On Scattering of Finite-Size and Finite-Volume One-dimensional Photonic Crystal Resonator Tag for THz Identification

A one-dimensional Photonic Crystal (PhC) resonator has been recently proposed as a Terahertz (THz) tag in the transmission mode with a sufficient coding capacity. This paper reports some investigations on the scattering of a finite-size PhC resonator tag in the mono-static mode for THz identification applications. In the mono-static mode, 1D PhC resonator tags are shown to exhibit notched spectral signatures where each tag should have a unique notch position. A complete analysis based on EM simulation and experiments is performed in order to study the effect of the finite extent of PhC resonator tags, in both area and volume, on notch characteristics (its depth and its quality factor). This is essential since notch characteristics influence the tag performance, including coding capacity and probability of notch detection. The notch characteristics of the resonator are shown to heavily depend on its volume (i.e. number of stacked layers). As the number of layers varies, a trade-off between the notch depth and the quality factor for finite-size resonators is reported. Increasing the number of stacked layers improves the resonator quality factor, but also degrades the notch depth, and consequently its discrimination from the spectral signature. EM simulation and measurements performed in W-band show that for a finite-size resonator of 4 cm × 4 cm, the notch disappears for the layer stack (HL)4HDH(LH)4. In addition, based on measurements, it is found that the highest quality factor that can be reached for a resolvable 6 dB depth notch is about 246 for the layer stack (HL)2HDH(LH)2.