NON-INVASIVE DETECTION OF HUMAN VITAL SIGNS USING CONCURRENT DUALBAND RF SENSOR

Abstract

Conventionally, the human vital signs are detected using invasive methods. A noninvasive detection of the vital signs is an attractive alternative over the conventional methods due to its two-fold advantage over them. Firstly, the attention and cooperation from the human subject under test are optional. Secondly, it does not cause distrace to the human being as in case of conventional methods. In addition, the non-invasive method of human vital sign detection is, in general, free from periodic maintenance. Since 1970s, researchers and academicians started the effort towards the development of RF systems based on Doppler principle for applications like healthcare, military and disaster management. All such reported efforts are characterized by their noninvasiveness and use of a particular single band during measurements. A number of noteworthy overseas research groups like the Centre for Radio Frequency Electronics Research (CREER) in Canada, Radio Frequency Circuits and Systems (RFCS) research group in the University of Florida, Department of Electrical Engineering at the University of Hawaii, Yonsei University in Seoul,Korea and the ’WiPLi’ Lab in the University of Udine, Italy carried out research towards the development of a human VSD Radar. In India, research groups at several premier technological institutes like Centre for Applied Research in Electronics (CARE), IIT Delhi, IIT Kanpur, IISc Bangalore and IIT Roorkee are engaged in the design and development of noninvasive RF sensor for a variety of day-to-day applications. IIT Bombay in Mumbai xiii Abstract is also engaged in the study of biological effects of radiation on the human body. For any non-invasive human vital sign measurement system, the detection accuracy and sensitivity are two very crucial factors. With single band operation, either accuracy or noise sensitivity in detection can be achieved in a particular operation. The challenging issue in front of the existing single band NIVSD system is to bridge the trade off between the detection sensitivity and the amount of noise in the received signal. The performance of the existing single band NIVSD systems may be improved by using multiband operation. While higher frequency allows signal detection even with very minute variations but at the cost of increased noise, the lower frequency band minimizes noise with inferior detection sensitivity. The cross-correlation between the individual base band signals will emphasize significant information present in both the bands while suppressing unwanted signal components. A concurrent multiband system can fulfill these requirements. Hence, this thesis aims at designing and development of a concurrent dualband RF system for human vital sign detection. Multiband transceiver architecture may be implemented using parallel, switchable or concurrent arrangements of the basic functional blocks. Use of parallel system architecture for the concurrent operation is less attractive due to high power consumption, complex hardware and its bulky nature. A switched mode multiband system suffers from the drawback of inconsistent measurement conditions for the same human subject due to switching delay. Consequently, these two schemes are not viable due to one or more reasons like the requirement of a large hardware, high-power consumption, and / or complex radio architecture. The current trend in the area of Microwave / Millimeter wave integrated circuit research is to reduce the system losses, component count and power consumption level so that the RF systems can be used as a portable handheld device. A concurrent multiband system, based on hardware sharing, fulfils all these criteria. In view of this, the present thesis aims at designing and development of a concurrent dualband RF sensor for human vital sign detection. xiv Abstract The research work reported in this thesis focuses on the design, implementation and characterization of a concurrent dualband RF sensor for non-invasive detection of human vital signs. Out of many vital signs, the human life and its existence can be ascertained by virtue of its respiration and heartbeat signal. Hence, respiration and heartbeat signal of the human being are considered as the vital sign for the experimentation. The proposed sensor operates simultaneously at dual frequency bands centered at 2.44 GHz and 5.25 GHz. The sensor prototype is developed using indigenously designed concurrent dualband subsystem and few commercially available components. Finally, a hardware prototype of the proposed RF sensor has been developed and experimentally characterised to validate the concept.