Gao Cheng

Experimental investigation of EMP shielding effectiveness of reinforced-concrete cell model

For studying the EMP shielding effectiveness, various shielding cell models are established, which are composed with mesh of reinforcement bars or reinforced-concrete. The results of experiments show that if the reinforcement mesh cells and reinforced-concrete shielding cells are specially designed, shielding effectiveness for an EMP plane wave can be about 40 dB and 20 dB for E-field and H-field respectively.

Analysis and Test of EM Shielding for Low-Frequency Magnetic Field

Electromagnetic shielding is the technique that reduces and prevents coupling of undesired radiated electromagnetic energy into equipment, so as to enable it to operate compatibly in its electromagnetic environment. Usually, the frequency considered for electromagnetic shielding design is above 10 kHz, but the lower frequency for some special demand is 50 Hz or even 0.01 Hz sometimes. This paper mainly studies the shielding design for low-frequency magnetic field, and the shielding effectiveness of single shielding and multimedia shielding are discussed separately. Moreover, the shielding effectiveness of a steel shielding enclosure and two different shielding doors for low-frequency magnetic fields in the near zone is measured.

Measurement of the electromagnetic constants of concrete materials by time-domain reflectometry

A dielectric constant and electrical conductivity measurement system based on time-domain reflectometry (TDR) probes that can be embedded into concrete structures have been designed. The calibration data in distilled water has shown that the measuring system can measure the dielectric constant and conductivity accurately. By using the embedded probes in concrete structures, changes of the electromagnetic properties through the curing stage of Portland concrete specimens are measured and presented in this paper.

Full-waveform measuring system for lightning current caused by lightning strikes to tall structures

In order to protect electronic devices against the effects of lightning strikes to tall structures, detailed information about the lightning currents are necessary. For this purpose, a full-waveform measuring system was set up on the north towers of Jiangyin Highway Bridge. In this paper, the calibration to this system is introduced and the results of simulating lightning currents are given.

Calculation of step voltage near lightning current

The method to obtain the step voltage near a lightning current by calculating the near zone horizontal electric field was introduced in the first part of this paper. Then, the relationship between the step voltage and the peak value of the lightning current, the electrical conductivity of ground and the radial distance to the lightning current was investigated. Finally some discussions on the safety zone near a lightning current were made.

The definition of EMP shielding effectiveness

In this paper the experimental results of the interference and damage effects of plane-wave EMP and pulsed magnetic field on microcomputer and microcomputer measuring and control apparatus are introduced. Then some important conclusions are obtained, and, on this basis, the author presents the definition of EMP shielding effectiveness.

The shielding effectiveness of steel enclosure for pulsed magnetic field

By global analysis of the generator, the loop antenna and the shielding enclosure with the FDTD method, the small-loop approach for measurement of the magnetic field shielding effectiveness was simulated numerically in this paper. Nonuniform meshes and reduced c FDTD method were adopted to solve the contradiction of selecting space step and time step: this makes it possible to calculate the steel shielding efficiency of large dimension. The interaction of shielding enclosure and loop antenna was modeled. The setup of the simulation coincides with the real conditions of engineering testing. The conclusions from the numerical calculation are: the waveform of EMP transparent though the steel shielding enclosure is greatly different from the incident EMP waveform. The rise time changes to be very slow and the width of pulse gets long. The calculating and real testing indicate that the shielding efficiency of the steel enclosure to the EMP with longer rise time (/spl mu/s) and wider duration (1ms) is only about 40 dB, the rise time of transparent pulsed magnetic field reaches ms and the pulse width is more than 10ms. The shielding efficiency of the steel enclosure to low frequency electromagnetic field is much lower.

Full-wave analysis of the EMP induced current in cables near the ground

The finite-difference time-domain (FD-TD) method is applied to the analysis of the EMP induced cortical current in coaxial cables near the ground in this paper. This method is a kind of full-wave analysis method. Not only transmission line current but also aerial current is considered in the calculation of induced current. This method is used to analyze all kinds of cortical induced current. The result in this paper is reasonable compared to relative data.

Analysis of the field within bounded wave simulator with a large test object in the working volume

A bounded wave simulator is an efficient broad bandwidth illuminator and has been widely used in simulating the EMP pulse propagating in free space with a plane wave model. A test object in the working volume will cause field distortion. In this paper, the FDTD method is used to calculate the field distributions when a test object is situated in the bounded wave simulator or in a radiated plane wave. The errors of the field distribution according to the different ratio of the test object dimensions to the height of the working space is calculated and compared with the field in free space, especially the tangential H field component on the conductor surface. The method to determine the maximum test size in an EMP simulator is corrected based on our discussion. The advantage of the new method is that the results are more reasonable than before.

Simulation analysis on the distributed capacitance of aircraft return conductor system

In the aircraft lightning indirect effects test, the lightning attachment points are represented by the current generator and return conductor attachments to the aircraft. The airframe and return conductors form a complex non-uniform multi-conductor transmission line. In order to analyze the distributed parameters of the coaxial return conductor system, the simplified model is built in the work to study the change rule of distributed capacitance with different return conductor arrangement. Besides, a lightning injection test model with the aircraft T50 is built, its distributed parameters are calculated by the electromagnetic simulation software FEKO, and then its characteristic impedances in different return conductor arrangements are determined. Thus, some useful rules are provided for characteristic impedance matching in aircraft lightning indirect effect test, and lay a foundation for further research on return conductor configuration.