Fig. 1. Flow chart of NCF preparation

Fig. 2. Photos of 0.5 mm thickness few-layer graphene under different magnifying powers. (a)(e) 1×; (b)(f) 5×; (c)(g) 10×; (d)(h) 20×

Fig. 3. Physical photograph and schematic of optical path for CCT-1800 terahertz time-domain spectrometer. (a) Physical photograph; (b) schematic of optical path

Fig. 4. Impact of mass fractions. (a) Schematic of NCF structure; (b) absorption curves under different mass fractions of NCF; (c) change in real part of relative impedance with frequency

Fig. 5. Temperature effect. (a) Photo of sample heating table; (b) absorption curves; (c) average absorptivity as a function of temperature

Fig. 6. Micrographs of nickel foam samples before and after compression. (a) Before compression; (b) after compression

Fig. 7. Compression effect. (a) Absorptivity comparison of nickel foam before and after compression; (b) schematic of multiple interference theory

Fig. 8. Absorptivity curves of few-layer graphene with different mass fractions. (a) 1 mm NCF; (b) 1.5 mm NCF