Fig. 1. Perfect metamaterial absorber: (a) The schematic of a unit cell; (b) simulation results for the absorption.

Fig. 2. Triple-band metamaterial absorber: (a) Topology structure of the element; (b) equivalent circuit models; (c) measured absorption as a function of frequency for TE mode radiation at different angles of incidence; (d) measured absorption as a function of frequency for TM mode radiation at different angles of incidence^[55].

Fig. 3. Terahertz metamaterial absorbers with broad band absorption: (a) Schematic of the whole unit cell; (b) simulation results of absorption for three different configurations of the I-shaped resonators^[59].

Fig. 4. Schematic geometry of unit cell for the ultra-broadband perfect metamaterial absorber: (a) the 3 D schematic of a unit cell; (b) the bottom layer with the split ring resonator-II; (c) the third layer with the split ring resonator-I; (d) the third layer with lumped resistances^[76].

Fig. 5. Schematic diagram of polarization and angle-independent metamaterial absorber unit cell: (a) Orthogonal polarization insensitive unit cell^[81]; (b) single-band metamaterial absorber unit cell^[84]; (c) four circular sector-based unit cell; (d) eight circular sector-based unit cell^[91].

Fig. 6. Dynamically tunable metamaterial absorber: (a) Tunable metamaterial absorber using varactor diodes^[103]; (b) schematic of the unit cell of the graphene based tunable metamaterial absorber^[105]; (c) liquid crystal tunable metamaterial perfect absorber^[106]; (d) mechanically stretchable and tunable metamaterial absorber^[107].

Fig. 7. Multifunctional reconfigurable 3D metamaterial^[134].