The transfer impedance, also called coupling resistance, is an evaluation criterion for the shielding of cabling systems.
Since shielding can have very different properties, the transfer impedance for cables has been defined in the responsible standardization bodies. The transfer impedance is a measure of the quality of the shielding and is defined as the ratio of the voltage along the shield of the disturbed system to the current of the disturbing system.
The transfer impedance is specified in EN 50173 to be 50 milli-ohms per meter (mOhm/m) at 1 MHz and 100 milli-ohms/m at 10 MHz. These values can only be achieved by complex shielding structures, such as double aluminum foil with cross- stranding. With combined shielding of aluminum foil and copper braiding with a coverage of more than 65 %, coupling resistances of less than 10 milli- Ohm/m at 10 MHz can be realized. The smaller the transfer impedance, the better the shielding effect.