Tunable dual-band metamaterial absorber at deep-subwavelength scale

Temperature‐Tunable Terahertz Perfect Absorber Based on All‐Dielectric Strontium Titanate (STO) Resonator Structure

“…Here, the functional STO ceramic material is selected to design the dielectric resonator structure since it has excellent electrical property and has widely been used to design various PAs. [ 36–40 ] The complex relative permittivity of STO material is related to the temperature and frequency. In our interested THz frequency range (0.1–0.3 THz), according to the damped harmonic oscillator model, the frequency‐dependent complex relative permittivity of the STO material can be given as [ 35,36 ] $$$$\begin{equation}{\varepsilon _{\rm{r}}}(\omega ,T) = {\varepsilon _\infty } + \frac{\alpha }{{\omega _0^2 - {\omega ^2} - {\rm{i}}\omega \gamma }}\end{equation}$$$$where the high‐frequency bulk permittivity ε ∞ = 9.6, temperature‐independent oscillator strength α = 2.3 × 10 10 m −2 , and ω is the angular frequency of incident THz wave.…”

“…Figure 1b,c shows the front and lattice views of the unit-cell structure of the designed PA, which is periodic arranged along the x-and y-directions (see Figure 1a For the proposed PA based on all-dielectric STO, the critical CMT can be used to investigate the perfect absorption. [37][38][39][40][41][42] It means that the proposed all-dielectric PA structure can be regarded as a coupling system, and the critical coupling concept can be employed for perfect absorption via coupling the guided resonance to the lossy STO for the normal incident THz wave. [43] The all-dielectric PA enables the phase-matched coupling between the guided resonance and free space radiation, resulting in the extreme confinement of EM field within the MCS structure STO.…”

“…[ 32–36 ] Meanwhile, the dispersion of STO material is not sensitive to a given temperature at a certain frequency range (0.1–0.25 THz). [ 36–40 ] It is worth noting that the larger Re ( ε r ) is favorable for the design of the deep subwavelength THz devices.…”

“…Here, the functional STO ceramic material is selected to design the dielectric resonator structure since it has excellent electrical property and has widely been used to design various PAs. [36][37][38][39][40] The complex relative permittivity of STO material is related to the temperature and frequency. In our interested THz frequency range (0.1-0.3 THz), according to the damped harmonic oscillator model, the frequency-dependent complex relative permittivity of the STO material can be given as [35,36] 𝜀 r (𝜔, T)…”

“…[33][34][35] The STO thin film has extensively been adopted to design THz PAs with tunable absorption since its complex permittivity can be modulated by thermal excitation. [36][37][38][39][40] For example, Luo et al proposed tunable PAs comprising metallic resonator structures with STO layers, which can achieve a broadband tuning range. [36] periodic metal-STO stack array placed on a metallic substrate, which can achieve tunable dual-band stronger absorption.…”