Partial element equivalent circuit

The main research activity in this area has been and are performed, by Albert Ruehli[1] at IBM Thomas J. Watson Research Center, starting with a publication in 1972. At that time the foundation of the PEEC method was presented, i.e. the calculation of the partial inductances. The PEEC method was extended to more generalized problems, including dielectric material and retardation effect.

The PEEC method is not one of the most common techniques used in EM simulation software or as a research area but it has just been starting to gain recognition and for the first time there is a session at the 2001 IEEE EMC Symposium named after the technique. In the mid-1990s, two researchers from the University of L'Aquila in Italy, Professor Antonio Orlandi and Professor Giulio Antonini, published their first PEEC paper and are now together with Dr. Ruehli considered the top researchers in the area. Starting year 2006, several research projects have been initiated by the faculty of Computer Science and Electrical Engineering of Luleå University of Technology in Sweden in the focus area of PEEC with the emphasis on computer-based solvers for PEEC.

PEEC is widely used for combined electromagnetic and circuit problems in various areas such as power electronics, antenna design, signal integrity analysis, etc. Using PEEC the designed model of a physical structure is transferred from the electromagnetic domain into the circuit domain. Therefore, external electrical components and circuits can be connected to the equivalent circuit which consists of extracted partial elements, in a straightforward manner. Moreover, since the final model consists of circuit elements, various components can easily be excluded from the circuit to simplify the problem while the accuracy is still ensured. For instance, for low-frequency problems, one can safely remove capacitive couplings without degrading the accuracy of the results and hence reduce the problem size and complexity.

The classical PEEC method is derived from the equation for the total electric field at a point[2] written as

An orthogonal metal strip with 3 nodes and 2 cells.

The corresponding PEEC circuit.

${\displaystyle {\vec {E}}^{i}({\vec {r}},t)={\frac {{\vec {J}}({\vec {r}},t)}{\sigma }}+{\frac {\partial {\vec {A}}({\vec {r}},t)}{\partial t}}+\nabla \phi ({\vec {r}},t)}$

where ${\displaystyle {\vec {E}}^{i}}$ is an incident electric field, ${\displaystyle {\vec {J}}}$ is a current density, ${\displaystyle {\vec {A}}}$ is the magnetic vector potential, ${\displaystyle \phi }$ is the scalar electric potential, and ${\displaystyle \sigma }$ the electrical conductivity all at observation point ${\displaystyle {\vec {r}}}$. In the figures on the right, an orthogonal metal strip with 3 nodes and 2 cells, and the corresponding PEEC circuit are shown.

By using the definitions of the scalar and vector potentials, the current- and charge-densities are discretized by defining pulse basis functions for the conductors and dielectric materials. Pulse functions are also used for the weighting functions resulting in a Galerkin type solution. By defining a suitable inner product, a weighted volume integral over the cells, the field equation can be interpreted as Kirchhoff's voltage law over a PEEC cell consisting of partial self inductances between the nodes and partial mutual inductances representing the magnetic field coupling in the equivalent circuit. The partial inductances are defined as

${\displaystyle L_{p_{\alpha \beta }}={\frac {\mu }{4\pi }}{\frac {1}{a_{\alpha }a_{\beta }}}\int _{v_{\alpha }}\int _{v_{\beta }}{\frac {1}{|{\vec {r}}_{\alpha }-{\vec {r}}_{\beta }|}}dv_{\alpha }dv_{\beta }}$

for volume cell ${\displaystyle \alpha }$ and ${\displaystyle \beta }$. Then, the coefficients of potentials are computed as

${\displaystyle P_{ij}={\frac {1}{S_{i}S_{j}}}{\frac {1}{4\pi \epsilon _{0}}}\int _{S_{i}}\int _{S_{j}}{\frac {1}{|{\vec {r}}_{i}-{\vec {r}}_{j}|}}\;dS_{j}\;dS_{i}}$

and a resistive term between the nodes, defined as

${\displaystyle R_{\gamma }={\frac {l_{\gamma }}{a_{\gamma }\sigma _{\gamma }}}.}$

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