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What’s the Difference between EMI EMS and EMC ?


Electromagnetic interference (EMI), electromagnetic susceptibility (EMS), and electromagnetic compatibility (EMC) are three important electrical engineering concepts that deal with managing electromagnetic emissions from electronic devices. This article provides an in-depth examination of EMI, EMS, and EMC, how they are defined, their relevance to electrical and electronic system design, measurement and testing methods, and best practices to address them.

What is Electromagnetic Interference (EMI)?

Electromagnetic interference refers to any electromagnetic disturbances or signals generated by electrical or electronic devices that can potentially disrupt the normal operation of other equipment.

EMI encompasses a wide range of conducted and radiated electrical noise effects:

  • Radiated EMI – Radio waves emitted and picked up by devices
  • Conducted EMI – Noise transmitted through wires and cables
  • Common Mode EMI – Currents flowing through ground loops
  • Electrostatic Discharge – Short high voltage spikes

Unwanted signals coupling via electrical conduction paths or electromagnetic radiation fields constitute EMI.

Causes and Sources of EMI

There are many potential causes and sources of troublesome EMI:

  • Switching power supplies and converters
  • Motors, relays, solenoids with brush noise
  • Oscillators, clocks, timing circuits
  • Wireless transmitters like WiFi, Bluetooth, RFID
  • Improperly filtered AC power lines
  • Static electricity buildup and discharge
  • Power electronics cycling large currents rapidly
  • Unshielded cables acting as antennas
  • Poor circuit return current flows

Any rapidly switching, arcing or oscillating current flow can potentially generate EMI.

Effects and Impact of EMI

EMI can induce a range of detrimental effects if it interferes with electronics:

  • Signal degradation causing data transmission errors
  • Noise disrupting audio or video signals
  • False triggering of logic circuits or sensors
  • Reduced sensitivity of RF receivers
  • Equipment overheating due to circulating currents
  • Device damage from electrical overstress
  • Interference causing safety hazards or equipment failures
  • Preventing devices from passing regulatory standards

So EMI can reduce performance, corrupt operation, or even permanently damage susceptible electronics.

EMI Units of Measurement

EMI signals are quantified based on:

  • Magnitude – Measured in Volts or Amps
  • Frequency – Hz, kHz, MHz etc.
  • Power – Watts or dBm
  • Field Strength – Volts/meter for radiated emissions

Specific EMI standards define appropriate units, detector types, and measurement distances.

EMI Measurement Equipment

Typical EMI measuring instruments include:

  • EMI Receivers – Swept frequency radiated and conducted emission scans
  • Spectrum Analyzers – View signals across a wide frequency range
  • EMI Test Receivers – Measure peak amplitudes at specific frequencies
  • EMI Probes – Antennas and clips to isolate EMI sources
  • LISN – Line Impedance Stabilization Network for conducted emissions
  • ESD Generators – Simulate and measure ESD events
  • TEM Cells – Enclosed area to test radiated immunity in controlled way

Field probes, current clamps, and other accessories gather detailed emissions data.

EMI Regulatory Standards

Mandatory EMI standards place limits on acceptable electromagnetic emissions from electrical products so they don’t interfere with radio communications services, other equipment, or exceed human exposure levels.

Some major EMI standards organizations include:

  • FCC – Regulates devices used in the United States
  • CISPR – International special committee on radio interference under the IEC
  • ETSI – Covers telecommunications equipment used in Europe
  • VCCI – Voluntary Control Council for Interference by Information Technology Equipment used in Japan

EMI Testing Techniques

To assess and troubleshoot EMI, various testing approaches are utilized:

Radiated Emissions Testing

  • Uses antennas to measure electric or magnetic fields emitted by a product

Conducted Emissions Testing

  • Injects disturbance signals on the power lines and measures emissions coupled to the AC mains

Electrostatic Discharge Testing

  • Delivers high voltage fast transients to equipment via contact or air discharge

Bulk Current Injection Testing

  • Injects RF disturbance into cables to simulate picked up ambient noise

Damped Oscillatory Wave Testing

  • Introduces ringing waveforms into power and signal lines which stress interface circuits

EMI Mitigation Techniques

There are various best practice techniques to reduce EMI in electrical devices:

  • Enclosure shielding to contain emissions
  • Cable shielding to prevent noise coupling
  • Input filter circuits to clean power lines
  • Output filter circuits to clean signals
  • Proper grounding and ground planes
  • Separating noisy circuitry via isolation or distance
  • Careful PCB layout and trace routing
  • Adding ferrites to cables to suppress common mode noise
  • EMI gaskets and contact finger stock for shields
  • Special conductive coatings and paints

With careful design, most electronics can be engineered to minimize troublesome emissions.

What is Electromagnetic Susceptibility (EMS)?


Electromagnetic susceptibility refers to how affected or immune electronic devices are to external electromagnetic interference introduced into their environment.

High levels of radiated and conducted electromagnetic energy exist ambiently:

  • Radio and TV broadcast signals
  • Wireless communications like WiFi, Bluetooth
  • Microwave sources including 5G small cells
  • Magnetic fields from transformers, motors, appliances
  • Electrostatic discharge events
  • Lightning strikes creating intense transient energy
  • Automotive ignition noise
  • Electric power line disturbances

This energy has the potential to couple into susceptible electronics, degrading performance.

Effects of EMS on Electronics

Excessive external electromagnetic energy can induce a range of harmful effects:

  • False circuit switching or activation
  • Noise on analogue signals degrading signal-to-noise ratio
  • Increased bit error rate in digital data streams
  • Physical damage to components from electrical overstress
  • Parasitic power absorption desensitizing RF receivers
  • Scan distortion in video displays
  • Unexpected reboots or lockups crashing systems
  • Permanent physical damage to circuits

Measuring EMS with Radiated Susceptibility Testing

Radiated susceptibility testing evaluates immunity of devices to radiated electromagnetic fields. The basic process involves:

  • Placing device under test inside an electromagnetic shielding enclosure
  • Introducing RF fields over a swept frequency range at defined power levels
  • Monitoring device operation for degradation while under test
  • Determine failure thresholds and margins beyond requirement limits

This method reveals weak points and helps improve robustness.

Improving Electromagnetic Immunity

To reduce EMS, electronics can employ:

  • Shielded enclosures to exclude ambient fields
  • Filtering on all conductive penetrations into enclosures
  • Internal component shielding
  • Proper grounding and ground planes as return paths
  • Cable braid shielding and shield terminations
  • Balanced signal interfaces less susceptible than unbalanced
  • Intrinsic device immunity enhanced by design

Defense in depth through multiple barriers provides maximum protection.

What is Electromagnetic Compatibility (EMC)?

Electromagnetic compatibility refers to the ability of electrical equipment and systems to operate properly together in their intended operational electromagnetic environment without causing or experiencing unacceptable degradation due to unintentional electromagnetic interference.

Establishing EMC requires addressing both emissions and susceptibility.

EMC Regulations and Standards

To prevent interference issues, regulatory agencies impose mandatory EMC regulations on certain classes of electronic products:

  • FCC Part 15 – Electronic device emissions limits for US market
  • CISPR 11 – International radio disturbance characteristics limits
  • CISPR 32 – Sets sound and TV broadcast receiver immunity limits
  • CISPR 35 – Limits for IT equipment emissions and immunity
  • EN 55032 – European standards for multimedia equipment emissions
  • EN 55024 – European generic immunity standard
  • ETSI EN 300 328 – Wideband transmission systems limits in Europe

Products must pass applicable standards to be sold in various geographic markets.

EMC Testing Overview

EMC testing validates conformance to emissions and immunity standards. Some major types include:

Radiated Emissions

  • Antenna probes radiated fields over frequency range
  • Determines unwanted ambient emissions

Radiated Immunity

  • Equipment is exposed to specified field levels
  • Must operate without impairment

Electrostatic Discharge

  • Direct and indirect ESD events applied
  • Verify correct function after ESD strikes

Electrical Fast Transient

  • High repetition transient spikes applied to I/O ports
  • Assesses interface robustness

Surge Immunity

  • Simulates power or signal line surges
  • Tests withstand even during power-off state

And more – harmonics, voltage fluctuation, conductive RF immunity etc.

EMC Design Techniques

To ensure EMC, engineers utilize:

  • Shielding – Contain emissions and exclude ambient noise
  • Filtering – Keep noise from entering/exiting circuits
  • Proper Grounding – Provide return paths and reduce ground loops
  • Cable Management – Prevent resonance and noise coupling
  • PCB Layout – Careful component placement, routing, stacking
  • ESD Protection – Suppress transients at interfaces
  • Isolation Circuits – Prevent conducted paths between noise sources
  • Quality Components – Low noise transistors, clocks, power supplies
  • Testing Margins – Design headroom beyond minimum standards

EMC Computational Modeling

Advanced modeling and simulation techniques help predict and address EMC issues early in the design phase:

  • 3D electromagnetic field solvers can model radiated emissions and susceptibility
  • IBIS circuit models help simulate conducted emissions at interfaces
  • Complex cable models show common mode current flows
  • SPICE modeling generates conducted emissions profiles
  • FDTD and FEM methods solve Maxwell’s equations

These powerful simulations complement hardware testing to reduce EMC issues and costs.

EMC Case Study – Automotive Sensors

Automotive sensors highlight the importance of EMC:

  • Many sensors like lidar, cameras, and radar operate at low power levels and are susceptible to radiated fields and transients.
  • Sensors are bathed in an electromagnetic stew – ignition system RFI, powerful WiFi and Bluetooth signals from mobile devices, increased 5G small cell radiation.
  • Nearby power cabling, controllers, motors, ignition systems, and relay coils generate intense magnetic and electric fields.
  • Load dump transient pulses during jump starting can fry vulnerable electronics.

Without EMC measures, sensor performance would be overwhelmed. Shielding, filtered power feeds, low noise circuit design, transient protection, video signal isolation, and extensive testing allows automotive sensors to function reliably despite the challenging electromagnetics environment.


In summary, addressing electromagnetic interference, susceptibility and compatibility is vital for designing and operating high quality, robust electrical and electronic equipment. EMI must be controlled at the source to prevent emissions from disrupting other devices while EMS requires hardening electronics to operate unaffected by ambient interference. By leveraging EMC engineering, regulatory standards, computational modeling, and comprehensive testing, modern electrical devices and systems can coexist and thrive in densely packed complex electromagnetic environments, enabling today’s electronics-driven world.


Q: How are EMI and EMC related?

A: EMC encompasses both EMI (emissions) and EMS (susceptibility). Controlling interference (EMI) and hardening immunity (EMS) ensures electromagnetic compatibility.

Q: What are the units used to measure EMI?

A: EMI is quantified based on the signal amplitude (dBuV, dBm), frequency (MHz) and distance (meters). Field strength is measured in units of volts/meter.

Q: What is the difference between conducted emissions versus radiated emissions?

A: Conducted emissions are interference signals transmitted through wires and cables. Radiated emissions are noises transmitted through the air as electromagnetic waves.

Q: What are common sources of EMI in electronic devices?

A: Switch mode power supplies, oscillators, motors, relays, wireless transmitters, static discharge, and poor cable shielding are frequent sources of EMI.

Q: How can susceptibility of electronics to EMI be improved?

A: Shielding, power line filtering, cable braid shielding, ESD protection, isolation, proper grounding, and low-noise components enhance immunity to EMI.

What is EMI PCB Design?

PCB EMI designers are constantly plagued with electromagnetic problems. System architecture engineers should still control compatibility and interfering with electromagnetics. Unfortunately, even minor design issues may lead to electromagnetic problems. There are also more general problems with diminishing board designs and faster speeds for consumers.

Electromagnetic compatibility, electromagnetic interference, and electromagnetic sensitivity are the three main challenges.

Electromagnetic compatibility or EMC requires electromagnetic energy production, transmission, and absorption usually utilizing bad architecture. Electromagnetic intrusion (EMI) relates to the undesirable and harmful impacts of EMC and electromagnetic interferences from environmental influences. Too much EMI may cause a product to be faulty or destroyed. Any PCB designer must obey EMC, EMS design rules to minimize the EMI quantity and effects.

What are EMI and EMC in PCB?

PCB electromagnetic interference

Both EMI and EMC are essential things to remember in the field of electronics. EMI stands for electromagnetic interference which is an electrical emission that interferes with most electronic equipment, materials, and RF systems. If an EMI gadget is incorrectly protected, it will not function. EMI can be the product of man-made events or natural events. Both electronics must be protected to secure electrical equipment and materials from electromagnetic radiation. EMI security ensures the devices stay completely functioning and operate without interruption. It may not function if a part is susceptible to interruption.

Each electronic piece of equipment produces electric noise that interrupts cables and wires and creates linked devices issues. EMC is the abbreviation for electromagnetic compatibility which is simply the term for describing the functioning of a computer or mechanism in an electromagnetic context. The distinction between EMI and EMC is that EMI is the word for radiation and that EMC is simply the ability of a radiation device.

What are EMI and EMS in PCB?

EMI (Electromagnetic Interference) and EMS (Electromagnetic Susceptibility) are emissions that are both radiated and carried out. EMI & EMS are unwanted and the fewer the healthier. EMC maintains that the electronic system does not communicate with other equipment. It also means that the system is immune from external intervention.

PCB EMS processes include the production of several diverse components, including engineered design, PCB manufacturing and installation, parts sourcing, turnkey or box construction, and practical testing.

Electromagnetic Interference compliant PCB design:

The use of best EMC practices in PCB architecture allows ensuring conformity with EMC requirements at a far slower pace of convergence than alternative EMC steps. When do you name an EMC-compliant PCB design? Ok, compliance with EMC relies on three prospects.

  • It does not impair other processes.
  • It should not be susceptible to pollution from other processes.
  • Above everything, it does not mess with itself.

Basics and Practical for PCB Design:

Electromagnetic Compatibility (EMC), while sometimes used as the synonym, is, in fact, the regulation of radiated and conducted electromagnetic interference, and weak EMC is one of the key causes for PCB restructuring. Indeed, an estimated 50% of first-run boards struggle because they either emit and/or are sensitive to unnecessary EM.

However, this loss rate is not in all industries. This is mostly due to strict legislation in some industries, such as the medical and aerospace sectors, or that the goods produced are engineered with EMC in mind. For example, smartphone developers live and breathe wireless networking and are known to minimize the possibility of unnecessary radiation.

The most serious problem of EMC is that of designers of PCBs for white products, including toasters, refrigerators, and washing machines, which join the wide variety of wirelessly wired Internet devices. Due to its potentially large capacity, re-spinning PCBs may also introduce delays in product launch. Worse still, product recalls could seriously damage the image and finances of the product.

Through EMI, EMC, EMS can guess the Noise Point in PCB:

There is no paucity of data on EMC architecture, and several organizations use their in-house PCB design and EMC regulations. Other outlets, such as regulatory authorities, IC suppliers, and consumers, may provide guidance. Acceptance of all the instructions at face value can, however, contribute to an over-defensive EMC approach and to project delays. Rules to decide what they refer to the new design can be assessed separately. That said, your simple principles of common sense will still be applicable.

For example, you can suppress noise sources on a PCB.

  • Maintain clock speeds as low as practicable as slow as possible rising edges (within the limits of the requirements);
  • Position the clock circuit at the middle of the floor, unless the clock has to abandon the board too (place it next to the connector),
  • Mount the board and melt the crystals on the clock;
  • Maintain clock loop areas as minimal as possible
  • Location of I/O drivers near the stage where the signals reach and exit the board.


PCB Electromagnetic Susceptibility

EMI is a disruption induced by an electromagnetic disorder that affects a device’s output. EMI may be natural sources, such as electrical storms and solar rays, but other computer devices or electrical systems may normally be more essential. If the disturbance occurs in the spectrum of radio frequency, it is often classified as RFI or RFI interference.

EMC calculates the capacity of a system to function as expected in its common operational area without compromising the ability of other devices to operate in the same environment as intended.

Compatibility and distortion in electromagnetic applications are particularly critical design concerns. If they are not considered early in product production, they can entail an expensive and time-consuming need for product reconstruction to comply with the EMC/EMI test and avoid product malfunction or safety harm.

PCB Design Minimizes Risk:

If a PCB is revamped, it can be prohibitively costly and lead to market delays and a lack of customer interest. If earthling, filtering, and shielding are not taken into consideration, the poor product design (from an EMC or EMI point of view). The product malfunction in the testing and the real world will result in the product becoming defective and not functioning as expected. Good product design incorporating simple PCB EMC concepts, such as efficient protection, grounding, and screening, would increase electromagnetic sensitivity at the same process and reducing electromagnetic radiation.

Testing EMI, EMC, and EMS in PCB:

In an automated device, electromagnetic emissions are calculated using different simulation techniques. In EMC research, machine simulation is also seen as the basic solution. The machine simulation is done using an optimization method to accurately calculate critical parameters. Several precautions are taken for electromagnetic radiation testing in an electrical environment.

  • The finite distance involved field simulation is applied to calculate commonly implemented radiation patterns throughout high power applications.
  • Typical mode current is assessed by considering considerations such as the impedance of the current mode antenna and the dispersed circuit constant.
  • The electric connection between the control and the ground plane would also affect current in common mode.

Raypcb uses a hi-end device and our model to test the frequency response of the electromagnetic radiation from the microstrip structure. We recognize the value of maintaining EMI, so we provide physical observations and design tips to keep your circuit secure and healthy.

Why It’s Important to Follow Electromagnetic Interference:

Electromagnetic disturbance sources are everywhere over us and can be classified in several ways:

  • Electrical circuits are used with human-made EMI. Of course, EMI may originate from environmental conditions such as cosmic noise and lightning, on the other side.
  • Continuous interference is an EMI source that sends a constant signal, which appears most often as background noise. Impulsive interference, commonly triggered by switching devices, lightning, and other non-constant causes, is transient.
  • Narrowband transmissions such as radio may be interfered with by oscillators and transmitters, but these channels often intermittently influence some areas of the spectrum. Interference with broadband impacts strong data signals such as TV which may come from multiple directions, including arc welders and solar noise.

Key Points:

An electrical signal consists of many pre-defined electronic components. If the configuration is not correct, multiple EMI/EMC problems may arise. The design of a PCB for each part has a significant impact on its EMC output and the volume of EMI produced. In developing a PCB, you must be aware of the EMI, EMC, and EMS effects of each variable. Only where proper PCB design practices are used will obtain good EMC efficiency, where designers must either remove the interruption source or defend the circuit against its adverse effects. Finally, the aim is to ensure the expected functionality of the EMC and EMS circuit board.

Electromagnetic compatibility of any integrated device shall be linked to electromagnetic noise production, transmission, and receipt. Electromagnetic noise in a PCB architecture is not a welcome character. We are very careful at Raypcb that signals should not conflict with each other while traces, wires, and even PCBs are operated in unison. EMC upgrades do not introduce additional costs to the finished product of the exact PCB configuration, which is why it is suggested during the initial development process.

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