How do I measure the shielding effectiveness of a gasket material for an RF enclosure?

Measuring the shielding effectiveness (SE) of a gasket material for an RF enclosure uses standardized test methods that quantify how much electromagnetic energy the gasket prevents from leaking through a gap or seam in the enclosure. The standard methods are: the transfer impedance method per IEEE 1302 (a coaxial fixture clamps the gasket sample between two flanges, forming a coaxial transmission line; the outer conductor has a gap that is bridged by the gasket under test; the ratio of the voltage appearing on the outside to the current flowing on the inside gives the transfer impedance Z_t; lower Z_t means better shielding: SE approximately 20 x log(Z_0 / Z_t)), the shielded box method per MIL-DTD-83528 (a standard metal box has a removable lid with a gasket groove; the gasket sample is placed in the groove, the lid is secured, and the SE is measured by comparing the received signal inside the box with and without the gasket under a range of compression forces), and the coaxial cell method (a gasket sample fills the gap in a coaxial test cell and the insertion loss is measured with a VNA; this gives the SE directly in dB). Key measurement parameters include: the frequency range (typically 10 MHz to 10 GHz for EMI gaskets), the compression force (gasket SE depends strongly on how tightly it is compressed against the mating surface; test at the expected application force, typically 1-10 N/cm), and the surface finish (rough or painted surfaces degrade gasket contact and reduce SE by 10-20 dB compared to clean, smooth metal).