Power supply & EMC coexistence in the medical space

February 24, 2016 // By Patrick Le Fèvre
From gadget to vital, connected devices and the Internet of Things (IoT) are everywhere and we see them gradually changing our lives throughout; the exponential development of small to large products embedding radio-transmitters is developing whilst creating some concerns, in terms of interferences and equipment disturbance, especially in the case of medical applications where it could have severe consequences!

With the multiplication of products transmitting radio signals, it becomes very complex for medical equipment manufacturers to ensure their equipment is secure, using either published IEEE standards or proprietary protocols, which many are operating at unlicensed frequencies in the ISM (Industrial, Scientific and Medical) or in the MICS (Medical Implant Communication Service) bands to properly operate, without interfering in been interfered by other equipment.

Consequently ensuring wireless coexistence in medicals applications, all over the world, regulatory bodies have focused efforts to standardize protocols and processes, which will require from power supplies manufacturers to include “Wireless Coexistence” testing and verification when designing power sources for medical equipment.

When the unpredictable could happen!

As the world would stop without reliable power, the power industry has a long history in building robust power systems. Industry permanently innovates new technology, improving energy efficiency, reliability and safety though out.

With the rapid development of multiple Connected Devices in medical applications, some may be powered by harvesting energy, making them very sensitive to radio interference whilst others might even get their power from radio-waves. Power supplies coexistence with radio signals and need to be considered differently from our previous experiences; especially with medical equipment installed outside professional healthcare controlled environment, such as at home.

As the number of connected devices and radio transmission within medical environments increased, starting in 2010, the number of cases of medical equipment reporting false alarms, having random failures, or malfunctioning, has grown significantly, warning the medical community about the coexistence of multiple radio transmitting equipment that patients' lives might depend upon.

In many cases of reported faults, it was very difficult to pinpoint the exact cause, until in-depth investigations revealed radio interferences were the root cause of the problem. In the US, the Food and Drug Administration (FDA) records malfunctions in a central database “MAUDE”, which includes a growing number of EMC problems.

When welding turns the alarm on

A patient affected by respiration and heart problems was connected to a very advanced ventilator at home, coupled to a wireless cardio-monitoring. The patient’s health was monitored from a remote healthcare center, which received a series of alarms. After calling the patient, who fortunately was doing very well, all alarms were classified as false, motivating the replacement of the monitoring units.

Despite replacing the system, randomly, it was still signaling warnings! Equipment manufacturers conducted thorough analysis, without finding either hardware or software issues. By coincidence a Nurse visiting the patient noticed a strange noise coming from the radio and, at the same time the monitoring alarm came on. Further investigations identified that a nearby industrial company was using a high energy welding equipment, which had a default shielding; radiating radio waves were interacting with the control loop of sensors, trigging alarms.

This example is probably anecdotal but is one of many motivating the medical industry to rethink Electromagnetics Interferences within the medical space ensuring everything works smoothly and safely.