This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modul...This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modulation pulse, achieving that the welding energy input can be effectively controlled and precisely regulated, the transition of pulse change is smooth and the welding process is stable and reliable. With the characteristics of sinusoidal waveform, such as infinite derivative continuity, eternal periodicity and limited control parameters, this article established the theoretical foundation for choiceness, unification and optimization of the parameters during the new sinusoid modulated pulse MIG welding. Bead-on-plate overlay welding is carried out on the pure aluminum sheet test sample for the test. The result indicated that during the welding process, the real-time current waveform is stable and clear; both the corresponding voltage and the instant welding energy waveform are very stable; the repeatability of the U-I graph plotted is high; its family of lines is clear, neat, and its distribution is concentrated showing that the welding process is stable and the neat and high quality ripple weld seam may be produced.展开更多
In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave ...In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave plasma jet was formed and the microwave-assisted ammonia synthesis can be realized.Impacts of various parameters including the gas flow rate,gas component,microwave absorbed power,pulse modulation frequency,and pulse duty cycle on ammonia synthesis were systematically investigated.To indicate the reaction path of ammonia synthesis,the distributions of both the gas temperature and active species were also studied using optical emission spectra technology.It is found that a considerable amount of ammonia was directly synthesized without involvement of any catalysts,the highest ammonia production rate and energy efficiency(EE),up to 2.93μmol·min^(-1) and 6.64×10^(-2)g·(k W·h)^(-1),respectively,were achieved under low microwave power of 84.42 W.The duty cycle has obvious influences on the synthesis efficiency,compared to a duty cycle of 80%,the ammonia synthesis rate,EE and nitrogen conversion decreased by about 22%at a duty cycle of 100%.This finding underscores the significance of incorporating pulse modulation in the microwave discharge process for ammonia synthesis.Furthermore,it was found that vibrational excitation of microwave plasma has a significant driving effect on ammonia synthesis.展开更多
For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the chang...For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the change of pulse duty cycle,the pulse modulation effect on benzene removal energy efficiency was investigated. The results show that pulse modulation can improve the energy yield and reduce the temperature of the chamber wall. There is an optimal duty cycle for achieving the maximum energy yield at a certain discharge voltage. The effect of initial benzene concentration on the decomposition efficiency and carbon selectivity in pulse modulation plasma were studied. The results indicate that the removal efficiency and carbon balance increase with the specific input energy( SIE) and decrease with the concentration. The energy yield increases with increasing initial concentration and achieves maximum around 180 J / L SIE for all initial concentrations.展开更多
A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulsc-tmxlulated(PM)radio-frequency(RF)glow discharge in atmospheric helium assisted by a sub-microsecon...A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulsc-tmxlulated(PM)radio-frequency(RF)glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge.The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge.Under the assistance of pulsed discharge,the electron density in RF discharge burst reaches the magnitude of 1.87 x 1017-3m within 10 RF cycles,accompanied by the formation of sheath structure.It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst.Furthermore,the dynamics of PM RF glow discharge arc demonstrated by the spatiotcmporal evolution of the election density with and without pulsed discharge.The spatial profiles of electron density,electron energy and electric field at specific time instants arc given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.展开更多
A retarding field energy analyzer（RFEA） is used to measure the time-averaged ion energy distributions（IEDs） on the substrate in both continuous wave（CW） and synchronous pulse modulated radio-frequency（RF） indu...A retarding field energy analyzer（RFEA） is used to measure the time-averaged ion energy distributions（IEDs） on the substrate in both continuous wave（CW） and synchronous pulse modulated radio-frequency（RF） inductively coupled Ar plasmas（ICPs）.The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase（i.e.,θ = 0） and a minimum value at the opposite phase（i.e.,θ = π）.Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.展开更多
Atmospheric pressure pulse-modulated radio-frequency(rf) plasmas have drawn growing attention due to their potential in applications.By selecting appropriate modulation parameters,the diffused and large-volume plasma ...Atmospheric pressure pulse-modulated radio-frequency(rf) plasmas have drawn growing attention due to their potential in applications.By selecting appropriate modulation parameters,the diffused and large-volume plasma can be generated in the pulse-modulated rf plasma with plenty of reactive oxygen species,which is essential for the biomedical application of helium–oxygen plasmas.In this paper,by means of a fluid model,the formation of the peak current in the first period(PCFP) in a pulse-modulated rf helium–oxygen discharge driven by a sinusoidal voltage is discussed,the existence of a reverse field near the anode caused by the negative and positive charges contributes greatly to the mechanism of PCFP.In the simulation,as oxygen admixture increases,the negative ions of O~- and O~-become dominative anions in the sheath region,which can’t be driven to the anode very quickly to build a reverse field,thus the PCFP eventually disappears.This study can effectively enhance the understanding of different transportation behavior of heavy negative ions and electrons,and further optimize pulsemodulated rf discharges with helium–oxygen mixtures in various applications.展开更多
Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions...Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions, neutrals, radicals and excited species） are involved in this simulation. Time evolution of the particle densities and electron temperature with different duty cycles are obtained, as well as the electronegativity nsiH-3 /ne of the main negative ion （Sill3 ）. The results show that, by reducing the duty cycle, higher electron temperature and particle density can be achieved for the same average dissipated power, and the ion energy can also be effectively reduced, which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.展开更多
A 3D temperature field distribution of biological tissue for superficial hyperthermia using a pulse modulated microwave （PMMW） was presented. A 3D sliced homogeneous phantom was radiated by the PMMW and an infrared ...A 3D temperature field distribution of biological tissue for superficial hyperthermia using a pulse modulated microwave （PMMW） was presented. A 3D sliced homogeneous phantom was radiated by the PMMW and an infrared thermal imager was applied to image temperature distribution throughout the phantom. The period of the PMMW is 3 s and the output power is 35 W. The temperature rises by at least 3 ℃ in the phantom when the duty cycle varies from 1/3, 1/2, 2/3 to 1 （denoted by scenarios 1-4）. Both the accumulative temperature-volume histogram and the relative depth-area ratio histogram show that the maximum temperature rise （MTR） is 6.6 and 8 ℃ in scenarios 2 and 3, and they are superior to scenarios 1 and 4. Furthermore, the PMMW can control temperature field distribution of biological tissue. It provides both preliminary basis for thermal volume control and new technology for temperature control and monitor in superficial hyperthermia.展开更多
A one-dimensional fluid/Monte-Carlo（MC）hybrid model is developed to describe capacitively coupled SiH_4/Ar discharge,in which the lower electrode is applied by a RF source and pulse modulated by a square-wave,to inv...A one-dimensional fluid/Monte-Carlo（MC）hybrid model is developed to describe capacitively coupled SiH_4/Ar discharge,in which the lower electrode is applied by a RF source and pulse modulated by a square-wave,to investigate the modulation effects of the pulse duty cycle on the discharge mechanism.An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase.Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species,such as electrons,ions,and radicals.The simulation results show that,the electron energy distribution f（ε）is modulated evidently within a pulse cycle,with its tail extending to higher energies during the power-on period,while shrinking back promptly in the afterglow period.Thus,the rate coefficients could be controlled during the discharge,resulting in modulation of the species composition on the substrate compared with continuous excitation.Meanwhile,more negative ions,like Si H_3^-and Si H_2^-,may escape to the electrodes owing to the collapse of ambipolar electric fields,which is beneficial to films deposition.Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components.展开更多
We propose a simple iterative algorithm based on a temporally movable phase modulation process to retrieve the weak temporal phase of laser pulses. This unambiguous method can be used to achieve a high accuracy and to...We propose a simple iterative algorithm based on a temporally movable phase modulation process to retrieve the weak temporal phase of laser pulses. This unambiguous method can be used to achieve a high accuracy and to simultaneously measure the weak temporal phase and temporal profile of pulses, which are almost transform- limited. A detailed analysis shows that this iterative method has valuable potential applications in the charac- terization of pulses with weak temporal phase.展开更多
Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effe...Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.展开更多
A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direc...A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements.Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format,probabilistic shaping,roll-off factor,baud rate,optical signal-to-noise ratio,and chromatic dispersion.The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios.Furthermore,the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network.Compared with the designed VGG-based CNN,the MobileNet-based MTL does not need to train all the classes,and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy,indicating great potential in various monitoring scenarios.展开更多
The four-level nested neutral-point-clamped(4L-NNPC)inverter is a competitive topology among the various medium-voltage multilevel converters,and its main issue is flying-capacitor voltage unbalance.In this article,a ...The four-level nested neutral-point-clamped(4L-NNPC)inverter is a competitive topology among the various medium-voltage multilevel converters,and its main issue is flying-capacitor voltage unbalance.In this article,a novel carrier-interleaved pulse width modulation(CIPWM)method that satisfies the volt-sec balance principle is proposed with an advanced carrier distribution rule.By adopting the proposed CIPWM method,the redundant switching states of 4L-NNPC inverters can be evenly distributed into the output PWM waveform in each carrier period,and natural flying-capacitor voltage balance can be achieved.Furthermore,an active balancing strategy is also proposed to eliminate the voltage unbalance caused by nonideal factors,which is realized by simply adjusting the duty cycle and with no need to adjust the redundant switching states for 4L-NNPC inverters.The simulation and experimental results verify the effectiveness of the proposed CIPWM method and the flying-capacitor voltage balancing strategy.展开更多
A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the ...A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation.展开更多
A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft swi...A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.展开更多
An exhaustive study of the noncontinuous-state laser dynamics associated with the transient optical process is significant because it reveals the complex physical mechanisms and characteristics in nonlinear laser syst...An exhaustive study of the noncontinuous-state laser dynamics associated with the transient optical process is significant because it reveals the complex physical mechanisms and characteristics in nonlinear laser systems.In this study,in-depth theoretical interpretation and experimental verification of the noncontinuous-state dynamics in laser system are presented,based on developed pulse-modulated frequency-shifted laser feedback interferometry(LFI).By introducing external pulse modulation,we investigate the nonlinear time-of-flight dynamics and related photon behaviors evolution of the pulsed LFI system by observing the changes in effective interference time sequences for interference realization and attainable minimum feedback photon number of the signal under various modulated noncontinuous states.Implementation of the pulse-modulated LFI scheme should exceed the pulse overlapping time window limit of 1.93μs to effectively extract and preserve the extracavity feedback photon information.Experiments reveal that the minimum feedback photon number of signals successfully measured by the pulsed LFI sensor is 0.067 feedback photons per Doppler cycle,exhibiting high sensitivity for extremely weak signal detection.Further,simultaneous measurement for velocity and distance of the moving object is performed to validate the feasibility and applicability of the pulsed LFI.The system can successfully achieve large-range simultaneous measurements within the velocity range of 73.5-612.6 mm∕s,over a distance of 25.5 km.This work opens the way to unexplored frontiers of pulsed LFI to fill the research gap in noncontinuous laser dynamics in this field,showcasing diverse and wide-ranging applications in the realm of integrated sensing,remote monitoring,and positioning and navigation.展开更多
As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is...As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.展开更多
The mismatch effect induced by the radial motion of a target is analyzed for linear frequency modulated （LFM） signals. Then, a novel integrated processing scheme is proposed to re- solve the delay-Doppler coupling e...The mismatch effect induced by the radial motion of a target is analyzed for linear frequency modulated （LFM） signals. Then, a novel integrated processing scheme is proposed to re- solve the delay-Doppler coupling effect in LFM pulse compression. Therefore the range and radial velocity of the target can be si- multaneously estimated with a narrowband LFM pulse. Finally, numerical simulation results demonstrate the effectiveness and good performance of the proposed method.展开更多
The research presented here is focused on the vibration condition of a small volume solder solder ball,which is placed on the surface of a soldering pad and is exerted a pulse modulated continuous wave laser heat sour...The research presented here is focused on the vibration condition of a small volume solder solder ball,which is placed on the surface of a soldering pad and is exerted a pulse modulated continuous wave laser heat source. Finite element method is applied to analyzed the temperature field in the solder ball, and experi- ment is conducted to test the vibration. the results show that,that, the temperature field flucturates with the same frequency as that of the laser pulse, which in turn causes a forced vibration of the same frequency in the liquid solder ball.展开更多
CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigate...CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.展开更多
基金National Natural Science Foundation Project （50875088） Guangdong Province Science and Technology Research Project （2010B010700001）+1 种基金 Huangpu District Science and Technology Research Project （1021） Panyu District Science and Technology Research Project （2010-Z-22-1）.
文摘This article proposed a new methodology and the principle of sinusoid modulated pulse MIG welding, and systematically established the universal mathematical model of computation of the parameters of the sinusoid modulation pulse, achieving that the welding energy input can be effectively controlled and precisely regulated, the transition of pulse change is smooth and the welding process is stable and reliable. With the characteristics of sinusoidal waveform, such as infinite derivative continuity, eternal periodicity and limited control parameters, this article established the theoretical foundation for choiceness, unification and optimization of the parameters during the new sinusoid modulated pulse MIG welding. Bead-on-plate overlay welding is carried out on the pure aluminum sheet test sample for the test. The result indicated that during the welding process, the real-time current waveform is stable and clear; both the corresponding voltage and the instant welding energy waveform are very stable; the repeatability of the U-I graph plotted is high; its family of lines is clear, neat, and its distribution is concentrated showing that the welding process is stable and the neat and high quality ripple weld seam may be produced.
基金supported by National Natural Science Foundation of China(Nos.52077026,51977023,52177126 and 12475253)the Fundamental Research Funds for the Central Universities(No.DUT23YG227)the Dalian Life&Health Guiding Project(No.2023ZXYG34)。
文摘In this study,we explored a one-step direct synthesis of NH3 under mild experimental conditions utilizing pulse-modulated microwave plasma technology at atmospheric pressure.At a substantial gas flow rate,a microwave plasma jet was formed and the microwave-assisted ammonia synthesis can be realized.Impacts of various parameters including the gas flow rate,gas component,microwave absorbed power,pulse modulation frequency,and pulse duty cycle on ammonia synthesis were systematically investigated.To indicate the reaction path of ammonia synthesis,the distributions of both the gas temperature and active species were also studied using optical emission spectra technology.It is found that a considerable amount of ammonia was directly synthesized without involvement of any catalysts,the highest ammonia production rate and energy efficiency(EE),up to 2.93μmol·min^(-1) and 6.64×10^(-2)g·(k W·h)^(-1),respectively,were achieved under low microwave power of 84.42 W.The duty cycle has obvious influences on the synthesis efficiency,compared to a duty cycle of 80%,the ammonia synthesis rate,EE and nitrogen conversion decreased by about 22%at a duty cycle of 100%.This finding underscores the significance of incorporating pulse modulation in the microwave discharge process for ammonia synthesis.Furthermore,it was found that vibrational excitation of microwave plasma has a significant driving effect on ammonia synthesis.
文摘For improving the energy efficiency of plasma volatile organic compounds( VOCs) decomposition, a pulse modulated power is used to drive the dielectric barrier discharge( DBD) plasma to treat benzene. Through the change of pulse duty cycle,the pulse modulation effect on benzene removal energy efficiency was investigated. The results show that pulse modulation can improve the energy yield and reduce the temperature of the chamber wall. There is an optimal duty cycle for achieving the maximum energy yield at a certain discharge voltage. The effect of initial benzene concentration on the decomposition efficiency and carbon selectivity in pulse modulation plasma were studied. The results indicate that the removal efficiency and carbon balance increase with the specific input energy( SIE) and decrease with the concentration. The energy yield increases with increasing initial concentration and achieves maximum around 180 J / L SIE for all initial concentrations.
文摘A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulsc-tmxlulated(PM)radio-frequency(RF)glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge.The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge.Under the assistance of pulsed discharge,the electron density in RF discharge burst reaches the magnitude of 1.87 x 1017-3m within 10 RF cycles,accompanied by the formation of sheath structure.It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst.Furthermore,the dynamics of PM RF glow discharge arc demonstrated by the spatiotcmporal evolution of the election density with and without pulsed discharge.The spatial profiles of electron density,electron energy and electric field at specific time instants arc given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.
基金Project supported by the Important National Science and Technology Specific Project,China(Grant No.2011ZX02403-001)the National Natural Science Foundation of China(Grand No.11675039)the Fundamental Research Funds for the Central Universities,China(Grand No.DUT16LK06)
文摘A retarding field energy analyzer（RFEA） is used to measure the time-averaged ion energy distributions（IEDs） on the substrate in both continuous wave（CW） and synchronous pulse modulated radio-frequency（RF） inductively coupled Ar plasmas（ICPs）.The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase（i.e.,θ = 0） and a minimum value at the opposite phase（i.e.,θ = π）.Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.
基金supported by National Natural Science Foundation of China(No.11975142)。
文摘Atmospheric pressure pulse-modulated radio-frequency(rf) plasmas have drawn growing attention due to their potential in applications.By selecting appropriate modulation parameters,the diffused and large-volume plasma can be generated in the pulse-modulated rf plasma with plenty of reactive oxygen species,which is essential for the biomedical application of helium–oxygen plasmas.In this paper,by means of a fluid model,the formation of the peak current in the first period(PCFP) in a pulse-modulated rf helium–oxygen discharge driven by a sinusoidal voltage is discussed,the existence of a reverse field near the anode caused by the negative and positive charges contributes greatly to the mechanism of PCFP.In the simulation,as oxygen admixture increases,the negative ions of O~- and O~-become dominative anions in the sheath region,which can’t be driven to the anode very quickly to build a reverse field,thus the PCFP eventually disappears.This study can effectively enhance the understanding of different transportation behavior of heavy negative ions and electrons,and further optimize pulsemodulated rf discharges with helium–oxygen mixtures in various applications.
基金supported by National Natural Science Foundation of China (No.10775025)Important National Science & Technology Specific Project of China (No.2011ZX02403-001)Program for New Century Excellent Talents in University of China (NCET-08-0073)
文摘Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions, neutrals, radicals and excited species） are involved in this simulation. Time evolution of the particle densities and electron temperature with different duty cycles are obtained, as well as the electronegativity nsiH-3 /ne of the main negative ion （Sill3 ）. The results show that, by reducing the duty cycle, higher electron temperature and particle density can be achieved for the same average dissipated power, and the ion energy can also be effectively reduced, which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.
基金Project(50977064) supported by the National Natural Science Foundation of China
文摘A 3D temperature field distribution of biological tissue for superficial hyperthermia using a pulse modulated microwave （PMMW） was presented. A 3D sliced homogeneous phantom was radiated by the PMMW and an infrared thermal imager was applied to image temperature distribution throughout the phantom. The period of the PMMW is 3 s and the output power is 35 W. The temperature rises by at least 3 ℃ in the phantom when the duty cycle varies from 1/3, 1/2, 2/3 to 1 （denoted by scenarios 1-4）. Both the accumulative temperature-volume histogram and the relative depth-area ratio histogram show that the maximum temperature rise （MTR） is 6.6 and 8 ℃ in scenarios 2 and 3, and they are superior to scenarios 1 and 4. Furthermore, the PMMW can control temperature field distribution of biological tissue. It provides both preliminary basis for thermal volume control and new technology for temperature control and monitor in superficial hyperthermia.
基金supported by National Natural Science Foundation of China(No.11275038)
文摘A one-dimensional fluid/Monte-Carlo（MC）hybrid model is developed to describe capacitively coupled SiH_4/Ar discharge,in which the lower electrode is applied by a RF source and pulse modulated by a square-wave,to investigate the modulation effects of the pulse duty cycle on the discharge mechanism.An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase.Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species,such as electrons,ions,and radicals.The simulation results show that,the electron energy distribution f（ε）is modulated evidently within a pulse cycle,with its tail extending to higher energies during the power-on period,while shrinking back promptly in the afterglow period.Thus,the rate coefficients could be controlled during the discharge,resulting in modulation of the species composition on the substrate compared with continuous excitation.Meanwhile,more negative ions,like Si H_3^-and Si H_2^-,may escape to the electrodes owing to the collapse of ambipolar electric fields,which is beneficial to films deposition.Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components.
基金Supported by the National Natural Science Foundation of China under Grant No 61205103
文摘We propose a simple iterative algorithm based on a temporally movable phase modulation process to retrieve the weak temporal phase of laser pulses. This unambiguous method can be used to achieve a high accuracy and to simultaneously measure the weak temporal phase and temporal profile of pulses, which are almost transform- limited. A detailed analysis shows that this iterative method has valuable potential applications in the charac- terization of pulses with weak temporal phase.
文摘Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.
基金supported by the National Key Research and Development Program of China (Grant No.2019YFB1803700)the Key Technologies Research and Development Program of Tianjin (Grant No.20YFZCGX00440).
文摘A designed visual geometry group(VGG)-based convolutional neural network(CNN)model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements.Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format,probabilistic shaping,roll-off factor,baud rate,optical signal-to-noise ratio,and chromatic dispersion.The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios.Furthermore,the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network.Compared with the designed VGG-based CNN,the MobileNet-based MTL does not need to train all the classes,and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy,indicating great potential in various monitoring scenarios.
基金supported by Beijing Natural Science Foundation under Grant L242006.
文摘The four-level nested neutral-point-clamped(4L-NNPC)inverter is a competitive topology among the various medium-voltage multilevel converters,and its main issue is flying-capacitor voltage unbalance.In this article,a novel carrier-interleaved pulse width modulation(CIPWM)method that satisfies the volt-sec balance principle is proposed with an advanced carrier distribution rule.By adopting the proposed CIPWM method,the redundant switching states of 4L-NNPC inverters can be evenly distributed into the output PWM waveform in each carrier period,and natural flying-capacitor voltage balance can be achieved.Furthermore,an active balancing strategy is also proposed to eliminate the voltage unbalance caused by nonideal factors,which is realized by simply adjusting the duty cycle and with no need to adjust the redundant switching states for 4L-NNPC inverters.The simulation and experimental results verify the effectiveness of the proposed CIPWM method and the flying-capacitor voltage balancing strategy.
文摘A pulse frequency modulation（PFM） circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation.
文摘A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.
基金National Natural Science Foundation of China(62275001,62105001)China Postdoctoral Science Foundation(GZC20242187)Zhejiang Province Postdoctoral Research Funding(ZJ2024097)。
文摘An exhaustive study of the noncontinuous-state laser dynamics associated with the transient optical process is significant because it reveals the complex physical mechanisms and characteristics in nonlinear laser systems.In this study,in-depth theoretical interpretation and experimental verification of the noncontinuous-state dynamics in laser system are presented,based on developed pulse-modulated frequency-shifted laser feedback interferometry(LFI).By introducing external pulse modulation,we investigate the nonlinear time-of-flight dynamics and related photon behaviors evolution of the pulsed LFI system by observing the changes in effective interference time sequences for interference realization and attainable minimum feedback photon number of the signal under various modulated noncontinuous states.Implementation of the pulse-modulated LFI scheme should exceed the pulse overlapping time window limit of 1.93μs to effectively extract and preserve the extracavity feedback photon information.Experiments reveal that the minimum feedback photon number of signals successfully measured by the pulsed LFI sensor is 0.067 feedback photons per Doppler cycle,exhibiting high sensitivity for extremely weak signal detection.Further,simultaneous measurement for velocity and distance of the moving object is performed to validate the feasibility and applicability of the pulsed LFI.The system can successfully achieve large-range simultaneous measurements within the velocity range of 73.5-612.6 mm∕s,over a distance of 25.5 km.This work opens the way to unexplored frontiers of pulsed LFI to fill the research gap in noncontinuous laser dynamics in this field,showcasing diverse and wide-ranging applications in the realm of integrated sensing,remote monitoring,and positioning and navigation.
基金supported by National Natural Science Foundation of China under Grant Nos.51477177 and 51641707
文摘As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.
基金supported by the Pre-Research Foundation of National Defence of China
文摘The mismatch effect induced by the radial motion of a target is analyzed for linear frequency modulated （LFM） signals. Then, a novel integrated processing scheme is proposed to re- solve the delay-Doppler coupling effect in LFM pulse compression. Therefore the range and radial velocity of the target can be si- multaneously estimated with a narrowband LFM pulse. Finally, numerical simulation results demonstrate the effectiveness and good performance of the proposed method.
文摘The research presented here is focused on the vibration condition of a small volume solder solder ball,which is placed on the surface of a soldering pad and is exerted a pulse modulated continuous wave laser heat source. Finite element method is applied to analyzed the temperature field in the solder ball, and experi- ment is conducted to test the vibration. the results show that,that, the temperature field flucturates with the same frequency as that of the laser pulse, which in turn causes a forced vibration of the same frequency in the liquid solder ball.
基金financially supported by the International Thermonuclear Experimental Reactor (ITER) Project from Ministry of Science and Technology of China (No.2011GB113004)the National High Technology Research and Development Program of China(No.2014AA032402)+1 种基金the Shanghai Commission of Science and Technology (Nos.11DZ1100402 and 13DZ0500100)the Natural Science Foundation of China(Nos.11204174 and 51372150)
文摘CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.
