Ruyu Fan

A Hybrid FDTD-SPICE Method for Transmission Lines Excited by a Nonuniform Incident Wave

This paper presents a hybrid finite-difference time-domain-simulation program with integrated circuit emphasis (FDTD-SPICE) method for lossless transmission lines excited by a nonuniform electromagnetic field. An FDTD code is used to compute the excitation fields of the lines. Additional voltage sources, which denote the effect of the excitation fields, are computed with the results obtained by the FDTD method and incorporated into a SPICE model. The hybrid method can be used for nonlinear or time-varying loads, because the SPICE model allows easy incorporation of nonlinear or time-varying loads. Three cases, two transmission lines and a network, all inside a cavity excited by an incident electromagnetic field, are computed by using the presented method. The numerical results are compared with those obtained by using a 3D FDTD code, and the agreement is generally good. The time needed by the hybrid method is much less than that needed by the FDTD code, because the lines can be ignored when the excitation fields of the lines are computed in the hybrid method.

SPICE Models to Analyze Radiated and Conducted Susceptibilities of Shielded Coaxial Cables

This paper presents simulation program with integrated circuit emphasis (SPICE) models for the analyses of the radiated and conducted susceptibilities of shielded coaxial cables. Derived from the transmission-line equations of shielded cables, these models can be directly used for the time-domain and frequency-domain analyses, and connected to nonlinear and time-varying loads with the models already available in SPICE. In the proposed models, the usual discretization of shielded cables is not needed, and both the transfer impedance and admittance have been taken into account. Results obtained with these new models are in a good agreement with those obtained by using other approaches.

STUDY OF LOSS EFFECT OF TRANSMISSION LINES AND VALIDITY OF A SPICE MODEL IN ELECTROMAGNETIC TOPOLOGY

This paper studies the loss effect of the line and the validity of a SPICE model for lossless transmission lines excited by an incident plane wave by using a simple structure — a single line over an infinite perfectly conducting ground excited by an incident electromagnetic field. The frequency domain current responses calculated by the Baum-Liu-Tesche (BLT) equation with the loss ignored are compared with those through the BLT equation with loss considered to study the loss effect of transmission lines. The loss effect study shows that the SPICE model for lossless transmission line can be used for nuclear electromagnetic pulse, ultra wideband, and the low-frequency range of high power microwave interaction with most systems. But for a sine or cosine wave of which the frequency equals the pole frequency of the line, the SPICE model may lead to significant error.

Analysis of EMP Coupling to a Device from A Wire Penetrating a Cavity Aperture Using Transient Electromagnetic Topology

This paper studies an electromagnetic pulse coupling to a device from a wire penetrating a cavity aperture by applying the transient electromagnetic topology (TEMT) method. The computation process is divided into two steps: The three dimensional finite-difference time-domain (FDTD) method is used to compute the excitation fields of the wire, and then the SPICE model of the wire is used to compute the current response of the device. The results obtained by the TEMT method are compared with those obtained numerically by using the FDTD method only and experimentally. And good agreement has been obtained. All the calculations are done in the time domain, and the TEMT method can be used to directly analyze nonlinear or time-varying loads. The wire does not have to be meshed in the TEMT method, so the TEMT method is more efficient than the FDTD method only.

SPICE MODELS FOR RADIATED AND CONDUCTED SUSCEPTIBILITY ANALYSES OF MULTICONDUCTOR SHIELDED CABLES

This paper presents SPICE models to analyze the radiated and conducted susceptibilities of multiconductor shielded cables in the time and frequency domains. These models, which can be used directly in the time and frequency domains, take into account the presence of both the transfer impedance and admittance, and allow the transient analysis when the termination is nonlinear or time-varying. The radiated and conducted susceptibilities are studied by using an incident plane-wave electromagnetic fleld and an injection current on the cable shield as the source, respectively. Results obtained by these models are in good agreement with those obtained by other methods.

Spice Simulation and Experimental Study of Transmission Lines with TVSs Excited by EMP

This paper presents the experimental study and SPICE simulation of transmission lines without or with transient voltage suppressors (TVSs) radiated by a fast rise-time electromagnetic pulse. TVSs are usually attached to transmission lines to protect terminal loads from surge interferences. The currents of the terminal loads and TVSs are obtained experimentally and numerically by using the SPICE circuits of transmission lines and TVSs. The results show that the induced energy dissipated through one termination will become larger when a TVS is attached to the other termination of the transmission line. And experimental results reveal that TVSs can provide protection for the loads, but the protection effectiveness may be not enough against fast rise-time surges.

SPICE Models for Prediction of Disturbances Induced by Nonuniform Fields on Shielded Cables

This paper presents SPICE models for the prediction of effects on shielded cables induced by nonuniform fields. Based on the transmission line theory, these models can be utilized to analyze shielded cables terminated with nonlinear or time-varying loads excited by nonuniform fields in the time domain. Two examples, a coaxial shielded cable and a two-parallel-wire shielded cable, both inside a cavity with a slot excited by an incident wave, are studied with the proposed models. The finite-difference time-domain method is employed to calculate the excitation fields of the cables, and then, the SPICE models are utilized to obtain the disturbances induced by the incident wave on the cables. The results obtained by the proposed models agree well with those obtained through other methods.

TRANSIENT ELECTROMAGNETIC TOPOLOGY AND ITS EXPERIMENTAL VALIDATION

Transient electromagnetic topology (TEMT) method is presented brie∞y flrst and then three typical conflgurations, namely, a transmission line network, a wire penetrating a cavity aperture and then connecting to a device, and two systems connected by a shielded cable radiated by an electromagnetic pulse, are analyzed by using the TEMT method. The currents induced at the loads obtained by the TEMT method are compared with those from the experiment. The good agreement of the numerical results with the experimental ones validates the TEMT method.

SPICE Model of a Single Twisted-Wire Pair Illuminated by a Plane Wave in Free Space

A SPICE model for the twisted-wire pair with uniform twists in free space is proposed in this paper, which is capable of calculating the transient terminal response of the twisted-wire pair terminated with nonlinear loads in the presence of a transient plane wave illumination. The model differs from its counterpart for a straight-wire pair in that an extra convolution is included in the source terms, which can be calculated efficiently by the recursive convolution method. For the sake of convenience, the derivation of the model is made in the frequency domain on the basis of the transmission-line theory. The resultant expressions are compared with the outcome of the method of moments, showing that the transmission-line model can be applied to the twisted-wire pair with loose twists. Furthermore, the low-frequency coupling properties and resonant peak of the twisted-wire pairs are investigated according to the derived approximate formulae. Based on the frequency-domain results, a SPICE model for the twisted-wire pair is proposed in the time domain before it is verified and applied to the twisted-wire pair terminated with nonlinear loads.

A Time-Domain Macromodel Based on the Frequency-Domain Moment Method for the Field-to-Wire Coupling

A time-domain macromodel method is proposed in this paper to deal with the field-to-wire coupling. The proposed method is equivalent to the frequency-domain moment method, but the size is greatly reduced. The extraction of the macromodel is actually a process of full-wave simulation. Once extracted, however, the proposed model could be repeatedly applied to arbitrary incident waves and terminal loads, including the nonlinear ones. The required computation time and storage are much less than making another full-wave simulation. Based on the small perturbation assumption, the method could also deal with the wires with small geometric uncertainties. Therefore, the proposed model is well applicable to the statistical analysis of the field coupling to the wires of the arbitrary shape, an extension to the previous statistical methods mainly based on the transmission line theory.