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In our increasingly wireless world, the air is full of electromagnetic signals carrying data from one place to another. While these new technologies advance our options in security, commerce and entertainment, they also produce potential interference that may cause concern for people with implanted medical devices.

One source of potential interference is the electronic article surveillance (EAS) systems that help retailers, libraries and other establishments prevent theft and track inventory. Also, early signs suggest potential concerns from the radio-frequency identification (RFID) systems that are now coming into more widespread use.

Georgia Tech's EAS/Medical Device E3 Test Center helps manufacturers improve compatibility between implantable medical devices and systems that radiate electromagnetic energy. The Center, which has focused on EAS systems for more than a decade, has recently expanded its operations and facilities to test new types of security and logistical systems - including RFID systems.

"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," explained Ralph Herkert, manager of the Center, which is part of the Georgia Tech Research Institute (GTRI).

Typically, manufacturers use filters to reduce electromagnetic interference, but medical devices pose special challenges. The operating frequencies and modulation characteristics of EAS systems and tag deactivators can fall in the same frequency band as biological signals, such as the heartbeat. Filters would not only eliminate the EAS signals but also the very signals that medical devices are 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.

Researchers at the Center simulate real-world conditions by placing a medical device in a tank of saline solution that simulates the electrical characteristics of body tissue and fluid. The tank then moves along a track that exposes the medical device to nine different EAS systems and five tag deactivators that use various types of magnetic, acoustic-magnetic and radio frequency technologies.

Several tests are performed with the device placed in different orientations to represent how people typically interact with EAS field emissions. Manufacturers use the resulting data to improve products and make sure they meet Food and Drug Administration (FDA) requirements. In fact, the Center's testing procedures have been used to develop a standardized test protocol for medical device and EAS manufacturers.

"By enabling manufacturers of EAS systems and medical devices to work together, the center reduces adversarial roles and minimizes problems before they occur," said Jimmy Woody, who spearheaded the establishment of the Center and served as its manager through 2001.

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. And because today's patients may use more than one medical device, the center has been evaluating possible interactions between different types of devices, such as bone-healing stimulators and implanted cardiac devices.

Most recently, the center has been investigating new types of security and logistics systems that could be potential emission threats to medical devices. For example, more companies are using radio frequency identification (RFID) systems for inventory control. Right now these devices typically are found on warehouse and shipping containers. Yet as costs decline, RFID technology may soon show up in stores on individual products.
In response, GTRI is acquiring RFID systems, which will be set up and used with the center's EAS testing protocols.

"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," said Gisele Bennett, director of GTRI's Electro-Optical Systems Lab (EOSL), which oversees the center.

Photo details:
Georgia Tech Photo: Gary Meek
GTRI Senior Research Engineer Ralph Herkert monitors the output of a pacemaker, which is mounted in a torso simulator in Georgia Tech's EAS/Medical Device E3 Test Center. The facility helps manufacturers improve compatibility between implantable medical devices and systems that radiate electromagnetic energy.