Revisiting “Non-Thermal” Batch Microwave Oven Inactivation of Microorganisms

Over the last few decades there has been active discussion concerning the mechanisms involved in “non-thermal” microwave-assisted inactivation of microorganisms. This work presents a novel non-invasive acoustic measurement of a domestic microwave oven cavity-magnetron operating at fo = 2.45 ± 0.05 GHz (λo ~ 12.2 cm) that is modulated in the time-domain (0 to 2 minutes). The measurements reveal the cavity-magnetron cathode filament cold-start warm-up period and the pulse width modulation periods (time-on time-off and base-time period, where time-on minus base-time = duty cycle). The waveform information is used to reconstruct historical microwave “non-thermal” homogeneous microorganism inactivation experiments: where tap-water is used to mimic the microorganism suspension;and ice, crushed ice, and ice slurry mixture are used as the cooling media. The experiments are described using text, diagrams, and photographs. Four key experimental parameters are indentified that influence the suspension time-dependent temperature profile. First, where the selected process time > the time-base, the cavity-magnetron continuous wave rated power should be used for each second of microwave illumination. Second, external crushed ice and ice slurry baths induce different cooling profiles due to difference in their heat absorption rates. In addition external baths may shield the suspension resulting in a retarding of the time-dependent heating profile. Third, internal cooling systems dictate that the suspension is directly exposed to microwave illumination due to the absence of surrounding ice volume. Fourth, four separated water dummy-loads isolate and control thermal heat transfer (conduction) to and from the suspension, thereby diverting a portion of the microwave power away from the suspension. Energy phase-space projections were used to compare the “non-thermal” energy densities of 0.03 to 0.1 kJ·m-1 at 800 W with reported thermal microwave-assisted microorganism inactivation energy densities of 0.5 to 5 kJ·m-1 at 1050 ± 50 W. Estimations of the “non-thermal” microwave-assisted root mean square of the electric field strength are found to be in the range of 22 to 41.2 V·m-1 for 800 W.

Study of Low-intensity 2450-MHz Microwave Exposure Enhancing the Genotoxic Effects of Mitomycin C Using Micronucleus Test and Comet Assay in vitro

Objective To determine the interaction between 2450-MHz microwaves (MW) radiation and mitomycin C (MMC). Methods The synergistic genotoxic effects of low-intensity 2450-MHz microwave and MMC on human lymphocytes were studied using single cell gel electrophoresis (SCGE) assay (comet assay) and cytokinesis-blocked micronucleus (CBMN) test in vitro. The whole blood cells from a male donor and a female donor were either only exposed to 2450-MHz microwaves (5.0 mW/cm2) for 2 h or only exposed to MMC (0.0125 μ/mL, 0.025 μg/mL, 0.05μg/mL and 0.1 μg/mL) for 24 h; and the samples were exposed to MMC for 24 h after exposure to MW for 2 h. Results In the comet assay, the comet lengths ( 29.1 μm and 25.9 μm) of MW were not significantly longer than those (26.3 μrn and 24.1 μm) of controls (P>0.05). The comet lengths (57.4 μm, 68.9 μm, 91.4 μm, 150.6μm and 50.6 μm, 71.7μm, 100.1 μm, 145.1 μm) of 4 MMC groups were significantly longer than those of controls (P<0.01). The comet lengths (59.1 μm, 92.3 μm, 124.5 μm, 182.7 μm and 57.4 μm, 85.5 μm, 137.5 μm, 178.3 μm) of 4 MW plus MMC groups were significantly longer than those of controls too (P<0.01). The comet lengths of MW plus MMC groups were significantly longer than those of the corresponding MMC doses (P<0.05 or P<0.01) when the doses of MMC were ≥50.025 μg/mL. In the CBMN, the micronucleated cell (MNC) rates of MW were 5% and 6%, which showed no difference compared with those (4‰ and 4‰) of controls (P>0.05). The MNC rates of 4 MMC groups were 8‰, 9‰, 14‰, 23‰ and 8‰, 8‰, 16‰, 30‰ respectively. When the doses of MMC were 3≥0.05 μg/mL, MNC rates of MMC were higher than those of controls (P<0.05). MNC rates of 4 MW plus MMC groups were 12‰, 13‰, 20‰, 32‰ and 8‰, 9‰, 23‰, 40‰. When the doses of MMC were 5≥0.05 μg/mL, MNC rates of MW plus MMC groups were much higher than those of controls (P<0.01). MNC rates of 4 MW plus MMC groups were not significantly higher than those of the corresponding MMC doses. Conclusion The low-intensity 2450-MHz microwave radiation can not induce DNA and chromosome damage, but can increase DNA damage effect induced by MMC in comet assay.

NUMERICAL STUDIES ON RESONANT AND ENHANCEMENT EFFECTS FOR COUPLING OF MICROWAVE PULSES INTO NARROW SLOTS

In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling process of microwave pulse into a slot is studied by using the modified FD-TD method, and the dependence of microwave coupling on slot sizes, the carrier frequencies and the polarization directions of the incident waves is analysed. Resonant and enhancement effects which occur in this process are observed. The condition at which the resonant effect takes place is also presented.

Damage effects and mechanism of the silicon NPN monolithic composite transistor induced by high-power microwaves

A two-dimensional model of the silicon NPN monolithic composite transistor is established for the first time by utilizing the semiconductor device simulator, Sentaurus-TCAD. By analyzing the internal distributions of electric field, current density, and temperature of the device, a detailed investigation on the damage process and mechanism induced by high-power microwaves （HPM） is performed. The results indicate that the temperature elevation occurs in the negative half-period and the temperature drop process is in the positive half-period under the HPM injection from the output port. The damage point is located near the edge of the base-emitter junction of T2, while with the input injection it exists between the base and the emitter of T2. Comparing these two kinds of injection, the input injection is more likely to damage the device than the output injection. The dependences of the damage energy threshold and the damage power threshold causing the device failure on the pulse-width are obtained, and the formulas obtained have the same form as the experimental equations, which demonstrates that more power is required to destroy the device if the pulse-width is shorter. Furthermore, the simulation result in this paper has a good coincidence with the experimental result.

Effects of microwave pulse-width damage on a bipolar transistor

This paper presents a theoretical study of the pulse-width effects on the damage process of a typical bipolar transistor caused by high power microwaves（HPMs） through the injection approach.The dependences of the microwave damage power,P,and the absorbed energy,E,required to cause the device failure on the pulse width τ are obtained in the nanosecond region by utilizing the curve fitting method.A comparison of the microwave pulse damage data and the existing dc pulse damage data for the same transistor is carried out.By means of a two-dimensional simulator,ISE-TCAD,the internal damage processes of the device caused by microwave voltage signals and dc pulse voltage signals are analyzed comparatively.The simulation results suggest that the temperature-rising positions of the device induced by the microwaves in the negative and positive half periods are different,while only one hot spot exists under the injection of dc pulses.The results demonstrate that the microwave damage power threshold and the absorbed energy must exceed the dc pulse power threshold and the absorbed energy,respectively.The dc pulse damage data may be useful as a lower bound for microwave pulse damage data.

Non-thermal effects of 0.1 THz radiation on intestinal alkaline phosphatase activity and conformation

Alkaline phosphatase(ALP) plays an integral role in the metabolism of liver and development of the skeleton in humans. To date, the interactions between different-duration terahertz(THz) radiation and ALP activities, as well as the influence mechanism are still unclear. In this study, using the para-nitro-phenyl-phosphate(p NPP) method, we detect changes in ALP activities during 40-minute THz radiation(0.1 THz, 13 m W/cm^2). It is found that the activity of ALP decreases in the first 25 min, and subsequently increases in the later 15 min. Compared with the activity of ALP being heated, the results suggest that short-term terahertz radiation induces a decrease in enzyme activity through the non-thermal mechanism. In order to explore the non-thermal effects of THz radiation on ALP, we focus on the impacts of 0.1 THz radiation for 20 min on the activity of ALP in different concentrations. The results reveal that the activity of ALP decreases significantly after exposure to THz radiation. In addition, it could be deduced from fluorescence, ultraviolet-visible(UV-vis), and THz spectra results that THz radiation has induced changes in ALP structures. Our study unlocks non-thermal interactions between THz radiation and ALP, as well as suggests that THz spectroscopy is a promising technique to distinguish ALP structures.

Establishment of injury models in studies of biological effects induced by microwave radiation

Microwave radiation has been widely used in various fields,such as communication,industry,medical treatment,and military applications.Microwave radiation may cause injuries to both the structures and functions of various organs,such as the brain,heart,reproductive organs,and endocrine organs,which endanger human health.Therefore,it is both theoretically and clinically important to conduct studies on the biological effects induced by microwave radiation.The successful establishment of injury models is of great importance to the reliability and reproducibility of these studies.In this article,we review the microwave exposure conditions,subjects used to establish injury models,the methods used for the assessment of the injuries,and the indicators implemented to evaluate the success of injury model establishment in studies on biological effects induced by microwave radiation.

Microwave sintering effects on the microstructure and mechanical properties of Ti–51at%Ni shape memory alloys

Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.

Joint effects of microwave and chromium trioxide on root tip cells of Vicia faba

The mutagemc effects of microwave and chromium trioxide （CrO3） on Vicia faba root tip were studied. Micronucleus assay and chromosomal aberration assay were used to determine the mitotic index, the micronucleus frequency and chromosomal aberration frequency of Vicia faba root tip cells induced by microwave and CrO3. The results showed that the micronucleus frequency decreased, and that the mitotic index and chromosomal aberration frequency showed linear dose responses to CrO3, in treatment of microwave for 5 s. In microwave of 25 s, the mitotic index decreased, the micronucleus frequency and chromosomal aberration frequency increased with increase of CrO3 concentration. We concluded that microwave and CrO3 had antagonistic effect on the mitotic index of Vicia faba root tip cells, but had synergetic effect on micronucleus frequency and chromosomal aberration frequency of Viciafaba root tip cells.

Effects of Low-Power Microwave Fields on Seed Germination and Growth Rate

Experiments were conducted to investigate the effects of low power microwave radiation on germination and growth rate in seeds. In the present paper, the bioeffects of low power (non-thermal intensity) microwave modulated with 1 KHz square wave have been studied. Experiments were performed in X-band frequencies using klystron based microwave test bench. Microwave parameters like frequency, power, exposure time and power density were varied while irradiating seed samples to study their influence on germination. The seed samples used for the experiment included wheat (Triticum aestivum), bengal gram (Cicer arietinum), green gram (Vigna radiate) and moth bean (Vigna Aconitifolia). Seed germination %, plant height, root length and dry matter % (biomass %) were recorded and compared with control seeds. The effects of different treatments were found to be stimulating the germination and seedling vigour of plants especially in power and exposure time treatments while increase in frequency and power density has reduced the seed germination and seedling vigour. The effect also varied with the nature of seeds.

Dielectric behaviors at microwave frequencies and Mossbauer effects of chalcedony, agate, and zultanite

In this study, dielectric properties within 8-12 GHz microwave frequencies, inductively coupled plasma-atomic emis- sion spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57Fe Mossbauer spectroscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm-1 to 4000 cm-1 range, ε＇ values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, eI and e~ values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57Fe Mossbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanoparticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.

“Hot Nano Spots” as an Interpretation of So-Called Non-Thermal Biological Mobile Phone Effects

Indications exist that mobile phones may cause non-specific biological effects. They are classified as being of implausible non-thermal nature due to low quantum energy and low specific absorption rate levels, even if considering worst cases of "hot spots" of only millimeter size. The considerations of this paper demonstrate that classical theory of polarization offers a conventional interpretation for all three the existence of so far unclarified effects, their low reproducibility and their low intensity. The basis of this explanation is given by the assumption that hot spots contain even hotter “nano spots” on a molecular level according to well known mechanisms of γ-relaxation. In this paper, the concept is put for discussion assuming a heterogeneous system that consists of water molecules as well as larger-sized functional molecules. A consistent interpretation through temperature increase on the level of nanometer sized molecular compounds promises to favor interdisciplinary discussions with respect to safety regulations.

Mechanism of Microwave Effects on Conductivity of Solution

The relation between microwave conductivity and normal conductivity of solution is compared in this thesis. By building mathematical model and theoretical analyses, it indicates that the relationship of in situ conductivity of solution in microwave field and temperature is similar to that in non-microwave field. It can be expressed by quadratic equation but the values of both conductivities are different. Microwave field has effect on the mean path δ or hot vibrational frequency ν of ions in solution. In microwave field, the mean energy barrier, which ions must surmount as they transit, is the function relation to temperature.

Effects on the Behavior and Neuroimmunity of Pulsed Microwaves with Different Peak Densities

Pulsed microwaves are widely used inradar,navigation, and communication. The average power density is low at narrow pulse widths or large pulse intervals,but pulsed microwaves at certain peak densities exert numerous biological effects, including

Percutaneous microwave ablation and transcatheter arterial chemoembolization for serum tumor markers and prognostics of middle-late primary hepatic carcinoma

BACKGROUND Primary hepatic carcinoma(PHC)has an insidious onset and is usually diagnosed in the middle and late stages.Although transcatheter arterial chemoembolization(TACE)is the preferred option for treating middle-and advanced-stage PHC,it has limited efficacy in killing tumor cells and poor long-term efficacy.TACE plus percutaneous microwave coagulation therapy(PMCT)is more effective than interventional therapy alone and can improve survival time.However,there are few reports on the effects of TACE and PMCT on serum marker levels and the prognosis of patients with advanced PHC.AIM To investigate the effect of PMCT+TACE on serum tumor markers and the prognosis of middle-late PHC.METHODS This retrospective study included 150 patients with middle-late PHC admitted to Zhongshan People’s Hospital between March 2018 and February 2021.Patients were divided into a single group(treated with TACE,n=75)and a combined group(treated with TACE+PMCT,n=75).Before and after treatment,the clinical efficacy and serum tumor marker levels[carbohydrate antigen 19-9(CA19-9),alpha-fetoprotein(AFP),and carcinoembryonic antigen(CEA)]of both groups were observed.The 1-year survival rates and prognostic factors of the two groups were analyzed.RESULTS The combined group had 21 and 35 cases of complete remission(CR)and partial remission(PR),respectively.The single group had 13 and 25 cases of CR and PR,decreased,with the decrease in the combined group being more significant(P<0.05).The 1-year survival rate of the combined group(80.00%)was higher than that of the single group(60.00%)(P<0.05).The average survival time within 1 year in the combined group was 299.38±61.13 d,longer than that in the single group(214.41±72.97 d,P<0.05).COX analysis revealed that tumor diameter,tumor number,and the treatment method were prognostic factors for patients with middle-late PHC(P<0.05).CONCLUSION TACE+PMCT is effective in treating patients with mid-late PHC.It reduces the levels of tumor markers,prolongs survival,and improves prognosis.

Synergistic effect of microwave irradiation and CaF2 on vanadium leaching

The effect and mechanism of microwave irradiation on vanadium leaching were studied via a comparison between microwave heating and conventional heating. The results show a synergistic effect of microwave irradiation and calcium fluoride （CaF2） on the vana- dium leaching efficiency. It is confirmed that the vanadium leaching process can be improved by microwave irradiation when CaF2 is present. The leaching rate of vanadium under microwave irradiation is increased by 8%-15% when 5wt% CaF2 is added; by contrast, in the absence of CaF2, the leaching rate is almost unaffected compared to that by conventional heating. Morphological analysis reveals that the particles are gradually eroded by acid under microwave irradiation, whereas some of the fine particles in samples subjected to conventional heating are tightly covered by a flocculent silicate product. Moreover, a large amount of A1 and V and a small amount of Si are dissolved from samples under microwave heating, as revealed by the elemental analysis of leachates. Fourier transform infrared spectroscopic analysis also indicates a higher mass transfer coefficient in the diffusion layer of the raw material by microwave irradiation. When CaF2 is present, the reaction energy barrier is lowered and the leaching process is controlled by the tightly covered product layer, resulting in a prominent effect of mi- crowave irradiation.

Damage effect and mechanism of the GaAs high electron mobility transistor induced by high power microwave

In this paper, we present the damage effect and mechanism of high power microwave （HPM） on AIGaAs/GaAs pseudomorphic high-electron-mobility transistor （pHEMT） of low-noise amplifier （LNA）. A detailed investigation is carried out by simulation and experiment study. A two-dimensional electro-thermal model of the typical GaAs pHEMT induced by HPM is established in this paper. The simulation result reveals that avalanche breakdown, intrinsic excitation, and thermal breakdown all contribute to damage process. Heat accumulation occurs during the positive half cycle and the cylinder under the gate near the source side is most susceptible to burn-out. Experiment is carried out by injecting high power microwave into GaAs pHEMT LNA samples. It is found that the damage to LNA is because of the burn-out at first stage pHEMT. The interiors of the damaged samples are observed by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. Experimental results accord well with the simulation of our model.

Microwave absorption and bandwidth study of Y_(2)Co_(17)rare earth soft magnetic alloy with easy-plane anisotropy

The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.

Synthesis of Y_2O_2S：Eu^（3＋） Phosphor by Microwave Thermal Effectand Its Luminescent Properties

The phosphor Y2O2S:Eu3+ powder crystal has been synthesized by using the microwave thermal method.The data of X-ray powder diffraction showed that the phosphor structure belongs to hexagonal system with lattice parameters a=0.3785 nm,c=0.6590nm.The excitation spectrum of the phosphor is a broad band with peak at λ(ex)= 261 nm.The main emission peak at λ(em)=626nm and the other emission lines peak at 595,617 and 706 nm are assigned to transitions of the Eu3+ respectively.Under 254 nm excitation,the chromatic coordinates of phosphor are x=0.665, y=0.330.The relative luminescent intensity is about 62% compared with the standard phosphor Y2O3:Eu3+.Under 365nm excitation this phosphor gives rise to an intense red light.The phosphor particle size has a medium diameter of 7.3μm.

The Origin of Cosmic Microwave Background Radiation

This paper explains the Olbers paradox and the origin of cosmic microwave background radiation (CMBR) from the viewpoint of the quantum redshift effect. The derived formula dispels the Olbers paradox, confirming that the CMBR originates from the superposition of light radiated by stars in the whole universe, not the relic of the Big Bang. The dark-night sky and CMBR are all caused by Hubble redshift—the physical mechanism is the quantum redshift of the photon rather than cosmic expansion. So this theory supports the infinite and steady cosmology.