Fig. 1. Diagrams of subwavelength trapezoidal metal groove arrays and their coordinates. (a) Structural parameters of trapezoidal metal groove and positive and negative propagation coefficients of electromagnetic field in trapezoidal groove; (b) subwavelength trapezoidal groove containing a large number of thin gratings; (c)-(e) definitions of the scattering coefficients r'a, ta,t'a, ra, and rm of rectangular grating

Fig. 2. Relationship between absorptivity A and groove depth h at different side inclination angles and groove depths. (a) wt=0.3λ; (b) wt=0.4λ

Fig. 3. Absorptivity A as a function of array period Λ when trapezoidal groove array in metal substrate is irradiated by unit plane wave with normal incidence. (a) wt=0.3λ, β=7.5°, h=0.515λ;(b) wt=0.3λ, β=7.5°, h=0.057λ; (c) wt=0.3λ, β=0°, h=0.056λ; (d) wt=0.4λ, β=7.5°, h=0.534λ; (e) wt=0.4λ, β=7.5°, h=0.063λ; (f) wt=0.3λ, β=0°, h=0.065λ

Fig. 4. Absorptivity A of trapezoidal groove in metal as a function of side inclination angle β and groove depth h