Researchers examine medical RFI from RFID devices
Martin Rowe- November 1, 2009
A research team at the Georgia Tech Research Institute (GTRI) has begun to study the effects that RFID devices may have on medical electronics. The team, headed by Ralph Herkert, director of GTRI's Medical Device Test Center, is working to develop a test procedure that manufacturers of paramedical devices and medical equipment can use to evaluate their immunity to RF signals (Ref. 1).
RFID, currently used for inventory control, has potential hospital and healthcare facility applications for tracking medical supplies, equipment, and even patients. Widespread introduction of the devices leads to potential RF immunity problems. Device manufacturers test their products for RF immunity, but no standard test protocol currently exists.
Ralph Herkert, director of the GTRI Medical Device Test Center, leads a team investigating how RFID devices can cause RF interference with implantable medical devices and stand-alone medical equipment. His goal is to develop test protocols for the medical-device industry. Ultimately, Herkert wants to determine if test instrumentation can be used to simulate the RFID signals, thus providing the means for performing repeatable tests without the need for a myriad of RFID equipment. T&MW Senior Technical Editor Martin Rowe spoke with Herkert by telephone on October 8, 2009.
Q: How can RFID devices interfere with medical devices?
A: The problem comes from electromagnetic emissions. Both paramedical devices and medical equipment could be subject to RF interference. There has been some concern as RFID is becoming more ubiquitous, and is being used in many new ways. When RFID first came out, it was more or less kept in the distribution chain, so the potential for people and other equipment being exposed to it was somewhat limited. But, as the uses for RFID continue to be developed, the potential for more and more interactions with other things increases.
Q: What sort of devices is RFID going into that would put it in proximity with medical devices?
A: It's used right now, being rolled out in a lot of hospital environments and healthcare facilities for tracking their assets. There are a lot of uses for it that are still being developed, such as tracking patients and pharmaceuticals. It's pretty limitless on how it could be used to make things more efficient because of the way it works. Basically, it's a way for tracking things and passing information wirelessly without the need for a lot of intervention from end users. That makes it a very useful technology for many applications.
Q: What's the frequency range that RFID uses?
A: It varies greatly, all the way from low frequency systems that are 125 kHz to 135 kHz, all the way up through HF, UHF, and 2.45 GHz systems. It is my understanding that there are also ultra-wide band systems available as well.
Q: Is any one facility likely to use such a wide frequency range, or would a hospital more or less standardize on one type?
A: More or less, I think that they would standardize on certain ones that worked well for the applications that they needed it to be used for. But when people are developing new applications for RFID, they may not always think about the other things that may be around that could be affected at those frequencies.
Q: Are the higher frequencies more of an interference problem than low frequencies?
A: My main experience is with implantable devices, which are likely to have sensing circuitry. For these devices, the lower frequencies usually can be more of an issue. In order to perform their required functions, these devices have to detect bodily functions, so they need pass bands where the signals that they're trying to detect can get through. In these instances, the lower frequencies can be more of an issue because they can get in through the pass bands that must be left open. Sometimes the higher frequency fields are modulated or pulsed in a way that also allows them to get through.
Q: Tell me about the procedure or the equipment process that you're working on.
A: We envision that the testing protocol will be similar to other testing that we regularly do here at GTRI, with some required changes. At GTRI, we've tested medical devices since the early 1970's. We started the Medical Device Test Center in the mid-1990s, and at that time the main concern was electronic article surveillance (EAS) systems. These are the anti-theft systems that are found in stores that people are guided through. The merchandise in the store is tagged, and they use the EAS gates to deter theft. But, these systems are constantly emitting their detection fields. We, along with the EAS and medical device communities, recognized that there were potential issues with these systems and some of the available medical devices. We set up the Test Center and continue to regularly test implantable and wearable devices to the fields of the EAS systems.
There are differences and similarities between the EAS and RFID devices. We have an RFID system that has been part of the Test Center for a couple of years. It was designed as a portal system that people walk through for use in a library. But if RFID continues being used for other applications, then people may be exposed to them without knowingly passing by them. RFID systems may exist in a building's infrastructure. So, I envision that in the testing protocol, we can't assume that somebody will be walking by all RFID systems in the same way that they walk through EAS systems. Instead people might be next to the RFID reader antennas or active tags and not realize it because they may not see or recognize them. RFID devices may be on the other side of the wall, you never know. There will probably need to be changes to some of the ways that we've tested devices to other environments.
Also, we're collaborating with AIM Global, the organization that's leading this effort, and MET Laboratories. We are focusing on the implantable and wearable devices while MET Laboratories is leading the effort to test medical equipment.
Q: Do you envision these being tested in some sort of chamber or some sort of isolated kind of environment?
A: In the GTRI Medical Device Test Center, when we are testing with the EAS gates, we are not in a chamber. We just have the actual systems set up and we have a computer-controlled positioner that we can move within or past the systems. We have a default test protocol. If you go to our Web site, you can download it and see how we do the tests. We have defined static tests and dynamic tests. They simulate actual scenarios that are people's normal interactions with those types of systems. We also test to metal detectors and tag deactivators. But as far as needing a chamber, I believe when we first start out testing, we will be using the actual RFID systems. We'll have to determine whether we need to go into a chamber-type environment.
We're also going to look at whether we can generate those same RFID signals with test equipment. That way in the future, when people want to perform the tests, they may not have to come up with a wide variety of RFID systems with which to test. They can just generate the emitted fields with the test equipment. But, we'll have to look at that because it depends on how much we can find out about the fields that are generated by the different types of RFID systems. I know there are standards that the manufacturers adhere to for interoperability, but there still may be some proprietary things that they do that may or may not be easy to determine and duplicate.
Q: Is the signal a pulsed kind of signal where the pulsing encodes the information?
A: Yes, the data is encoded in different ways. I believe another reason for pulsing the signals is when there are multiple antennas in an installation. That's one way they can be multiplexed. If the RFID devices were all using continuous wave (CW) signals, they could also potentially interfere with each other, and they may not meet emissions requirements. Interestingly, for implantable devices, that's one of the ways that some of the potential issues could be alleviated. For some of the higher frequencies, if they were able to just run using CW signals, in all likelihood, we wouldn't see as much interference with some of the implantables.
1. "Avoiding Interference: GTRI is Developing Protocols for Testing Effects of RFID Systems on Medical Devices," Georgia Tech Research Institute, Atlanta, GA. www.gtri.gatech.edu.