Shielded Cable: When To Use

Electromagnetic interference (EMI) is prevalent throughout the factory floor. This is why data and signal cables are usually protected with insulated conductors and wrapped with a conductive layer. Shielding reduces electrical noise and reduces its impact on signals and also lowers electromagnetic radiation. Shielding prevents crosstalk between cables near each other. Shielding not only protects cable but it can also protect machinery and people as well.

Power cables are constructed to be electromagnetic compatible (EMC) to minimize noise generation, which affects many other systems like radio and data communication.

Communication cables are shielded to prevent the effects on the data transmitted from EMI. To further prevent cross talk and coupling, communication cables are also paired and individually shielded.

In some applications, such as those needing servo cables, double or even triple shielding is required: around individual conductors, around twisted pairs, and around the entire cable.

Some applications do not require shielded cables. For example, if a cable will be used in a cabinet or otherwise away from other sources of noise, it does not need to be shielded, as it will be protected from noise and EMI already.

Cable shielding uses either a braided, spiral design or metal-coated Mylar or foil shield. The shielding wraps around each conductor to mitigate noise by 85% to 100%, depending on the configuration. The maximum shielding a braided shield can have is 90%. Spiral shields can offer 98%, while metal-coated Mylar can deflect 100% of EMI.

Using a thin layer of Mylar or aluminum foil eliminates the gaps you may encounter with braided designs. The foil is attached to a polyester backing to provide 100% coverage. However, because it is thin, it can make applying connectors a challenge. Foil shielding can also be damaged in high-flex applications, so spiral or braided designs work best there.

Just as described, braided shielding is made of a mesh of bare or tinned copper wires woven together. It is easy to terminate when crimping or soldering a connector. Because of the braiding, small gaps of coverage do occur, thus resulting in the only 90% shield rating. 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.

Unlikely competitor for diamond as best thermal conductor: Boron arsenide potential for cooling applications

The discovery that the chemical compound of boron and arsenic could rival diamond, the best-known thermal conductor, surprised the team of theoretical physicists from Boston College and the Naval Research Laboratory. But a new theoretical approach allowed the team to unlock the secret to boron arsenide's potentially extraordinary ability to conduct heat.

Smaller, faster and more powerful microelectronic devices pose the daunting challenge of removing the heat they generate. Good thermal conductors placed in contact with such devices channel heat rapidly away from unwanted "hot spots" that decrease the efficiency of these devices and can cause them to fail.

Diamond is the most highly prized of gemstones. But, beyond its brilliance and beauty in jewelry, it has many other remarkable properties. Along with its carbon cousins graphite and graphene, diamond is the best thermal conductor around room temperature, having thermal conductivity of more than 2,000 watts per meter per Kelvin, which is five times higher than the best metals such as copper. Currently, diamond is widely used to help remove heat from computer chips and other electronic devices. Unfortunately, diamond is rare and expensive, and high quality synthetic diamond is difficult and costly to produce. This has spurred a search for new materials with ultra-high thermal conductivities, but little progress has been made in recent years.

The high thermal conductivity of diamond is well understood, resulting from the lightness of the constituent carbon atoms and the stiff chemical bonds between them, according to co-author David Broido, a professor of physics at Boston College. On the other hand, boron arsenide was not expected to be a particularly good thermal conductor and in fact had been estimated -- using conventional evaluation criteria -- to have a thermal conductivity 10 times smaller than diamond.