Electromagnetic shielding how does it work

The naked eye cannot see all the potential interference in the air. EMI shielding protects you from that. EMI shielding materials consist of one of three types of metal but come in a variety of forms. Sometimes engineers will use a combination of materials to create the best EMI shielding solution. Pre-tin plated steel costs less than the other metals used in EMI shielding, but it works well for lower frequencies, typically in the kHz range up to the lower GHz range.

Carbon steel, in particular, provides low-frequency shielding properties that the other metals do not provide. It also protects the steel from corrosion and ultimately rust. Copper alloy is also commonly known simply as alloy It consists of copper, nickel, and zinc.

People use it most often because it resists corrosion so well. It has a permeability of 1, which means it is ideal with MRI machinery where magnets cannot be present. Copper is different than the copper alloy Of all the metals in EMI shielding, copper is the most reliable because it works best at reducing both magnetic and electrical waves. You can find copper in just about any place needing EMI shielding from hospital equipment to basic home computers.

Copper costs more than other alloys or pre-tin plated steel. It does, however, have a higher rate of conductivity, which makes it so effective as an EMI shield. Because of its strength-to-weight ratio and high conductivity, aluminum can work well as an EMI shield material. Compared to copper, aluminum has nearly 60 percent of conductivity. Aluminum has a downside, though.

It corrodes more easily than the other metals and has high oxidation properties. Oxidation will compromise the integrity of the metal, making it weak. A gasket is a seal that fills the space between two surfaces. EMI shielding gaskets work in a similar way except they exist to protect electronics from interference.

EMI shielding of the past consisted of metal sheets that fabricators formed into specific shapes to fit into housing or enclosures. This worked well for thin metal sheets of aluminum, copper, and steel.

If weathering or time deforms the sheets, the sheets stay in the same shape, and the circuits they're supposed to protect will leak. EMI gaskets look like a sieve or ruggedized touchscreen made from particle-filled silicones. These gaskets work well in the heat as well as the cold, making them an ideal solution for EMI problems.

EMI materials can take many shapes. For example, conductive silicones work well as window films that help shield electronics from magnetic and electrical waves in commercial settings. The material and form of the EMI protection depend solely on the type of electronics that need the shielding and the frequencies involved. For example, technicians will use metallic foil or plaited braid to shield equipment wires.

You can also use coaxial cables with EMI shields built into the wire construction. Technicians will wrap wire bundles in foil or they will apply cable braid over an entire construction. Even the connectors have EMI shielding with braiding or foil attached to the metal covers giving the appliance or device complete protection. For a printed circuit board, the shielding has a ground plane built into it and a metal box over the sensitive elements.

Technicians then surround the delicate components with a Faraday cage arrangement. Audio speakers have an inner metallic casing that blocks EMI specifically caused by common nearby elements like microwaves or televisions. When magnetic fields have less than a Khz range, you can use conductive points and magnetic materials.

Technicians will also use sheet metal, metal foam, conductive plastics, or mesh metal screening. Shieling foil tapes have specific characteristics that make them ideal for EMI shielding. They resist corrosion and are flame retardant. They're also flat and embossed which makes them ideal for shaping around odd corners and shapes. EMI shielding can also come in the form of carbon foam. Foam has a distinct advantage as an EMI shielding material because of its flexibility.

It serves more than one function. For example, some foam provides fire protection. An electromagnetic wave consists of two components: an electric component and a magnetic component. Both of them travel at the same frequency and are perpendicular to each other. A conductive material blocks the electric components while a material with high magnetic permeability blocks the magnetic components. Since a component of an electromagnetic wave cannot exist without the other, it is enough to protect one component.

When it comes to EMI shielding, there are different mechanisms involved to filter out each. Enumerated below are the three mechanisms of EMI shielding. In order to achieve EMI reflection, the material must have mobile charge carriers.

This means the material used for shielding must be conductive. The incoming electromagnetic wave interacts with the mobile charge carriers present in the conductive shield.

This interaction causes the charges to flow and redistribute along the conductor creating an opposing electromagnetic field. The electromagnetic field generated by the redistribution of charges cancels out the external magnetic field. In this mechanism, the higher the conductivity of the material, the better is the shielding characteristics.

The problem with this mechanism is that a discontinuity on the enclosure that is larger than the wavelength of the external electromagnetic field will defeat its shielding properties.

Thus, in the enclosure design, the sizes of holes and openings are minimized. However, this is not possible for higher electromagnetic wave frequencies. The only way to counter this in high-frequency EMI is through the use of filtering devices. Another problem is the skin effect, which is seen in AC circuits. When AC flows through the conductor, the charges tend to accumulate at the surface or the top-most layers of the conductor which increases the current density in that area.

The inner section is used less which lowers the conductivity and ultimately, the performance of the shield. This effect is highly evident in high-frequency electromagnetic waves. A solution for this is to increase the surface area of the conductor, thereby increasing the effective conducting cross-section. Another solution is by electroplating the surface with a highly conductive material at the surface such as silver or copper.

To achieve EMI absorption, the material must have electric and magnetic dipoles. These are materials with high dielectric constant and high magnetic permeability. In the presence of an external magnetic field, the magnetic field lines are cut since they tend to travel through the material. An enclosure with this property absorbs the magnetic field lines by creating a pathway within itself. A problem in using these materials, however, is that they do not have high conductivity.

Thus, they are less efficient in protecting from the electric component of the electromagnetic wave. Some industry professionals also believe incorrectly that all particle-filled silicones are just too thick to support thinner electronic designs. The cost of older, particle-filled products also discouraged their use.

For years, the filler material of choice for shielding silicones was silver-aluminum. The U. EMI gaskets made of silicones filled were pure silver were even more expensive. Today's electronic designers can specify alternative particle fills that cost less but still provide strong EMI shielding.

In addition to silver and silver-aluminum, silver-copper and silver-glass are used. Today, cost-effective nickel-graphite silicones perform at the shielding level of silver-aluminum products. These nickel-graphite silicones meet the shielding effectiveness requirements of MIL-DTL, which sets a minimum shielding effectiveness of dB at RF frequencies between 20 and 10, Hz.

Thanks to innovations in silicone compounding, particle-filled elastomers can meet demanding shielding requirements along with other project specifications. For example, because nickel-graphite silicones are available in 30, 40, and 45 durometer Shore A , they're soft enough for enclosure gaskets.

Other, higher-durometer shielding elastomers that use fluorosilicone as the base elastomer can resist fuels and chemicals. These fluorosilicone compounds come in 50, 60, and 80 durometers Shore A for applications that require EMI gaskets made of harder materials.

Unlike older shielding elastomers, newer shielding materials contain enough metal filler to ensure effective EMI shielding and electrical conductivity. Plus, these conductive silicones support reliable, cost-effective fabrication. During gasket cutting , particle-filled silicones won't stretch or become deformed. Connector holes align properly, and the material's structural properties support greater tear resistance - an important consideration for thinner wall gaskets.

Product designers can also specify the use of an adhesive backing for ease-of-installation. For shielding applications where Z-axis conductivity is required, particle-filled silicones can support the use of electrically-conductive adhesives.