Electrostatic Discharge (ESD) Risks in Wearable Medical Devices: Evaluating the Standard Test Method and Developing a Current Prediction Model
Pecht, Michael G
MetadataShow full item record
Electrostatic discharge (ESD) is a critical reliability concern for wearable medical devices. In recent years, numerous reports of device malfunction resulting in patient adverse events, and medical device recalls have been attributed to ESD. To mitigate the risk of device malfunction, sufficient ESD immunity standards and accurate ESD prediction models that represent severe discharges during usage are necessary. Thus, ESD test configurations that represent realistic discharges of wearable devices in healthcare applications need to be developed, and the severity of the ESD events need to be compared with the existing ESD immunity standards. The U.S. Food and Drug Administration (FDA) recognizes the IEC 60601-1-2 collateral standards, within which the IEC 61000-4-2 standard is the recommended ESD test method. The severity of the discharges depends on the electrical impedance of the body and the discharging structure. To identify the realistic discharge scenarios for wearable medical devices, the proper body posture, device location, and the realistic discharge setup need to be determined. A research gap in the literature on electrostatic charging of a human body was that only standing posture was considered. Moreover, current prediction models developed in ESD literature are not based on the physical impedance parameters of the human body and the test setup. Through conducting surveys, electrostatic measurements in a local hospital, and conducting laboratory studies in a climate chamber, a large set of electrostatic charging activities performed routinely by patients and hospital personnel were identified. ESD measurements for these scenarios showed that the IEC 61000-4-2 is not sufficient for these devices since the peak currents and maximum current derivatives of realistic discharges were up to 1.9 and 2.4 times larger than the standard specifications, respectively. A physics-based model for current waveform prediction was developed using the electrical impedance of the discharging structure and the human body in the identified postures of standing on the floor, sitting and lying down on a hospital bed and two device locations (hand and waist). Discharge waveforms at spark lengths between 100% to 50% of the Paschen’s length were simulated with reasonable accuracy.