The next generation of RFI shielding for 5G and IoT
18 March 2021
EMC is the acronym for electromagnetic compatibility, which means the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to other equipment in that environment.
This is achieved by good board design, filtering and RFI/EMI shielding of the enclosure.
In the past, RFI shielding has addressed frequencies mainly of up to 10 GHz, but the requirement for RFI/EMI shielding is continuing to grow with many more electronic devices entering the market. The requirement is also changing, as frequencies used are getting higher and 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 are providing 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 important 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 you have at home, only need to meet the minimum EMC requirement to the same level as street lighting.
The increased number of sensors, communication and control devices that will be 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 a short-range radar of 24GHz to a long range which gives greater accuracy at 77-84GHz. This higher frequency gives better separation between objects that can be confusing for 24GHz systems.
Microwave absorbing pads are also a requirement in these Lidar sensors to narrow the beam of the radar, 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. 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 main frequency band for the launch of 5G. For higher data rates, higher frequencies are required in the millimetre wave bands of 24GHz up to 86 GHz. Even higher frequencies are on the table for the future, but the controversy regarding these high frequencies is rife. There are comments that frequencies at 96GHz can be weaponised with skin-heating effects to fertility problems, headaches, etc., which of course we have all heard about since the introduction of mobile telephone technology, but no evidence of these effects have 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, which will give greater flexibility and a better production layout. The very high speed of 5G will also eliminate lag and improve productivity.
All these 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 component and material manufacturers is to meet the demands of these higher frequencies. As mentioned previously, the demand for 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 comparison between 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 may 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 silicone 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 as 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 0.008?cm at max, giving a shielding effectiveness at 10Ghz of 102db, whereas nickel-coated graphite will have a volume resistivity more than 10 times greater, but will exhibit a similar shielding effectiveness.
Nickel-coated graphite in silicone is the most cost-effective conductive elastomer. It gives excellent shielding characteristics, even though the material is much more resistive than precious metal-plated particle elastomers. This excellent 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 as it is 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 percent less than silver-plated aluminium in silicone and 70 percent less than silver-plated copper in silicone. Kemtron produces 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 its research and development programmes for new materials to meet the growing demands of its customers. This includes new elastomer fillers, elastomer compounds and additive manufacturing of elastomeric materials.
Kemtron is based in Braintree, UK, and, as well as conductive elastomers, manufactures a full range of shielding gaskets and components, providing a comprehensive EMI shielding service to the electronics and enclosure industry.
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