The requirements for enclosure electromagnetic
compatibility (EMC) are continually increasing as
In the United States, the Federal Communications
Commission (FCC) establishes the requirements and
regulates the amount of permissible electromagnetic
interference (EMI). In Europe, the Electromagnetic
Compatibility (EMC) Directive 89/336/EEC governs
EMC performance. Japan, China, and other countries
have their own regulations, which in many cases mirror
the US or EU standards.
Electrical device manufacturers have traditionally
turned to metallic enclosures to both reduce emissions
and protect against external noise. In general, metal
enclosures provide the best performance but suffer
from issues with galvanic corrosion and oxidation that
can reduce their effectiveness.
For composites, carbon fibers or other conductive
fillers are added to make the material conductive.
They can result in enclosures with EMI reduction of
up to 40dB over a wide frequency range, which may
suffice for many applications.
The carbon can take different forms, including:
carbon nanotubes (CNTs), graphene platelets, short
or long carbon fibers, carbon microspheres, and
The electrical performance varies with both the type
of filler and its concentration. The bulk resistivity of
TE Connectivity’s CNT-filled plastic, for example,
decreases from 10 Ω-cm to under 1 Ω-cm as the filler
is increased from one to ten percent volume.
The filler also has a significant effect on the strength
of the material: long carbon fibers can result in a
composite strength comparable to that of metal.
There are additional options for increasing the
shielding performance of composite materials.
Electroless plating is a chemical process that deposits a
pure, thin metal coating onto the plastic and provides
a high level of shielding. Stahlin’s nickel shielding, for
example, can provide an average attenuation of 60 dB
over a frequency range of 10 kHz to 10 GHz.
For higher levels of protection, a copper mesh can be
injection-molded onto a composite enclosure to give
shielding of -80 dB up to 25 GHz.
Of course, as much as we EE types might like to think
otherwise, thermal and mechanical factors also play
a role in enclosure selection. Nonmetallic enclosures
are poor conductors of heat, which is a double-edged
sword depending on whether you want to keep heat
out or get rid of it!
Manufacturers of composite enclosures offer a
variety of solutions for applications where heat
dissipation might be an issue, such as thermoelectric
cooling, integrated thermal inserts or heat sinks, and
By some estimate, over 100,000 materials have been
developed over the last 50 years. Given the number
of possible options, it’s desirable to work closely with
a supplier to match composite formulation (including
the filler and EMC performance desired) to the
application requirements. ECN
Low Carbon Steel Lowest cost Coating needed for rust protection Yes
Stainless Steel High corrosion resistance Higher cost than LC steel Yes
Aluminum Rust resistant Lower impact resistance than steel Yes
Lighter than steel Lower corrosion resistance
Polycarbonate High impact resistance Higher cost than PVC No
PVC Lower cost Lower impact resistance No
Low corrosion resistance
Polymer-Fiberglass High corrosion resistance UV deterioration No
Composite High strength-to-weight ratio
Polymer-Carbon High corrosion resistance Higher cost than fiberglass Yes
Composite High strength-to-weight ratio composites
Figure 2: Comparison of different enclosure materials. (Source: ISA)