Electromagnetic compatibility (EMC) connectors are primarily used in military, aerospace and industrial applications to provide enhanced electromagnetic interference (EMI) protection. Power and signal connections must have access to the system. These access points can be weak points in EMC performance.
EMC connectors and wiring systems often feature enhanced shielding, EMI gaskets, cable sealing jackets, and proper grounding. These connectors need to provide protection from a combination of EMI sources, including (Figure 1):
Conductive coupling
Capacitive coupling
Inductive coupling
Radiative coupling
Figure 1. Four sources of EMI. Image credit: Lapp)
Shielding and Grounding
Shielding and grounding are essential tools for controlling EMI. They work in tandem to prevent unwanted interference from entering the system, to control any EMI generated by the system, and to prevent interference with nearby systems.
EMI shielding and grounding uses copper, nickel, aluminum and other conductive metals as well as carbon-based conductive materials such as graphite, graphene and carbon nanotubes.
Shielding reflects or absorbs EMI to create a barrier. It can take the form of conductive housings, coatings, tapes, foams, metal braids, and more. The shield must be properly grounded to effectively absorb EMI.
Grounding is often associated with safety and is required for most system designs. Grounding also provides a stable reference voltage (typically 0V) for all circuits in the system and supports reliable operation. Grounding connected to the shield provides a low impedance path that removes unwanted energy from the protected system.
Gaskets and sealing sleeves are also important
Gaskets and seals are specialized structures for EMI shielding and grounding, respectively EMI gaskets fill gaps and seams in the enclosure that are affected by EMI leakage, both into and out of the system.
Gaskets are typically located where they are regularly removed for maintenance. They can be realized using metal mesh, conductive elastomers and conductive foam. Gaskets usually do not require a ground connection.
EMI Sealing Sleeves, also known as Cable Sealing Sleeves, are used when shielded cables penetrate the enclosure. The sealing sleeve is designed to securely attach the cable shield to ground. Cable glands also provide protection against moisture and dust, e.g. IP66, and can act as a strain relief.
Rectangular EMC connectors
Rectangular EMC connectors utilize EMI gaskets, sealing sleeves and other forms of shielding and grounding. They are typically designed for through-board mounting and can have two gaskets, one between the bottom of the connector and the bulkhead, and the other between the two halves of the connector shell (Figure 2).
Figure 2. Rectangular EMI connector with conductive coating on the housing, two gaskets and a cable sealing sleeve to ensure maximum EMC performance. (Photo: ILME)
The surfaces of the contact washers should be electrically conductive for optimum performance. The contact between the cable shield and the cable sealing sleeve should ensure an even and complete connection to ground.
Cable shields are sometimes connected to the ground of the connector. This can result in EMI coupling to other parts of the connector, which can degrade EMC performance. Connecting the cable shield to the connector may also result in discontinuities in the shield, creating EMI leakage points.
Circular EMC Connectors
In circular EMC connectors, the basic elements of continuous shielding and effective grounding are realized in different ways. For example, EN3645 is an ultra-compact circular connector specification widely used in military, aerospace and industrial applications. It is available in a variety of sizes with various contact arrangements and coupling methods. These connectors are specifically designed to support high levels of EMC.
The EN3645 connector has a continuous metal-to-metal bottom with no gap between the two halves of the connector for maximum EMI grounding. The connector is grounded when the housings meet, even before the contacts engage. Other design features include (Figure 3)
Silicone seals maximize tear resistance and sealing memory.
Self-locking threaded coupling.
Continuous metal-to-metal touchdown for maximum EMI grounding.
High-strength trapezoidal threads ensure continuity between housings.
Grounding finger provides dedicated ground connection for EMI protection.
Extended mounting holes for flexible installation of standard EN3645 box or wall sockets.
Contact retention system ensures uninterrupted contact under severe vibration.
Figure 3. Cutaway view of the internal design features of the EN3645 subminiature circular connector. (Photo: TE Connectivity))
Summary
EMC connectors are important in military, aerospace, and industrial systems, where they rely on shielding and grounding to control EMI. They rely on shielding and grounding to control EMI. cable glands and gaskets are important design features to improve EMC performance. Features such as continuous metal-to-metal bottoming and grounding fingers can improve the EMC performance of circular connectors.