About Electromagnetic Interference in Cables: Installations like data centers, offices, and factory floors are normally electrically noisy environments.
Electrical noise, either conducted or radiated as electromagnetic interference, could significantly disrupt the operation of equipment nearby.
Although the cable jacket and insulation protect the cable from abrasions, scrapes, moisture, and chemicals, they don’t protect the cable from electrical noise. The article below will discuss electromagnetic interference in cables.
What is Electromagnetic Interference?
EMI (electromagnetic interference) is interference or unwanted noise in a circuit or electrical path caused by an external source. It is often referred to as radio interference. EMI causes electronics to malfunction, completely stop functioning, or function poorly.
EMI sources could be human-made or natural. Modern error correction, high-quality equipment, and electrical shielding could help reduce its effects.
An example of EMI is when you place your phone next to a speaker or powered audio equipment, and you hear a series of beeps or unpleasant noises.
How is Electromagnetic Interference in Cables Generated?
Cables could be the main receiver or source of EMI. As the receiver, your cable could pick up interference from other sources. On the other hand, as a source, your cable could radiate noise like an antenna or conduct noise to other electronics.
Unshielded cables feature an insulated plastic jacket that protects the wires. However, capacitive sensing that detects changes in the electrical field around the central conductor in the cable is able to make its way through the plastic jacket.
On the other hand, shielded cables feature outer shielding that creates a barrier separating the electric field around the central conductor from anything outside. Once you create a barrier around the central conductor in the cable, the electric field eliminates past the barrier, thus shielding.
Shielding surrounds all power-carrying conductors of your cable and protects it by identifying noise and conducting it to the ground. Furthermore, it reflects any signal interference.
Cable Shielding Types
Cables are available with different shielding options, each with varying effectiveness.
Foil Shield: Good
- Low cost
- 100% coverage over core conductors
- Lightweight
- Protection at frequencies over 15 KHz
Foil shields use Kapton/aluminum or polyester/aluminum to offer complete coverage and constant contact with the helically served drain wire.
The drain wire creates an electrical connection between the circuit ground and the shield. You can use foil shielding over single conductors, twisted pairs or triads.
Braid Shield: Better
- High physical strength
- RFI/EMI resistance in data, power, and control applications
- Protection at low frequencies (up to 15 KHz)
Braid shielding is a woven mesh of tined, nickel-plated, silver-plated, bare copper wires. Cable braid shields offer a minimum coverage of 85%. Furthermore, they provide a low resistance path to the ground and are easier to terminate when attached to a connector.
Copper features a higher conductivity compared to aluminum, allowing the weave to provide more mass for noise conduction.
MultiShield (Foil and Braid): Best
- High physical strength
- Easy termination
- Protection over frequency ranges
In scenarios where physical strength is an important factor, and the cable environment is extremely noisy, it is advisable to opt for a multishield cable.
It uses a triple laminate (aluminum/polyester/aluminum) foil and tinned copper braid to enhance physical strength and improve signal interference shielding.
Often, multiconductor cables have different pairs individually shielded to prevent crosstalk between each other.
Cable Shielding Application
And how can you shield your cables?
When is EMI Shielding Needed?
Normally, situations that you’ll likely need EMI shielding include;
- Aerospace and military certified cables: you need additional safety for aerospace and military applications such as EMP (electromagnetic pulse) control.
- Regulatory restrictions: when you need your product to adhere to certain industry standards.
- Safety and Security systems: sensitive equipment needs protection from interfering or harmful frequencies.
What Types of Cable Shielding Do You Need?
When deciding on the type and amount of shielding, you need to consider the factors below.
- Noise level
- Cable cost
- System configuration
- Cable weight, diameter, and flexibility
- Type of signal interferences (ESI, EMI, or RFI)
What Types of Cables are Susceptible to EMI
Below are the various types of cables that are susceptible to EMI.
- Speaker wire
- Phone
- Coaxial
- USB
- DisplayPort/HDMI
- Ethernet
- 3.55 mm mini jack audio cable
- RCA and component video
- Digital coaxial
HDMI Cable
Shielded Cable Assemblies
The most vital step is to ground the drain wire of your shielded cable. The cable shielding and termination should provide a low-impedance path to the ground.
The cable foil/braid and drain wire are cable shields and share an electrical connection. If you fail to properly ground your shielded cable, it reduces the shield’s effectiveness.
Normally, instead of trying to group the entire shield, you can use the drain wire to ease the termination of your cable shield for soldering or crimping.
Some environments only require a foil shield, while others require a braid shield or a combination of both. Ensure you use the cable better suited for its intended application. Cables that are constantly flexed need spirally wrapped shields, not braid shields.
Keep in mind that foil shields could be dangerous for flex applications, and therefore, it’s advisable to avoid using them.
Also, don’t forget to properly ground the equipment you plan on connecting your cable to.
Whenever possible, use an earth ground. With most connector designs, you can enjoy 3600 termination of your shield.
The connectors in your shielded cable assembly offer the same shielding effectiveness as your actual cables.
The connectors should be made with cast zinc, aluminum backshells, or metal-coated plastic.
If you use a high-quality connector with a low-quality cable, you won’t improve performance, and the same applies vice versa.
Conclusion
If your setup is suffering from issues due to EMI, now you know the way to go is with shielded cables. Contact Cloom Tech for custom-shielded cable assemblies designed to suit your intended application.
