Shielding Quality
Performance metric used to quantify the effectiveness of a cable shield in preventing the leakage of electromagnetic energy. Lower values of transfer impedance attenuation indicate a more effective shield that better isolates internal signals from the external environment. It relates the current flowing on the outside of the shield to the voltage induced on the inside.
Frequency Dependency
Shielding effectiveness varies significantly across the frequency spectrum. At low frequencies, the transfer impedance attenuation is dominated by the DC resistance of the shield. As the frequency increases, the skin effect and the inductive coupling through gaps in the braid become the controlling factors.
Measurement Procedure
Testing involves placing a cable sample inside a specialized fixture, such as a triaxial tube. The transfer impedance attenuation is calculated by measuring the ratio of the longitudinal voltage to the injected current. Repeatable results require precise control over the termination of the shield and the impedance of the test equipment.
Factors like the braid weave angle and the presence of a drain wire influence the final reading. High-quality aerospace cables are designed to maintain a flat response into the gigahertz range.
Installation Variable
Physical damage or improper connector termination increases the impedance. Regular inspection of the transfer impedance attenuation ensures that the system maintains its immunity to external interference throughout its lifecycle.
