Excellent flexibility and flex life as well as 85 to 95 percent coverage are characteristics of spiral shields. Spiral shields are also easy to terminate and are most effective at providing low frequency protection.
Spiral shields can lose effectiveness if the individual strands of the shield separate, something that can occur after a high number of flex cycles.
Spiral shield showing strands opening after high number of flex cycles. By Hank Mancini. Subscribe to our Molex Insights blog to get the latest trends, research and insights. Andorra Unit. Arab Emir. Vincent Venezuela Brit. This includes TVs, laptops, cell phones, tablets, etc.
Electromagnetic energy is energy expressed in waves. It's everywhere and comes in many forms. When trying to prevent EMI it's important to understand what type of energy you want to block. Different materials are more effective at stopping different kinds of energy.
Additionally, if you use a perforated shielding medium, you must ensure the holes aren't large enough for the energy waves to escape.
Electromagnetic shielding is a barrier that covers electronics to prevent EMI. It is also sometimes referred to as radiation shielding.
RF shielding and magnetic shielding are two sub-types of EMI shielding. RF shielding is specific to the blocking of radiofrequency electromagnetic radiation. Magnetic shielding is a little different since you can't block a magnetic field the same way you can electromagnetic energy. This is because a magnet's field lines run from its north pole to its south pole and monopole magnets don't exist.
Instead, you must redirect the magnetic field lines. You can achieve this by separating two magnets with a magnetic barrier. When doing so, the magnetic field lines of the magnets will interact with the barrier. This causes the lines of both magnets to bounce back before reaching the magnet on the other side.
Because the magnetic lines of the magnets can't interact, their impact on each other is either decreased or nullified. Much of today's technology requires magnets to work. Like EMI, you must prevent magnetic interference or it can impede the operation of other magnetic devices. Some shields combine conductive and magnetic mediums to prevent interference from both EMI and magnetism. Alternating currents have a tendency not to go through the center of a solid conductor.
Instead, they travel closer to the surface. This is called the skin effect. Skin depth is how far underneath the surface of a conductor a current will travel and decreases as frequency increases.
In an EMI shield, you want a material with enough skin depth to prevent a frequency from penetrating. You can determine skin depth with this calculator. We are in the age of science fiction. Everywhere we turn there are electronic devices.
Each one can interfere with another if it isn't properly shielded. The main goal of an electromagnetic shield is two-fold. It isolates a device's energy so it doesn't affect anything else and blocks external energy from getting in.
Without shielding, electronics wouldn't function as designed or may even stop working altogether. Brownouts are any type of partial service outage, while a blackout is a full outage. Brownouts and blackouts are not limited to power outages. If there is a power outage and a transfer sequence is in place, you'll start receiving power from a generator. When this happens, it's called an EFT. If you were to remove the plastic jacket from a phone line you'd see another layer covering the wires. This second layer is usually a metallic foil or metallic plaited braid that protects the lines against EMI.
It is a type of RF shielding that reduces static during phone calls. A power fault is any abnormality in an electrical current. A short circuit is an excellent example of a power fault, but it is not the only kind.
Power faults are sometimes caused by an EMI. There are many types of EMI shielding materials and new materials are getting introduced all the time. When deciding which shielding material to use, you need to consider shielding effectiveness SE. SE is the strength of the intruding electric field in comparison to a device's electric field.
Shielding effectiveness is measured in decibels dB. This Shielding Effectiveness Calculator can help you determine your specific needs.
Aluminum is a cost-effective shielding material for ultra- to super-high radio waves. It's high conductivity and strength-to-weight ratio make it an excellent choice for EMI shielding. Keep in mind though that aluminum is non-ferrous so you can't use it to block magnetic forces.
Additionally, fabricating EMI shields of aluminum present some challenges as it is difficult to solder. You'll also have to keep an eye on any shield made of aluminum as it can corrode over time. Copper is a very versatile metal. It's highly conductive, capable of blocking Radio waves and magnetic. This makes it an ideal choice for applications that require all three types of shielding.
Copper's malleability means you can use it in a wide array of devices. It's also easy to combine with other metals to form alloys like brass making it even more adaptive. Copper's only real drawback is its price tag when compared with other materials.
It is easy to terminate when crimping or soldering a connector. If the cable is not moving or flexing, this coverage should be sufficient. However, the braided design does add cost and weight to the final design. If an environment is extremely noisy, a cable may use multiple layers of shielding with both the braided and foil designs. Sometimes pairs of wires are shielded individually in addition to the entire cable being shielded.
This is done to prevent crosstalk between pairs. Besides the braid covering, the maximum admissible diameter of the single strand of braid and the angle of twist to the axial axis of the conductor are also determined in the manufacturing.
The thinner the single strand and the smaller the angle of twist, the more flexible is the cable. However, the diameter of the single wire is restricted due to the mechanical requirements. A cable shield consists of a respective amount of strands, depending on the braiding machine 16, 24, The total amount of strands equals the number of strands in a braiding element times the amount of elements. The strand diameter, the angle of twist and the folding number also determine the density of a shield.
The single strands are combined to make larger strands.
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