Fig. 1. Equivalent circuit model for the TE polarization of (a) a square loop aperture element, (b) a square aperture element, (c) a shorted square loop aperture element; and for TM polarization of (d) a shorted square loop aperture element.

Fig. 2. Operational principle of the model: morphology transforming between two different elements.

Fig. 3. (a) 3D schematic of the unit cell, where Tx =Ty=15  mm, a= 6  mm, b= 5.5  mm, and c= d= 0.5  mm; the plane wave propagates along the z direction. (b) The frequency response obtained from full-wave simulation with different values of θ for both polarizations.

Fig. 4. Morphologies of the sample with external stimulation of (a) high temperature and (b) low temperature.

Fig. 5. Measurement results of the sample at different temperatures under (a) TE polarization and (b) TM polarization.

Fig. 6. Measurement results of the sample at different temperatures under (a) TE polarization and (b) TM polarization for different cycles.

Fig. 7. Distributions of (a), (c) the surface currents and (b), (d) the electric fields for TE polarization under normal incidence when (a), (b) θ= 180° and (c), (d) θ= 130° at 14.3 GHz.

Fig. 8. Distributions of (a), (c) the surface currents and (b), (d) the electric fields for TM polarization under normal incidence when (a), (b) θ= 180° and (c), (d) θ= 130° at 6.8 GHz.