in the cavity driven by pseudospin interaction can emit an electromagnetic wave. By measuring the frequency of this radiation field, the pseudospin interaction between two graphene sheets can be determined quantitatively.

Microwave absorbing properties of composites containing ultra-low loading of optimized microwires

A set of composite absorbers with ultra-low loading of down to 0.017 wt.% short-cut microwires were prepared and investigated in terms of their magnetic and microwave properties in the X-band (8–12 GHz). The key parameters that could factor into the performance of the present absorbers have been systematically studied from micro to macro scale, i.e., the magnetic domain structure modulated by different internal stress scenarios, microwire aspect and composite filling ratio, and relative importance of impedance matching and material loss. Longer wires (9 mm) and wires after suitable treatment lead to the enhancement of microwave absorbing property mainly due to the larger magnetic loss resulted from the natural ferromagnetic resonance, which is induced in the domain rotation and reversal process. The internal stress modification by removal of glass and joule annealing has profound effects in formulating the microwave absorption frequency and intensity of microwire composites by tailoring the domain structure and local anisotropy field. It is found that the composites with microwires annealed at 132 mA for 15 min obtain the minimum reflection loss and broadest absorption bandwidth with reference to −10 dB at 1.5 mm thickness, which is −25.7 dB (0.81 GHz) at 11.39 GHz caused by the relative high attenuation constant and best matching condition where Zreal is 1.026 and Zimag is −0.102. This indicates that impedance matching plays a dominant role in tailoring the microwave absorbing property. Remarkably, the unconventional absorption frequency - matching thickness relation based on the quarter-wavelength model offers possibility to address the limitation of thickness for low frequency absorbing application.