What Does dB Mean? Reading Shielding Values Correctly
What the 80, 100 or 120 dB values in shielded room quotes really mean, and what you should check when you compare quotes from suppliers.
3 min readOctober 27, 2026
How Does a Faraday Cage Work?
A Faraday cage is a space completely enclosed by a conductive material. When an outside electromagnetic wave hits this conductive surface, currents form on the surface and most of the wave cannot get in.
The same works in reverse: the signal emitted by a device inside cannot get out either. That is why Faraday cages are used both to protect and to conceal.
What Is It Made Of?
For small cabins, fine perforated metal or wire mesh may be enough. Room-sized builds use galvanized steel or copper-clad panels joined so that no signal leaks between them.
The hard part is not the walls but the door, ventilation, power and data penetrations. These points need special gasketed doors, honeycomb air filters and line filters.
Why Is Performance Measured in dB?
A cage's success is measured by how much it attenuates the outside signal and is expressed in decibels (dB). 60 dB means the signal is weakened a thousand times, 100 dB a hundred thousand times.
The main factors that set the price are the required dB level, frequency range, room size, number of doors and interior equipment. That is why the intended use should be clarified first for an accurate quote.
Faraday Cages at Home and in the Lab
The perforated metal sheet in a microwave oven door is the best-known everyday Faraday cage: it keeps microwaves inside while letting light through. A phone losing signal in a lift is the same effect occurring unintentionally.
In the lab, a cage is built to protect measurements from outside noise or isolate a device from networks. A desktop cage is enough for small experiments, while applications you work inside need a shielded room; see the options on our Faraday cage page.
Frequently Asked Questions
Does aluminum foil make a Faraday cage?
It gives some attenuation in short, simple trials, but seams and tears make it unreliable protection.
Must a Faraday cage be grounded?
Not for shielding, but grounding is recommended for safety and for equipment inside to work correctly.
How large can the cage holes be?
Hole size is chosen by the wavelength of the highest frequency to block; the higher the frequency, the smaller the holes.
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