Showing papers by "Yanyu Wei published in 2003"

Review of the Novel Slow-Wave Structures for High-Power Traveling-Wave Tube

Abstract: All-metal slow-wave structures are being paid great attention because of their advantages, such as good heat dissipation, high power capacity, wide passband, good wholeness of structure and large size etc. The emphases in this paper concentrate on the present state of study of four types of structures: helical groove, ring-plane, folded waveguide and periodically loaded waveguide, including theoretical analyses and practical applications. The problems and directions for future studies of these types of slow-wave circuits are also discussed. It is pointed out that all-metal slow-wave structures are suitable for applications in millimeter wave vacuum devices, like TWT, BWO, Gyro-TWT, and relativistic devices.

Analysis of a novel brazed helix tape slow wave structure with high power capability

Abstract: Summary form only given, as follows. Summary form only given. In order to enhance the power capability of the helix traveling wave tube, a novel helical slow wave structure (SWS) supported by 8 wedge shaped discontinuous dielectric pillars which exist only at the helix tape in each pitch, is developed in this paper. Each pillar can be easily brazed with the helix tape and the metal envelope by means of a special soldering way. This kind of discontinuous support mode can safeguard the dielectric supporting pillar not be broken due to the thermal stress in the case of high temperature. A hybrid model is developed, which can be used to analyze the dispersion characteristics and interaction impedance of the tape helix, by considering the helix radial thickness and the influences of these discontinuous dielectric pillars. The dispersion equation and interaction impedance of this kind of helical SWS are obtained. The numerical calculating results using this hybrid model presented in the paper show good agreements with the HFSS simulation results. All the results presented here can provide a strong basis on design of this kind of novel helical slow wave structure.

Simplified approach to the nonlinear analysis in helix slow-wave-structure for a traveling wave tube

Abstract: A stationary 1-D nonlinear code based on Lagrangian disk model is developed on the basis of a simple set of analytical expressions to study nonlinear dynamics in the helix slow-wave structure used in a traveling wave tube. The loss profiles such as triangular and Gaussian types are modeled as stairsteps and a simple formula is developed to found the loss at a plane for such loss profile. In contrast to the earlier works in nonlinear theory, at present, no numerical method is used at any stage. The method, introduced in this work, is general in nature because it can handle (a) multi-section structure with sever, (b) different loss profiles, namely, center (Gaussian) and tip (triangular: increasing or decreasing), (c) space charge effect on the electrons, (d) backward waves arising due to reflections, etc. Accuracy of the theory and code is verified with comparison of the computed present results with the results from simulation code MAGIC and published elsewhere and found to be in good agreement. The generation and suppression of the harmonic power are studied for a typical structure. It is found that the introduction of resynchronization section of the reduced pitch enhances the fundamental power with the reduction of the second harmonic power. In addition, the method can be used for any helix slow-wave-structure consisting of homogeneous/inhomogeneous dielectric support rods in isotropic/anisotropic overall metallic enclosure, because the axial propagation constant and interaction impedance obtained for any structure and model such as sheath and tape helix approximations or from any simulation codes can be used as the input in the program to make the code more general.

Conductor-centered arbitrarily-shaped helical-groove slow-wave structure for TWTs

Abstract: Summary form only given, as follows. Helical-Groove waveguide(HGW) traveling wave tube (TWT) is one of the potential alternative candidates for high power millimeter wave sources. In this paper, we present the analysis of the novel helical-groove waveguides, the conductor-centered arbitrarily-shaped helical-groove structures, for a possible employment in a wide band TWTs in slow-wave regime. By making use of field theory and admittance, the dispersion relation, interaction impedance are derived. Numerical analysis has performed with HGW-2[3] code to investigate the physical parameters including the groove shape, the radius of the center rod on the wave properties of the electromagnetic (EM) wave propagating through the conductor-centered arbitrarily-shaped helical-groove structure. As it shown from the dispersion characteristics, the profile of the groove takes large influence on high cut-off frequency, passband and wave velocities. This analysis also shows the interaction impedance and small signal gain of TWT with the variation of the physical parameters, indicating the bandwidth of HGW-TWT can be increased largely by choosing a conductor-centered arbitrarily-shaped helical-groove structure with a triangle profile of the groove.

Influence of electric pulse duration on the action on a biological cell

Abstract: Summary form only given, as follows. Electric pulses are widely used for manipulation of biological cells, for example, cell fusion, rotation, dielectrophoresis, and electroporation. In recent years, the biological effects of ultrashort (/spl sim/ns) electric pulses on cells and tissues were studied and reported. It is obvious that parameters like pulse height, duration, front edge, back edge, and repetition rate, of an electric pulse are all important for biological effects arising from the pulse. There are plenty of experiment studies of the influence of these parameters. We report our analysis and calculation results of the influence of pulse duration. The tendency of our calculation results is consistent with experiment results.