Dec 12, 2017Researchers at Cornell University have found a way to use an RFID signal for more than merely identifying a unique tag or linking a tag to a sensor. The solution that the team has tested—and hopes could be commercialized—instead uses the RFID signal to measure human or animal health. The system, which the team developed and tested this calendar year (the first prototype was completed in April), focuses on the modulation of an RFID tag transmission to a reader that would indicate the vital signs of a person within range of the tag and reader. RFID signals, transmitted via coupling to a person's body, can reach a reader with signal properties that indicate that person's vital signs.
The system has been tested with UHF RFID tags and readers on people and rats at the university to prove that RFID can collect vital signs, such as respiration rate and effort, heart rate and blood pressure, without touching a person or animal. If the researchers are able to team up with an RFID technology partner for productization, they hope the solution could be used in the health-care market or for animal testing and research.
No one, whether human, rodent or other animal, enjoys being handled by others as they collect vital signs. The process of attaching cuffs or body electrodes is inconvenient for a patient and his or her care provider, while vital-sign collection can be downright distressing for rats that must have a spot shaved before a sensor can be attached to their skin.
In seeking a less invasive method for collecting vital-sign information, the team is employing RFID technology in an untraditional way. Professor Edwin Kan co-authored the resulting paper, which was published this month at Nature Electronics (see Monitoring Vital Signs Over Multiplexed Radio by Near-Field Coherent Sensing).
A harmonic UHF RFID tag and reader work well with the system, Kan says A harmonic RFID system employs a separate spectrum for downlink and uplink signals between the tag and reader, as opposed to conventional RFID systems in which the downlink and uplink are in the same band, though modulated differently. In the case of human patients, a tag is placed within the near field of the individual motion source (such as a patient's heart). Because the system could operate with multiple patients at any given time, users could link a particular tag's unique ID number with a specific patient. To ensure that the tag remains within close range of that individual, Kan says, it can be attached to clothing, or a chip and antenna could be sewn directly into an outfit. It could also be worn on a wristband.
When the tag is interrogated, its signal is altered slightly by environmental conditions in the near-field region; the Cornell system is designed to measure and interpret those changes as the radio waves pass through the person's body. The heart, for instance, moves blood, and both the presence and movement of liquid alters the backscatter of an RFID tag's response to a reader. Kan likens vital signs to hitchhikers, explaining that when the reader interrogates a passive UHF tag, it responds with a transmission coupled with the body, and the modifications based on the movement inside the body (within a few hertz) act as information that "hitches a ride" on the transmission back to the reader.
The collected data could be managed and interpreted in back-end software that receives the information from a reader, Kan says. Alternatively, he adds, it could be managed on the reader itself, as a software-defined radio (SDR) using a microcontroller built into the reader. The computation is much less than required for an audio or video signal, he notes.
Since the system measures movement, it can identify when and how often a person's lungs inflate and deflate (indicating a breath), when his or her heart pumps, and the individual's blood pressure, provided that two tags are used, each measuring the time of a heartbeat. The system could calculate the time lapse between two heartbeat measurements in order to understand the patient's blood pressure. The tags could also be placed near an eyebrow to track eye movements.
Kan continues to work on modifying the system to improve the accuracy of RFID signal measurements. He says the team is seeing a 98 percent accuracy rate of vital sign measurements when used with normal motion, though he would like to bring that ratio closer to 100 percent. "The main interference comes from sudden motion in the room," he states, especially the motion of a patient whose vital signs are being measured. Because sudden motion could interfere with the results, he says, the present system is better designed for health-care applications rather than something like sports, in which an individual wearing a tag would be likely to be in motion at any given moment.
For monitoring animals, Kan says, the applications are intriguing. For instance, rats undergoing laboratory testing could have their vital signs measured without the need to shave them or apply probes. According to Kan, the team attached an RFID tag to each rat by building the tag into a neck harness worn by the animal. However, he has also been able to capture the necessary data from an RFID tag antenna on which the rodent is laying down.
Because transmission data can be collected continuously, Kan adds, the solution compiles considerably more data points than the periodic measurements of vital statistics from wired blood-pressure cuffs or manual vital-sign measurements. "In that way," he states, "we have much more data" than a traditional system. The solution has also been tested on approximately eight people, including Kan himself. Now, he says, "We need a partner to take it from prototype to product."
