It is a form of insulation in that it reduces or prevents the transfer of energy. In this case, electromagnetic energy, being between a high output device and the environment or protects a sensitive device from electromagnetic fields in the environment.
Environmental electromagnetic conditions are, by their nature, unpredictable. Shielding is designed to remove this performance threat. Whenever electricity flows in a conductor, a magnetic field is generated.
The fields generated are related to the amount of power being dissipated. So power-hungry devices such as motors and transformers will produce significant fluctuating fields.
Motors have electromagnetic fields that switch at high frequencies to keep them running. This is an ideal way of producing interference. Electromagnetic Interference EMI is the adverse effect of these electromagnetic fields on other devices. The interference is produced as the fluctuating field traverses other devices or their connecting cables or PCB tracks.
Each traverse induces a voltage which may be quite small. However, data processing devices run on low voltages and these induced voltages are relatively large and can easily corrupt input and output data signals. Conductive materials form a barrier to electromagnetic interference.
EMI shielding is a technique of creating a barrier that prevents leakage of strong electromagnetic fields that can interfere with sensitive devices and signals. They can be installed to isolate the electromagnetic field source or as an enclosure of the device that needs protection.
Electromagnetic interference, or radio frequency interference RFI , is a problem for most electronics since it can decrease the performance of the circuit or even cause it to fail. Electronics deal with small voltages and currents which can easily be disrupted by an electromagnetic field. Electromagnetic interference EMI is the coupling of signals from one system to another. There are three components to create an EMI: the source, path, and the receiver.
The two systems are the source and the receiver. The receiver, or the victim, is the sensitive signal or device in which its output signal is distorted by the interference.
The path is where signal coupling occurs which can be through four modes. EMI can be classified according to the duration of the interference. Types of interference are continuous and pulse interference. A continuous interference is a type of EMI where the source continuously emits the unwanted signal. Continuous interference is generally characterized as low energy and low frequency.
Examples of continuous interference are radio frequencies, electromagnetic field leaks from industrial equipment, power transmission lines, etc. On the other hand, pulse, intermittent, or transient interference is an EMI that occurs only in a short duration. Pulse interference is characterized by high bursts of energy which can be repetitive or random events. Repetitive is usually artificial making it predictable in terms of amplitude and duration. Random events can be artificial and naturally occurring such as lightning strikes, power surges, electrostatic discharge, and so forth.
Another classification of EMI is by the length of the wave bandwidth of the disturbance which can be narrowband or broadband. The definition of the two depends on the bandwidth of the signal on the receiver, termed as the resolution bandwidth. A narrowband disturbance has a bandwidth of less than or equal to the receiver, while broadband disturbance has greater bandwidth. With the understanding of the nature of EMI, it is clear that it can affect its surroundings in various ways.
It can affect electronics that are in contact conducted EMI , in close proximity without contact capacitive and magnetic EMI , and even over large distances radiated EMI. Along with the progress of the information age, the increased utilization of electronics for data processing and communication creates considerable pollution to the electromagnetic wave spectrum, on top of the other disturbances caused by electrical transmission and distribution systems and natural phenomena such as lightning strikes and solar flares.
Below are some effects of EMI. To address these problems, international organizations developed electromagnetic compatibility EMC standards. EMC is the property or characteristic of an equipment to operate correctly in an electromagnetic environment without generating or transmitting electromagnetic energy to other equipment.
EMI shielding is one of the methods of achieving EMC aside from grounding, filtering, and bonding techniques. Our EMI shielding and thermal interface material portfolios are designed to give customers the ultimate in design flexibility. An EMI shielding gasket is a mechanical device that helps protect electronics from electromagnetic interference.
Traditionally, EMI shielding has been fabricated from metal sheets and formed into shapes that fit electronic housings or enclosures. Aluminum, copper, and steel are strong and rigid, but thin metal sheets can deform under the pressures that are required for sealing.
Once metal EMI shields are deformed, they tend to remain in that shape and may allow leakage to and from electronic circuits. Today, EMI shielding materials include flexible metal screens, metal wires, and metal foams. Coatings made of metallic inks are also applied to the interiors of electronic enclosures to provide EMI shielding solution.
Each of these shielding methods has its advantages, but particle-filled silicone combines the electrical properties of metal with the material properties of silicone rubber. For product designers who need to meet a variety of sealing and insulation challenges, silicone filled with metal or metal-coated particles are an excellent choice. Learn how Modus is redefining the traditional supplier relationship.
For example, the EMI gaskets that are used in some ruggedized touchscreens are made of particle-filled silicones that attenuate EMI emissions, provide electrical conductivity , and ensure environmental sealing in conditions ranging from desert heat to arctic cold.
These EMI shielding gaskets must cushion the device from mechanical shock and be soft enough to avoid interfering with the display's touch function. Material costs and ease-of-fabrication are also important for gasket designers in many different industries. Particle-filled silicones are used in some demanding applications, but can these conductive elastomers really meet all of your application's requirements?
Are EMI shielding gaskets made of these materials cost-effective, and do particle-filled elastomers support design for manufacturability? Silicone resists sunlight, water, and a wide range of temperatures, but loading them with a high percentage of metal particles can have negative tradeoffs. That's why historically, some gasket designers rejected particle-filled silicones as too hard or too brittle. Other engineers have complained about part size limitations based on mold dimensions and long lead times for sheet materials.
Some industry professionals also believe incorrectly that all particle-filled silicones are just too thick to support thinner electronic designs.
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