Frequency Coded Orientation Insensitive Chipless RFID Tags for Vital Signs Monitoring

Frequency coded chipless RFID (Radio Frequency Identification) tags are commonly used in various applications including Vital Signs Monitoring and are going to replace several existing technologies like barcodes in the near future. There is an increase in demand for Orientation Insensitive Chipless RFID tags in Vital Signs Monitoring keeping in mind the varying postures of subjects. Reflections from the background objects and orientation of the tags are the major problems for the Chipless RFID technology in a working environment for Vital Signs monitoring which can be overcome by the usage of orientation-insensitive RFID tags. Diamond and octagonal slit-shaped RFID tags are designed and presented in this article. These designs have the advantage of reading from any orientation in the roll axis of the tag and RFID reader antenna. The design is compact in nature and encodes 4 bits with the help of four resonators operating in the ISM (Industrial, Scientific, and Medical) band which can be identified as suitable for Vital Signs Monitoring. The designs proposed have a physical footprint of 25 mm $\times25$ mm $\times1.6$ mm designed using FR-4 epoxy substrate and are simulated in a 3D electromagnetic simulator. The design has a read range of approximately 50 cm.