Final Report

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Final Report

Testing RFID Interference with Electronic Medical Devices
ECE4007 Senior Design Project
Section L03, RFID Interference Group
Alexander Adams, Team Leader

Jason Cordero

Eric Faust


December 12, 2008

Table of Contents

Executive Summary ii
1. Introduction 1
2. Test Equipment

2.1 RFID Readers 2

2.2 Electronic Medical Devices 3
3. Experiment Setup

3.1 Preliminary Test

3.2 Incremental Test
4. Results
5. Conclusions
6. Design Discussion
7. References

Executive Summary

Countless industries have found applications for Radio Frequency Identification (RFID) technology to identify or track objects. The health care industry is no exception to this trend, with numerous RFID products being developed and implemented in hospitals and healthcare facilities throughout the United States and around the world. These RFID applications include access control, patient identification, tracking of medical equipment, verifying proper disposal of biological waste, and many more. All of these RFID devices have the potential to improve the quality of healthcare and the efficiency with which clinical services are rendered.

With this growth, there is a growing concern regarding the safety of RFID devices used in proximity to critical care devices. The concern stems from the potential for electromagnetic interference (EMI) to impact the operation of sensitive medical equipment. RFID and medical equipment rely on separate standards and recommended practices for their implementation, but there are limited guidelines regarding their joint operation. Papers have been written about this subject, with at least one prior author claiming to have found an alarming number of EMI incidents.

The study reported in this paper sought to induce EMI artifacts in six electronic medical devices at a hospital in Atlanta, GA using two commercially available RFID readers. Practicality of testing was a critical consideration and, as such, the team sought out experts in the field to provide commentary. Each electronic medical device was subjected to RFID interference testing while operating without a patient connected. The results of this study indicate that safe implementation of RFID in hospitals may be viable, although this study was by no means an exhaustive test of all RFID devices currently used in hospitals.

1. Introduction

It is no surprise that Radio Frequency Identification (RFID) technology has made a mark on various industries around the world. In manufacturing, RFID has led to improved operational efficiency and productivity across a wide range of applications. The retail sector has benefited from better inventory management, improved security and reduced cost [1]. Now, the healthcare industry is seeking to gain from the potential of this remarkable technology. Hospitals are currently using RFID to track the movements of staff, patients and mobile equipment with potential benefits that include reduced treatment errors and improved record keeping. These RFID products have the potential to improve the quality of healthcare and the efficiency with which healthcare services are rendered [2],[3].

Recently, some clinical researchers have expressed concerns about the safety of using RFID readers in close proximity to critical care equipment. These concerns stem from the potential for RF signals to induce current to flow in electrical circuits that control the critical care equipment. The induced current can be of sufficient amplitude to damage electromechanical components or produce life-threatening artifacts. Several papers describing RFID devices in hospitals give at least some treatment to the potential for EMI incidents, and at least one study was devoted entirely to this subject [4].

Given the many life-saving applications of RFID in hospitals, we set out to design an experiment to show that safe implementation of RFID in the vicinity of electronic medical devices may be possible. Several medical devices were chosen based on prior reports of EMI incidents. The EMI tests were performed at a large community hospital in Atlanta, and the testing protocol was modeled after the American National Standards Institute recommended practice for estimating RF immunity (ANSI C63.18) [5], i.e. to obtain results that could be compared with results reported in prior and future EMI studies.

2. Test Equipment

The EMI tests were conducted using two types of equipment-- RFID readers producing the EMI source and critical care equipment functioning as the devices under test (DUT). Given that a room in a hospital could have one RFID tag, multiple tags, or no tags, we decided to test the critical care equipment with no RFID tags, while keeping the RFID reader in a constant discovery mode.

2.1 RFID Readers (Stimuli)

The following sections discuss the motivation for selecting each of the two RFID readers that were used in the experiment with reader specifications in Table 1.

RFID Reader

Frequency Range

Read Range

Output Power

Motorola MC9090-G

902-928 MHz

6.09 cm to 304.8 cm

1W (4W EIRP)

Dynasys Dual Band Reader

13.56 MHz and 134.2 KHz

10.16 cm to 12.7 cm


Table 1. RFID reader specifications

2.1.1 Motorola MC9090-G (915 MHz Passive RFID)

The first RFID reader tested was a Motorola MC9090-G RFID handheld mobile computer, shown in Fig. 1 above. This passive RFID reader operates at 915MHz and was chosen primarily because the hospital that provided the test equipment already uses this reader for inventory tracking. Unlike stationary readers that can be fixed to a ceiling or wall far away from sensitive equipment, the MC9090-G is mobile, increasing the likelihood that it will be operated in close proximity to a critical care device. Also, the RF field generated by this reader is a directional beam that focuses the radiated RF energy onto a relatively small area. These characteristics make the MC9090-G a likely source of EMI.

2.1.2 Dynasys Dual Band RFID Reader (13.56 MHz and 134.2 KHz Passive RFID)

The second reader tested was a Dynasys Dual Band RFID Reader. This passive RFID reader operates at both 134.2 KHz and 13.56 MHz, as described in Table I. This reader was selected because both RFID signals have relatively long wavelengths that can pass around a human body. These wavelengths are commonly used for identifying badges and gaining access to locked doors. The higher frequency of 13.56 MHz is the longest wavelength that contains enough signal content to read multiple tags at the same time. Given the potential for both 134 KHz and 13.56 MHz applications in a hospital setting, the Dynasis Dual Band RFID reader was selected for EMI testing.

2.2 Electronic Medical Devices (DUTs)

Six electronc medical devices were selected for the EMI study, listed in Table II.



Alaris PC 8000

Infusion Pump

SARNS 9000

Cardiopulmonary Bypass Device

Ohmeda RGM 5250

Respiratory Gas Monitor

Medtronic 5388

External Pacemaker

Datascope CS300

Intra-Aortic Balloon Pump

Flo-Lab 2100-SX

Vascular Flow System

Table 2. DUTs and functions

Each device was currently in use at the hospital where the EMI study was performed, and some of these devices were in service for more than 12 months. The rationale for testing each device is presented in the following sections.

2.2.1 Alaris PC 8000

According to a recent study [4], infusion pumps like the Alaris PC 8000 suffered from severe EMI failure, with some models completely shutting down when separated from an 868 MHz passive RFID

reader by as much as 100 cm. This poor EMI performance, along with the serious consequences that could result from a malfunction, made this a good choice for EMI testing.

2.2.2 SARNS 9000

The same study that reported several EMI incidents among infusion pumps also tested the SARNS 9000 cardiopulmonary bypass device and recorded an EMI incident when used in close proximity to an 868 MHz passive RFID reader [4]. It is noteworthy that 868 MHz readers are not used in the US, but the FCC approved 915 MHz reader used in our study comes very close to the same frequency.

2.2.3 Ohmeda RGM 5250

Since the Ohmeda RGM 5250 is a monitoring device, a temporary malfunction would not pose an immediate threat to the safety of a patient. Still, complete device failure for an extended period of time could have life threatening consequences. The unit tested was also one of the oldest monitoring devices still in service at the hospital.

2.2.4 Medtronic 538

The Medtronic 5388 external pacemaker is a critical care device that could injure a patient if ectopic pacing signals were induced by a nearby RFID reader. This particular pacemaker was also selected because a previous study reported significant EMI incidents for this device [4]. During the testing of the Medtronic 5388, a BioTek PMA-1 analyzer was used to evaluate the pacemaker’s performance.

2.2.5 Datascope CS300

The Datascope CS300 intra-aortic balloon pump was also tested because it is another commonly used medical device with a high potential for life threatening consequences in the event of an EMI failure. We were prompted to test this device because a prior study tested a similar device, the Datascope 97 and found that EMI caused this device to stop operating [4].

2.2.6 Flo-Lab 2100-SX

The Flo-Lab 2100-SX is another vital monitoring device that reports critical data about a patient. The data could be distorted by artifacts produced by an EMI; therefore, this device was also tested.

3. Experiment Setup

The experiment consisted of two parts. First, a preliminary test was done to see if any EMI incidents could be induced and to determine a starting point for the second test. If an EMI incident resulting in a loss of critical functionality was observed during the preliminary test, an incremental test was performed to obtain the minimum separation distance between the RFID reader and the medical device before an EMI incident occurred. Fig. 1 shows a flow chart of the experiment starting at the beginning of the preliminary test.

Fig. 1 Experiment Flow Chart

Testing was conducted in the biomedical engineering department of a community hospital in Atlanta. No changes were made to the room in order to produce results that would reflect real world behavior. The room contained several desktop computers and an 802.11 wireless router, and staff members were permitted to enter and exit the office during the test period.

3.1 Preliminary Test

The preliminary test was performed using the selected RFID readers and the critical care medical devices listed above. The medical devices were operated without a patient connected to the equipment, while each RFID reader was swept systematically around the device at measured distances. One experimenter was responsible for moving the reader around the medical device and ensuring that the reader was directed towards the nearest surface of the medical device. Another experimenter watched the medical device looking for any sign of an EMI.

The sweeping of the RFID reader around the medical device continued with the separation distance decreasing until an EMI incident occurred or the reader housing contacted the surface of the medical device. If an EMI incident was observed during the preliminary test, a measurement of the separation distance was recorded.

3.2 Incremental Test

The incremental test was performed for each combination of electronic medical device and RFID reader that experienced a critical EMI incident during the preliminary test. During this test, the RFID reader was attached to one end of a string with discrete markings on it and the other end of the string was held against closest surface of the medical device, as depicted in Fig. 2.

Fig. 2 Incremental Test Setup

The purpose of the string was to maintain an accurate measurement of the position of the RFID reader with respect to the medical device using the length of the string and its angular displacement from a fixed reference orientation. The faceplate reference of the medical device was chosen based on the position of the RFID reader during the preliminary test when an EMI incident was observed, and the initial separation distance was chosen to be 10cm greater than the separation distance that was recorded during the preliminary EMI.

With the RFID reader and medical device connected by the string, one experimenter swept the reader around the device while keeping the string taught and directing the RF energy of the reader towards the medical device. The other experimenter observed the operation of the medical device, looking closely for any signs of an EMI. If no EMI incident was observed, the length of the string was reduced by 5cm, and the EMI test was repeated. When an EMI was observed, the distance and angular displacement values were recorded, and the length of the string was increased by 5cm. The incremental increases were repeated until EMI effects were no longer observed.

4. Results

The only EMI incident to occur during this experiment took place while testing the Ohmeda RGM 5250 and consisted of a speaker buzzing. As this incident did not affect the critical functions of the device, a rough distance measurement was found to be approximately 35 cm and incremental testing was deemed unnecessary.

5. Conclusions

The results of this study indicate that safe implementation of RFID in hospitals is possible at the frequencies and power levels used in this study. This study was by no means an exhaustive test of all commercially available RFID readers or the wide range of critical care devices that are used in hospitals. Hence, this study does not rule out the possibility that some RFID readers may induce life-threatening EMI events when used in close proximity to a critical care device.

When a hospital is evaluating an RFID product, the staff performing this evaluation should carefully consider and test the RFID product in close proximity to critical care equipment to determine whether a life-threatening EMI could occur. It is also important to consider the affects of attaching a patient to a medical device when the patient and medical device are not grounded. In this situation, the patient’s body acts like an antenna, absorbing the RF energy and conducting this energy to the medical device.

6. Design Discussion

Initially this project was intended to have a design component in which the team would design and test covers for the DUTs out of an EMI shielding fabric. Since there were no significant EMI incidents, the cover design was deemed futile for the DUTs utilized. However, that decision is not an indication that the concept of designing a cover or curtain to shield against EMI is without merit.

While the shield concept is designed to reduce EMI in the primary range of the RFID readers themselves, another possibility is that the EMI is being caused by very low frequency spurs generated by the RF bursting. Most commercial RFID readers generate a pulse train consisting of a brief burst and then silence until the next burst. This method of transmission creates spurious harmonics that could be the reason for EMI in some equipment.

There are two plausible methods of correcting for low frequency EMI caused by the bursting pattern. The first of these is to shape the RF bursts in such a way that the spurious signals are diminished. The key to shaping the bursts is to slow the transition time from the silent state to the transmission state. This can be done in a variety of ways such as exponential ramping where the RF signal amplitude grows exponentially and decreases similarly. The second method of correcting for burst pattern EMI is to construct high-pass filters around critical function circuits. This would allow the electronic medical devices to essentially eliminate low frequency noise due to burst pattern EMI while still maintaining a higher frequency of operation.


  1. Bhattacharya, M.; Chao-Hsien Chu; Mullen, T., "A Comparative Analysis of RFID Adoption in Retail and Manufacturing Sectors," RFID, 2008 IEEE International Conference on , vol., no., pp.241-249, 16-17 April 2008.

  2. Ching-Huan Kuo; Houn-Gee Chen, "The Critical Issues about Deploying RFID in Healthcare Industry by Service Perspective," Hawaii International Conference on System Sciences, Proceedings of the 41st Annual , vol., no., pp.111-111, 7-10 Jan. 2008.

  3. Cangialosi, A.; Monaly, J.E.; Yang, S.C., "Leveraging RFID in hospitals: Patient life cycle and mobility perspectives," Communications Magazine, IEEE , vol.45, no.9, pp.18-23, September 2007.

  4. R. van der Togt; E. J. van Lieshout; R. Hensbroek; E. Beinat; J. M. Binnekade; P. J. M. Bakker, “Electromagnetic Interference from Radio Frequency Identification Inducing Potentially Hazardous Incidents in Critical Care Medical Equipment,” JAMA, vol. 299, no. 24, pp. 2884-2890, June 2008.

  5. "American National Standard recommended practice for an on-site, ad hoc test method for estimating radiated electromagnetic immunity of medical devices to specific radio-frequency transmitters," ANSI C63.18-1997 , vol., no., pp.-, 31 Dec 1997.

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