Chipless RF Identification Sensors for Vital Signs Monitoring: A Comprehensive Review

Radio-frequency identification (RFID) technology is prominent in detecting and tracking objects using low-power wireless transmissions. By integrating sensing and identification functions into the RFID reader/interrogator, the system can be capable of monitoring vital parameters, such as temperature, blood pressure, heartbeat, glucose content, the information of individual patients, and so forth in real time. It is also critical for the younger generation besides the elderly to pay attention to vital signs monitoring for diseases, such as cardiac arrest, myocardial infarction, sleep apnea, and tachypnea. Conventional vital signs monitoring methods like sophisticated anesthesia machines, in which different systems are integrated to monitor a patient's heart rate, blood pressure, oxygen saturation, and temperature, are intrusive in nature and cause inconvenience to the users since more dedicated sensors need to be worn. For the enabling of continuous and comfortable monitoring of vital signs, chipless RFID is the best-suited technology because of its tremendous optimization in hardware, lower cost, ease of design, and installation. This article presents various noninvasive methods of monitoring vital signs, like sleep apnea, heart rate, respiration rate, body temperature, and posturography with the help of chipless RFID technology. The article discusses literature related to vital signs monitoring with chipless RFID sensors, smart-sensing materials, and their classification and applications. Chipless RFID data coding techniques like frequency shift coding and hybrid coding are also discussed. Furthermore, some recently published review articles are compared with the proposed article, showing the multifarious features.