Electromagnetic radiation is all around us, from radio signals to industrial equipment. In such conditions, protection against electromagnetic interference (EMI) is particularly relevant. One of the most effective solutions remains the Faraday cage, a structure whose principle of operation was discovered back in the 19th century. Modern shielding technologies are being improved through the use of precision alloys with unique physical and chemical properties. In this article, we will consider the structure and operating principle of a Faraday cage, the requirements for materials for its manufacture, and modern precision alloys that are ideal for these purposes.
Electromagnetic interference and the role of the Faraday cage
EMFs pose a serious threat to precision electronics, communication systems and critical equipment. Their sources can be any device connected to the power grid and located nearby: laptops, magnetic mixers, potentiostats, climate chambers, telephones, antennas, etc. Interference distorts measurement results, introducing significant noise into the signal.
The Faraday cage effectively protects the interior from EMF due to its ability to block external electromagnetic fields. The effectiveness of shielding directly depends on the properties of materials, primarily their electrical conductivity, magnetic permeability and structural integrity.
The history of the invention: from experiment to industry standard
The Faraday cage was created in 1836 by Michael Faraday, an outstanding English physicist. While studying the effects of electricity and magnetism on conductive materials, he found that a closed metal shell effectively blocks external electromagnetic fields.
In one of the first experiments, Faraday placed an electrometer inside a metal container that was exposed to an external electric field. Despite the applied voltage, the device did not record any changes inside — this was the first scientific confirmation of the shielding effect.
Since then, the principle of operation of the Faraday cell has become the basis for many technologies used in medicine, industry, electronics and defense.
The principle of operation of the Faraday cell
The Faraday cage is a closed metal shell (solid or mesh) that shields the interior from electromagnetic effects. Her work is based on the following physical principles:
- Induced surface charge. Under the influence of an external electric field, free charges on the surface are redistributed, creating an opposite field that compensates for the external one.
- Eddy currents (Foucault currents). In alternating electromagnetic fields, closed currents occur in conductors, creating an opposite magnetic field that weakens or neutralizes the initial one.
- Full shielding of the internal volume. When the shell is continuous, the waves are reflected and absorbed without penetrating, which makes the inner zone electrically neutral.
Frequency dependence and design requirements
The effectiveness of shielding depends on the frequency of the external field:
- High frequency waves (radios, microwaves) are effectively blocked by metal shells.
- Low-frequency and quasi-static magnetic fields require use soft magnetic materials with high magnetic permeability.
The main design requirements are:
- Sheath must be completely closed — slots and holes dramatically reduce shielding efficiency, especially at frequencies above 100 MHz.
- Cell size the grid must be significantly smaller than the wavelength of the shielded radiation.
- Material used must have good electrical conductivity.
The Faraday cage does not provide absolute protection. Slowly changing magnetic fields can partially penetrate inside — special soft magnetic materials are required to block them.
Applications: from medicine to cybersecurity
Shielding technology is used in a wide variety of fields:
- Telecommunications and radio engineering. Protection of sensitive equipment from external electromagnetic interference, which can distort signals or cause device malfunctions. This is especially important in conditions of dense urban development.
- Medicine. Protection of patients and medical personnel from the effects of electromagnetic radiation, for example, during MRI diagnostics. Screening of rooms where highly accurate diagnostics and treatment are carried out.
- Scientific research. Creating conditions free from external electromagnetic influences, which is necessary when conducting high-precision experiments in physics, chemistry and other sciences.
- Industry. Protection of production equipment from electromagnetic interference caused by high-voltage equipment, robotic lines and induction heaters.
- Cybersecurity. Creating shielded rooms (SCIF — Sensitive Compartmented Information Facility) to protect against electronic espionage.
In the modern world, Faraday cells are finding new applications. In data centers, shielded rooms are used to protect servers from electromagnetic interference. IN automotive industry shielding principles are used to protect electronic control systems.
Everyday examples
- Microwaves. The metal body and the fine mesh on the door do not allow microwave radiation to penetrate outside. This is why a cell phone loses its signal if you put it in a switched off microwave oven.
- Airplanes. They are regularly hit by lightning during the flight, but thanks to the aluminum body, passengers remain safe.
- Bank cards. Special wallets made of metallized fabric provide protection against unauthorized reading.
- Cables. The shielded wires use the Faraday cage principle to protect the signal from interference.
- Elevators. The absence of a mobile phone signal in the elevator is due to the fact that the metal cabin blocks radio waves.
Cars are also Faraday cages. The metal body protects passengers not only from rain, but also from electromagnetic effects. However, modern cars with lots of plastic and glass don't work as effectively as a Faraday cage as older models.
Materials: what is important for shielding
For a Faraday cage to perform its functions most effectively, the materials used for its manufacture must have a number of key properties:
- High electrical conductivity. It is necessary to reflect and distribute Foucault currents. The most effective are copper, aluminum and alloys based on them.
- High magnetic permeability. It is especially important for low-frequency and static magnetic fields.
- Mechanical strength and wear resistance. It is relevant for installation, transportation and operation under conditions of vibration, shock loads or corrosive environments.
- Processability. The material should be easy to cut, bend, weld and other types of machining without compromising its protective properties.
- Economic feasibility. The balance between cost and safety characteristics is important for mass production and large projects.
In general, a Faraday cage can be made from any material capable of conducting electricity: wire mesh, metal sheets, or coils of wire. It can be of any shape, for example, in the form of a box, sphere or cylinder, and of any size, from very small to huge.
Precision alloys: reliable EMF protection
Precision alloys with high uniformity, stable physical and mechanical properties and precise chemical composition are ideal for shielding, particularly in conditions where high accuracy and reliability are required. Soft magnetic alloys with high magnetic permeability and low losses are especially effective.
Key features:
- High magnetic permeability. It contributes to the effective shielding of electromagnetic fields.
- Low coercive force — the minimum magnetic field strength required to demagnetize the material. Ensures their rapid return to their original state after the cessation of exposure to the magnetic field.
- Low hysteresis losses (magnetization-demagnetization cycle). It is important when used in dynamic systems with frequent changes in the magnetic field.
Popular brands of precision alloys for shielding:
- 50N. Nickel-iron alloy (50% Fe, 50% Ni). It has high magnetic permeability and increased saturation induction. Suitable for shielding in radio engineering, microwave cameras and radiation safety systems.
- 79NM. It contains 79% nickel, 15% iron and 4% molybdenum. It provides effective shielding of weak alternating magnetic fields. It is used in medical diagnostics, measuring equipment and military electronics.
- 81NMA. Composition: 81% Ni, 10% Fe, 5% Mo, 3% Ti. The most sensitive alloy with maximum permeability and minimal response to mechanical and thermal effects. Ideal for high-precision screens in the space and nuclear industries.
These alloys can be used in the form of thin cold-rolled strips, sheets or finished components, depending on the specific application.
PZPS alloys
The St. Petersburg Precision Alloy Plant offers cold-rolled strip made of soft magnetic alloys of 50N, 79NM, 81NMA grades that comply with GOST and TU. The products are characterized by:
- stable thickness;
- high magnetic characteristics;
- excellent plasticity.
In addition, others are available at the PZPS special materials: heat-resistant, corrosion-resistant, structural steels and alloys for the nuclear and aerospace industries.
Works at the factory research center (Research Center), equipped with modern analytical, metallographic and measuring equipment. Thanks to its own research center, PZPS not only produces alloys according to individual customer requirements, but also participates in creating innovative solutions in the field of shielding and electronics.
