Anisotropic Permittivity
Mathematical matrices that describe the directional dependence of relative permittivity in non-isotropic media characterize the propagation of electromagnetic waves in structured materials. The dielectric tensor provides a three-by-three matrix of values that accounts for variation in material properties along the x, y, and z axes. It is critical for modeling laminates where woven glass fibers create directional differences in electrical performance.
Using a single scalar value for such materials leads to inaccurate impedance and propagation velocity calculations.
Field Propagation
Electrodynamic modeling of signal paths in multi-layer boards reveals how directional permittivity differences affect differential pair skew. Incorporating the dielectric tensor into numerical solvers allows for the calculation of electric field distribution in the presence of woven glass fibers and resin. This calculation shows that the signal velocity changes depending on the routing angle relative to the fiber direction.
It allows designers to predict and mitigate trace-to-trace skew in high-speed differential signals by optimizing the routing layout.
Substrate Analysis
Characterization of high-frequency substrate materials helps identify the directional variations in impedance for complex board geometries. Modeling the dielectric tensor ensures that the variations in laminate properties do not cause impedance mismatches. It prevents unexpected signal reflections during high frequency operation.