Transfer Impedance

Protecting signal cables for external interference is critical to ensuring the reliability of transmitted signals and data. This test is among the most common means to evaluate if a cable's shield can protect the contained circuits from EMI. But not all shielding is the same. The materials and construction play an important role in the shielding effectiveness. With so many different means of protecting the signal, the surface transfer impedance test is a reliable means of assessing the shield performance at any frequency.

Transfer impedance is the measurement of the current flowing on a shield surface to the voltage developed on the opposite side of the surface. Cable shields are designed to reduce transfer impedance, thus increasing shield effectiveness.

The pass/fail criteria are identified by the individual specification, but in general, the lower the surface transfer impedance, the better the shielding.