# Shielding effectiveness (dB)

> Attenuation expressed logarithmically: 10 dB removes 90% of power density, 20 dB removes 99%, 30 dB removes 99.9%.

- Canonical URL: https://emfbase.com/glossary/shielding-effectiveness
- Collection: Glossary
- Record id: `glossary:shielding-effectiveness`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/glossary/shielding-effectiveness

## Key values

- **Category:** measurement

## Definition

Shielding effectiveness is the ratio of incident to transmitted field, in decibels, at a stated frequency. Datasheet figures are measured on flat samples in a test fixture; installed performance is governed by seams, edges and penetrations and is routinely 10–20 dB worse. Because the scale is logarithmic, a small dB shortfall is a large change in transmitted power.

## Sources

- `sbm-2024` Institut für Baubiologie + Nachhaltigkeit (IBN) (2024). *Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024)*. https://buildingbiology.com/site/downloads/SBM-2024_EVALUATION_GUIDELINES_EN.pdf — ngo, link checked 2026-08-12

Data licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Dataset version 2026.08.1. Retrieved from EMFBase, https://emfbase.com.

This record is reference data, not medical or legal advice. Regulatory limits, scientific guidelines and precautionary values are labelled separately and answer different questions.