In the field of high-speed digital signal testing, electromagnetic compatibility (EMC) and signal integrity (SI) issues are receiving increasing attention. Permeability (μ), which measures a material's response capability in an alternating magnetic field, directly impacts PCB transmission lines, power integrity, and the performance of shielding materials. Therefore, accurately measuring permeability is a crucial step for understanding and optimizing the electromagnetic characteristics of high-speed systems.

Permeability typically consists of a real part (μ′) and an imaginary part (μ″), corresponding to energy storage capacity and loss characteristics, respectively. For testing in the GHz frequency range, traditional DC measurement methods are no longer sufficient. We employ a method using a Vector Network Analyzer (VNA) combined with fixture-based measurements to determine complex permeability by inverting S-parameters (such as S21), enabling detailed modeling of materials at high frequencies.

The specific process involves: preparing a toroidal sample of standard dimensions, placing it into a dedicated test fixture, acquiring scattering parameter data, and then calculating the permeability spectrum based on transmission line theory or the Nicolson-Ross-Weir algorithm. The test results are not only used for material selection but can also be input into 3D simulation software to improve system-level simulation accuracy.

As signal rates exceed 56 Gbps and even reach 112 Gbps, higher demands are placed on the high-frequency characteristics of materials. Low-loss magnetic materials have become an effective means for suppressing common-mode noise and EMI. Consequently, systematic permeability testing not only serves component evaluation but is also a vital part of high-speed interconnect design.