Medical Equipment EMC and Electrical Susceptibility Issues
Incidents of medical equipment EMC susceptibility failures highlight the necessity of adequately accessing the electrical and electromagnetic environment of modern medical facilities. Many of these were featured in the January 2020 IN Compliance Banana Peels column. While the need for reliable operation of medical equipment is obvious, this requirement is shared by many types of equipment that involve critical safety concerns. Often product developers depend on compliance requirements for verification of their products capabilities, but this should approach should not encompass the entire product assessment process for safety critical devices.
Understanding Possible Causes of Failures
Electromagnetic Interference (EMI)
EMI can damage electronic circuits or cause intermittent functional anomalies. EMI can be generated by environmental factors. Sources of naturally occurring EMI include:
• Radio Atmospheric – (Sferic) Broadband impulses that occur as a result of lightning.
• Solar Radiations – Including Solar Flares and Aurora Borealis resulting when charged particles emanating from the sun interact with Earth’s magnetic field.
• Cosmic Noise – Radiation caused by planets and other stars other than the sun. (Generally, this does not pose a significant risk to modern electronics.)
EMI can also be caused by other electrical and electronic systems in the proximity of a device. Potential sources of interference include any number of analog or digital sources including the intentional jamming of Wi-Fi devices.
EMI can be classified into broadband and narrowband. Broadband EMI is usually from unintentional radiators. Sources of broadband include power convertors, electrical motors, and digital circuits. Narrowband is usually generated by intentional transmitters. These include TV and radios stations, cellular phones, Wi-Fi and Bluetooth devices. EMI can enter a circuit either by radiated energy or energy coupled onto wiring such as power inputs. These energies are further categorized into radio and magnetic. Magnetic refers to low frequencies generally below 100 kHz. Radio extends from 100 kHz to the GHz range.
Electromagnetic Compatibility (EMC)
Electronic products are potential sources of energy that could interfere with the normal operation of electronic devices in the vicinity. This energy may be transmitted both in radiated and conducted forms. Radiated may be comprised of digital signals generated by the circuitry, energy generated by Point of Load (PoL) voltage regulators, or inappropriate usage of intentionally radiated Bluetooth or Wi-Fi signals (e.g. transmission protocol or excessive bandwidth).
Conducted energy could be introduced onto power or interconnecting cables.
Disruptions to the power supply network can result in intermittent malfunction or damage to electronic products. These effects can be generated by inductive loads such as electrical motors when turned on and off. They can also be caused by lightning strikes or power grid momentary failures.
Electrostatic Discharge (ESD)
ESD can damage circuitry. ESD failures are caused by the rapid transfer of charge (current) and the short duration, high-energy radiated electromagnetic fields generated during the ESD event. The effects of these failures may be immediate or latent (delayed), with the failure mode ranging from a temporary deviation in the subsystem’s specified performance to damage requiring repair or replacement of the device. Electronic systems and components are susceptible to ESD exposure during manufacturing, packaging, transportation, handling, and installation phases of their life cycle. These discharges can occur in any area but are of highest probability in hot dry climates. Discharges often occur as a result of human contact. These discharges can be in excess of 10,000 Volts.
Understanding the Product’s Intended Environment
For any product, understanding the aforementioned causes of susceptibility as they relate to the intended environment of usage is of great importance. A modern medical facility is packed full of electronic devices that are radiating energy and causing electrical supply fluctuations. Medical facilities also have a high density of people that can create ESD events. These same people are also using wireless devices that can cause susceptibility and communication issues for safety critical devices.
For other safety critical products intended environments may include locations such as industrial facilities where electrical disturbances due to switching of highly inductive and capacitive loads are likely to be present. These industrial environments may also have highly radiative and conductive potential for interference due to the usage of heavy machinery emissions.
This critical analysis of a products intended environments including manufacture, transportation, installation, and usage can provide a susceptibility assessment and analysis. This susceptibility assessment and analysis can identify potential causes of susceptibility, provide risk assessment, and lead to a test matrix that will provide essential design verification of a product.
CVG Strategy Expertise
CVG Strategy EMI/EMC consultants can provide susceptibility analysis and recommend appropriate test methodologies to ensure reliable operation of safety critical products. Our team has decades of experience in automotive commercial, aerospace, and defense sector testing. We can also provide assessment for coexistence of products using Wi-Fi protocols.