Fig. 1. (a), (b) Schematic of a planar anapole metamaterial with dumbbell-shaped apertures, which is illuminated by a normally incident plane wave with the electric field along the y axis. The structure parameters are radius R, width G, separation between the two circular cuts W, Px=1,000  μm, Py =500  μm, and the thickness of the stainless-steel sheet t=200  μm. (c) Simulated and Lorentz fitted transmission resonance at 0.26 THz for the planar metamaterial when R=100, W=300, and G=75  μm.

Fig. 2. (a) Surface current in the x-y plane, (b) magnetic field in the x-z plane, and (c) electric field in the x-y plane at the resonance of 0.26 THz for the planar metamaterial. The black arrows represent the direction of the surface current and magnetic field in (a) and (b), respectively. (d) Schematic of the excitation of toroidal dipole T and electric dipole P in the unit cell; M represents the head-to-tail magnetic moment, and j represents the surface current.

Fig. 3. (a) Five leading scattered powers of multipole decomposition for the planar metamaterial, where P, M, T, QE, and QM are electric dipole, magnetic dipole, toroidal dipole, electric quadrupole, and magnetic quadrupole, respectively. (b) Phase of Cartesian P and ikT. The orange dots represent the phase difference between them. The grey dotted line indicates the location of the corresponding resonant transparency at 0.26 THz.

Fig. 4. Transmission spectra of planar metamaterials and corresponding scattered powers of the T and P at resonance (a), (b) with respect to R when W=300  μm and G=75  μm; (c), (d) with respect to W, when R=100  μm and G=75  μm; and (e), (f) with respect to G, when R=100  μm and W=300  μm. The phase difference between P and ikT remains constant at π.

Fig. 5. Three anapole resonance bands produced by varying G when R and W are fixed. In the case of band A: W=300  μm and R=100  μm; band B: W=150  μm and R=50  μm; and band C: W=100  μm and R=33  μm.

Fig. 6. Measured (solid line) and simulated (dotted line) transmission spectra of four anapole metamaterials with different values of G=33, 54, 78, and 95 μm, respectively. Inset: microscopic top view of a fabricated planar anapole metamaterial with R=100  μm, W=300  μm, and G=78  μm.