(color online) Mode 1: (a) simulated E field distribution on x=1.5 mm plane, (b) geometry of unit cell operating in mode 1, (c) equivalent transmission E field of the unit, and (d) sketch of the operation mechanism. Mode 2: (e) simulated E field distribution on x=1.5 mm plane, (f) geometry of unit cells operating in mode 2, (g) equivalent transmission E field of the unit, and (h) sketch of the operation mechanism. Mode 3: (i) simulated E field distribution on x=1.5 mm plane, (j) geometry of unit cells operating in mode 3, (k) equivalent transmission E field of the unit, and (l) sketch of the operation mechanism.