Fig. 1. Schematic of (a) metal-insulator-metal 2D meta-absorber and (b) metal-resin 3D meta-absorber. (c) Absorption and reflection spectra of the 2D and 3D metamaterial absorber under y-polarization. (d) Comparison of absorption spectra.

Fig. 2. (a) Fabrication process of the proposed terahertz meta-absorber. (b) Photograph of TPP 3D printing system. (c) Reflection mode of THz-TDS system.

Fig. 3. (a) Schematic of the metal-resin 3D metasurface of arrays. (b) Geometry of the metasurface unit cell structure. Scanning electron microscope (SEM) images of the fabricated metasurface arrays with (c) oblique and (d) top views.

Fig. 4. (a) Images of 3D-printed unit cell from the laser scanning confocal microscope (LSCM). (b) SEM image of rough edges on the structure surface. Cross-section profiles of the proposed meta-absorber along the (c) x-direction and (d) y-direction.

Fig. 5. (a) SEM image of top view. (b) Absorption and reflection spectra of the meta-absorber under y- and x-polarization. (c) Absorption spectra of simulation and coupled mode theory fitting. (d) Real part and imaginary part of the effective impedance Z.

Fig. 6. Distributions of the (a) electric field and (b) magnetic field under y-polarized incidence. Distributions of the (c) electric field and (d) magnetic field under x-polarized incidence.

Fig. 7. (a) SEM image of the collapsed structure. (b) SEM image of the column bottom with higher laser power. Absorption spectra of the meta-absorber with (c) parameter l1 ranging from 100 to 140 μm and (d) parameter h changing from 60 to 80 μm. (e) Gap g of adjacent resonators. (f) Absorption in the case of no metal deposition on the side and underneath.

Fig. 8. (a) Schematic diagram of incident angle of y-polarized incidence. (b) Absorption performance of the meta-absorber with a change of the incident angle from 0° to 88°.

Fig. 9. (a) Reflected TDS signals of metasurface sample and gold reference. (b) Measured absorbance spectra. (c) Calculated absorbance spectra of the analyte with refractive index of 1–1.8. (d) Relative frequency shift of the proposed meta-absorber versus analyte refractive index.

Fig. 10. (a) Measurements of absorbance spectra of DCH with solution concentrations of 0.1 mg/mL, 0.5 mg/mL, 1 mg/mL, 2 mg/mL, 4 mg/mL. (b) Extracted results and (c) contour map between DCH solution concentrations and peak intensity as well as peak frequency.