Designing medical devices for EMC

May 27, 2016 //By Anthony Robinson
Designing medical devices for EMC
The medical technology (MedTech) world, along with the wider healthcare industry, has experienced a trend for more portable and wearable devices in the last few years.

The problem is that these devices require lighter and equally portable batteries and chargers that use switch mode power supplies (SMPS) a technology that is prone to higher electromagnetic interference (EMI), not a useful characteristic for devices intended for use in life critical medical environments. In this article, we look at the implications of designing medical devices in light of changes to European IEC 60601-1-2 EMC regulations.

Battery technology has adapted rapidly to meet demand for smaller, lighter and more powerful devices. Keeping pace with this innovation, customers now demand increasingly lighter, more portable and faster chargers and Accutronics achieves this while providing a highly efficient and low loss power conversion by using SMPS. However, a by-product of the high frequency switching process is that electromagnetic and radio frequency interference (EMI/RFI) is increased.

As medical devices are used in professional and home healthcare environments it's important that EMI levels are minimised to eliminate the risk of chargers and power supplies causing interference and voltage fluctuation of life-critical devices, such as heart monitors and electrocardiogram (ECG) and anaesthesia machines and ventilators. To regulate allowable limits of EMI, European legislation, IEC 60601-1 third edition, regulates the general requirements for the basic safety and essential performance of medical electrical equipment. IEC 60601-1-2 fourth edition is a collateral standard for electromagnetic disturbances and introduces specific requirements and tests.

As part of the design process at Accutronics, an initial customer requirement consultation allows us to develop a top-level medical battery specification. Customers are usually conscious of the fact that they want to create a highly stable device with a very low susceptibility to EMI. However, one of the biggest challenges we face is when battery integration is an afterthought, despite the fact that smart battery features and charging capability drastically affect the user experience and are equally as important as the ergonomic design process.

In order to overcome this challenge, design verification engineers must ensure that electronic design meshes perfectly with mechanical design as well as compliance and approval testing. Some of the more stringent aspects of the EMC regulations require very specific limits on insulation, electrical isolation, impedance, creepage as well as clearance tolerances.

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