Risky Play: A Risk-based Case Study for Common Mode Current Assessment of a Medical Plasma Device

The latest regulations of the European Union require an EMC risk assessment, and reports show an increase in EMI-related adverse incidents for medical devices designed in line with rule-based standards. However, a lack of research on risk-based methodology highlights the need for a better understanding to predict risk arising from radiated emissions and couplings due to common mode currents, beyond standardized measurements. This study investigates whether the common mode current behavior of a medical plasma device can be assessed by measuring and relatively comparing them for five scenarios that represent use- and limiting cases. Additionally, the study examines the dependence of common mode currents and common mode input impedances. It was found that the chosen scenarios establish an upper frequency limit for common mode currents, and knowledge of common mode input impedances alone is insufficient to predict their behavior. The device’s source behavior and mode conversion play important roles. The measurements provide valuable insights into the device’s behavior and can be used to design effective countermeasures to control the risk of radiated emissions and couplings from the device, associated with common mode currents.