EMFBase
Quantities & units

Shielding attenuation

Decibels of field reduction provided by a material. Every 10 dB is a factor of 10 in power density: 30 dB removes 99.9%, 10 dB removes 90%.

Symbol ASI unit dB

Last verified 12 August 2026.

Also searched as: dB attenuation, shielding effectiveness

Symbol
A
SI unit
dB
Units in use
dB

What it measures

Ratio of incident to transmitted field, band-dependent and geometry-dependent. Manufacturer dB figures are measured on flat samples in a test fixture; installed performance is usually lower because of seams, edges and reflections.

Units

Multiplier to the SI unit (dB).

dB (decibel)
1 dB = 1 dB

Relationships to other quantities

S_after = S_before / 10^(dB/10)
For field strength in V/m the divisor is 10^(dB/20).

Sources

  1. nist-si The International System of Units (SI), NIST Special Publication 330 — National Institute of Standards and Technology. government, link checked 2026-08-12.

Same record, other formats