Multi-State Multi-Resonator Spectral Signature Barcodes Implemented by Means of S-Shaped Split Ring Resonators (S-SRR)

 Abstract — Spectral signature barcodes functional at the S frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide (CPW) transmission line by means of multiple S-shaped split ring resonators (S-SRRs), each one tuned to a different frequency. The main particularity of this work is the fact that more than two logic states (i.e., three or four, depending on the implementation) are assigned to each resonant element. By this means, the total number of bits of the barcode (for a given number of resonators) is increased, as compared to previous approaches based on two logic states per resonator. This multi-state functionality is achieved by rotating the S-SRRs. Such rotation modulates the line-to-resonator coupling intensity, and consequently the notch depth at the S-SRR fundamental resonance. Therefore, by considering three or four fixed rotation angles (or orientations) between the line axis and the S-SRR (for the tri- and four-state multi-resonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation, are achieved. This multi-state strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth is improved as compared to two-state based barcodes or to multi-state barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multi-resonator barcodes with eight S-SRRs (providing 4 8 = 65.536 different codes, or 16 bits) and with nine S-SRRs (equivalent to 18 bits), occupying a spectral bandwidth of 1 GHz and less than 6.75 cm 2 and 8.2 cm 2 , respectively, are designed, fabricated and characterized.