Every electronic device produces some electromagnetic interference, and every one has to keep working in the interference of its neighbours. Electromagnetic compatibility deals with both sides, emission and immunity. As equipment gets smaller, faster and more connected, the question comes up in every industry, with different constraints each time.
This article goes through four sectors with concrete examples. The parts mentioned along the way are described on the page of our EMI gaskets and thermal interface pads.
🔧 EMC in industry: part of the design
Two families of techniques are used. Avoidance acts on the source of the interference: remove it, or lower its emissions. Mitigation acts on the path: filtering and shielding. On the mechanical side, this means enclosures that stay electrically continuous at their seams, and, since a shield also holds heat in, a thermal path for the components underneath it.
🚗 Automotive: more electronics, less room
Electrification puts a great deal of electronics into little space: control units, driver-assistance sensors, radar, infotainment. Interference between them has to be kept under control, and much of it is decided early, as our article on common EMC design mistakes explains.
What is at stake
- Traction inverters, DC-DC converters and on-board chargers are sources of noise.
- Radar, cameras, satellite navigation and infotainment are sensitive receivers, in the same vehicle.
- Plastic housings, chosen for weight, shield only once they carry a conductive layer.
- CISPR 25 sets limits and measurement methods to protect on-board receivers, from 150 kHz to 5,925 MHz.
An example
A traction inverter switches hundreds of volts at high frequency, a short distance from a radar sensor that works with very weak signals. The battery enclosure is another case: its gasket is very long and usually has to seal as well as shield, which is why conductive extruded profiles laid in a groove are used there.
🏥 Medical: immunity as a safety matter
In a hospital, devices work side by side: imaging, monitors, operating-theatre instruments, equipment connected to the patient. For a medical device, EMC is part of safety.
What is at stake
- Monitors and infusion pumps run next to mobile phones, Wi-Fi, RFID readers and electrosurgical units.
- Some hospital areas do not allow mobile phones at all.
- Leaks at the seams of an enclosure have to be reduced, in both directions.
- IEC 60601-1-2 sets the requirements, with levels that depend on where the device is used: a professional healthcare facility or home healthcare.
An example
The door of an MRI room has to close a shielded room many times a day. It carries beryllium copper contact fingers all round its frame, and those fingers are a wear part that has to be kept clean.
For the gaskets and thermal pads used in this field, see our page on EMC for medical devices.
✈️ Aerospace: many sources in a closed space
Passengers are asked to switch off their phones at take-off for an EMC reason: the effect of many small sources adds up. On board, radar, avionics and lightning are the main sources of interference. Our page on EMI shielding for aerospace goes into the parts used.
Technical constraints
- Avionics boxes leak through their covers, access panels and connector cut-outs.
- Weight counts for every part, gaskets included.
- On aluminium, the gasket filler has to be galvanically compatible with the flange.
- Fuel, hydraulic fluid and de-icing fluid attack some materials; vibration is constant.
🛡️ Defence: equipment and platform
Military equipment works among radars, radios and navigation systems packed onto one vehicle or one ship. Two American standards share the subject: MIL-STD-461 covers the emissions and susceptibility of equipment and subsystems, MIL-STD-464 the electromagnetic environment of the complete platform.
Specific needs
- Two surfaces that look flat leave gaps that can radiate like slot antennas.
- At sea, galvanic corrosion between the gasket filler and the flange comes first.
- Fuels and solvents call for a fluorosilicone base.
- Hatches, doors and access panels have to shield and seal at the same time.
The standards are presented on our page about EMC requirements in defence.
A typical case
On military ground vehicles, knitted wire mesh gaskets are used to protect control units and communication equipment. On ships, communication and navigation equipment sits behind hatches and access panels that need the same continuity.
📘 In brief: RTCA DO-160
RTCA DO-160, "Environmental Conditions and Test Procedures for Airborne Equipment", is the reference for equipment carried on aircraft; in Europe it is published as EUROCAE ED-14. It covers:
- the environment: temperature, altitude, vibration;
- radio-frequency emissions, conducted and radiated (section 21);
- radio-frequency susceptibility.
Its tests qualify the finished equipment, not a gasket: a shielding part contributes to the result, together with the joint, the compression and the surfaces.
🔥 A technical point: why EMC and thermal management go together
Miniaturisation puts more components on each board, and with them more interference and more heat. The two meet at the same place: a board-level shield is fitted closest to the source of the noise, which is also where the heat has to be removed.
- A thermal interface material placed between the component and the shield, or between the component and the housing, gives the heat a path out.
- A component that runs even slightly too hot lasts less long.
- A silicone thermal pad fills the gap and stays electrically insulating.
EMC is more than a regulatory box to tick. Vehicles, hospital devices, aircraft and military platforms share the same problem, complex electronics exposed to varied interference, and answer it under different constraints: weight in an aircraft, corrosion at sea, safety at a hospital bed. In each case the result depends on shielding, electrical continuity at the joints and a way out for the heat.
❓ Frequently asked questions
What are examples of electromagnetic interference?
FM radio, between 87.5 and 108 MHz, disturbed by a vacuum cleaner, a drill or an LED driver with poor suppression. The buzz in loudspeakers next to a GSM phone. In industry: a variable speed drive disturbing a communication module in the same cabinet.
How is electromagnetic interference detected?
In an EMC laboratory. Radiated emissions are measured with antennas in an anechoic or semi-anechoic chamber; conducted emissions are measured on the power and signal lines, generally below 30 MHz. Pre-compliance tests during development give an early picture.