The regulation of memory effect and its influence on discharge properties of a dielectric barrier discharge driven by bipolar pulse at atmospheric-pressure nitrogen

The regulation of memory effect that the residual charges generated during and after discharge act on the initiation and development of subsequent discharge is explored by adjusting the pulse parameters,which have an influence on the discharge characteristics.The memory effect is quantified by the measurement of‘wall voltage’through a series of reference capacitors.The influences of memory effect on the discharge properties corresponding to rising/falling time50–500 ns,pulse width 0.5–1.5μs,and frequency 200–600 Hz are analyzed.It is found that the‘wall voltage’increases from 1.4 kV to 2.4 kV with rising/falling time from 50 ns to 500 ns,it varies in the range of 0.18 kV with frequency of 200–600 Hz,and 0.17 k V with pulse width of 0.5–1.5μs.The propagation velocity of wavelike ionization under the negative pulse slows down from 2184 km s-1to 1026 km s-1 as the rising/falling time increases from 50 ns to 500 ns due to the weakening of the electric field by the surface memory effect.More intense and uniform emission can be achieved through faster rising/falling time and higher frequency based on the volume memory effect,while pulse width has less influence on the emission uniformity.Furthermore,similar laws are obtained for spectral and discharge intensity.Therefore,the memory effect is most effectively regulated by rising/falling time,and the discharge properties are affected by the surface and volume memory effect.

Simulation of Secondary Electron and Backscattered Electron Emission in A6 Relativistic Magnetron Driven by Different Cathode

Prticle-in-cell（PIC） simulations demonstrated that,when the relativistic magnetron with diffraction output（MDO） is applied with a 410 kV voltage pulse,or when the relativistic magnetron with radial output is applied with a 350 kV voltage pulse,electrons emitted from the cathode with high energy will strike the anode block wall.The emitted secondary electrons and backscattered electrons affect the interaction between electrons and RF fields induced by the operating modes,which decreases the output power in the radial output relativistic magnetron by about 15%（10%for the axial output relativistic magnetron）,decreases the anode current by about 5%（5%for the axial output relativistic magnetron）,and leads to a decrease of electronic efficiency by 8%（6%for the axial output relativistic magnetron）.The peak value of the current formed by secondary and backscattered current equals nearly half of the amplitude of the anode current,which may help the growth of parasitic modes when the applied magnetic field is near the critical magnetic field separating neighboring modes.Thus,mode competition becomes more serious.

Three-dimensional simulation method of multipactor in microwave components for high-power space application

Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain method and the panicle tracing method, such an algorithm is self-consistent and accurate since the interaction between electromagnetic fields and particles is properly modeled. In the time domain aspect, the generation of multipactor can be easily visualized, which makes it possible to gain a deeper insight into the physical mechanism of this effect. In addition to the classic secondary electron emission model, the measured practical secondary electron yield is used, which increases the accuracy of the algorithm. In order to validate the method, the impedance transformer and ridge waveguide filter are studied. By analyzing the evolution of the secondaries obtained by our method, multipactor thresholds of these components are estimated, which show good agreement with the experimental results. Furthermore, the most sensitive positions where multipactor occurs are determined from the phase focusing phenomenon, which is very meaningful for multipactor analysis and design.

Effects of Linear Falling Ramp Reset Pulse on Addressing Operation in AC PDP

The effects of linear falling ramp reset pulse related to addressing operation in an alternating current plasma display panel （AC PDP） were studied. The wall charge waveforms were measured by the electrode balance method in a 12-inch coplanar AC PDP. The wall charge waveforms show the relationship between the slope ratio of the falling ramp reset pulse and the wall charges at the end of the falling ramp reset pulse which influences the addressing stability. Then the effects of the slope ratio of the linear falling ramp reset pulse on the addressing voltage and addressing time were investigated. The experimental results show that the minimum addressing voltage increases with the increase of the slope ratio of the falling ramp reset pulse, and so does the minimum addressing time. Based on the experimental results, the optimization of the addressing time and the slope ratio of the falling ramp pulse is discussed.

Amplification of terahertz/infrared field at the nodes of Ranvier for myelinated nerve

The myelination of axons was the last major evolution in the vertebrate nervous system.Myelin promotes the speed of action potential by two orders,and modulates the conduction of neurons,important for learning new skills.However,the intrinsic mechanism for high-speed information propagation in myelin in the nervous systems is still unclear.We propose that myelinated nerve fibres serve as dielectric waveguides for the high-frequency electromagnetic information in a certain mid-infrared to terahertz spectral range.Based on the structure characteristics of myelinated nerve composed of periodic nodes of Ranvier and myelin sheath,the energy for the signal propagation is supplied and amplified when crossing the nodes of Ranvier via a periodic relay.In this work,we exploit the quasi-quantum model of amplification for neural terahertz/infrared information at the nodes of Ranvier,and prove the existence of biomolecular ensemble for three-energy-level amplification,revealing the essential mechanism of high-speed electromagnetic information transmitting in myelinated nerves.

Active-Thermal-Tunable Terahertz Absorber with Temperature-Sensitive Material Thin Film

It is shown that active-tunable terahertz absorbers can be realized in a sandwich-structured system comprising an ultrathin dielectric film(polyimide) on a temperature-sensitive substrate(InSb) with a metal film on the back by utilizing the intrinsic carrier density(N) variation in InSb. When increasing the temperature from 250 to 320 K, N in InSb varied from ～5.50×1015 to ～2.98×1016 cm–3. Fixing the thickness of dielectric film with the value of 1.37 μm, the absorption peak shifted from 1.41 to 3.29 THz while keeping absorption higher than 99%. This active tunability can respond to even a slight temperature perturbation, and shows polarization insensitivity as well as high tolerance of incidence-angle(absorption peak can still exceed 90% even the incidence angle reaches 60°). Besides, the refractive index of polyimide(PI) has thermal stability at the terahertz range and the merit of good workability. These characteristics guarantee the stability of activetunable performance. The peculiarities and innovations of this proposal promise a wide range of high efficiency terahertz devices, such as thermal sensors, spatial light modulators(SLMs) and so on.

Optimization of T-shaped waveguide branches in two-dimensional photonic crystals

The interval and the radius of a pair of defect dielectric rods in waveguide channels near the branching region of a T-shaped waveguide branches are simultaneously varied, and their effects on the transmission properties are investigated using the finite-difference time-domain （FDTD） method. Numerical results show that there is an optimized region where the relative bandwidth of high-transmission （total transmittance ≥0.95） band of the branches is larger than 17%, which is higher than that of the existing same structures （11.60%） with fixed interval. These results provide for engineering application of simple T-shaped waveguide branches with high transmission.

Compact beam splitters based on self-imaging phenomena in one-dimensional photonic crystal waveguides

A fundamental 1× 2 beam splitter based on the self-imaging phenomena in multi-mode one-dimensional （1D） photonic crystal （PC） waveguides is presented, and its transmission characteristics are investigated using the finite-difference time-domain method. Calculated results indicate that a high transmittance （〉95%） can be observed within a wide frequency band for the 1×2 beam splitter without complicated structural optimizations. In this letter, a simple and compact 1×4 beam splitter is constructed by combining the fundamental 1×2 beam splitter with the flexible bends of 1D PC waveguides. Such beam splitters can be applied to highly dense photonic integrated circuits.