Understanding EMC Connectors and how they protect against EMI

Electromagnetic compatibility (EMC) connectors are primarily used in military, aerospace, and industrial applications to provide enhanced protection from electromagnetic interference (EMI). Power and signal connections must have access to the system. Those access points can be weak links in EMC performance.

EMC connectors and cabling systems often have features like enhanced shielding, EMI gaskets, cable glands, 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. The four sources of EMI. (Image: Lapp)

Shielding and grounding

Shielding and grounding are basic tools for controlling EMI. They work together to prevent unwanted interference from entering a system, contain any EMI generated by the system, and prevent interference with nearby systems.

EMI shields and grounds use copper, nickel, aluminum, and other conductive metals and carbon-based conductive materials like graphite, graphene, and carbon nanotubes.

Shielding reflects or absorbs EMI to produce a barrier. It can take the form of conductive enclosures, coatings, tapes, foams, metal braids, etc. Shielding must be properly grounded to absorb EMI effectively.

Grounding is often associated with safety and is required for most system designs. Grounding also provides a stable reference voltage (usually 0V) for all the circuits in a system and supports reliable operation. Ground connected to a shield provides a low-impedance path, removing unwanted energy from the protected system.

Gaskets and glands can also matter

Gaskets and glands are specialized structures that implement EMI shielding and grounding, respectively. An EMI gasket fills gaps and seams in enclosures subject to EMI leakage, either into or out of the system.

Gaskets are often found in locations that are periodically disassembled for maintenance. They can be implemented using metal meshes, conductive elastomers, and conductive foams. Gaskets don’t generally need a ground connection.

EMI glands, also called cable glands, are used when shielded cables penetrate an enclosure. The gland is designed to connect the cable shield to the ground securely. Cable glands also offer protection from moisture and dust, such as IP66, and can act as strain relief.

Rectangular EMC connectors

Rectangular EMC connectors employ EMI gaskets, glands, and other forms of shielding and grounding. They are often designed for bulkhead mounting and can have two gaskets, one between the bottom of the connector and the bulkhead and another between the two halves of the connector housing (Figure 2).

Figure 2. Rectangular EMI connector with a conductive coating on the housing, two gaskets, and a cable gland to ensure maximum EMC performance. (Image: ILME)

The surfaces that contact the gaskets should be conductive for the best performance. The contact between the cable shielding and the cable gland should ensure a uniform and complete connection to the ground.

The cable shielding is sometimes attached to the connector’s ground. That can result in coupling the EMI into other parts of the connector and inferior EMC performance. Connecting the cable shielding to the connector can also result in a discontinuity in the shield covering, creating a point for EMI leakage.

Circular EMC connectors

In circular EMC connectors, the basic elements of continuous shielding and effective grounding are implemented differently. For example, EN3645 is a widely used subminiature circular connector specification for military, aerospace, and industrial applications. It’s available in various sizes with various contact arrangements and coupling methods. These connectors are specifically designed to support high levels of EMC.

EN3645 connectors have continuous metal-to-metal bottoming with no gaps between the connector halves for maximum EMI grounding. The connector is grounded when the shells meet, even before the contacts engage. Additional design features include (Figure 3):

Silicone seals that maximize tear resistance and seal memory.
Self-locking threaded coupling.
Continuous metal-to-metal bottoming for maximum EMI grounding.
High-strength trapezoidal thread for shell-to-shell continuity.
Grounding fingers provide a dedicated ground connection for EMI protection.
Elongated mounting holes for flexible mounting with standard EN3645 box or wall mount receptacles.
A contact retention system ensures uninterrupted contact under severe vibration.

Figure 3. Cutaway view of the interior design features of an EN3645 subminiature circular connector. (Image: TE Connectivity)

Summary

EMC connectors are important in military, aerospace, and industrial systems. They rely on shielding and grounding to control EMI. Cable glands and gaskets can be important design features for improving EMC performance. Features like continuous metal-to-metal bottoming and grounding fingers can enhance the EMC performance of circular connectors.