Electromagnetic interference (EMI) is a type of undesirable interference generated within electronics. It can cause them to malfunction or stop working entirely. It is not a big deal if the television powers down or the Wi-Fi slows down. However, EMI affects more than consumer electronics. As the implantable medical device market grows, more people are at risk.
What is EMI and how does it work?
EMI – also referred to as radiofrequency interference when in the radio frequency – is a phenomenon that occurs when an electromagnetic (EM) field disturbs an electrical device’s operation. It is relatively common.
When the EM signals of one device interfere with those of another, noise is generated, disrupting normal functioning. Signal degradation, malfunctions, control signal corruption and physical damage are likely outcomes. These phenomena can manifest as video distortions, slow network speeds, data packet loss, unexpected reboots or fried circuit components.
The two primary types of EMI are narrowband and broadband. Categorisation depends on whether the signals affect a narrow or broad range of frequencies on the EM spectrum. Also, depending on the emission duration, they can be impulse or continuous.
Where does EMI come from?
Conductive EMI is caused by EM signals formed while an electrical system is powered on. Whenever an electric current flows through a circuit, a small magnetic field is generated. Changing electric currents and voltages form EM waves, which all electronics emit to some degree during operation.
Radiated EMI is another form of undesirable interference. EM signals don’t need a physical connection to be disruptive. Instead, they can travel through the air. For example, a microwave may disrupt a Wi-Fi signal.
Sources exist aside from the operation of electrical or electronic devices. Lightning creates high levels of natural EM energy over a wide frequency range. Solar flares are the source of powerful, unpredictable EM radiation. Even auroras can manifest electromagnetic activity when waves in space interact with the particles within the aurora.
How EMI impacts medical devices
Disruptive EM signals create noise, which adversely affects performance. It can lead to malfunctions, signal degradation or operational issues, compromising functionality. Everything from spinal cord stimulators to ventricular assist devices is affected.
All devices experiencing EMI can malfunction or behave unexpectedly. A microwave slowing the network speed is inconvenient, but trivial. It is a different story for medical implants. If those behave in ways they shouldn’t or fail catastrophically, people’s lives are at risk.
Research shows EMI can potentially trigger shocks in permanent pacemakers and malfunctions in implantable cardioverter-defibrillators. Evidence suggests it can occur during surgical procedures if the hospital’s electronics are unshielded. If the implant registers EMI as a cardiac signal, it could stop pacing, leading to bradycardia or even cardiac arrest.
Various symptoms of EMI-induced malfunctions include nausea, shocks, magnetism, vertigo and overheating. They may not be life-threatening, but they are uncomfortable to experience. In more severe cases, the interference could damage the implant, forcing the patient to get a replacement much sooner than anticipated.
Who is responsible for reducing EMI?
Medical device manufacturers are the main entities responsible for protecting implantable medical devices from EMI. The UK Office for Product Safety & Standards requires that electronics supplied in or into Great Britain do not exceed EM disturbance thresholds and operate without inappropriate degradation of their intended use.
Medical device manufacturers are the first line of defence. However, the burden is not theirs alone – those who install, manage or influence implants also have an obligation to protect patients from EMI.
Health care providers should follow the guidelines from the British Heart Rhythm Society, which outline general measures to minimise the risk of potential EMI in the surgical environment. They should also inform patients of the dangers and sources associated with interference.
According to the United Kingdom Health and Safety Executive’s Control of Electromagnetic Fields at Work Regulations, even employers must protect workers from EMI. They are legally required to evaluate EM fields and take action if exposure is excessive. When appropriate, they must also provide training, health surveillance and medical examinations.
Control methods manufacturers use
The three primary control methods medical device manufacturers use to control, block or redirect EMI include shielding, filtering, and reprogramming.
Shielding
EMI shielding involves enclosing electronics within an electrically conductive shell. Even cables and connectors are shielded. The coating blocks external EM waves to safeguard devices from disruptive EM fields.
Filtering
Electronic filters prevent conductive EMI by blocking the interfering EM signals. By suppressing noise, they can maintain a consistent voltage. Low-pass EMI filters are ideal for medical devices because they suppress high-frequency noise while allowing important signals to pass to and from the device.
Reprogramming
EMI exposure during surgical procedures may lead to inappropriate device function. Temporarily reprogramming the device may be the best approach for high-risk cases. A trained cardiac physiologist can conduct the process using a device programmer. Alternatively, an individual can apply a clinical magnet.
Challenges manufacturers still face
Since EMI comes from man-made and natural sources, there is virtually no way to prevent it. Instead, professionals in the electronics and health care sectors must find ways to defend against it.
EMI is relatively common, but may go unnoticed, as it can manifest differently in each affected individual. Given that around 33% of NHS spend is dedicated to implants and prostheses, addressing the risks of interference-induced malfunctions in implantable medical devices is particularly urgent.
Manufacturers, hospitals, employers and patients should work together to maximise device protection while minimising exposure risks. Their ongoing collaboration could help improve patient outcomes and save lives.
Protect implantable medical devices
Protecting medical implants from disruptive EM fields will require intense research and development. Past professionals have already laid the groundwork, but more needs to be done to ensure patients’ protection. With implantables becoming increasingly common, time is of the essence.
About the author:
Zac Amos is the Features Editor at ReHack. With over four years of writing in the technology industry, his expertise includes cybersecurity, automation, and connected devices.
