Section 6.2.3.3 of ISO 19642-2 defines the surface transfer impedance test using the tri-axial method. This measures the EMC screening effectiveness of the cable shield.
Surface transfer impedance quantifies how much external electromagnetic energy couples through the screen to the inner conductor, and is the primary measure of cable shielding quality for automotive EMC compliance.
IEC 62153-4-3 specifies the triaxial test method for measuring the surface transfer impedance of cable screens and connectors. Surface transfer impedance quantifies how much electromagnetic energy couples through a cable shield from external fields to the internal conductors.
The test uses a triaxial test fixture consisting of the cable under test placed inside a precisely dimensioned outer tube. A current is injected on the outer surface of the cable shield and the voltage developed on the internal conductor is measured, typically expressed in milliohms per meter.
This measurement is fundamental for characterizing the shielding quality of screened cables used in aerospace, military, telecommunications, and industrial applications. Lower transfer impedance values indicate better shielding performance.