Monitoring of Vital Signs Using UHF RFID Tags

Technology Overview

This technology uses a method known as near field coherent sensing (NCS), for monitoring vital signs such as heart rate, breathing rate and blood pressure, through modulating radio frequency (RF) signals with mechanical motions from the body and internal organs.

In NCS, RF energy is directed into the body tissue and internal organs by an ultra high frequency (UHF) RF identification (RFID) tag; the movements of the body and internal organs modulate the backscattered signal of the RFID tag. By post-processing the backscattered signal, the vital signs can be derived.

NCS can be implemented as passive RFID tag backscattering or as active RFID tag antenna reflection. The multiplexing technique in passive and active RF transmission facilitates simultaneous sensing for multiple points and multiple persons.

Technology Features & Specifications

An ultra low cost implementation of NCS is done by using passive harmonic RFID tags, where the vital signals are modulated on the harmonic backscattering together with the tag ID. Using harmonic backscattering will isolate the downlink (reader-to-tag) and uplink (tag-to-reader) with a large frequency separation, which increases both the signal to noise ratio and sensitivity.

Besides the ultra low cost, the simple and robust packaging of the passive RFID tag enables its direct integration into fabric material, e.g., in a shirt at the location of the chest to detect breath rate and heart rate.

The NCS method makes use of both the amplitude and phase of the electromagnetic field. The external chest movement when a person breathes can be evaluated accordingly by the phase. The respiration rate can be easily retrieved, and the respiration effort can be further interpreted with the phase variation. The heartbeat signal is modulated on amplitude and is thus immune to the breath movement. With an additional RFID tag at the wrist, differences in timing of the waveforms can be detected, and comparing these differences offers calculated estimates of the blood pressure (BP) through the pulse transit time (PTT).

CDMA protocol is used to enable simultaneous monitoring of multiple persons and also multiple points on the same person.

Potential Applications

Non-contact, non-invasive, continuous monitoring of patients’ vitals such as heart rate, breathing rate and effort, and blood pressure.

Market Trends and Opportunities

Monitoring the heart rate, blood pressure, respiration rate and breath effort of a patient is critical to managing their care, but current approaches are limited in terms of sensing capabilities and sampling rates. The measurement process can also be uncomfortable due to the need for direct skin contact, which can disrupt the circadian rhythm and restrict the motion of the patient. This approach, which does not require direct skin contact, offers two possible implementations: passive and active RFID tags. To minimize deployment and maintenance cost, passive tags can be integrated into garments at the chest and wrist areas. To maximize reading range and immunity to multipath interference caused by indoor occupant motion, active tags could be placed in the front pocket and in the wrist cuff. This system is capable of monitoring multiple people simultaneously and could lead to the cost-effective automation of vital sign monitoring in care facilities.

Customer Benefits

NCS opens up new opportunities for vital sign monitoring with accuracy, patient comfort, convenience and low cost.

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