Otis Singleton
Electric shielding, also known as electrostatic shielding, is a method of limiting the electric field to a certain region of space. It involves the use of barriers made of conductive or magnetic materials to reduce or redirect electromagnetic fields (EMFs). This process is commonly used to protect sensitive electronic circuits and devices from static damages and electromagnetic interference. In cars, for instance, the metallic body acts as an electrostatic shield, protecting the occupants from lightning strikes. Electric shielding is also applied to enclosures and cables to isolate electrical devices and wires from their surroundings.
| Characteristics | Values |
|---|---|
| Definition | In physics, electric shielding, or screening, is a method or process of limiting the electric field to a certain region of space. |
| Other Names | Electric shielding is also known as electrostatic shielding. |
| Process | Electric shielding involves barricading an area with conductive or magnetic material to lower the electromagnetic field. |
| Materials Used | Materials used for electric shielding include thin layers of metal, sheet metal, metal screen, and metal foam. Common sheet metals include copper, brass, nickel, silver, steel, and tin. |
| Applications | Electric shielding is used in defence applications, electronic goods, cars, elevators, and more. |
| Effectiveness | The effectiveness of electric shielding depends on the material used, its thickness, the size of the shielded volume, and the frequency of the fields of interest. |
| Considerations | Engineers must consider the heating and expansion of shields when designing them. Shields should also be manufactured with sufficient precision and strength to prevent short circuits. |
| Maintenance | Electric shields need regular cleaning and maintenance to remove coatings and prevent contamination. Bead blasting is a cost-effective method for cleaning shields. |
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What You'll Learn
Faraday Cages
Electric shielding, or electromagnetic shielding, is the practice of reducing or redirecting electromagnetic fields (EMF) in a space. This is done with barriers made of conductive or magnetic materials.
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Sensitive electronic circuits
Electric shielding, also known as EMI (electromagnetic interference) shielding, is a crucial method of protecting sensitive electronic circuits from external electromagnetic signals. It involves the use of manufacturing techniques and materials to prevent signals from any form of interruption.
To combat this, engineers employ various EMI shielding techniques. Metal enclosures, or "shield cans", are commonly used to protect sensitive components. Metals such as aluminium, copper, steel, and nickel are chosen for their electrical conductivity and ability to reflect or absorb electromagnetic radiation. Copper, for example, is highly effective at shielding electric and magnetic fields and is often used in medical devices. Gaskets and seals made from conductive materials are also used to close gaps in electrical enclosures, reducing interference.
In addition to metal enclosures, conductive coatings or paints containing copper, nickel, or metallic inks can be applied to non-metal surfaces like plastic casings, providing an additional layer of shielding. Shielding films and foils are also used for irregular shapes or when metal enclosures are impractical.
Proper grounding, bonding, and termination are essential for effective EMI shielding design. Grounding connects shielding components to a common reference point, while bonding creates a continuous, low-impedance path between components, ensuring electromagnetic energy is diverted away from sensitive electronics.
EMI shielding is vital in industries such as aerospace, medicine, and automotive electronics, where sensitive electronic control units require protection from electromagnetic interference.
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Materials used for shielding
Electric shielding, also known as electromagnetic shielding, is a method or process of limiting the electric field to a certain region of space. It is often necessary when performing highly sensitive electrical measurements.
The materials used for electromagnetic shielding include thin layers of metal, sheet metal, metal screen, and metal foam. Common sheet metals for shielding include copper, brass, nickel, silver, steel, and tin.
The effectiveness of a shield, that is, how well it reflects or absorbs/suppresses electromagnetic radiation, is affected by the physical properties of the metal. These may include conductivity, solderability, permeability, thickness, and weight. For example, electrically dominant waves are reflected by highly conductive metals like copper, silver, and brass, while magnetically dominant waves are absorbed/suppressed by less conductive metals such as steel or stainless steel.
Another commonly used shielding method is to coat the inside of an enclosure with a metallic ink or similar material. The ink consists of a carrier material loaded with a suitable metal, typically copper or nickel, in the form of very small particulates. It is sprayed on to the enclosure and, once dry, produces a continuous conductive layer of metal, providing effective shielding.
In the case of high-frequency electromagnetic radiation, the radiation energy is absorbed by the skin, and there is no electromagnetic field inside. This is known as the skin effect. Equipment sometimes requires isolation from external magnetic fields, in which case shields made of high magnetic permeability metal alloys can be used, such as sheets of permalloy and mu-metal or with nanocrystalline grain structure ferromagnetic metal coatings.
Other materials used for shielding include:
- Aluminum, which has a high strength-to-weight ratio, is durable, easy to form, non-ferrous, corrosion-resistant, and cost-effective.
- Pre-tin-plated steel, which is steel covered with a layer of tin, making it less susceptible to rust and increasing its soldering capability.
- Monel, an alloy made of nickel and copper combined with small amounts of iron, manganese, carbon, and silicone. It is stronger than nickel, has great corrosion resistance, good conductivity, and excellent mechanical characteristics.
- Mu-metal, an alloy typically made of nickel and iron. It is malleable, easy to work with, and can be made into thin sheets. It shields both electronic and magnetic fields.
- Copper alloy 770, a copper, nickel, and zinc alloy used in EMI shielding applications mainly for its corrosion-resistant properties.
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Applications of electric shielding
Electric shielding, also known as electromagnetic shielding, is the practice of reducing or redirecting electromagnetic fields (EMF) in a space with barriers made of conductive or magnetic materials. It is used to isolate electrical devices and cables from their surroundings.
Faraday Cages
One of the most well-known applications of electric shielding is the Faraday cage, invented by Michael Faraday in 1800. A Faraday cage is an enclosure made of conductive materials that distribute electrostatic charges and electromagnetic fields across its exterior surface, thereby cancelling out the charges in its interior. Faraday cages are used in a variety of applications, including:
- MRI scanning rooms: Faraday cages are used to prevent external radio frequency signals from interfering with data from the MRI machine.
- Microwave ovens: The electromagnetic energy within the oven is contained, and the exterior acts as a shield from radiation.
- Analytical chemistry: Faraday cages are used to reduce noise while making sensitive measurements.
- Lightning protection: During a lightning storm, the metallic body of a car acts as a Faraday cage, protecting its occupants from lightning strikes.
Cable Shielding
Electric shielding is also commonly used to encase cables, providing protection from electromagnetic interference. This is particularly important in applications such as:
- Coaxial cables: The central conductor in a coaxial cable is protected by connecting the outer conductor to the ground, which acts as an electrostatic shield.
- Shielded cables: These cables have a wire mesh surrounding an inner core conductor, preventing the escape or addition of signals to the core conductor.
Electronic Goods
With the growth of the electronics industry, electric shielding has become increasingly important for plastic-housed electronic goods. This can be achieved through methods such as:
- Metallic ink coatings: Spraying the inside of an enclosure with metallic ink, typically containing copper or nickel particulates, creates a continuous conductive layer that provides effective shielding.
- Metal coatings: Metals such as copper, brass, and nickel are used to coat electronic enclosures, providing a lightweight and conductive barrier against electromagnetic interference.
- Carbon fiber: Carbon fiber is a lightweight and conductive material well-suited for handheld electronic devices, providing attenuation against ambient EMI.
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Shielding design considerations
Electric shielding, also known as electromagnetic shielding, is the process of reducing or redirecting electromagnetic fields (EMF) in a given space. This is achieved by using barriers made of conductive or magnetic materials.
When designing an electric shield, there are several factors to consider. Firstly, the type of material used is crucial. Common materials for electromagnetic shielding include thin layers of metal, sheet metal, metal screen, and metal foam. Different metals have varying physical properties, such as conductivity, solderability, permeability, thickness, and weight, which affect their shielding effectiveness. For example, highly conductive metals like copper, silver, and brass reflect electrically dominant waves, while less conductive metals like steel or stainless steel absorb or suppress magnetically dominant waves.
Secondly, the thickness of the material is important. The amount of reduction in the electromagnetic field depends on the thickness of the material used. A thicker material will provide greater shielding effectiveness.
Thirdly, the size, shape, and orientation of holes in the shield must be considered. Any holes in the shield should be significantly smaller than the wavelength of the radiation being blocked. This ensures that the shield effectively approximates an unbroken conducting surface.
Additionally, the size and shape of the shielded volume are important factors. The effectiveness of the shield depends on how well it encloses the space and blocks external electromagnetic fields.
Furthermore, the frequency of the electromagnetic fields that the shield is designed to block should be considered. Different frequencies may require different shield designs or materials to effectively block or redirect the fields.
It is important to note that in some cases, a qualified expert, such as a medical physicist or medical health physicist, should be consulted during the design process to ensure the required degree of protection is achieved.
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Frequently asked questions
Electric shielding, also known as electrostatic shielding, is a process of limiting the electric field to a certain region of space. It is often necessary when performing highly sensitive electrical measurements.
Electromagnetic shielding is a type of electric shielding that involves reducing or redirecting the electromagnetic field (EMF) in a space with barriers made of conductive or magnetic materials. It is used to isolate electrical devices and cables from their surroundings.
A Faraday cage, also known as a Faraday shield, is an enclosure made of conductive materials that blocks external electric fields. It was invented by Michael Faraday in 1800 and works by concentrating charges on its surface, leaving the interior of the cage free of any charge.
Electric shielding is commonly used in cars, where the metallic body acts as an electrostatic shield, protecting the occupants from lightning. It is also used in elevators to shield cell phones and radios from external interference. In electronic devices, electric shielding protects sensitive circuits from static damages.
