Modelling of bulk current injection method for a coaxial cable

Modelling of Bulk Current Injection Method for a coaxial cable Uwe Stürmer, Gervin Thomas, Heiko Köhne, Werner John Fraunhofer Institut for Reliability and Microintegration Berlin/Paderborn Gustav-Meyer-Allee 25, 13355 Berlin eMail: uwe.stuermer@izm.fraunhofer.de Introduction In this abstract an SPICE model for the Bulk Current Injection (BCI) method is introduced. With this model is it possible to predict how intensive an inductive coupling affect a coaxial cable at his ends. Hence to draw conclusions from, if the device that is connected at the end of the cable, ensure the complete operability. Modelling Based on measurements of a coaxial cable over a ground plane an advanced model was build, that used an classical approach with T- equivalent circuit. The enhancements are described below. The internal- and external conductor described each with a classical conductor model. To ensuring the symmetry a T-equivalent circuit model is used. Rinnen and Raußen are the DC-resistance of the internal- and external conductor. Linnen and Laußen represent the inductance of the internal- and external conductor. Cinmasse and Cmasse are described the capacitive coupling of each conductor with the ground plane. Additionally to the already used conductor sizes of the coaxial cable the transfer impedance are also used. These transfer impedance was realised with a current-controlled-current-source, a coil, a resistor and a voltage-controlled-voltage-source . With the help of current-controlled-current-source the current through the external conductor are gripped and than routed through the resistor RS with the in series connected coil LS. The resistor RS and the coil LS together build the transfer impedance. Due to the current through the transfer impedance a voltage across the transfer impedance exist. With the voltage-controlled-voltage-source this voltage are given to the internal conductor. This transfer impedance described the complete coupling between internal- and external conductor. The model is shown in figure 1. Final BCI Model To model the complete coaxial cable repeated segments of the visualized equivalent circuit from figure 1 connected together. To complete the model, additionally the BCI clamp is modelled. It is adequate to measure the current at the input of the clamp. To model the clamp a voltage-source is used, that provide a voltage that are equivalent according to amount the lowest measured current. After that a frequency depending voltage-controlled-voltage-source is connected following of a coil. This coil is coupled with the coil of the external conductor at the coupling point (clamp position in reality) of the coaxial cable. figure 1: Conductor segment of the BCI Modell Comparison between Simulation and Measurement In the frequency range between 10 MHz and 160 MHz measurements was made. In figure 2 is presented a comparison between measurements and simulation. figure 2: Comparison between simulation and measurements The comparison shows, that the model warranted a good worst-case estimation. Conclusion In the future experiments and simulation with different cable lengths will be made and compared. Also a accurate analysis of the coupling between cable and Clamp is preferable. For that, the transfer impedance of the BCI clamp must be determined. Literature S. Caniggia; L. Vitucci, M. Acquaroli A. Giordano. Measurements and Spice Models for Data Signal Lines under Electrical Fast-Transient Test. Brugge: EMC 2000 Brugge, S. 357-362. R. Tiedemann. Schirmwirkung koaxialer Geflechtsstrukturen. Dresden: Technische Universität Dresden 2000-2001 , S. 169