March 30, 2016

Composite Enclosures: Their Effectiveness In EMI Shielding

There are several types of electronic enclosures to reduce electromagnetic emissions emanating from industrial and electronic devices. These include plastic, aluminum, stainless steel, die cast aluminum and rack mount enclosures. Besides these, you’ll also find composite enclosures which are used in the defense and aerospace industry, and is fast penetrating the consumer, medical and automotive sector. When it comes to reinforced composite polymers, they come with the dual benefits of reproducing the strength and durability of metals and providing resistivity to corrosion. Though the proliferation of composites has been slower into the avionics and electrical systems, we have witnessed a higher volume of composite manufacturing for electromagnetic interference (EMI) shields and enclosures.

Composite Enclosures Their Effectiveness In EMI Shielding

Composites are Replacing Metals in EMI Shielding

Though materials like aluminum, nickel and steel alloys have been the preferred choice for electronic enclosures, composites are replacing the metals in a number of applications. As far as metals are concerned, they offer outstanding protection against solvents, gasoline, hydraulic oils and alcohol when used in industrial applications. However, their major downside is that they are not suitable for use in wireless applications because they need an external antenna. This is where composites play a crucial role in EMI shielding. They are made of highly-efficient engineered polymers together with a filler material. Plastics used in electronic enclosures generally have high-temperature and moldable thermoplastic like Polyetherimide (PEI), Liquid Crystal Polymer (LCP), Polyphenylene Sulfide (PPS) or Polyether Ether Ketone (PEEK). Each of them has diverse characteristics and the choice of material is based on the probable fluid exposure and necessary operating temperature.

The fillers used in composite enclosures improve structural strength and leave room for alteration of the variables to offer you the best in terms of electrical, weight, environmental and mechanical performance in your target application. You can choose from filler materials like glass fibers and different types of carbon like nanotubes or microspheres. Besides being used in enclosures, composites are ideal for the medical industry where carbon fiber composites are employed to manufacture micro-biosensors and microelectrodes.

Creation of Complex Shapes:

If you’re using metal enclosures for shielding purposes, you need to stamp them. This process is not only expensive, but also time-consuming, and most of the time, it’s not possible to get the desired shapes. Composite materials are better in this regard as the advanced molding technology helps you produce intricate shapes including partitions, integrated connector shells, standoffs as well as three-dimensional shapes or features.

With selective metallization, you can put circuit traces as well as add shielding. You can even include embedded antennas into your enclosure to make it lightweight.

Shielding Performance:

The need for electronic enclosures is increasing constantly as benchmarks and guidelines for electromagnetic compatibility (EMC) proliferate. The Federal Communications Commission in the US has clearly laid down the standards for EMC compatibility, and also controls the level of permissible EMI. Though manufacturers of electrical devices have always relied on metallic enclosures to lessen emissions or eliminate external noise, metal enclosures have issues like oxidation and galvanic corrosion that may have an impact on shielding effectiveness. This is the reason for choosing composites that come with carbon fibers and other types of conductive fillers to make the shielding material more conductive.

Enclosures with conductive filler material can lead to EMI reduction by up to 40 dB over a huge range of frequency. You’ll get different kinds of carbons such as graphene platelets, carbon microspheres, carbon nanotubes (CNTs), long or short carbon fibers and carbon particles. If you opt for nickel shielding, expect a standard reduction of 60 dB over a frequency scale of 10 kHz-10 GHz. And, if you’re looking for improved shielding effectiveness, you can consider a copper mesh that can be injection-molded into a composite enclosure to provide shielding of -80 dB to 25 GHz.

When choosing electronic enclosures, go for composites. The right shielding supplier who understands your application needs, composite formation and filler requirements for effective EMI shielding, will be able to guide you through the process.


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