In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shieldi...In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.展开更多
In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation, analytic expressions of both temperature and thermal stress fields in the target are deduced o...In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation, analytic expressions of both temperature and thermal stress fields in the target are deduced on the basis of the non-Fourier conduction law and the thermo-elastic theory. Taking a stainless steel target as an example, we can solve the analytic expressions under appropriate boundary conditions by using the finite difference method and MATLAB software, and then reveal the evolution law of both surplus temperaturt, and thermal stress in the target. The results indicate that the temperature curves in the target irradiated by a multi-pulsed laser take on a delayed character in different sections away from the boundary, which is only affected by its relaxation time. The front of the stress wave is very steep in the non-Fourier numerical solutions, which presents an obvious thermal shock, so it is necessary to consider the non-Fourier effect of semi-infinite body under the high energy laser radiation.展开更多
Research progresses on Cherenkov and transit-time high-power microwave(HPM)sources in National University of Defense Technology(NUDT)of China are presented.The research issues are focused on the following aspects.The ...Research progresses on Cherenkov and transit-time high-power microwave(HPM)sources in National University of Defense Technology(NUDT)of China are presented.The research issues are focused on the following aspects.The pulse-shortening phenomenon in O-type Cerenkov HPM devices is suppressed.The compact coaxial relativistic backward-wave oscillators(RBWOs)at low bands are developed.The power efficiency in M-Type HPM tubes without guiding magnetic field increased.The power capacities and power efficiencies in the triaxial klystron amplifier(TKA)and relativistic transit-time oscillator(TTO)at higher frequencies increased.In experiments,some exciting results were obtained.The X-band source generated 2 GW microwave power with a pulse duration of 110 ns in 30 Hz repetition mode.Both L-and P-band compact RBWOs generated over 2 GW microwave power with a power efficiency of over 30%.There is approximately a 75% decline of the volume compared with that of conventional RBWO under the same power capacity conditions.A 1.755 GHz MILO produced 3.1 GW microwave power with power efficiency of 10.4%.A 9.37 GHz TKA produced the 240 MW microwave power with the gain of 34 dB.A 14.3 GHz TTO produced 1 GW microwave power with power efficiency of 20%.展开更多
We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase...We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure,the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 m W, 51.3 m W,and 13.2 m W, respectively. The total single pulse output power is 69.8 m W, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.展开更多
The velvet electron emission characteristics and beams' brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery em...The velvet electron emission characteristics and beams' brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery emission is much stronger than that from the centre. The periphery emission contributes much more to the formation of the cathode plasma than the centre emission, which leads to diode impendence breakdown. The relationship between the cathode plasma expansion and the initial emittance of the cathode is deduced to describe the characteristics of the multi-pulsed vacuum diode. The emittance of the multi-pulsed beams is measured to be less than 1000mm·mrad. The brightness of the electron beams is better than 1× 10^8A/(m·rad)2.展开更多
TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetiti...TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.展开更多
In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge (DBD) under atmospheric pressure. The finiteelement method is employed to solve the mode...In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge (DBD) under atmospheric pressure. The finiteelement method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.展开更多
The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functi...The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functioning and topology connections are given in order to understand the multi-pulse converter. Using the 24 and 48-pulse topologies switching functions models are presented. The models correctly represent commutations of semiconductor devices in multi-pulse converters, which consequently allows a precise representation of harmonic components. Additionally, time domain models that represent harmonic components are derived based on the switching functions models. Switching functions, as well as time domain models are carried out in the original abc power system coordinates. Effectiveness and precision of the models are validated against simulations performed in Matlab/Simulink?. Additionally, in order to accomplish a more realistic comparison, a laboratory prototype set up is used to assess simulated waveforms.展开更多
Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitat...Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitation. A two-degree-of-freedom nonlinear nonautonomous system governing equations of motion for the rectangular thin plate is derived by the von Karman type equation and the Galerkin approach. A one-to- one internal resonance is considered. An averaged equation is obtained with a multi-scale method. After transforming the averaged equation into a standard form, the extended Melnikov method is used to show the existence of multi-pulse chaotic dynamics, which can be used to explain the mechanism of modal interactions of thin plates. A method for calculating the Melnikov function is given without an explicit analytical expression of homoclinic orbits. Furthermore, restrictions on the damping, excitation, and detuning parameters are obtained, under which the multi-pulse chaotic dynamics is expected. The results of numerical simulations are also given to indicate the existence of small amplitude multi-pulse chaotic responses for the rectangular thin plate.展开更多
According to the transit-time difference measurement method,we proposed a design scheme of ultrasonic heat meter based on TDC-GP21.The measurement unit TDC-GP21 mainly completes transit-time measurement and inlet,outl...According to the transit-time difference measurement method,we proposed a design scheme of ultrasonic heat meter based on TDC-GP21.The measurement unit TDC-GP21 mainly completes transit-time measurement and inlet,outlet temperature measurement functions.Control unit and data processing unit based on MSP430F4152 of TI corporation complete functions including peripherals control,data analysis,temperature compensation algorithm,flow pattern compensation algorithm and low power consumption control.The design meets the Town Construction Professional Standard CJ 128-2007,and furthermore,some performances can be improved.展开更多
Regional lightning protection is a complete theoretical system,mainly including:lightning interception technology(LIPT),lightning strong electromagnetic pulse high-energy absorption technology(MSPD),and regional light...Regional lightning protection is a complete theoretical system,mainly including:lightning interception technology(LIPT),lightning strong electromagnetic pulse high-energy absorption technology(MSPD),and regional lightning activity law analysis technology(RLLA).Lightning interception technology uses dispersive waveguide resonant cavity technology to achieve the functions of 46.55 m longer than upward leader of ordinary lightning rod,significantly reducing lightning strike point current by 40%,optimizing space electromagnetic field environment,and effectively intercepting overhead and side lightning strikes,and overcome the limitations of traditional lightning rod.The lightning strong electromagnetic pulse high-energy absorption technology uses distributed parameter balance technology,special disconnector for short circuit current,and parity pairing technology to achieve stronger surge absorption capacity than traditional single pulse SPD and international advanced technical indicators such as timely breaking under power frequency short circuit current,and good energy and time coordination.The analysis technology of regional lightning activity laws accurately identifies lightning strike points through comprehensive analysis of regional lightning activity laws,physical parameters of ion clouds,and the impact on ground electric fields.The three core technology systems complement each other,achieving all-round protection against direct lightning strike and lightning electromagnetic pulse.Several projects achieved zero lightning damage,effectively ensuring the safety of buildings and electronic and electrical equipment in the protected area.展开更多
The C-band three-cavity transit-time effect oscillator (3C TTTO) is a novel high power microwave device based on the transit-time effect of the three-cavity (3C) resonator. The operational principle of this device is ...The C-band three-cavity transit-time effect oscillator (3C TTTO) is a novel high power microwave device based on the transit-time effect of the three-cavity (3C) resonator. The operational principle of this device is briefly expounded in this paper, and the theoretical and experimental researches on the radial insulation diode, the 3C resonator, the double-gap output cavity and the circular waveguide bevel cut radiation antenna are presented in detail. By using the analytic method, the eigen modes and their field distributions of the 3C resonator are developed, and some basic laws of the transit-time effect are obtained in non-π mode field of the 3C resonator. At last, the experimental results are given. This device generated RF peak power in excess of 400MW with 15ns FWHM, and its beam-wave power conversion efficiency is about 17%.展开更多
The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The t...The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The tested cathodes include velvet,carbon fibers,carbon nano-tubes (CNTs) and dispenser cathodes.The results indicate that all four are able to emit multi-pulsed beams.For velvet,carbon fiber and CNTs,the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse.For dispenser cathodes tested in the experiment,although there is a little difference from pulse to pulse for some reason,thermal-electric field emission may be the main process.展开更多
To better understand the physical processes of multi-pulse laser drilling,this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation system.The evolution characteristics sug...To better understand the physical processes of multi-pulse laser drilling,this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation system.The evolution characteristics suggested a two-phase process of rapid penetration followed by moderate penetration.As revealed in the ejection and vaporization behavior,the keyhole evolution was dominated by ejection and vaporization during the rapid and moderate penetration stages,respectively.In a single laser-pulsed drilling experiment,the driving mechanism itself was found to be affected by the dimensionless laser power density.The effect of dimensionless laser power density on depth increment was then discussed by comparing the experimental observations with numerical simulation results.The results further confirmed the driving mechanism of the keyhole evolution.The results in this paper are useful for understanding the driving mechanism of the keyhole evolution during multi-pulse laser drilling.展开更多
The Auto-Transformer Rectifier Unit(ATRU) is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, t...The Auto-Transformer Rectifier Unit(ATRU) is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.展开更多
To improve the harmonic suppression ability of multi-pulse rectifier,a 12-pulse rectifier based on zigzag autotransformer by DC side active compensation strategy is proposed.By controlling the small capacity current i...To improve the harmonic suppression ability of multi-pulse rectifier,a 12-pulse rectifier based on zigzag autotransformer by DC side active compensation strategy is proposed.By controlling the small capacity current inverter to generate compensating currents and injecting the currents directly into the DC side of the system,the grid-side currents of the rectifier can be approximated to sine wave.Using zigzag autotransformer as phase-shifting transformer can block the zero sequence current components and reduce the equivalent capacity of the rectifying system.The study on harmonic distortion rate of grid-side currents with the variation of the load shows that the harmonic content of the compensated rectifier decreases significantly under various load conditions.The harmonic content of the grid-side currents of the proposed active injection rectifier is only 1.17%,and the equivalent capacity of the rectifier is calculated.The results show that the rectifier can not only suppress the harmonic currents,but also have a lower equivalent capacity.展开更多
The multi-pulse orbits and chaotic dynamics of a simply supported laminated composite piezoelectric rectangular plate under combined parametric excitation and transverse excitation are studied in detail. It is assumed...The multi-pulse orbits and chaotic dynamics of a simply supported laminated composite piezoelectric rectangular plate under combined parametric excitation and transverse excitation are studied in detail. It is assumed that different layers are perfectly bonded to each other with piezoelectric actuator patches embedded. The nonlinear equations of motion for the laminated composite piezoelectric rectangular plate are derived from von Karman-type equation and third-order shear deformation plate theory of Reddy. The two-degree-of-freedom dimensionless equations of motion are obtained by using the Galerkin approach to the partial differential governing equation of motion for the laminated composite piezoelectric rectangular plate. The four-dimensional averaged equation in the case of primary parametric resonance and 1:3 internal resonances is obtained by using the method of multiple scales. From the averaged equation, the theory of normal form is used to find the explicit formulas of normal form. Based on the normal form obtained, the energy phase method is utilized to analyze the multi-pulse global bifurcations and chaotic dynamics for the laminated composite piezoelectric rectangular plate. The analysis of the global dynamics indicates that there exist multi-pulse jumping orbits in the perturbed phase space of the averaged equation. Based on the averaged equation obtained, the chaotic motions and the Shilnikov type multi-pulse orbits of the laminated composite piezoelectric rectangular plate are also found by numerical simulation. The results obtained above mean the existence of the chaos in the Smale horseshoe sense for the simply supported laminated composite piezoelectric rectangular plate.展开更多
Expressway toll station is listed by lightning protection experts as one of the five difficult problems in the field of international lightning protection.So far,the direct lightning protection of the expressway toll ...Expressway toll station is listed by lightning protection experts as one of the five difficult problems in the field of international lightning protection.So far,the direct lightning protection of the expressway toll station is mainly based on the electrical geometry model-rolling ball method.Lightning rod or lightning belt is installed on the high pole lamp of the toll square and the ceiling of the toll island as a flash catching device to intercept lightning.The lightning rod is a section of metal conductor with the tip.From the process of the connection between up leader generated by the lightning rod and down leader of lightning,the lightning rod has the ability to attract the lightning rod,and can prevent lightning strike of the protected objects within a certain range.From the perspective of lightning protection methods and means,lightning protection plays an interception role against lightning discharge,also called interceptor.A large number of practice has proved that the lightning rod plays an important role in protecting the building structure from lightning damage.With the development of electronic information society,the limitations of lightning rod are more and more prominent,resulting in more and more lightning strike accidents.In 2019,China invented a new flash connection device-lightning interceptor that can overcome the limitations of lightning rod and has applied it on expressways,which has achieved remarkable results.In this paper,the physical parameters of lightning receiving process by the lightning interceptor and the lightning rod are compared,and the solution to prevent direct lightning strike at expressway toll station is proposed.展开更多
The ε-Fe3N-based magnetic lubricant which is stable and high saturation magnetization has been prepared by a homemade DBD device under the atmospheric pressure. The results show that the NH3 flow rate, the applied pe...The ε-Fe3N-based magnetic lubricant which is stable and high saturation magnetization has been prepared by a homemade DBD device under the atmospheric pressure. The results show that the NH3 flow rate, the applied peak-to-peak voltage and the mass ratio of surfactant and carrier lubricant have important effects on the phase structure, the magnetic properties, the size of ferroparticles and the stability of the ε-Fe3N-based magnetic lubricant. TEM images show the e-Fe3N ferroparticles are dispersed in the carrier lubricant homogeneously, and the cluster phenomenon is not observed. The stable e-Fe3N-based magnetic lubricant with the saturation magnetization of 50.11 mT and the mean ferroparticle size of 11 nm is prepared successfully. The main particles of the atmospheric-pressure Ar/NH3/Fe(CO)5 DBD plasma are NH, N, N+, Fe, N2, Ar, Ha, and CO; NH is a decomposition product of NH3. Fe and N active radicals are two elementary species in the preparation of the c-Fe3N-based magnetic lubricant in the atmospheric-pressure DBD plasma. There are two discharge modes for DBD plasma, namely, multi-pulse APGD and filamentary discharge. By increasing the applied peak-to-peak voltage from 4600 to 7800 V, the discharge mode is changed from single-pulse APGD with filamentary discharge to two-pulse APGD with filamentary discharge, and the Lissajous figure also converts from a quadrilateral with one step to two steps on the right-hand side.展开更多
In this paper,the complicated dynamics and multi-pulse homoclinic orbits of a two-degree-of-freedom parametrically excited nonlinear nano-oscillator with coupled cubic nonlinearities are studied.The damping,parametric...In this paper,the complicated dynamics and multi-pulse homoclinic orbits of a two-degree-of-freedom parametrically excited nonlinear nano-oscillator with coupled cubic nonlinearities are studied.The damping,parametrical excitation and the nonlinearities are regarded as weak.The averaged equation depicting the fast and slow dynamics is derived through the method of multiple scales.The dynamics near the resonance band is revealed by doing a singular perturbation analysis and combining the extended Melnikov method.We are able to determine the criterion for the existence of the multi-pulse homoclinic orbits which can form the Shilnikov orbits and give rise to chaos.At last,numerical results are also given to illustrate the nonlinear behaviors and chaotic motions in the nonlinear nano-oscillator.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 61701516)
文摘In order to reduce the external magnetic field and improve the conversion efficiency of high-power microwave generation devices with low external magnetic field,a novel diode with an embedded soft magnetic and shielding structure is proposed.The soft magnetic material is designed to enhance the local magnetic field in the diode region.Moreover,the diode applies a shielding structure which can reduce the radial electric field.From simulation research,it is found that the emission and transmission quality of the electron beam with low magnetic field is greatly improved when loading this diode.Through simulation research,it is verified that the diode can increase the conversion efficiency of the transit-time oscillator(TTO)from 30%to 36.7%.In our experimental study,under the conditions of a diode voltage of 540 kV and a current of 10.5 kA,the output microwave power is 1.51 GW when loading the novel diode and the microwave frequency is 4.27 GHz when an external guiding magnetic field of 0.3 T is applied.The corresponding conversion efficiency is improved from 20.0%to 26.6%,which is 6.6%higher than that of a device loaded with a conventional diode.Our experiments have verified that this novel diode can effectively improve the conversion efficiency of high-power microwave sources operating with low magnetic field,and contribute to the miniaturization and compactness of high-power microwave devices.
基金supported by the Chinese Natural Science Fund (No.10572020)
文摘In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation, analytic expressions of both temperature and thermal stress fields in the target are deduced on the basis of the non-Fourier conduction law and the thermo-elastic theory. Taking a stainless steel target as an example, we can solve the analytic expressions under appropriate boundary conditions by using the finite difference method and MATLAB software, and then reveal the evolution law of both surplus temperaturt, and thermal stress in the target. The results indicate that the temperature curves in the target irradiated by a multi-pulsed laser take on a delayed character in different sections away from the boundary, which is only affected by its relaxation time. The front of the stress wave is very steep in the non-Fourier numerical solutions, which presents an obvious thermal shock, so it is necessary to consider the non-Fourier effect of semi-infinite body under the high energy laser radiation.
基金supported by the National Natural Science Funds Fund of China under Grant No.11505288Provincial Natural Science Foundation of Hunanscientific effort project of NUDT.
文摘Research progresses on Cherenkov and transit-time high-power microwave(HPM)sources in National University of Defense Technology(NUDT)of China are presented.The research issues are focused on the following aspects.The pulse-shortening phenomenon in O-type Cerenkov HPM devices is suppressed.The compact coaxial relativistic backward-wave oscillators(RBWOs)at low bands are developed.The power efficiency in M-Type HPM tubes without guiding magnetic field increased.The power capacities and power efficiencies in the triaxial klystron amplifier(TKA)and relativistic transit-time oscillator(TTO)at higher frequencies increased.In experiments,some exciting results were obtained.The X-band source generated 2 GW microwave power with a pulse duration of 110 ns in 30 Hz repetition mode.Both L-and P-band compact RBWOs generated over 2 GW microwave power with a power efficiency of over 30%.There is approximately a 75% decline of the volume compared with that of conventional RBWO under the same power capacity conditions.A 1.755 GHz MILO produced 3.1 GW microwave power with power efficiency of 10.4%.A 9.37 GHz TKA produced the 240 MW microwave power with the gain of 34 dB.A 14.3 GHz TTO produced 1 GW microwave power with power efficiency of 20%.
基金Project supported by the National Natural Science Foundation of China(Grant No.51905528)the Key Research Project of Bureau of Frontier Sciences and Education+1 种基金Chinese Academy of Sciences(Grant No.QYZDY-SSW-JSC008)the National Key Research and Development Project,China(Grant Nos.2019YFB2005600 and 2018YFB2003403)。
文摘We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure,the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 m W, 51.3 m W,and 13.2 m W, respectively. The total single pulse output power is 69.8 m W, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.
文摘The velvet electron emission characteristics and beams' brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery emission is much stronger than that from the centre. The periphery emission contributes much more to the formation of the cathode plasma than the centre emission, which leads to diode impendence breakdown. The relationship between the cathode plasma expansion and the initial emittance of the cathode is deduced to describe the characteristics of the multi-pulsed vacuum diode. The emittance of the multi-pulsed beams is measured to be less than 1000mm·mrad. The brightness of the electron beams is better than 1× 10^8A/(m·rad)2.
文摘TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.
基金supported in part by China Foundation for the Author of National Excellent Doctoral Dissertation(No.200338)Fundamental Research Funds for the Central Universities of China(No.xjj20100160)
文摘In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge (DBD) under atmospheric pressure. The finiteelement method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.
文摘The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functioning and topology connections are given in order to understand the multi-pulse converter. Using the 24 and 48-pulse topologies switching functions models are presented. The models correctly represent commutations of semiconductor devices in multi-pulse converters, which consequently allows a precise representation of harmonic components. Additionally, time domain models that represent harmonic components are derived based on the switching functions models. Switching functions, as well as time domain models are carried out in the original abc power system coordinates. Effectiveness and precision of the models are validated against simulations performed in Matlab/Simulink?. Additionally, in order to accomplish a more realistic comparison, a laboratory prototype set up is used to assess simulated waveforms.
基金Project supported the National Natural Science Foundation of China (Nos. 10732020,11072008,and 11102226)the Scientific Research Foundation of Civil Aviation University of China (No. 2010QD04X)the Fundamental Research Funds for the Central Universities of China (Nos. ZXH2011D006 and ZXH2012K004)
文摘Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitation. A two-degree-of-freedom nonlinear nonautonomous system governing equations of motion for the rectangular thin plate is derived by the von Karman type equation and the Galerkin approach. A one-to- one internal resonance is considered. An averaged equation is obtained with a multi-scale method. After transforming the averaged equation into a standard form, the extended Melnikov method is used to show the existence of multi-pulse chaotic dynamics, which can be used to explain the mechanism of modal interactions of thin plates. A method for calculating the Melnikov function is given without an explicit analytical expression of homoclinic orbits. Furthermore, restrictions on the damping, excitation, and detuning parameters are obtained, under which the multi-pulse chaotic dynamics is expected. The results of numerical simulations are also given to indicate the existence of small amplitude multi-pulse chaotic responses for the rectangular thin plate.
基金National Natural Science Foundation of China(No.61071087)Natural Science Foundation of Shandong Province(No.ZR2011FM018)
文摘According to the transit-time difference measurement method,we proposed a design scheme of ultrasonic heat meter based on TDC-GP21.The measurement unit TDC-GP21 mainly completes transit-time measurement and inlet,outlet temperature measurement functions.Control unit and data processing unit based on MSP430F4152 of TI corporation complete functions including peripherals control,data analysis,temperature compensation algorithm,flow pattern compensation algorithm and low power consumption control.The design meets the Town Construction Professional Standard CJ 128-2007,and furthermore,some performances can be improved.
基金Supported by Lightning Multi-pulse Intelligent Monitoring System Optimization Technology Project of Guangdong Yuedian Dianbai Hot Water Wind Farm(SFC/DBW-Z-FW-23-006).
文摘Regional lightning protection is a complete theoretical system,mainly including:lightning interception technology(LIPT),lightning strong electromagnetic pulse high-energy absorption technology(MSPD),and regional lightning activity law analysis technology(RLLA).Lightning interception technology uses dispersive waveguide resonant cavity technology to achieve the functions of 46.55 m longer than upward leader of ordinary lightning rod,significantly reducing lightning strike point current by 40%,optimizing space electromagnetic field environment,and effectively intercepting overhead and side lightning strikes,and overcome the limitations of traditional lightning rod.The lightning strong electromagnetic pulse high-energy absorption technology uses distributed parameter balance technology,special disconnector for short circuit current,and parity pairing technology to achieve stronger surge absorption capacity than traditional single pulse SPD and international advanced technical indicators such as timely breaking under power frequency short circuit current,and good energy and time coordination.The analysis technology of regional lightning activity laws accurately identifies lightning strike points through comprehensive analysis of regional lightning activity laws,physical parameters of ion clouds,and the impact on ground electric fields.The three core technology systems complement each other,achieving all-round protection against direct lightning strike and lightning electromagnetic pulse.Several projects achieved zero lightning damage,effectively ensuring the safety of buildings and electronic and electrical equipment in the protected area.
文摘The C-band three-cavity transit-time effect oscillator (3C TTTO) is a novel high power microwave device based on the transit-time effect of the three-cavity (3C) resonator. The operational principle of this device is briefly expounded in this paper, and the theoretical and experimental researches on the radial insulation diode, the 3C resonator, the double-gap output cavity and the circular waveguide bevel cut radiation antenna are presented in detail. By using the analytic method, the eigen modes and their field distributions of the 3C resonator are developed, and some basic laws of the transit-time effect are obtained in non-π mode field of the 3C resonator. At last, the experimental results are given. This device generated RF peak power in excess of 400MW with 15ns FWHM, and its beam-wave power conversion efficiency is about 17%.
基金Supported by National Nature Science Foundation of China(10575090)State Key Laboratory of Advanced Materials (Beijing University of Science and Technology, 20082D-10)
文摘The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources.The tested cathodes include velvet,carbon fibers,carbon nano-tubes (CNTs) and dispenser cathodes.The results indicate that all four are able to emit multi-pulsed beams.For velvet,carbon fiber and CNTs,the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse.For dispenser cathodes tested in the experiment,although there is a little difference from pulse to pulse for some reason,thermal-electric field emission may be the main process.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672304,11502269,11272316,and 11272317)the Plan of Beijing Municipal Commission of Science and Technology(Grant No.Z181100003818015)
文摘To better understand the physical processes of multi-pulse laser drilling,this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation system.The evolution characteristics suggested a two-phase process of rapid penetration followed by moderate penetration.As revealed in the ejection and vaporization behavior,the keyhole evolution was dominated by ejection and vaporization during the rapid and moderate penetration stages,respectively.In a single laser-pulsed drilling experiment,the driving mechanism itself was found to be affected by the dimensionless laser power density.The effect of dimensionless laser power density on depth increment was then discussed by comparing the experimental observations with numerical simulation results.The results further confirmed the driving mechanism of the keyhole evolution.The results in this paper are useful for understanding the driving mechanism of the keyhole evolution during multi-pulse laser drilling.
文摘The Auto-Transformer Rectifier Unit(ATRU) is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.
基金National Natural Science Foundation of China(No.51767013)Science and Technology Research and Development Plan of China Railway Corporation(No.2017J012-A)Lanzhou City Science and Technology Program for Innovation and Entrepreneurship of Talents(No.2017-RC-51)。
文摘To improve the harmonic suppression ability of multi-pulse rectifier,a 12-pulse rectifier based on zigzag autotransformer by DC side active compensation strategy is proposed.By controlling the small capacity current inverter to generate compensating currents and injecting the currents directly into the DC side of the system,the grid-side currents of the rectifier can be approximated to sine wave.Using zigzag autotransformer as phase-shifting transformer can block the zero sequence current components and reduce the equivalent capacity of the rectifying system.The study on harmonic distortion rate of grid-side currents with the variation of the load shows that the harmonic content of the compensated rectifier decreases significantly under various load conditions.The harmonic content of the grid-side currents of the proposed active injection rectifier is only 1.17%,and the equivalent capacity of the rectifier is calculated.The results show that the rectifier can not only suppress the harmonic currents,but also have a lower equivalent capacity.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10872010, 10732020 and 11072008)the National Science Foundation for Distinguished Young Scholars of China (Grant No. 10425209)+1 种基金the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipalitythe Ph.D. Programs Foundation of Beijing University of Technology (Grant No. 52001015200701)
文摘The multi-pulse orbits and chaotic dynamics of a simply supported laminated composite piezoelectric rectangular plate under combined parametric excitation and transverse excitation are studied in detail. It is assumed that different layers are perfectly bonded to each other with piezoelectric actuator patches embedded. The nonlinear equations of motion for the laminated composite piezoelectric rectangular plate are derived from von Karman-type equation and third-order shear deformation plate theory of Reddy. The two-degree-of-freedom dimensionless equations of motion are obtained by using the Galerkin approach to the partial differential governing equation of motion for the laminated composite piezoelectric rectangular plate. The four-dimensional averaged equation in the case of primary parametric resonance and 1:3 internal resonances is obtained by using the method of multiple scales. From the averaged equation, the theory of normal form is used to find the explicit formulas of normal form. Based on the normal form obtained, the energy phase method is utilized to analyze the multi-pulse global bifurcations and chaotic dynamics for the laminated composite piezoelectric rectangular plate. The analysis of the global dynamics indicates that there exist multi-pulse jumping orbits in the perturbed phase space of the averaged equation. Based on the averaged equation obtained, the chaotic motions and the Shilnikov type multi-pulse orbits of the laminated composite piezoelectric rectangular plate are also found by numerical simulation. The results obtained above mean the existence of the chaos in the Smale horseshoe sense for the simply supported laminated composite piezoelectric rectangular plate.
基金Supported by Regional Lightning Protection Engineering Technology Research and Development Project(PhaseⅡ)in Guangdong Yuedian Dianbai Wind Farm(SFC/DBW-ZX-FW-22-006)。
文摘Expressway toll station is listed by lightning protection experts as one of the five difficult problems in the field of international lightning protection.So far,the direct lightning protection of the expressway toll station is mainly based on the electrical geometry model-rolling ball method.Lightning rod or lightning belt is installed on the high pole lamp of the toll square and the ceiling of the toll island as a flash catching device to intercept lightning.The lightning rod is a section of metal conductor with the tip.From the process of the connection between up leader generated by the lightning rod and down leader of lightning,the lightning rod has the ability to attract the lightning rod,and can prevent lightning strike of the protected objects within a certain range.From the perspective of lightning protection methods and means,lightning protection plays an interception role against lightning discharge,also called interceptor.A large number of practice has proved that the lightning rod plays an important role in protecting the building structure from lightning damage.With the development of electronic information society,the limitations of lightning rod are more and more prominent,resulting in more and more lightning strike accidents.In 2019,China invented a new flash connection device-lightning interceptor that can overcome the limitations of lightning rod and has applied it on expressways,which has achieved remarkable results.In this paper,the physical parameters of lightning receiving process by the lightning interceptor and the lightning rod are compared,and the solution to prevent direct lightning strike at expressway toll station is proposed.
基金supported by National Natural Science Foundation of China (Grant Nos. 11605020 and 21673026)by the National Natural Science Foundation of Liaoning Province, China (Grant No. 2015020585)
文摘The ε-Fe3N-based magnetic lubricant which is stable and high saturation magnetization has been prepared by a homemade DBD device under the atmospheric pressure. The results show that the NH3 flow rate, the applied peak-to-peak voltage and the mass ratio of surfactant and carrier lubricant have important effects on the phase structure, the magnetic properties, the size of ferroparticles and the stability of the ε-Fe3N-based magnetic lubricant. TEM images show the e-Fe3N ferroparticles are dispersed in the carrier lubricant homogeneously, and the cluster phenomenon is not observed. The stable e-Fe3N-based magnetic lubricant with the saturation magnetization of 50.11 mT and the mean ferroparticle size of 11 nm is prepared successfully. The main particles of the atmospheric-pressure Ar/NH3/Fe(CO)5 DBD plasma are NH, N, N+, Fe, N2, Ar, Ha, and CO; NH is a decomposition product of NH3. Fe and N active radicals are two elementary species in the preparation of the c-Fe3N-based magnetic lubricant in the atmospheric-pressure DBD plasma. There are two discharge modes for DBD plasma, namely, multi-pulse APGD and filamentary discharge. By increasing the applied peak-to-peak voltage from 4600 to 7800 V, the discharge mode is changed from single-pulse APGD with filamentary discharge to two-pulse APGD with filamentary discharge, and the Lissajous figure also converts from a quadrilateral with one step to two steps on the right-hand side.
基金supported by the National Natural Science Foundation of China(Grant Nos.11290152,11072008 and 11372015)the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality(PHRIHLB)
文摘In this paper,the complicated dynamics and multi-pulse homoclinic orbits of a two-degree-of-freedom parametrically excited nonlinear nano-oscillator with coupled cubic nonlinearities are studied.The damping,parametrical excitation and the nonlinearities are regarded as weak.The averaged equation depicting the fast and slow dynamics is derived through the method of multiple scales.The dynamics near the resonance band is revealed by doing a singular perturbation analysis and combining the extended Melnikov method.We are able to determine the criterion for the existence of the multi-pulse homoclinic orbits which can form the Shilnikov orbits and give rise to chaos.At last,numerical results are also given to illustrate the nonlinear behaviors and chaotic motions in the nonlinear nano-oscillator.