Terminology Used
We'll start be defining some common terms related to Electromagnetic Compatibility.
RFI - Radio Frequency Interference - The result of unwanted noise first recognized as a problem due to electromagnetic energy. This problem was mostly in the 15 kHz to 1000 MHz (RF) range, thus the name.
EMI - Electromagnetic Interference - It was later recognized that the interference could come from as low as DC and going as high as 300 GHz, encompassing the entire electromagnetic spectrum where both radio and microwaves exist. This is the name most commonly used today for this type of interference.
EMC - Electromagnetic Compatibility - It has become more accepted with the recognition that neither the source of the electromagnetic energy nor the receptor circuit really bears the responsibility of the interference. It is now common to define the compatibility of any equipment within its intended working environment. An EMC investigation can include both measuring the noise emitted by a device, as well as the device’s ability to receive disturbance and still function as intended.
Understanding EMI
In any EMI situation, there are generally three components, a source of electromagnetic energy, some form of propagation medium (transmitted via air or a conductor), and lastly a victim.
The source can be a different system, referred to as “inter-system EMI”, or it can exist within the same system known as “intra-system EMI”. In either case, the result is undesirable effects in the receptor circuit.
Effects of EMI
The effects of EMI can range from simple nuisance to all out disaster depending on the affected systems. It can cause interference to TV, radio or telephone, sprinkler controller reset, an automated system malfunction, computer crashes, ATM malfunction, aeronautical communication and control malfunction, cardiac pacemaker or other medical device malfunctions.
The concept of Electromagnetic Compatibility is that devices should perform as expected, without degradation of essential performance within their environment. Other devices in that environment shall not cause interference to critical systems or licensed radio services.
Reasons or Causes of EMI
Some EMI is caused by the unintentional noise emitted by a circuit or device. This can be a side effect of poor signal integrity or signal degradation, fast, high energy transients or pulses. Unintentional sources can include non-linear devices such as semiconductors, inductors etc., power fluctuations, distortions due to reflections, an electromagnetic pulse.
Electromagnetic interference can be caused by intentional radiators as well if the device experiencing interference is not adequately immune to such signals. Common sources are cell phones, wireless networks, and any of the growing number of common wireless devices around us today.
Other sources could include natural phenomenon such as an electrostatic discharge from a touch, lightning strikes nearby, or even a phenomenon known as a coronal mass ejection (CME) following large solar flares during high solar activity.
Some of the causes are controllable, while others are not. In the case of natural causes or intentional sources authorized to operate within the radio spectrum, the focus would be to ensure our device is adequately immune if functional reliability is critical.
Is EMC difficult?
EMC is often considered complex, difficult or even “magical”. Factors that make it complex are orders of magnitude change, the levels of EMI are expressed in logarithmic units of the power ratio of one physical property to another. Types of circuits that contribute can be analog, digital or power circuits. The effects of stray capacitors or inductors are difficult to assess, and electromagnetic fields themselves are invisible.
Electromagnetic compatibility can be very difficult, there is no question, but it's not “magical”. Through our “Learning Center” series we hope to provide you with the basic building blocks to simplify what is often considered a daunting task.
