{
  "id": "quantities:attenuation",
  "collection": "quantities",
  "slug": "shielding-attenuation",
  "name": "Shielding attenuation",
  "summary": "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%.",
  "status": "verified",
  "lastVerified": "2026-08-12",
  "data": {
    "aliases": [
      "dB attenuation",
      "shielding effectiveness"
    ],
    "quantityId": "attenuation",
    "symbol": "A",
    "siUnit": "dB",
    "units": [
      {
        "symbol": "dB",
        "name": "decibel",
        "toBase": 1
      }
    ],
    "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.",
    "conversions": [
      {
        "to": "power-density",
        "formula": "S_after = S_before / 10^(dB/10)",
        "note": "For field strength in V/m the divisor is 10^(dB/20)."
      }
    ]
  },
  "sources": [
    {
      "id": "nist-si",
      "title": "The International System of Units (SI), NIST Special Publication 330",
      "publisher": "National Institute of Standards and Technology",
      "url": "https://www.nist.gov/pml/special-publication-330",
      "kind": "government",
      "retrieved": "2026-08-12"
    }
  ],
  "links": {
    "self": "https://emfbase.com/api/quantities/shielding-attenuation",
    "html": "https://emfbase.com/quantities/shielding-attenuation",
    "markdown": "https://emfbase.com/quantities/shielding-attenuation.md",
    "collection": "https://emfbase.com/api/quantities"
  }
}