Shielded Cable: When To Use Full-time Job6 months ago - Security & Safety - Detroit - 120 views
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.
The team found the calculated thermal conductivity of cubic boron arsenide is remarkably high, more than 2000 Watts per meter per Kelvin at room temperature and exceeding that of diamond at higher temperatures, according to Broido and co-authors Tom Reinecke, senior scientist at the Naval Research Laboratory, and Lucas Lindsay, a post-doctoral researcher at NRL who earned his doctorate at BC.
Broido said the team used a recently developed theoretical approach for calculating thermal conductivities, which they had previously tested with many other well-studied materials. Confident in their theoretical approach, the team took a closer look at boron arsenide, whose thermal conductivity has never been measured.
Unlike metals, where electrons carry heat, diamond and boron arsenide are electrical insulators. For them, heat is carried by vibrational waves of the constituent atoms, and the collision of these waves with each other creates an intrinsic resistance to heat flow. The team was surprised to find an unusual interplay of certain vibrational properties in boron arsenide that lie outside of the guidelines commonly used to estimate the thermal conductivity of electrical insulators. It turns out the expected collisions between vibrational waves are far less likely to occur in a certain range of frequencies. Thus, at these frequencies, large amounts heat can be conducted in boron arsenide.
How Does Sound Absorbing Material Work?
Sounds are occurring all around us, at every moment of the day, and some of them are held more clearly than others.
If you've been trying to soundproof your home and block certain noises, you've likely looked into the marvel of sound absorbing materials and how they can help.
How does sound absorbing material work?
A material with sound absorbing properties is able to take the energy created from sound and turns it into another type of energy. These dense but soft materials help to absorb the sound or vibrations as the waves hit it, and it deforms this energy which reduces its effect.
To give you a better understanding of what sound absorbing materials do, we've created a simple guide that answers all of the questions you need to know. With a simple explanation of the science behind sound and absorption, you’ll be better equipped to choose a soundproofing material that works.
Without sound, there would be no need for sound absorption methods, so it's a good idea to understand the science behind how it’s made and where it goes.
A sound wave is created by a vibration that is sent through the air at varying lengths, like when someone yells, and these can be categorized as either high or low-frequency sounds depending on their length.
A high-frequency sound wave can be reflected by thin materials, whereas low-frequency sound waves pass through them. Any soundwave that’s allowed to continue traveling will make noise unless there are materials or objects in the way.
When none of this sound is absorbed, it creates noise, and if your goal is to prevent this noise from occurring, you need the right materials and setup to absorb them completely.
Electrically Conductive Adhesives
Electrically conductive adhesive products are primarily used for electronics applications where components need to be held in place and electrical current can be passed between them.
Depending on gap between components, most general adhesives (such as anaerobics, cyanoacrylates, epoxies, and acrylic-based adhesives) act as an electrical insulator. Some offer improved thermal conductivity to help with thermal management of electronic components and heat sinks, directing heat away from sensitive components. Because in many cases (particularly when using an anaerobic or cyanoacrylate adhesive) there is no glue line control and effectively parts are touching (with adhesives filling in microscopic crevices), some electrical charge can still be transferred as there is enough metal to metal contact still occurring.
Certain temperature-sensitive electronic components cannot be soldered (as the intense heat of liquid solder and the soldering iron can cause damage to the component). This type of application calls for an electrically conductive adhesive that can be used in place of solder. PCBs with components attached to both sides can also benefit from using an electrically conductive adhesive as assembly process is easier without risk of components dropping off the underside when parts are soldered on the top. Using electrically conductive adhesive for an entire electrical assembly negates the requirement to undergo a solder re-flow process.
Applications for electrically conductive adhesives aren’t just limited to bonding components onto PCBs or die attach, they can be very useful for other electronic applications where substrates are temperature sensitive – such as for touch-panels, LCD displays, coating and bonding RFID chips, and mounting LEDs. Solar cells also use adhesives instead of solder as there is less warpage and damage to the sensitive wafers that make up solar cells.
Which material is used for electromagnetic shielding?
Typical materials used for electromagnetic shielding include sheet metal, metal screen, and metal foam. Common sheet metals for shielding include copper, brass, nickel, silver, steel, and tin. Shielding effectiveness, that is, how well a shield reflects or absorbs/suppresses electromagnetic radiation, is affected by the physical properties of the metal. These may include conductivity, solderability, permeability, thickness, and weight. A metal's properties are an important consideration in material selection. For example, electrically dominant waves are reflected by highly conductive metals like copper, silver, and brass, while magnetically dominant waves are absorbed/suppressed by a less conductive metal such as steel or stainless steel.
Further, any holes in the shield or mesh must be significantly smaller than the wavelength of the radiation that is being kept out, or the enclosure will not effectively approximate an unbroken conducting surface.
Another commonly used shielding method, especially with electronic goods housed in plastic enclosures, is to coat the inside of the enclosure with a metallic ink or similar material. The ink consists of a carrier material loaded with a suitable metal, typically copper or nickel, in the form of very small particulates. It is sprayed on to the enclosure and, once dry, produces a continuous conductive layer of metal, which can be electrically connected to the chassis ground of the equipment, thus providing effective shielding.
Electromagnetic shielding is the process of lowering the electromagnetic field in an area by barricading it with conductive or magnetic material. Copper is used for radio frequency (RF) shielding because it absorbs radio and other electromagnetic waves. Properly designed and constructed RF shielding enclosures satisfy most RF shielding needs, from computer and electrical switching rooms to hospital CAT-scan and MRI facilities.