Modal analysis methods and design of chipless RFID tags with natural fractal shapes

Chipless Radio Frequency Identification (RFID) tags are receiving more and more attention. Chipless tags lead to minimizing the fabrication cost of RFID System and maintaining the good electromagnetic performance. The main goal of this thesis is the synthesis of the electromagnetic signature of fully printed chipless RFID tags based on their eigenmodes. Given the possibly large interference from the environment and the extraction of rich information from the tag based on its shape is considered the main challenge of the design of the chipless tags. In this thesis two important contributions are presented: First, a design of a chipless tag is proposed based on the experimental characterization of a printed antenna with natural fractal geometry in terms of impedance matching, etc. The complex shape of the tag with a unique electromagnetic signature allows the minimization of the tags’ falsification. Second, an eigenmodes approach is proposed to control the current distribution on a scatterer. The technique is based on the Method of Moments and on the Singular Value Decomposition. A methodology is developed based on the proposed eigenmodes approach to selectively excite certain modes on the tag using multiple near-field excitation. A beamforming process is also used on receive to realize a selective sensitivity to particular modes. The methodology leads to the extraction of an independent spectral signature for the tag and to better distinguishing if from its environment. Besides, the eigenmodes approach has been reformulated through an integration of the Gram matrix, so as to minimize the influence of the structures’ discretization on the responses from the tag. The proposed eigenmodes technique can be exploited for different applications such as MiMO, imagery, banknotes security, etc...
(FSA - Sciences de l'ingénieur) -- UCL, 2017