Georgia Tech Studies Medical Device Interference

What should you do first if you see someone collapse as they are walking out of an electronic retailer or department store? Call for medical help? Attempt to revive them? The best answer may be something not as obvious -- pull them away from the electronic article surveillance systems (EAS) or disable the transmitter. The devices that scan for tags on garments and in boxes to catch shoplifters require a considerable amount of RF to activate these devices. The RF fields can be high enough to interfere with the functioning of some medical devices.

As medical devices become more common in controlling heart rhythms or in dispensing insulin in a diabetic, the impact of RF on these devices has to be considered. Georgia Tech last week said it had expanded testing capability at its research center to help reduce interference from these devices.

Ralph Herkert, manager of the center, said "EAS systems may cause medical devices to do anything from shutting down to invoking therapy at the wrong time--not a good thing if you're wearing a defibrillator, which is supposed to shock the heart when needed."

Although filters can be used to reduce electromagnetic interference in medical devices, information from Georgia Tech indicated that operating frequencies and modulation characteristics of EAS systems and tag deactivators fall in the same frequency band as biological signals, such as the heartbeat. Filtering would not only eliminate the EAS signals but also the very signals that medical devices had been designed to detect.

"Instead of filters, medical device manufacturers must deal with the interference in other ways, such as refining their firmware algorithms," Herkert said.

The Georgia Tech researchers emulated real world conditions by putting a medical device in a tank of saline solution that simulated the characteristics of body tissue and fluid. The tank is moved along a track and exposed the device to nine different EAS systems and five tag deactivators that use various types of magnetic, acoustic-magnetic and RF technologies.

Georgia Tech said, "Although the center initially tested pacemakers and defibrillators, today it conducts research on a variety of medical devices including implantable hearing devices, drug-infusion pumps, neurostimulators, cardiac monitors and glucose monitors."

The researchers also realize that EAS and tag deactivators are not the only threat. Gisele Bennett, director of GTRI's Electro-Optical Systems Lab, which oversees the center, said, "As RFID becomes ubiquitous, testing medical devices against RFID readers and active tags in all frequency ranges will be an essential growth area of the EAS/Medical Device E3 Test Center."