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 to an alternating magnetic field, directly affects PCB transmission lines, power integrity, and the performance of shielding materials. Therefore, accurately measuring permeability is a key step in understanding and optimizing the electromagnetic characteristics of high-speed systems.

Permeability typically includes a real part (μ′) and an imaginary part (μ″), which represent energy storage capability and loss characteristics, respectively. For measurements in the GHz frequency range, traditional DC measurement methods are no longer sufficient. Instead, we use a vector network analyzer (VNA) combined with a fixture setup to extract complex permeability through S-parameter measurements (such as S21), enabling precise modeling of material behavior at high frequencies.

The process involves preparing a standard-sized ring-shaped sample, embedding it into a dedicated test fixture, obtaining scattering parameter data, and then calculating the permeability spectrum based on transmission line theory or the Nicolson-Ross-Weir (NRW) 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 data rates surpass 56 Gbps and even reach 112 Gbps, the demands on high-frequency material properties continue to grow. Low-loss magnetic materials have become an effective means of suppressing common-mode noise and EMI. Therefore, systematic permeability testing not only supports component evaluation but is also an important aspect of high-speed interconnect design.