Emissions From Medical Devices

The FCC's main concern with RF emissions from electronic devices is possible interference with communications devices such as commercial radio and TV receivers. From the point of view of agencies regulating medical devices (in the United States the FDA), the concern about unintentional electromagnetic emissions extends to the way in which they could interfere with diagnostic or therapeutic medical devices. Note the word unintentional, since these standards do not apply directly to medical devices that intentionally generate electromagnetic signals (e.g., telemetry ECG transmitters, electrosurgery equipment, magnetic resonance imagers) which require special emissions that limit exemptions at specifically allocated frequency bands.

EN-60601-1-2 sets forth requirements for emissions based on the CISPR-11 standard developed by the International Electrotechnical Commission's Special Committee on Radio Interference (CISPR). These requirements address both radiated emissions (i.e., electromagnetic interference coupled to victim receivers over wireless paths), as well as conducted emissions (i.e., electromagnetic interference coupled to power lines and other conductors) from medical equipment.

Emission limits are set based on the type of setting the device will be used. Class A requirements are the least stringent and apply to medical devices intended to operate in areas where receivers are not usually present. Class B requirements apply to equipment that may operate in close proximity to radio and TV receivers, such as in a patient's home or hospital room.

Conducted emissions are tested below 30 MHz, while radiated emissions are tested above 30MHz. Although both emission mechanisms overlap, regulatory agencies set this boundary because low-frequency interference is primarily conducted (since low frequencies do not radiate very efficiently without intentionally designed antenna elements) and high-frequency interference is primarily radiated (since high frequencies are conducted poorly through inductive wires).

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