The motivation for shielding an enclosure or structure is often to prevent electromagnetic interference (EMI) or radio frequency interference (RFI) from outside sources leaking in. For example, it is common to shield server rooms to prevent unwanted noise from nearby devices and powerlines leaking in and causing a malfunction. What’s seldom discussed within shielding though is the need to prevent signals generated within the room from escaping outside. 

For residential or commercial buildings, this aspect of shielding is often trivial; however, within military installations where encryption is paramount, signals must be transmitted discretely and with high fidelity to avoid combatant interception.  

Since the 1960s, the standard for containing signal leakage (and thus preserving transmission fidelity to avoid interception) is the telecommunications electronics material protected from emanated spurious transmissions, or TEMPEST. The standard is used to establish countermeasures for unintentional electromagnetic emissions. 

Military bunkers – often constructed decades ago from masonry materials – are highly prone to signal leakage despite their remote locations. Here, signal leakage is electromagnetic energy from communication systems that penetrates the physical boundaries of an enclosure (the walls of the bunker in this example). EMI-transparent materials like plastics, glass and masonry building materials do little to contain electromagnetic energy within the structure. 

Materials that Reduce Signal Leakage

The solution to contain signal leakage is to use electrically conductive materials around the outer parameter of the facility. Though metal sheeting might seem an easy solution for containing signals, it is often impractical to retrofit existing structures. Metal can also be problematic as it is prone to oxidation when exposed to the elements, demanding frequent rework and maintenance. 

Here, electrically conductive coatings are a practical solution to shield bunkers and installations since they are cost-effective, conform to intricate geometries and make it easy to rebuild existing structures.

Water-Based Conductive Coatings for Signal Confinement

MG Chemicals’ water-based conductive coatings are particularly useful for creating a Faraday cage within an enclosed space. These coatings do not contain harmful solvents and therefore do not emit pungent odors that can take days or weeks to fully fade. Further, these coatings are non-flammable, allowing users to store excess materials without risk of ignition. MG Chemicals’ water-based conductive coatings adhere to a variety of substrates – including masonry and other building materials – that make it easy to retrofit older installations. 

The polymer system is highly flexible, allowing it to conform to the finer contours and imperfections of older structures. This feature is highly relevant for containing signals at ultra high frequencies (UHF), where even tiny, millimeter-sized gaps in the shield and cause leaks. Imperfections like holes can be plugged with putties or epoxy and painted over to ensure complete continuity of the shield.

Users must also be aware that conductive paint alone will not eliminate leaks. Fully shielded units require additional materials such as gaskets for doors and filtered connectors for cables to ensure complete signal fidelity.

While the polymer system governs features like adhesion and flexibility, the coating’s conductive flake governs the overall attenuation (ability to contain signals). The choice of which coating system will work depends on the needed attenuation, a measure of reduction in signal strength as a function of frequency. 

MG Chemicals’ 841WBU and 842WBU provide shielding between 20 and 100dB across a broad frequency range. Figure 1 below compares the shielding attenuation of 841WBU (nickel) to 842WBU (silver) from 10 kHz to 40 GHz per the IEEE-299.1:2013 standard.

Water-based electrically conductive coatings are an easy, practical solution to quickly retrofit existing bunkers for EMI containment. These coatings conform to the imperfections of masonry structures, allowing users to create Faraday cages within aged buildings to safeguard highly sensitive transmissions. With these materials, it is easy to redesign old facilities to comply with TEMPEST requirements, eliminating the threat of communication interception by enemy combatants. 

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