A Case Study On EMI/EMC In Medical Devices Using HD Displays
IQwave™ is a device that is used to perform therapy for skin cancer and is one of the most advanced devices for electroporation in the world. The software guides the user/physician to perform the treatment through several steps, each of which has a specific purpose.
More details on the product can be viewed here.
The device has a standard 13-inch screen. The body of the device is made of aluminum. The device has a membrane keyboard with integrated touch.
The device contains a set of capacitors that are used to store the electric energy. The pulses are distributed through a high voltage connector and a high voltage cord to the probe. On the probe, sterile single-use electrodes deliver the energy into the skin.
The GUI software in the device runs on a Single Board Computer or SBC. The user interface guides the physician through the treatment cycle which has different steps, each having a specific purpose.
The Need for EMC/EMI Compliance
IQwave™, being a medical device of class IIA, had to undergo Electromagnetic Interference and Compatibility (EMC/EMI) tests according to the IEC 60601-1-2/CISPR11 standards. We did an EMC test on the device, as is, for compliance to standards. The results from the EMC test showed that the device’s electromagnetic emission levels were higher than the prescribed limits at certain frequencies.
The pre-EMC test’s aim was to identify the source of the excess radiation and find a solution to remove the radiated emission and keep the levels well below the prescribed limits. After a thorough analysis, we realised the EMI/EMC radiations were high and narrowed the issues down to the SBC area.
Identifying The Culprits
We identified three components as being of interest regarding the higher levels of radiation initially. The SBC itself, the LCD panel screen that is used in the device, and, the display driver board for the LCD panel.
After some study and problem identification, we replaced the display driver board with a different chipset that came with EMC/EMI compliance certifications.
The radiation levels did go down but there were still some regions beyond the threshold. We then looked at the LCD, changed its resolution multiple times and tested the results. In compliance with EMC standards, to keep the EMI radiation of IQWave™ device at the prescribed level, an optimal display resolution was chosen.
This change, in turn, disturbed the UI and delivered fragmented images. To make the UI consistent with the newly adapted display resolution, we re-coded the UI component and representation graphs.
It is The Connector, Stupid
Further tests did show reduced radiation levels in most of the regions albeit a couple of spikes that were above the threshold. We used a hand-held frequency sniffer to check around the device and found that the spikes originated from the HDMI cable that connects the SBC to the display driver board. We added ferrite beads on either side of the HDMI cable to suppress radiation.
The final EMC tests revealed that the EMC/EMI radiation were well below the threshold levels as per the IEC 60601-1-2/CISPR11 standards.
This exercise formed a critical part of getting CE certification for the product.