Hybrid Electromagnetic Solvers for EMIEMC

Abstract

With advances in technology and increased design complexity in the automotive industry, Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC) issues are becoming increasingly important. An accurate system level analysis is required from an early design stage to detect and mitigate problems at the initial stage. The major difficulty encountered in automotive simulation is to deal with different geometric scales, ranging from a fraction of wavelengths (Printed Circuit Board) to multiple wavelengths (harness). When the problem size becomes larger, traditional full wave solvers like Finite Element Method (FEM), Method of Moment (MoM) or Finite Time Domain Difference (FDTD) lose their efficiency as calculation of domain interactions become computationally costly. There is an opportunity to combine different solvers in a hybrid framework to efficiently analyze such system-level problems. This thesis addresses the challenge and proposes different modelling and simulation methods for EMC test setups using a hybrid approach. The first part of this work is an efficient 2.5D solver development for power distribution network (PDN) analysis of automotive boards. Design of power ground layout of a multi-layered Printed Circuit Board (PCB) is crucial for low noise and stable power supply. 2.5D tools are better suited for early stage PDN analysis over 3D full-wave electromagnetic solvers due to faster simulation times. In this work, a non-orthogonal 2.5D PEEC formulation is proposed, employing quadrilateral mesh elements for efficient simulation of the PDN. Individual stamps for resistance, inductance, capacitance and conductance elements for a unit quadrilateral cell are derived. Further, the methodology is enhanced to capture coplanar coupling through introduction of mutual inductance and capacitive terms between neighboring PEEC cell-pairs. Numerical results demonstrate good accuracy compared to a 3D full-wave commercial tool for layered PCB geometries. The efficiency of the proposed method is benchmarked against commercial solvers. The second part of the work is focused on the model-based simulation methodology for system-level immunity characterization at an early design stage. The Bulk Current Injection (BCI) method is one of the commonly used immunity test for automotive ICs. In this test, a common mode RF current of a specified value is injected into the cable harness using an injection clamp. The DUT functionality is monitored under this RF disturbance over a frequency range typically up to 400 MHz. The simulation framework for BCI test is comprised of a hybrid 2D-3D electromagnetic solver and a circuit solver. First, an accurate circuit model of injection clamp with multiple cables is developed. Although, there are circuit models reported in literature for clamps with a single cable, they do not directly lend themselves to multiple cable formulation. The proposed clamp model is validated with measurements. Then, IC immunity model (ICIM) is inducted into the simulation environment to accurately predict the immunity behavior of an IC. The proposed method is validated by comparing the simulation prediction with the actual BCI measurement. Finally, an approach comprising of Method of Moments and Harmonic Balance method is used to capture the non-linear response of active elements like transistors or diodes in an automotive board. It is demonstrated that a traditional Harmonic Balance approach will fail at high noise voltage levels which may be a likely scenario in many BCI tests with high injection clamp current specifications. A Line-Search intermediate step is introduced to address this issue. Numerical results demonstrate that the proposed method converges to accurate results faster. The third problem is focused on improving the simulation efficiency of a radiation emission (RE) test bench in the automotive application. As the device under test (DUT) and the measuring antenna are electrically far apart, the back scattered field from the antenna is quite minimal and can be neglected. By using the unidirectional coupling between these domains, a substantial reduction in memory requirements and computational time can be achieved in comparison to traditional multi-domain hybrid FEM-MoM. Also further speed up is achieved by reusing the domain-to-domain interaction terms. Next part of this research is focused in finding the source of radiation in the emissions setup. The source of radiation can be from common mode current on the cable harness or from the DUT. A method based on Huygens box is proposed to quantify the radiation from cable and DUT at each frequency. On each cell of the Huygens box the value of electric field computed at the observation point taking the Electric Current (J) and Magnetic Current (M) on that cell as sources and this information on the Huygens box is used to quantify the radiation.

Some part of the presented work is used at Simyog, an IISc incubated start-up, to develop a simulation software called Compliance-Scope which allows the designer to predict the EMI/EMC performance of electronic hardware modules at an early design stage