Figure 1 illustrates the Transfer Impedance test results of various EMI gaskets on the market.
The test time is hours versus minutes for transfer impedance testing.
Transfer Impedance test data provides a very accurate ([+ or -]2dB) level of the conductivity of an EMI gasket over the frequency range of 10 kHz to 18 GHz against any of the structural materials and finishes used by the electrical and electronic industry.
where [V.sub.BCI]([omega]) is the induced voltage on the BCI probe, [V.sub.inc]([omega]) the incident voltage to the DC supply loop, and [Z.sub.T]([omega]) the transfer impedance
of the BCI probe.
At the frequencies of interest, the transfer impedance
is much larger than the transfer admittance, and this is because the electric field shielding of the shield is much better than the magnetic field shielding, which means that the shield current is more important than the shield-to-ground voltage for the induced voltage of the load [R.sub.1].
The magnitude transfer impedance [Z.sub.T]([omega]) is obtained in dB[OMEGA] from the S-parameter [S.sub.21,fixture] ([omega]), which can be measured in the calibration procedure.
where [V.sub.BCI]([omega]) is the induced voltage on the BCI probe, [V.sub.inc] the incident voltage to the DC supply loop, and [Z.sub.T]([omega]) the transfer impedance of the BCI probe.
A braid will allow a certain amount of signal from the inside of the cable to leak through the surface transfer impedance ; however, little influence is on the simplified modeling for the reduced CCs and ignored in this work.
[10.] Sali, S., "Transfer impedance of braided coaxial cables at radio and microwave frequencies," M.
Although there are several variants for both approaches, the two most widely used in the RF gasket industry are MIL-DTL-83528 (radiated) and SAE ARP 1705 (transfer impedance).
The SAE ARP 1705 transfer impedance test measures the electrical characteristics of the RF gasket material.
Figure 5 illustrates the relationship between the radiated and transfer impedance methods.