What is a
Faraday cage?

A Faraday cage is an enclosed structure made of electrically conductive material that shields against electric and electromagnetic fields. The principle is named after the British physicist Michael Faraday, who first described it in 1836.

What began as a physics experiment now forms the basis for professional shielding solutions: In medicine, for example, this principle protects MRI examination rooms from high-frequency interference signals; in information security, it forms the basis for electromagnetic radiation protection; and in industry and research, it creates controlled electromagnetic environments.

On this page, you will learn how a Faraday cage works, where you might encounter this principle in everyday life, what materials are used, and how it is implemented in professional shielding solutions.

Principle of Operation: How Does a Faraday Cage Work?

A Faraday cage consists of an enclosure made of electrically conductive material that is as closed as possible. When an electric or electromagnetic field strikes this enclosure, electric charges and currents are distributed throughout the conductive material in such a way that the effect of the field is greatly reduced inside the cage.

In the case of high-frequency electromagnetic waves—such as radio, cellular, or Wi-Fi signals—a significant portion of the incident energy is reflected by the conductive surface or attenuated within the material. The shielding attenuation indicates the extent of this phenomenon. It is expressed in decibels (dB) and depends, among other factors, on frequency, material, design, and—in particular—the quality of all junctions and feed-throughs.

For professional shielding solutions, therefore, a conductive wall alone is not sufficient. Doors, windows, ventilation systems, filters, cable and media routes, as well as all connections between the individual shielding elements, must be incorporated into the shielding design. Even minor design flaws can significantly affect the shielding performance of the entire system. Critical components such as RF doors and RF windows must be integrated into the overall design on a project-by-project basis.

HF Doors & HF Windows

Faraday Cages in Everyday Life

We also encounter the principle of the Faraday cage in everyday life:

Professional shielding systems are based on the same fundamental physical principle, but with specific requirements regarding frequency range, shielding attenuation, and design. In RF booths and shielded rooms, therefore, the precise interaction of all components determines the actual shielding effectiveness.

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Cars and Airplanes:

Conductive exterior structures can dissipate electrical charges—for example, in the event of a lightning strike—through the outer skin.

Shielded Cables:

Conductive shielding reduces electromagnetic interference affecting the transmitted signals.

Microwave oven:

The metal housing and the fine-mesh screen in the door limit the outward propagation of electromagnetic waves.

A Faraday cage and magnetic field shielding are not the same thing

A Faraday cage is used primarily to shield against electric and high-frequency electromagnetic fields. Static magnetic fields, on the other hand, pass through a conductive enclosure virtually unimpeded, while low-frequency magnetic fields are attenuated only to a limited extent.

For applications involving strong static magnetic fields—such as MRI systems—additional magnetic field shielding made of suitable ferromagnetic materials is therefore used. These shielding elements specifically redirect magnetic field lines, thereby operating on a different physical principle.

In complex projects, both types of shielding can be combined. Schwarz designs and implements both RF shielding and magnetic field shielding, tailoring both systems to the specific application and structural conditions.

Magnetic field shielding

What materials is a Faraday cage made of ?

Various electrically conductive materials can be used for a Faraday cage. Which material makes the most sense from a technical and economic standpoint depends, among other things, on the required frequency range, the necessary shielding attenuation, the design, and the structural conditions.

Aluminum

Combines excellent electrical conductivity with low weight, corrosion resistance, and good workability. Schwarz uses aluminum in particular for its modular RF shielding enclosures.

Copper

It has very high electrical conductivity and is also used for RF shielding. Depending on the design and application, copper can be used, for example, as sheet metal, foil, or braided mesh.

Steel

It can be used both for structural RF shielding and, when made of appropriately selected materials, for magnetic field shielding. In the case of magnetic field shielding, the focus is not on the material’s electrical conductivity but on its magnetic permeability.

Shielding fabrics and braids

These are used in particular where flexible or breathable transitions are required. Here, too, the key factor is their electrically conductive and structurally reliable integration into the overall system.

Shielding Attenuation: How Many dB Does Each Application Require?

Shielding Attenuation
20 dB
40 dB
60 dB
80 dB
100 dB
120 dB

Reduction in field strength
Factor of 10
Factor of 100
Factor 1,000
Factor 10,000
Factor 100,000
Factor 1,000,000

Shielding attenuation describes the factor by which the field strength inside is reduced compared to the outside. Because it is expressed in decibels, the factors increase rapidly.

The required shielding attenuation depends on the specific application and the relevant frequency range. For MRI applications, approximately 90 to 100 dB is typically required; Schwarz can achieve up to 120 dB on a project-specific basis. For information security, industry, research, and laboratories, shielding attenuation is designed on a project-specific basis according to protection requirements, the source of interference or measurement task, and the relevant frequency range.

What matters is not the highest possible individual value, but rather the shielding performance required for the respective application across the defined frequency range.

Where is a Faraday cage used in professional settings?

The Faraday Cage in MRI and Medicine

MRI systems operate using high-frequency signals and are sensitive to electromagnetic interference from their surroundings. A professionally constructed RF shielded enclosure forms a Faraday cage around the examination room and creates the electromagnetic environment necessary for reliable imaging.
Schwarz designs and builds complete RF shielded enclosures for MRI systems from various manufacturers and with different field strengths, including doors, windows, filters, feedthroughs, quench systems, and interior fittings.
RF Enclosures for MRI Rooms

Eavesdropping-proof and radiation-proof rooms (information security)

In security-critical areas, confidential information must be protected against unintentional disclosure. Depending on the security requirements, a room can, for example, be designed to be tap-proof, radiation-proof, or a combination of both.
The Faraday cage serves as the technical foundation for electromagnetic emission protection: The conductive enclosure reduces electromagnetic emissions and prevents their uncontrolled propagation outside the protected area. To ensure acoustic security against eavesdropping, additional structural soundproofing measures are implemented, which include doors, walls, ceilings, floors, and technical penetrations.
The specific requirements are defined by national and international regulations. In Germany, for example, guidelines issued by the Federal Office for Information Security (BSI) may apply. Which requirements apply to a given project are determined on a project-by-project basis.
Schwarz designs and builds such shelters for, among others, the federal government, government agencies, the German Armed Forces, embassies, and other security-critical facilities and companies.
rooms that are secure against eavesdropping and radiation

Faraday Cages in Industry

In industrial testing and production environments, electromagnetic interference can affect measurements, testing processes, or sensitive electronics. Faraday cages and RF shielded rooms create controlled electromagnetic conditions for test benches, measurement and calibration areas, and other technically sensitive applications.
Schwarz develops project-specific shielding solutions, integrating the necessary doors, gates, windows, filters, and ventilation and media conduits into the overall system.
RF Shielding for Industry

The Faraday Cage in Research and the Laboratory

Research facilities and laboratories require controlled electromagnetic environments to perform sensitive measurements in a reproducible manner. Shielded and measurement chambers reduce external electromagnetic interference while also preventing signals from escaping the test room.
Schwarz develops project-specific shielded rooms and chamber systems tailored to the measurement task, the required frequency range, and shielding attenuation.
Shielding and Measurement Cabins

Project Insight: High-Voltage Testing Facility

Safely designed and professionally integrated

One of our current projects demonstrates that the Faraday cage principle is not limited to conventional room sizes: For the new high-voltage laboratory of PFISTERER Holding SE in Winterbach, Schwarz is working with the client, mainka GmbH & Co. KG, to implement a large-scale electromagnetic shielding system for high-voltage direct current (HVDC) transmission applications.

7,800 m² of shielding area with approximately 1,800 shielding modules
Integration into a 50 x 30 x 28 m high-voltage hall
Shielding gates up to 5 x 7 m, as well as shielding doors and windows in various designs

View the project overview on LinkedIn

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Faraday cage, shielding cage, shielded enclosure, RF enclosure:  
What’s the difference?

Term
Faraday cage
Shielding cage
Shielded booth / measurement booth
RF cabin

Definition
Basic physical principle: A physically enclosed, electrically conductive enclosure reduces electric and electromagnetic fields within the protected area.
General term for a structural implementation of this principle, ranging from small enclosures to walk-in shielded rooms.
A room- or cabin-shaped shielding solution, primarily for measurement, testing, and laboratory applications.
Professionally constructed room shielding for high-frequency electromagnetic fields, including RF doors, RF windows, filters, ventilation, and cable and media feed-throughs. Typical applications: MRI rooms, information security, industry.

In practice, these terms are not always used consistently. Therefore, what matters most is not so much the terminology as the technical requirements: Which frequencies must be shielded, with what level of shielding attenuation, and what interface requirements must the overall system meet?

How Schwarz Shielding Implements Faraday Cages

Based on this principle, Schwarz Shielding Systems develops and implements professional shielded rooms and enclosure systems for a wide variety of technical requirements. The shielded room is viewed as a complete technical system:

1. Planning and Structural Design

2. In-house production of key components

3. Installation of the system

4. Final metrological inspection

Critical components, such as HF doors and HF windows, are integrated into the overall design on a project-by-project basis. The modular aluminum enclosures provide high shielding performance while allowing for flexible installation. Depending on the design, this can facilitate future modifications, expansions, or the replacement of individual components.

Frequently Asked Questions About the Faraday Cage

Is a car a Faraday cage?

Yes, to a large extent. A closed metal body conducts electrical currents—for example, in the event of a lightning strike—away through the outer skin, thereby reducing the electromagnetic field inside the vehicle. Vehicles with a high proportion of plastic or an open design, such as convertibles, offer this protection only to a limited extent. A vehicle cannot be compared to a professional RF shielded chamber, which is designed and metrologically tested for specific frequency ranges and shielding attenuation.

Is an airplane a Faraday cage?

Essentially, yes. An aircraft’s conductive outer structure can divert lightning currents around the cabin and thus exhibits the properties of a Faraday cage. As with a car, however, a professional RF shielded room is not comparable to this.

Is a house or motorhome a Faraday cage?

Only to a limited extent. A house is not a continuously conductive shell; even in reinforced concrete structures, windows, doors, and openings weaken its effectiveness. For RVs, it depends on the construction method and materials. A defined, metrologically verified shielding attenuation is generally not present.

Does a Faraday cage need to be grounded?

Grounding and equipotential bonding must be planned in accordance with the specific application as well as the electrical and safety requirements. For RF shielding effectiveness, it is not a matter of simply “as much grounding as possible,” but rather the electrically conductive and RF-technically correct design of the entire shielding system.

How high is the shielding attenuation of a Faraday cage?

That depends on the application and the relevant frequency range. For MRI applications, 90 to 100 dB is often required; Schwarz achieves up to 120 dB depending on the specific project. The decisive factor is the shielding performance required for the application across the defined frequency range, not the highest possible individual value.

Shielding Attenuation

Can you build a Faraday cage yourself?

This physical principle can be demonstrated relatively easily using conductive materials. Professional shielding with defined and reproducible shielding attenuation, on the other hand, is significantly more complex. In particular, doors, joints, windows, ventilation systems, and cable and media penetrations can significantly affect the shielding performance and must be integrated into the overall system.

What is the difference between a Faraday cage and magnetic field shielding?

A Faraday cage primarily shields against electric and high-frequency electromagnetic fields. Magnetic field shielding, for example against the strong static magnetic fields of an MRI scanner, on the other hand, uses suitable ferromagnetic materials that specifically direct the magnetic flux. Both systems operate on different principles but can be combined within a single project.

Magnetic Field Shielding

What is the difference between a Faraday cage and a soundproof room?

A Faraday cage can serve as the basis for the electromagnetic radiation shielding of a protected room. Additional structural soundproofing measures are required to ensure acoustic eavesdropping protection. Depending on the protection requirements, a room can be designed to be eavesdrop-proof, radiation-proof, or equipped with both protection functions. The specific design is project-specific, in accordance with the applicable requirements, and is inspected and certified.