Feature Racks, Cabinets & Enclosures
Waveguides take the heat M
David Wall at Kemtron discusses the importance of ventilation in enclosures and how a new style of waveguides offers a re-enforced structured solution
ost electronic enclosures need some form of air ventilation to keep cool the electronics within. If this is a RFI/EMI shielded enclosure then the overall shielding effectiveness of the enclo- sure can be compromised. For many commercial applications perforated sheet, metal or metallised plastic will suffice but for high performance requirements waveguides provide superior shielding over a wide frequency range. Waveguides can be circular, rectangular or honeycomb shaped. The principle is that of ‘Waveguide beyond cutoff’.
Honeycomb vent structure The honeycomb vent is a series of tubes that acts as a waveguide, guiding electromagnetic waves into or out of the enclosure, but as the tubes are long enough then it attenuates those waves. Typically the tube should be at least three times as long as the diameter. Good practice is four times. Therefore a 3.18mm cell should be 12.7mm long. The most cost effective is alu- minium honeycomb because it offers high shielding performance, light weight and good airflow as it is 96 per- cent open area. A typical shielded enclosure will use two honeycomb ventilation panels one as the inlet and one for the exhaust.
Aluminium honeycomb vents are supplied in an aluminium frame with an emi gasket to ensure a good electri- cally conductive bond with the enclo- sure. Many frame styles are available to suite different mounting methods. Kemtron's standard honeycomb
vent uses two layers of 3.18mm cell by 6.4mm thick laid at 90°, this is known as cross cell. Cross cell honeycomb improves shielding performance by eliminating any polarising effects. Slant honeycomb 30°, 45° or 60° can also be supplied to stop any moisture running back down the honeycomb into the enclosure.
Typical shielding performance of a 12.7mm thick cross cell vent is: 200KHz in H (magnetic field) 71db 100MHz in E (Electric field) 105db 500MHz in P (Plane wave) 93db 2GHz in P (plane wave) 94db 10GHz in P (Plane wave) 90db The company’s standard finish (Kempass) for aluminium vent panels is compliant with the RoHS directive and applies permanganate passivation which is a chromate free, inorganic and non toxic coating. The process produces a dense, uniform coating consisting of aluminium and reduced manganese oxides giving a light yellow colour to the surface. The surface finish is conductive with a low contact resistance. It also meets all requirements of MIL-C- 5541E for corrosion and electrical con- ductivity. Surtec 650, tin or nickel plating finishes are also available. The company are also able to offer a full range of painted finishes to match enclosure finishes or military colours. To help with design requirements there are a range of customisable features available.
David Wall is MD of Kemtron
These include a protective kick plate that can be incorporated in to the vent to prevent damage to the honey- comb. Other vents available are com- mercial grade standard sized fan vents, steel, stainless steel and brass to special order. Kemtron
www.kemtron.co.uk Enter 210
Plastic is fantastic for future growth of cellphone market T
he use of plastic resin in the cellphone market is a multibillion-dollar business, with tremendous growth expected in the coming years. The global market for molded plastic components used in cellphones is set to amount to $3.5 billion in 2013, up from $3.3 billion in 2012, according to a report by IHS. In terms of weight, total plastic resin usage in all cellphones - smartphones and other mobile handsets included - will increase to 336,000 metric tons in 2017, up from 282,000 metric tons in 2013. “Plastic components are becoming increasingly important in mobile handsets, and especially in smartphones,” said Kristin Squires, chemicals industry consultant with IHS. “Amid rising competition in the market, smartphone original equipment manufacturers (OEM) are seeking ways to drive down costs for raw materials, manufacturing and assembly. plastic offers multitude ways to cut these expenses.”“Plastics components allow for a
Electronics OCTOBER 2013
great deal of design flexibility as well as product and functional differentiation,” said Don Bari, Senior Director, Chemicals Consulting, for IHS. “OEMs are using a plastic resin called acrylonitrile butadiene styrene (ABS), along with polycarbonate and ABS/polycarbonate blends. By using these plastics in the product housings, the OEMs can offer lightweight products that are visually attractive to customers.” The cellphone market offers opportunities for a large variety of plastic resins including ABS, polycar- bonate, nylon and polymethyl methacrylate (PMMA). ABS and polycarbonate are both attractive materials for exterior components due to their strength and aesthetic appeal. Polycarbonate cellphone housing may have a chemical coating to improve its scratch-
resistance.In addition to enclosures, plastics are used in many applications. IHS
www.ihs.com
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