PhD defence « Motion-modulated Chipless RFID and Sensing for Long-range Applications »

Thesis abstract:

This thesis proposes a new type of backscatter communication based on motion-modulated chipless Radio Frequency IDentification (RFID) tags. Basically, the chipless RFID refers to the technique in which fully passive RF tags that mainly consist of resonant scatterers are identified based on their radar backscatter signature. Chipless tags are designed using different RCS synthesis approaches and the detection process of the signal reflected from the tag in a complex environment can benefit from all the radar signal processing methods that have been already developed. In spite of significant improvements that have been achieved in different aspects of the chipless technology during recent years, the read range of this RFID technique is still limited by less than one meter. This read range limitation is essentially caused by the fact that, for definite frequency components in the transmitted signal,  the backscattering from the chipless tag and the huge reflection from the environment share the same frequency components as what has been sent, which cause the chipless tag, as a non-modulated transponder, to not be easily detected. Motion-induced modulations like the micro-Doppler effect are considered in this thesis to be integrated with the chipless RFID technique such that improves the read range of the chipless tags. Motion-modulated chipless RFID is presented as an effective backscatter communication method for the identification and sensing of moving objects at large distances based on coherent reflectometry techniques. 

To clearly explain the concept, the different methods of backscatter communication are classified from a system point of view based on the two fundamental properties of linearity and variation in time. The principle of classical chipless RFID technology and the motion-modulated chipless RFID are described with general mathematical demonstrations, while the performance of the two approaches is compared in terms of read range. Three different types of motion-induced modulation namely phase (Doppler) modulation, polarization modulation, and directional modulation are addressed based on the developed analytical model for scattering from moving resonant scatterers. The modulation process in each case is theoretically described, and the performance of the motion-modulated tag is experimentally verified in terms of identification capability and large read range. The proposed concept has been also employed in real applications such as healthcare monitoring and commercial identification scenarios.

Members of the jury: