17-02-2022 | | By Kemtron Ltd
EMC is the acronym for electromagnetic compatibility, which refers to the ability of equipment to function in its electromagnetic environment without introducing intolerable electromagnetic interferences. This is achieved by good board design, filtering and RFI/EMI shielding of the enclosure.
In the past, RFI shielding has addressed frequencies mainly up to 10 GHz, but the requirement for RFI/EMI shielding continues to grow with many more electronic devices entering the market. The requirement is also changing as the frequencies being used are getting higher.
Ultra-reliable low latency communications between devices are needed in safety-critical applications requiring real-time access to rapidly changing data, such as Advanced Driver Assistance Systems (ADAS), which are becoming common in new vehicles.
Electric vehicles provide a new market for EMC products with shielding required for battery management systems, DC-DC converters, LED lighting and sensors. The electric vehicle charging infrastructure is also vital as the success of electric vehicles will rely on charging your vehicle quickly. The fast chargers found on motorways and service stations require shielding for the dc-dc converters. Lower power charging points like those at home only need to meet the minimum EMC requirement to the same level as street lighting.
The increasing number of sensors, communication and control devices required for autonomous vehicles means that EMC between them is of the utmost importance. The Lidar used in vehicles for adaptive cruise control is changing from short-range radar 24GHz to long-range, which gives greater accuracy at 77-84GHz. This higher frequency provides better separation between objects, which can be confusing for 24GHz systems. Microwave absorbing pads are also a requirement in these Lidar sensors to narrow the radar beam so that in a cruise control situation, it only measures the distance from the vehicle in front and not vehicles coming alongside. EMC is safety-critical for autonomous driving vehicles, and any interference to the vast number of sensors that will be utilised could be catastrophic.
Another area where frequencies are getting higher is the long-awaited and possibly controversial 5G network. As I understand, European regulators have identified the 3.4-3.8GHz band and plan to harmonise it to make it suitable for 5G.
It will be the primary frequency band for the launch of 5G. For higher data rates, higher frequencies are required in the millimetre wave bands 24GHz up to 86 GHz. Even higher frequencies are on the table for the future, but the controversy regarding these high frequencies is rife. Comments that frequencies at 96GHz can be weaponised with skin heating effects to fertility problems, headaches, etc., which of course we have all heard since the introduction of mobile telephone technology, but no evidence of these effects has been found to be true. High frequency for high data rate 5G will need many more base stations than 4G, and the low power of these base stations should ensure health problems do not become an issue.
For industry, the introduction of 5G opens huge advances in the IoT (Internet of things) or IIOT (Industrial internet of things) with the connectivity of machines, vehicles and systems. Industrial 5G will be a wireless network eliminating cables within that environment, giving greater flexibility, better production layout and the very high speed of 5G will eliminate lag and improve productivity.
New systems based on 5G will need to meet EMC legislation and RFI shielding of the enclosures and components needed. The challenge for RFI shielding components and material manufacturers is to meet the demands of these higher frequencies. As mentioned earlier, the demand up to 10GHz has been the norm, and there is a test standard for conductive elastomers MIL-DTL-83528. This standard is a good tool for comparing shielding manufacturers and ensures good performance. The only problem with these high-frequency requirements is that the standard stops at 10GHz, and the test method is not suitable above this. RFI shielding effectiveness testing at higher frequencies for shielding gaskets is available but not to any recognised standard, so results vary between test methods.
Electrically conductive elastomers are the preferred materials for shielding enclosure seems at higher frequencies. The manufacture of electrically conductive Elastomer is a balance of electrically conductive particle loading and distribution throughout the elastomer base (mainly silicon or fluorosilicone). The distribution must be sufficient to ensure that the particles are in contact with each other to ensure a good conductive path through the Elastomer, but the loading must not be so great to cause the material to lose its elastomeric properties. In short, electrically conductive rubber. The electrical properties of the conductive Elastomer are measured in volume resistivity – ohms-cm and shielding effectiveness stated in dB; however, the two do not directly correlate with each other.
The volume resistivity of silver-plated aluminium in silicone will be max 0.008Ωcm giving shielding effectiveness at 10Ghz of 102db. In contrast, nickel-coated graphite will have a volume resistivity of more than 10 times greater but exhibits similar shielding effectiveness.
Nickel coated graphite in silicone is the most cost-effective conductive Elastomer giving excellent shielding characteristics even though the material is much more resistive than precious metal-plated particle Elastomers. This superior performance can be accredited to the fact that the nickel graphite particles are very irregular in shape and have sharp edges. When the gasket is put under pressure being compressed between two surfaces, the particles dig into the surface, giving very low contact resistance. Graphite is also a good microwave absorber, thereby enhancing the shielding performance. Nickel graphite in silicone costs approximately 60% less than silver-plated aluminium in silicone and 70% less than silver-plated copper in silicone. Kemtron produce a flame-retardant version of nickel graphite in silicone, Tested and approved to the international standard UL94V-0 by Underwriters Laboratories for flame retardancy, file number E344902.
Electrically conductive elastomers can be moulded, extruded and fabricated into complex shapes to suit customers’ requirements.
Kemtron also continues with our research and development programs for new materials to meet the growing demands of our customers. This includes new elastomer fillers, elastomer compounds and additive manufacturing of elastomeric materials.
For further information please contact Kemtron Ltd
on Tel: +44 (0) 1376 348115 Fax: +44 (0) 1376 345885
or visit our web site www.kemtron.co.uk.