EMF & Faraday Glossary — Every Term, Plainly Defined

Plain-English definitions for every term you'll meet around Faraday bags, EMF, and RF shielding. Each entry is written to stand alone — no fear-marketing, and where a number can't be verified outside a lab, we say so.

Jump to: A · B · C · D · E · F · G · I · K · M · N · R · S · W

A

Attenuation

The reduction in signal strength as a radio wave passes through a material or shield. Shielding products attenuate signals rather than "deleting" them — how much depends on the material, construction, and frequency, and real attenuation figures require laboratory measurement.

B

Bluetooth

A short-range wireless protocol operating around 2.4 GHz, used by headphones, trackers (like AirTags), and car systems. A properly sealed Faraday bag blocks Bluetooth along with other common RF signals.

C

Conductive Fabric

Textile woven with metal fibers (typically silver, copper, or nickel) so it conducts electricity and can act as a flexible RF shield. It's the working material inside Faraday bags and EMF clothing, and is sold by the panel for DIY projects.

D

dB (Decibel)

A logarithmic unit used to express how much a signal is reduced: every 10 dB represents a 10× reduction in power. Shielding-effectiveness claims quoted in dB are only meaningful when backed by a published lab test at stated frequencies — treat unsourced dB numbers in shielding marketing with skepticism.

E

Earthing / Grounding

Connecting the body or an object to the Earth's surface potential, e.g. through grounding sheets plugged into an outlet's ground line. Grounding is NOT shielding: a grounded sheet does not block wireless signals, and a Faraday enclosure works without being grounded.

Electromagnetic Hypersensitivity (EHS)

A term for symptoms that some people attribute to EMF exposure. The World Health Organization notes the symptoms are real for those affected, but blinded studies have not established EMF exposure as the cause. We don't sell products as EHS treatments.

EMF (Electromagnetic Field)

A field of combined electric and magnetic forces produced by anything carrying electricity or transmitting radio signals — power lines, appliances, phones, routers. EMF spans a huge frequency range; household exposure at typical levels falls within international (ICNIRP) guidelines.

EMI (Electromagnetic Interference)

Disturbance to an electronic device caused by electromagnetic energy from another source — the reason your speaker buzzes when a phone is near it. Shielding materials and EMI tape are used to keep devices from interfering with each other.

EMP (Electromagnetic Pulse)

A brief, intense burst of electromagnetic energy — from a nuclear detonation, certain weapons, or an extreme solar storm — that can induce damaging currents in electronics. Sealed all-metal enclosures are the standard preparedness measure, but no consumer product's EMP performance can be verified outside a specialized lab.

F

Faraday Bag

A flexible pouch lined with conductive fabric that blocks wireless signals (cellular, Wi-Fi, GPS, Bluetooth, RFID) reaching a device sealed inside — and stops the device transmitting out. Named after the Faraday cage principle. See What is a Faraday Bag?

Faraday Cage

Any conductive enclosure that redistributes electromagnetic fields around its exterior so the interior is shielded, demonstrated by Michael Faraday in 1836. MRI rooms, shielded lab chambers, Faraday bags, and DIY builds all use the same principle.

Frequency

How many times a radio wave oscillates per second, measured in hertz (Hz). Consumer wireless spans roughly 700 MHz–6 GHz (plus mmWave 5G above 24 GHz); higher frequency means shorter wavelength, which affects what mesh sizes and materials shield effectively.

G

GPS

Satellite positioning signals received (not transmitted) by your device around 1.5 GHz. Blocking GPS reception — for example, sealing a tracker or phone in a Faraday bag — prevents the device from knowing or reporting its location.

I

ICNIRP

The International Commission on Non-Ionizing Radiation Protection — the scientific body whose exposure guidelines most countries' RF safety limits are based on. Consumer devices sold legally must comply with limits derived from these guidelines.

K

Keyless Entry

Car systems that unlock and start the vehicle when the key fob's low-power radio signal is detected nearby. Convenient, but the always-on signal is what relay attacks exploit.

M

mmWave (Millimeter Wave)

The high-frequency band of 5G (24 GHz and above) with very short wavelengths. Short range and poor penetration mean it's deployed mainly in dense urban spots; its short wavelength also makes fine, tight shielding construction more important.

N

NFC (Near Field Communication)

The very short-range (a few centimeters) radio protocol behind contactless payments and keycards, operating at 13.56 MHz. RFID/NFC blocking cards and sleeves are designed for exactly this band.

R

Relay Attack

A car-theft technique where thieves use radio equipment to capture and extend a key fob's signal from inside a house to the car outside, unlocking and starting it without touching the key. Shielding the fob — a Faraday pouch or box — breaks the relay by making the signal unreachable.

RF (Radio Frequency)

The portion of the electromagnetic spectrum used for wireless communication, roughly 3 kHz to 300 GHz. "RF shielding" means reducing these signals specifically — it says nothing about magnetic fields from power lines, which behave differently.

RFID (Radio-Frequency Identification)

Technology where a reader powers and reads a small tag by radio — used in contactless cards, passports, key cards, and inventory tags. Payment cards use the 13.56 MHz band, which is what RFID-blocking products target.

RFID Skimming

Reading someone's contactless card data without consent using a concealed reader at very close range. Documented but rare in practice — blocking sleeves and cards make it physically impossible rather than just unlikely.

S

SAR (Specific Absorption Rate)

The regulatory measure of how much RF energy the body absorbs from a device, in watts per kilogram. Every legally sold phone must test under the SAR limit (1.6 W/kg in the US, 2.0 W/kg in the EU); SAR is a compliance measure, not a hazard score.

Shielding Effectiveness

The measured performance of a shield, expressed in dB at specific frequencies, determined in laboratory tests such as IEEE 299 or MIL-STD-188-125. Without a published test report, a shielding-effectiveness number is marketing, not measurement — we say this as a seller of shielding products.

Silver Fiber

Textile thread with a silver coating, making fabric conductive so it can attenuate RF signals across the covered area. Silver is used because it stays conductive when woven and washed and is naturally antibacterial; it's the basis of most EMF clothing.

Skin Depth

How far an electromagnetic wave penetrates into a conductive material before it is mostly absorbed — higher frequencies and better conductors mean shallower penetration. It's why even thin metal layers shield high-frequency signals effectively.

Smart Meter

A utility meter that reports usage over a cellular or mesh radio network, transmitting in short bursts. A meter's RF output can be measured with an RF meter if you want real numbers for your home rather than internet claims.

W

Wavelength

The physical length of one radio-wave cycle — from over a meter (FM radio) to millimeters (mmWave 5G). Shielding rule of thumb: openings in a shield must be much smaller than the wavelength being blocked, which is why fine mesh works and chicken wire doesn't for cellular frequencies.

Wi-Fi

Wireless networking at 2.4 GHz and 5/6 GHz. A sealed Faraday bag blocks Wi-Fi both directions; a router shield only attenuates the field around the router — expect a weaker but working network, not a dead one.

Keep Learning

Start with the EMF & Faraday Knowledge Base for guides organized by topic, or jump straight to What is a Faraday Bag?