Polymerization of Potassium Azide in Liquid Nitrogen Using Nanosecond-Pulsed Spark Plasma.

In this manuscript, we report on the synthesis of a polynitrogen material from a potassium azide precursor using nanosecond-pulsed spark discharge plasma in liquid nitrogen. The polynitrogen material was characterized using Raman and Fourier transform infrared (FTIR) spectroscopy and identified as K2N6, with planar N6 rings and K- ions that have P6/mmm symmetry. An analysis of the mechanism behind such a transformation shows the importance of direct plasma-chemical effects in polymerization, while the crystal structure changes are believed to be due to plasma-emitted radiation in the ultraviolet range.

Efficient degradation of the refractory organic pollutant by underwater bubbling pulsed discharge plasma: performance, degradation pathway, and toxicity prediction.

It is essential to develop an efficient technology for the elimination of refractory contaminants due to their high toxicity. In this study, a novel underwater bubbling pulsed discharge plasma (UBPDP) system was proposed for the degradation of Orange II (OII). The degradation performance experiments showed that by enhancing the peak voltage and pulse frequency, the degradation efficiency of OII increased gradually. The removal efficiencies under different air flow rates were close. Reducing OII concentration and solution conductivity could promote the elimination of OII. Compared with neutral and alkaline conditions, acidic condition was more beneficial to OII degradation. The active species including ·OH, ·O2-, 1O2, and hydrated electrons were all involved in OII degradation. The concentrations of O3 and H2O2 in OII solution were lower than those in deionized water. During discharge, the solution pH increased while conductivity decreased. The variation of UV-vis spectra with treatment time indicated the effective decomposition of OII. Possible degradation pathways were speculated based on LC-MS. The toxicity of intermediate products was predicted by the Toxicity Estimation Software Tool. Coexisting constituents including Cl-, SO42-, HCO3-, and humic acid had a negative effect on OII removal. Finally, the comparison with other technology depicted the advantage of the UBPDP system.

Nano-pulsed discharge plasma-induced abiotic oligopeptide formation from diketopiperazine.

Conventional oligopeptide synthesis techniques involve environmentally harmful procedures and materials. In addition, the efficient accumulation of oligopeptides under Hadean Earth environments regarding the origin of life remains still unclear. In these processes, the formation of diketopiperazine is a big issue due to the strong inhibition for further elongation beyond dipeptides. Hydrothermal media enables environmentally friendly oligopeptide synthesis. However, hydrothermal oligopeptide synthesis produces large amounts of diketopiperazine (DKP), due to its thermodynamic stability. DKP inhibits dipeptide elongation and also constitutes an inhibitory pathway in conventional oligopeptide synthesis. Here, we show an efficient pathway for oligopeptide formation using a specially designed experimental setup to run both thermal and non-thermal discharge plasma, generated by nano-pulsed electric discharge with 16-23 kV voltage and 300-430 A current within ca. 500 ns. DKP (14%) was converted to dipeptides and higher oligopeptides in an aqueous solution containing alanine-DKP at pH 4.5, after 20 min of 50 pps thermal plasma irradiation. This is the first study to report efficient oligopeptide synthesis in aqueous medium using nano-pulsed plasma (with thermal plasma being more efficient than non-thermal plasma) via DKP ring-opening. This unexpected finding is implicative to evaluate the pathway how the oligopeptides could have accumulated in the primitive Earth with high-energy plasma sources such as thunder as well as to facilitate the green synthesis of oligopeptides.

Sterilizing Ability of High-Voltage Pulsed Discharge Plasma with Cavitation for Microorganisms Including Radio-Resistant Bacterium in Water.

There are various purification methods have been developed and applied to industrial wastewater with contaminated microorganisms. We previously reported that high-voltage pulsed discharge plasma with cavitation effectively kills Escherichia coli cells. We attempted to expand the application of this disinfection method by using microorganisms such as Bacillus subtilis, Deinococcus radiodurans, and Schizosaccharomyces pombe. These microbial cells were treated with the discharge plasma, and the cell viability, DNA damage, and morphological changes were analyzed to evaluate the bactericidal effect. Interestingly, D. radiodurans, a radio-resistant bacterium showed relatively high sensitivity to the discharge plasma. On the other hand, B. subtilis and S. pombe showed the resistance, showing both sporogenesis. The amount of DNA damage in the treated cells corresponded to the cell viability, but most of the treated cells did not show any morphological changes.

PVP/Highly Dispersed AgNPs Nanofibers Using Ultrasonic-Assisted Electrospinning.

Silver nanoparticles (AgNPs) are novel materials with antibacterial, antifungal, and antiviral activities over a wide range. This study aimed to prepare polyvinylpyrrolidone (PVP) electrospinning composites with uniformly distributed AgNPs. In this study, starch-capped ~2 nm primary AgNPs were first synthesized using Atmospheric pressure Pulsed Discharge Plasma (APDP) at AC 10 kV and 10 kHz. Then, 0.6 wt.% AgNPs were mixed into a 10 wt.% PVP ethanol-based polymer solution and coiled through an Ultrasonic-assisted Electrospinning device (US-ES) with a 50 W and 50 kHz ultrasonic generator. At 12 kV and a distance of 10 cm, this work successfully fabricated AgNPs-PVP electrospun fibers. The electrospun products were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High-Resolution TEM (HR-TEM), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Thermogravimetric (TG), and X-ray Photoelectron Spectroscopy (XPS) methods.

Optical emission spectroscopy measurement of plasma parameters in a nanosecond pulsed spark discharge for CO2/CH4 dry reforming.

In this paper, a nanosecond pulsed spark discharge in CO2/CH4 mixture gas at atmospheric pressure is studied with optical emission spectroscopy. A high-voltage pulse is applied across two plate-shaped electrodes at a repetition frequency of 1 kHz. Emphatically, plasma parameters of this discharge are estimated by spectroscopic methods for giving an insight into the underlying dry reforming reaction mechanism. The time-averaged optical emission is mainly caused by atomic spectral lines of excited O, H, and C+, and C2 swan bands. The vibrational temperature of 8500 ± 50 K and rotational temperature of 3200 ± 100 K are estimated by the excited C2 molecules, respectively. The electron density is calculated by Stark broadening of O (844.6 nm), Hα (656.3 nm), and Hß (486.1 nm) for 3.4 âˆ¼ 7.71 × 1017 cm-3 while C+ (723.6 nm) for 4.37 × 1018 cm-3 with an electron excitation temperature of 0.58 eV that is estimated by the intensity ratio of Hα and Hß. The determination of plasma parameters offers essential data for subsequent reaction kinetics research of the plasma-assisted dry reforming of CH4.

Removal of ammonia nitrogen and phenol by pulsed discharge plasma combined with modified zeolite catalyst.

In this work, the removal of ammonia nitrogen and phenol by pulsed discharge plasma (PDP) and modified zeolite was investigated. The Fe-zeolite and Mn-zeolite catalysts were prepared by the impregnation method. Catalysts' morphology, specific surface area, and chemical bond structure were characterized. Based on the pollutants removal experiments, Fe-zeolite (0.01) in the PDP system had better catalytic oxidation of phenol and adsorption effect of ammonia nitrogen. The removal efficiency of the pollutants increased with the increase of discharge voltage and solution conductivity, but decreased with the increase of discharge distance. During the plasma discharge process, the pH value in the solution decreased, and the solution conductivity gradually increased. After PDP/Fe-zeolite system treatment, the toxicity of the wastewater was significantly reduced. This study provided a new treatment method for inorganic and organic pollutants treated by PDP.

Ns-pulsewidth pulsed power supply by regulating electrical parameters for AFM nano EDM of nm-removal-resolution.

Nano electro discharge machining (nano EDM), as a frontier processing method in the research stage of exploration, has an important application prospect in the machining of metal and alloy materials for achieving nanoscale removal resolution. A pulsed power supply used in nano EDM is expected to limit a single pulse energy to nJ order of magnitude for improving the removal resolution of single pulsed discharge even to nanoscale. One developing direction is to decrease pulsewidth of the pulsed power supply. Conventional pulsed power supplies hardly output a single pulse and continuous pulses with nanosecond (ns) pulsewidth, resulting in too large single pulsed energy ofµJ order of magnitude usually. In this research, a novel pulsed power supply is designed for realizing the ns-pulsewidth with controllable pulsewidth and peak voltage. The key novelty lies in a cascaded circuit with two triodes working in the state of ultra-fast avalanche conduction, where pF capacitors are applied to adjust the pulsewidth and pulsed energy precisely. Performance tests verified that a single pulse of 5 ns pulsewidth or continuous pulses up to 9 MHz can be outputted. Furthermore, nano EDM experiments of single pulsed discharge are carried out under the conditions of nanometer (nm) discharge gap and nm-tip tool electrode based on an atomic force microscope (AFM) system. The special results are achieved: a single pulsed energy can reach down to 1.75 nJ by outputting a pulsewidth of 10 ns, and a nano-EDM crater is only about 182 nm in diameter with regular shape and little recasting. Those results verify the possibility of AFM-tip-based nano EDM for machining nanostructures.

Novel combination of high voltage nanopulses and in-soil generated plasma micro-discharges applied for the highly efficient degradation of trifluralin.

Cold plasma is considered a highly competitive advanced oxidation process for the removal of organic pollutants from soil. Herein, we describe for the first time the combination of in-soil generated plasma micro-discharges with the advantageous high voltage nanosecond pulses (NSP) towards the high-efficient degradation of trifluralin in soil. We performed a detailed parametric analysis (pulse frequency, pulse voltage, soil thickness, soil type, energy efficiency) to determine the optimum operational conditions. High trifluralin degradation was achieved even at the higher soil thickness, indicating that the production of plasma discharges directly inside the soil pores enhanced the mass transfer of plasma reactive oxygen and nitrogen species (RONS) in soil. The energy efficiency achieved was outstanding, being up to 2-3 orders of magnitude higher than those reported for other plasma systems. We identified the intermediate degradants and proposed the most dominant degradation pathways whereas a thorough exhaust gases analysis, optical emission spectroscopy (OES) and active species inhibition by using trapping agents revealed the main RONS involved. This effort constitutes a significant advancement in the "green" credentials and application of plasma-induced degradation of pollutants as it describes for the first time the removal of the highly harmful and toxic pesticide trifluralin from soil and provides a novel perspective towards the future development of cold plasma-based soil remediation technologies.

Investigation on the role of the free radicals and the controlled degradation of chitosan under solution plasma process based on radical scavengers.

This study investigated the role of various active species (OH, O, and H2O2) under solution plasma process (SPP) degradation based on the influence of different radical scavengers on the degradation effect and ESR spectra. The structures of oligochitosan with different radical scavengers were characterized by FT-IR, 1H NMR, and XRD analysis. The results indicated that OH, O, and H2O2 played important roles in SPP degradation. The degradation effect of the O was even higher than that of the OH. The physical effects (e.g. UV light and shockwaves) of SPP method or Fenton's reaction might contribute to the degradation treatment. Furthermore, the different scavengers could adjust the degradation effect of the corresponding free radicals. FT-IR, 1H NMR, and XRD analysis revealed that the primary chemical structure of chitosan was not changed by the scavengers. This study found that the controlled degradation by addition of a radical scavenger is feasible. Therefore, this study provided a straightforward analysis of the role of the free radicals and the controlled degradation of chitosan under SPP treatment, which will be beneficial to further develop SPP techniques for chitosan degradation.

Comparison of batch and circulating processes for polyphenols extraction from pomelo peels by liquid-phase pulsed discharge.

The study was an attempt to compare batch and circulating processes for polyphenols extraction from pomelo peels by liquid-phase pulsed discharge (LPD) in order to assess the extraction efficiency of the two processes. Response surface methodology was used to optimize batch (8-12 kV discharge voltage, 30-50 mL/g liquid to solid ratio and 2-4 min extraction time) and circulating (8-12 kV discharge voltage, 30-50 mL/g liquid to solid ratio and 20-40 mL/min flow rate) extractions. The highest polyphenols yield was 2.50 ± 0.02% at 42.2 mL/g, 12 kV and 4 min in batch extraction, while circulating extraction produced the most polyphenols (2.42 ± 0.01%) at 43.7 mL/g, 10.4 kV and 27.6 mL/min. The results showed that batch extraction achieved much greater yields than circulating extraction with lower-cost equipment. Therefore, batch extraction was a promising technology for the separation of high value-added products from pharmaceuticals and fine chemicals.

Efficient removal of antibiotic thiamphenicol by pulsed discharge plasma coupled with complex catalysis using graphene-WO3-Fe3O4 nanocomposites.

Pulsed discharge plasma (PDP) induced complex catalysis for synergetic removal of thiamphenicol (TAP) was investigated using graphene-WO3-Fe3O4 nanocomposites. The prepared samples were characterized systematically in view of the structure and morphology, chemical bonding state, optical property, electrochemical property and magnetic property. Based on characterization and TAP degradation, the catalytic performance followed: graphene-WO3-Fe3O4>graphene-WO3>WO3, and the highest removal efficiency and kinetic constant could reached 99.3% and 0.070 min-1, respectively. With increase of catalyst dosage, the removal efficiency firstly enhanced and then declined. Lower pH value was beneficial for TAP degradation. The prepared graphene-WO3-Fe3O4 owed higher stability and lower dissolution rate of iron ion. The rGO-WO3-Fe3O4 could decompose O3 and H2O2 into more ·OH in PDP system. The degradation intermediates were characterized by fluorescence spectrograph, LC-MS and IC. Based on the detected intermediates and discrete Fourier transform (DFT) analysis, degradation pathway of TAP was proposed. Besides, the toxicity of intermediates was predicted. Finally, catalytic degradation mechanism of TAP by PDP with graphene-WO3-Fe3O4 was summarized.

Understanding of TiO2 catalysis mechanism in underwater pulsed discharge system: Charge carrier generation and interfacial charge-transfer processes.

Compared with traditional photocatalysis system, TiO2 charge carrier generation and interfacial charge-transfer process may be influenced by various chemical and physical effects in underwater pulsed discharge plasma system. Here, the role of high-energy electron, ozone in TiO2 charge carrier generation and transfer process has been investigated using phenol as the probe molecule. The introduction of electron-trapping agent (KH2PO4) have an inhibiting effect on TiO2 catalytic activity, indicating high-energy electrons played a significant role in TiO2 catalytic process. EPR analysis showed that TiO2 could be activated to initiate pairs of electron-hole by high-energy electrons from plasma, and the electrons on the conduction band (CB) could be trapped on the oxygen vacancies. XPS analysis showed that the Ti3+OH species formed during discharge process due to the capture of CB electrons by Ti4+OH groups located at the TiO2 surface. The CB electrons transfer processes on TiO2 surface was strongly dependent on the redox potential of electron acceptors, which adsorbed on the TiO2 surface. The CB electrons can be transferred to dissolved O3, resulting in more OH production. Meanwhile, the CB electron also transferred to benzoquinone adsorbed on TiO2, resulting in accumulation of hydroquinone.

Degradation of trimethoprim in aqueous by persulfate activated with nanosecond pulsed gas-liquid discharge plasma.

The persulfate activation by nanosecond pulsed gas-liquid discharge (NPG-LD) is employed to degrade the trimethoprim (TMP) in water. The results show that persulfate addition enhances the degradation of TMP by NPG-LD through an obvious synergetic effect. With treatment time of 50 min, the high removal efficiency and energy yield reach 94.6% and 0.57 gkWh-1 in air NPG-LD with the addition of persulfate, respectively, which is 13.5% and 0.09 gkWh-1 higher than that in solo air NPG-LD, respectively. Correspondingly, the calculated synergetic factor achieves 1.62, indicating the synergetic effect is established. The activation mechanism of persulfate by NPG-LD is analyzed by the measurement of reactive species and the effects of radical scavenger addition on TMP removal. It is found that the synergetic effect between NPG-LD and persulfate is attributed to the increased production of OH, H2O2, and . Besides, the TMP degradation by NPG-LD and persulfate synergetic system is influenced by discharge working gas, pulse voltage, addition dosage of persulfate, initial TMP concentration, and initial pH value. Subsequently, the degradation pathway of TMP is analyzed using LC-MS/MS.

Multi-catalysis induced by pulsed discharge plasma coupled with graphene-Fe3O4 nanocomposites for efficient removal of ofloxacin in water: Mechanism, degradation pathway and potential toxicity.

Herein, degradation of ofloxacin (OFX) by pulsed discharge plasma (PDP) coupled with multi-catalysis using graphene-Fe3O4 nanocomposites was inspected. The graphene-Fe3O4 nanocomposites were prepared by hydrothermal synthesis, and their morphology, specific surface area, chemical bond structure and magnetic property were characterized systematically. Compared with sole Fe3O4, the specific surface area of graphene-Fe3O4 nanocomposites increased from 26.34 m2/g to 125.04 m2/g. The prepared graphene-Fe3O4 nanocomposites had higher paramagnetism and the magnetic strength reached 66.05 emu/g, which was prone to separate from solution. Graphene-Fe3O4 nanocomposites could further accelerate OFX degradation compared to sole Fe3O4. When graphene content was 18 wt%, graphene-Fe3O4 nanocomposites exhibited the highest catalytic activity, and the removal efficiency of OFX enhanced from 65.0% (PDP alone) to 99.9%. 0.23 g/L dosage and acid solution were beneficial for OFX degradation. Higher stability of graphene-Fe3O4 nanocomposites could be maintained although four times use. Graphene-Fe3O4 nanocomposites could catalyze H2O2 and O3 to produce more ·OH. The degradation products of OFX were identified by liquid chromatography mass spectrometry (LC-MS) and ion chromatography (IC). According to the identified products and discrete Fourier transform (DFT), the degradation pathway was inferred. Further toxicity assessment of products manifested that the toxicity of oral rat 50% lethal dose (LD50) and the developmental toxicity of OFX were reduced.

Combination of liquid-phase pulsed discharge and ultrasonic for saponins extraction from lychee seeds.

A skillfully combined method of liquid-phase pulsed discharge and ultrasonic (LPDU) had been developed for saponins extraction from lychee seeds. Single factor and response surface methods were used to optimize the system, respectively. The optimized conditions included 30% aqueous ethanol, 62.66 mL/g ratio of liquid to solid, 3 mm centre hole diameter of hollow electrode, 123 mL/min flow velocity, length of serpentine pipe of 15 cm, 276 W ultrasonic power, 47 °C ultrasonic temperature, and discharge voltage was fixed at 14 kV. Under these conditions, it obtained a maximum saponins yield of 51.30 ± 0.08 mg/g with 10 min, which was higher than those of LPD (42.33 ± 0.98 mg/g) with 24 min, ultrasonic assisted extraction (UAE) (41.80 ± 1.31 mg/g) with 30 min and maceration (38.72 ± 1.13 mg/g) with 180 min. Meanwhile, the energy consumption of LPDU was 7560 kJ/kg, which was notably lower than those of LPD (8820 kJ/kg), UAE (25875 kJ/kg) and maceration (10248 kJ/kg). We found that the saponin constituents of LPDU were similar to LPD, UAE, ME by HPLC content detection method, and found that LPDU had the highest degree of tissue damage after scanning electron microscope (SEM) comparison, which verified the reason for its high extraction efficiency. The results showed that LPDU was an effective technology for saponins extraction, which may be potentially applied in cosmetics, medicines and food chemistry.

Enhanced removal of toluene by pulse discharge plasma coupled with MgO cathode and graphene Mn-Ce bimetallic oxide.

Herein, MgO cathode and graphene Mn-Ce bimetallic oxide were utilized to jointly enhance the removal of toluene in pulsed discharge plasma (PDP). Compared to the common cathode, the MgO cathode enhanced the density of high energy electrons, and then induced to higher removal of toluene. However, the removal of toluene by PDP/MgO system was still insufficient, and there was a large amount of underutilized O3 in the products. Based on this, Mn-Ce/graphene catalysts were introduced into PDP/MgO system. The Mn-Ce (8:1)/graphene catalyst had the highest catalytic activity. Under the discharge power of 2.1 W, toluene degradation rate and CO2 selectivity increased by 27.5% and 22.0%, respectively. This was ascribed to the synergistic effect of the solid solution formed between MnOx and CeOx, increasing the proportion of Oads on the surface of the catalyst. The higher Oads/Olatt ratio lead to the better catalytic activity, which was conducive to the complete transformation of the intermediate products to CO2 and H2O. According to the detected products, the degradation pathway and the mechanism of toluene degradation were proposed finally. The PDP itself, field emission effect of MgO cathode and catalytic effect of Mn-Ce/graphene for jointly improve the toluene removal and CO2 selectivity.

Pulsed discharge plasma induced WO3 catalysis for synergetic degradation of ciprofloxacin in water: Synergetic mechanism and degradation pathway.

Pulsed discharge plasma (PDP) was adopted to induce WO3 for synergetic degradation of ciprofloxacin (CIP) in water. WO3 was firstly characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), Photocurrents and Photoluminescence. The degradation results showed that PDP could induce WO3 photocatalysis successfully, and a synergetic effect was established in PDP/WO3 system. After 60 min treatment time, 0.16 g/L WO3 increased the CIP removal from 71.3% to 99.6%, with the enhancement of the first-order kinetic constant from 0.020 min-1 to 0.081 min-1. Then, the effect of peak voltage, air flow rate and pH on CIP removal was evaluated. Active species trapping test verified that ·OH and ·O2- played the major role for plasma-degradation of CIP degradation, whereas OH and h+ were conductive to catalytic degrade CIP. WO3 addition lead to the decline of O3 and enhancement of OH no matter in deionized water or CIP solution. The degradation process was explored using fluorescence spectrograph, liquid chromatography-mass spectrometry (LC-MS) and ion chromatography (IC). Finally, the possible degradation pathways of CIP degradation were proposed. The reuse test suggested WO3 possessed excellent catalytic performance as well as good stability.

Degradation of antibiotic chloramphenicol in water by pulsed discharge plasma combined with TiO2/WO3 composites: mechanism and degradation pathway.

Pulsed discharge plasma (PDP) combined with TiO2/WO3 composites for chloramphenicol (CAP) degradation was investigated. The prepared TiO2/WO3 composites were characterized by scanning electron microscope, transmission electron microscope, nitrogen adsorption apparatus, zeta sizer, X-ray diffraction, Raman spectra, UV-Vis absorption spectroscopy, X-ray photoelectron spectroscopy, photocurrent and electrochemical impedance spectroscopy. The degradation performance showed that the addition of TiO2/WO3 composites significantly enhanced the removal efficiency of CAP in PDP system. At a peak voltage of 18 kV, the highest removal efficiency of CAP could reach 88.1% in PDP system with 4 wt% TiO2/WO3, which was 36.8% and 26.0% higher than that in sole PDP system and PDP/TiO2 system, respectively. The TiO2/WO3 composites significantly accelerated interfacial charge transfer process compared to the pure TiO2. Besides, the effect of catalyst dosage and peak voltage on CAP removal was evaluated. OH, O3O2-, h+ and high-energy electrons contributed to CAP degradation in PDP-TiO2/WO3 system. Addition of TiO2/WO3 composites can decompose O3 and produce more OH and H2O2. The degradation intermediates were measured by liquid chromatography-mass spectrometry (LC-MS) and ion chromatography (IC). The cycling degradation experiment showed that the TiO2/WO3 composites have good reusability as well as stability.

Nanosecond pulsed uniform dielectric barrier discharge in atmospheric air: A brief spectroscopic analysis.

The paper proposes a simple and convenient approach to represent the discharge uniformity of nanosecond-pulse dielectric barrier discharge (DBD) in air by observation of the ratio of N2+ (B3Σu+ → X3Σg+, 0-0, 391.4 nm) to N2 (C3Πu → B3Πg, 2-5, 394.3 nm) intensities. The DBDs at different pulse peak voltages, discharge gap distances, dielectric materials and thicknesses were investigated by recording their single-pulse-shot discharge images and N2+/N2 ratios to verify the feasibility of the above innovative approach. The results show that the ratios of N2+/N2 are in the range of 0.18-0.6within our experimental parameters, which is respect to the reduced electric field (E/N, where E is the field strength and N is gas number density) strength of 260-440 Td (1 Td = 10-17 V·cm2). And it is indicated that a lower N2+/N2 ratio would be found in a higher pulse peak voltage or/and a lower discharge gap distance, which benefits for improving the discharge uniformity of nanosecond-pulse DBD. The thickness and permittivity of dielectric material also affect the E/N strength and discharge uniformity to a certain extent, but the effects are ambiguous due to additional factors of dielectric materials. In addition, the theoretical basis and application scope of this approach were also discussed.