Shielding Effectiveness
Definition of Shielding Effectiveness
A physical quantity is needed to describe the shielding performance of electromagnetic absorber products.
This is usually expressed as shielding effectiveness (SE).
The formula for shielding effectiveness is:
SE=20lg(E1/E2) (dB)
E1 = field strength without the shielding product
E2 = field strength with the shielding product
Using magnetic field strength gives magnetic shielding effectiveness; using electric field strength gives electric shielding effectiveness.
Shielding effectiveness is expressed in decibels (dB). The table shows the relationship between attenuation and decibels:
Before Shielding | After Shielding | Attenuation | Shielding Effectiveness |
1 | 0.1 | 90% | 20lg(1/0.1)=20dB |
1 | 0.01 | 99% | 20lg(1/0.01)=40dB |
1 | 0.001 | 99.9% | 20lg(1/0.001)=60dB |
1 | 0.0001 | 99.99% | 20lg(1/0.0001)=80dB |
1 | 0.00001 | 99.999% | 20lg(1/0.00001)100dB |
Shielding Effectiveness
The source gives typical enclosure shielding levels of below 40 dB for consumer products, around 60 dB for military equipment, above 80 dB for TEMPEST equipment, and around 100 dB for shielded rooms or chambers. Shielding above 100 dB is difficult and costly to manufacture.