Feature: Connectors
The enclosure material is the first line of defence against EMI
Safe housing Perhaps the most important aspect of EMI resistance is the connector enclosure’s material and topology. Te enclosure material is the first line of defence against
EMI. Conductive metallic enclosures are ideal here, because electromagnetic waves coming or going induce a current in the enclosure. As a result, they act as an insulating shield, as opposed to non-conductive enclosures, usually plastic, that are transparent to EMI and allow the interference to pass through unimpeded. Enclosure material is so important that even the slightest
change can make a big difference. For instance, traditional EMI-resistant enclosures have been plated with cadmium to reduce corrosion. Tis thin layer also helps increase the material’s opacity to EMI. Unfortunately, cadmium has toxic effects on kidneys as well as the skeletal and respiratory systems. Recently, however, a growing number of enclosures are being
plated with zinc-nickel to make them RoHS-compliant. Zinc- nickel offers similar EMI shielding and corrosion resistance but without cadmium with its health impacts. Te second line of defence is topology, or shape, of the
connector enclosure. For example, imagine a rectangular enclosure. Here, sharp edges act as weak points for EMI to leak in and out of the connector, and flat faces create impromptu waveguides where the EMI is trapped and interferes with itself, creating even more electromagnetic noise.
Filtering out the noise So, with a topologically-smooth, zinc-nickel-plated stainless- steel enclosure, we’ve severely limited EMI flux either emitted or absorbed by the connector. Backshells like the Amphenol M85049, Polamco 35 Series and Sunbank M85049 are specifically designed to give a 360-degree connection with the cable braid, offering the best EMI protection for the wire itself. This way there’s nowhere for EMI to leak out of the
connection; but, what about EMI generated by or already present in the wiring itself ? This can be addressed in two ways. The first is to
use braided coaxial cabling. Like conductive connector enclosures, coaxial cables include a conductive sheath to protect the signal wire from EMI. For best protection, the coaxial sheath should be grounded to the backshell of the connector to allow an escape route for EMI-induced current. The second approach is to include filtering components
in the connectors that are tuned to pass power and signal frequencies but remove EMI frequencies. Using filters is quite convenient because they can easily be retroactively applied to typically noisy networks with little to no need for equipment rework or redesign.
Fitting into the right space Some spaces where connectors should fit are hard to see or difficult to reach. Blind mate connectors achieve a connection through a
sliding or snapping action or by using guide pins, without the use of special tools. Unlike other connector types, many blind-mate connectors have self-aligning features that correct small misalignments when mating and help guide the connectors into the correct mating position. This feature is quite different from the more rigid coupling mechanisms found on threaded or bayonet couplings, reducing the chance of connector damage and preventing problems caused by incorrect mating. Since users might not be able to see if the connectors
are correctly mated, blind mate connectors can also provide auditory confirmation to give confidence that the connection is properly made. Again, this is a significant improvement from guessing that a reliable connection was made, especially when the application depends heavily on a stable connection. There are various connector types available with blind-
mating options, including power and/or signal connectors with either cable- or board-mount options, multi-pin connectors for cabling between racks and panels, optical connectors, and RF connectors. Blind mate connectors are also available in various orientations, including wire-to- board, board-to-board and wire-to-wire.
When to use blind mate connectors? Blind mate connectors are a popular choice in a variety of mission-critical applications. From medical equipment to electric power transmission systems and military radar equipment, they excel in any situation where the receptacle is hidden or recessed so it is difficult to see or reach. This includes the back of an interface card plugged into a chassis and other “black box” installations. Using blind mate connectors provides several benefits,
including reduced production, installation and maintenance costs, shorter assembly times and a minimal impact on the size and weight of designs. Furthermore, using blind mate connectors results in fewer mismated connections – invaluable in mission-critical applications where any unplanned downtime is disastrous. It’s important to remember that blind mate connectors
are also designed to be extremely durable. If mistreatment occurs, they remain reliable and continue to perform as expected. PEI-Genesis understands the frustrations of trying to
mate connectors in hard-to-reach, not easily visible spaces. It also knows that the ability to achieve a stable, reliable and correct connection is crucial to any design, whether engineering downhole test equipment for the oil and gas industry or power and data connections essential to autonomous vehicle safety.
www.electronicsworld.co.uk July/August 2021 39
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