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. 2023 Dec 25;15(1):43.
doi: 10.3390/mi15010043.

Double-Strip Array-Based Metasurfaces with BICs for Terahertz Thin Membrane Detection

Yanchun Shen  1 , Jinlan Wang  1 , Hongyu Sheng  2 , Xiaoming Li  1 , Jing Yang  1 , Hongmei Liu  1 , Dejun Liu  3
Affiliations

Double-Strip Array-Based Metasurfaces with BICs for Terahertz Thin Membrane Detection

Yanchun Shen et al. Micromachines (Basel). .

Abstract

A double-strip array-based metasurface that supports the sharp quasi-bound states in the continuum (quasi-BICs) is demonstrated in terahertz regions. By tuning the structural parameters of metal strips, the conversion of BICs and quasi-BICs is controllable. The simulated results exhibit an achieved maximum Q-factor for quasi-BICs that exceeds 500, corresponding to a bandwidth that is less than 1 GHz. The optical response of quasi-BICs is mainly affected by the properties of substrates. Resonant frequencies decrease linearly with increasing refractive index. The bandwidth of quasi-BICs decreases to 0.9 GHz when n is 2.2. The sharp quasi-BICs are also sensitive to changes in material absorption. Low-loss materials show higher Q-factors. Thus, the selection of a suitable substrate material will be beneficial in achieving resonance with a high Q value. The sensitivity of DSAs for molecules is assessed using a thin membrane layer. The DSAs show high sensitivity, which achieves a frequency shift of 70 GHz when the thickness of the membrane is 10 μm, corresponding to a sensitivity of 87.5 GHz/RIU. This metasurface with sharp quasi-BICs is expected to perform well in THz sensing.

Keywords: bound states in the continuum; high quality; metasurface; terahertz detection.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Configuration of double-wire arrays; (b) the unit cell of double-strip arrays.
Figure 2
Figure 2
(a) For TE waves, the transmission spectra of DSAs with different L2. (b) For TM waves, the transmission spectra of DSAs with different L2.
Figure 3
Figure 3
(a) The transmission spectra of double-strip arrays with different L2s. (b) The corresponding Q-factor and resonant frequency with L2 changes. (c) The relation between Q-factor and asymmetric parameter α.
Figure 3
Figure 3
(a) The transmission spectra of double-strip arrays with different L2s. (b) The corresponding Q-factor and resonant frequency with L2 changes. (c) The relation between Q-factor and asymmetric parameter α.
Figure 4
Figure 4
(a) The transmission spectrum of DSAs when L2 is 185 μm, where the inset figure is the field distribution of 0.484 THz; (b) field vectors of 0.484 THz for quasi-BICs; (c) field vectors of 0.820 THz for WA.
Figure 4
Figure 4
(a) The transmission spectrum of DSAs when L2 is 185 μm, where the inset figure is the field distribution of 0.484 THz; (b) field vectors of 0.484 THz for quasi-BICs; (c) field vectors of 0.820 THz for WA.
Figure 5
Figure 5
(a) The calculated transmission spectra for different PE thicknesses; (b) the changing trend of resonant frequency and width with the alters of PE thickness d.
Figure 6
Figure 6
(a) The calculated spectra of DSAs for different n; (b) the spectral map for different n; (c) the relationship between n and the resonant frequency and bandwidth.
Figure 7
Figure 7
(a) The calculated spectra with different loss tangent; (b) resonant frequency and bandwidth of quasi-BICs as a function of tanδ.
Figure 8
Figure 8
(a) The calculated spectra with different BSA thicknesses (st); (b) the summary of resonant frequency and frequency shift for different thicknesses (st).
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