EMC Compliance Testing of Electronic Medical Devices

Electronic medical devices are complex instruments. They can not only keep hearts pumping and continuously monitor blood glucose levels, but they also have to keep working without fail in complicated electromagnetic (EM) environments. To keep patients safe, all electronic medical devices must meet electromagnetic compatibility (EMC) standards.

Definitions

The U.S. Food and Drug Administration (FDA) characterizes medical devices as anything that helps diagnose, treat, cure, or prevent diseases. Electronic medical devices are those that physically alter bodily functions without using a chemical reaction that do not serve a cosmetic function.

The agency defines EMC as the ability of a medical device to function safely and effectively in its intended EM environment. By achieving EMC compliance, a device is immune to electromagnetic interference (EMI), and does not emit excessive EM disturbances, or emissions, that might interfere with other equipment. EMI can cause a device to not perform as intended and can lead to hazardous situations, including delays or errors in diagnosis, treatment, or monitoring that can result in serious injury or death.  EMI disturbances can come from phenomenon such as radio waves, power surges, radio frequency (RF) disturbances, and electrostatic discharges (ESD). Figure 1 shows potential sources of EMI. Electronic medical devices must meet emissions limits to minimize interference with other equipment, both medical and non-medical.

Potential sources of electromagnetic interference on electronic medical devices.

Figure 1. Potential sources of electromagnetic interference on electronic medical devices.

Case Study  

In the past, other electronics and medical devices have caused EMI with each other.

In one instance, doctors implanted a dual chamber-pacing system in the left subclavian region of a 79-year-old grandma. The device reported 21 different episodes of EMI over a six-month period. Every occurrence lasted between 12 and 75 seconds with the majority either in the morning or in the evening. The patient felt no symptoms during these times.

Researchers spoke with the family and determined that all of these events coincided with the woman opening up an induction heating (IH) rice cooker. They believe this is the first case of documented inappropriate ventricular pacing by a bipolar pacemaker due to EMI from an IH rice cooker.

An exact reason for the EMI is not clear but the relatively high sensitivity of the medical device could be to blame. Researchers set the pacemaker at 0.3 mV to detect episodes of atrial tachyarrhythmia. When researchers recreated the problem, they did not observe EMI when they raised the device setting to 0.5 mV.

Additionally, the design of the rice cooker could have played a role. The device has unshielded coils, and it increases the magnetic fields when the lid is open to keep the temperature constant, as seen in Figure 2. Researchers say rice cookers are more likely to expose someone to interfering signals at chest height because they are typically kept on a counter.

In this case, researchers suggested that the rice cooker be turned off before opening the lid to avoid the unwanted EMI.

Schematic design of an induction heating rice cooker

Figure 2. Schematic design of an induction heating rice cooker.

Setting Standards

A series of international standards are in place for electronic medical devices and systems that directly apply or transfer energy to the patient. The International Electrotechnical Commission (IEC) sets these standards which the United States, Canada, and the European Union all follow. The primary goal is to ensure patient safety while using medical electrical equipment by minimizing the risk of electrical hazards such as electric shocks or burns.

The IEC 60601 series lays out nearly 100 technical standards for the safety and essential performance of medical equipment. This includes clinical thermometers, infusion pumps, infant incubators, laboratory centrifuges, and medical device sterilizers.

Three of the main IEC 60601 standards are:

  • IEC 60601-1: This is the basic standard that specifies the general requirements for the basic safety and essential performance of medical electrical equipment and systems. It covers aspects such as electrical hazards, mechanical hazards, thermal hazards, radiation hazards, biological hazards, and software safety.
  • IEC 60601-1-2: This standard specifies the requirements and tests needed for EMC compliance. It covers both emissions and immunity aspects.
  • IEC 60601-1-6: This standard specifies a process for a manufacturer to analyze, specify, design, verify, and validate usability. This usability engineering process assesses and mitigates any risk caused by correct use and use errors.

Earning FDA Certification

FDA approved medical devices in 2024.

Figure 3. Medical devices the FDA has approved so far in 2024.

In the U.S., the FDA’s Center for Devices and Radiological Health (CDRH) has been investigating incidents of medical device EMI since the late 1960s. CDRH now has regulatory authority over thousands of medical devices and manufacturers. A list of medical devices that the FDA cleared or approved in 2024 appears in Figure 3.

In 2022, the FDA released new guidance intended to lay out how medical device manufacturers need to demonstrate EMC compliance. It applies to all in vitro diagnostic products and accessories that are electrically-powered or have functions or sensors that are implemented using electronic circuitry.

Intended Use Environments  

To start EMC testing, the intended use environment must be specified. This information will determine the appropriate testing for EM disturbances. There are three intended use environments to choose from including professional healthcare facilities, home healthcare, and special environments. Figure 4 shows examples of typical medical device locations within intended use environments.

After an intended use environment has been selected, designers need to describe each potential malfunction, disruption, or degradation due to EMI that could cause harm to the patient or user. The severity of each instance is placed in one of three categories:

  • Medical device-related deaths and serious injuries
  • Medical device-related non-serious adverse events
  • Medical device-related event without reported or potential harm
Examples of typical medical device locations with intended use environments. Courtesy: FDA.

Figure 4. Examples of typical medical device locations with intended use environments. Courtesy: FDA.

Pass/Fail Criteria

Each medical device’s intended use environment and potential problems determine immunity pass/fail criteria when addressing EMI. The pass/fail criteria are fundamental when determining if the course of EMC testing is sufficient to show that the medical device is safe and performs as intended. Criteria can be different for transient or continuous EM phenomena. Transient phenomena include ESD, electrical fast transients/ bursts, surges, and voltages dips and interruptions.  Continuous phenomena can be conducted and radiated RF disturbances and power-frequency magnetic fields.

Some EMC test standards list general pass/fail criteria, but they are typically not specific to a device’s function, modes, indications for use, intended use, and essential performance. Devices with the same hardware could even have different criteria. For example, an adult ventilator would have different criteria than one for neonatal patients because of the physiological characteristics of the intended patient.

Completing Testing

The FDA suggest following these guidelines when it comes time to start testing:

  • Test the device as a system with all medical device accessories, components, and subsystems connected and functioning as intended. Non-medical equipment that could affect the ability of the medical device to function properly should also be tested as a part of the system, this includes mobile phones, tablets, and computers.
  • If EMC testing is performed on a subsystem level, each subsystem not included in physical testing should be simulated, including any potential third-party medical devices or connections.
  • Medical devices should be tested while configured for their intended use. This means if a device can work in battery and in mains power mode, it needs to be tested in both modes. If batteries need to be tested, they need to be removed and tested separately for immunity to ESD.
  • Patient simulators should be used when appropriate.
  • If a device is intended to use wireless technology the function should be on and communicating with other medical device subsystems or ancillary equipment during EMC testing.

Designers can submit the results for all emissions and immunity tests to the FDA for approval after completing the testing.

Simulating Problems  

The FDA recommends that manufacturers address potential problems early in the design and development process. By discovering safety risks in a timely manner and putting mitigation measures into place, they ensure safety. Ansys EMC Plus simulation makes testing earlier easier.

EMC Plus is a full-platform EM modeling and simulation tool offering design-to-validation workflow for EMC. When it comes to complex devices and platforms, EMC Plus offers a faster time to value experience than similar products on the market. EMC Plus has an easy-to-use user-interface built on Ansys Discovery with automated workflows and wizards to get new users simulating in a fraction of the time. The software also allows for GPU acceleration for faster results. New in 2024R2 is the ability to do specific absorption rate (SAR) modeling.

Application areas include EM environmental effects (E3), full vehicle with cables, EMI/EMC in full devices, and RF de-sense in devices. Full device simulation includes printed circuit boards, cables, and mechanical enclosures and can analyze shielding effectiveness, radiated emissions/immunity, and conducted emissions/immunity.

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