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Triple-band terahertz metamaterial perfect absorber based on nested gold rings for high-performance refractive index sensing: a numerical investigation

JIANJUN LIU1, JIANHUA LONG1, JIAN LI1,*

Affiliation

  1. School of Intelligent Engineering, Shaoguan University, Shaoguan Guangdong, 512005, China

Abstract

A triple-band perfect absorber based on terahertz metamaterials is proposed in this paper for high-sensitivity refractive index sensing. The unit structure is designed with nested gold resonators, consisting of a 0.6 µm-thick gold bottom layer and a resonant layer that includes an outer split ring with four symmetric openings, a middle-closed ring and an innermost closed square ring. Under normal incidence, the absorber generates three near-perfect absorption peaks at 0.8106 THz, 1.1507 THz and 1.5573 THz, with absorption rates of 99.91%, 99.78% and 99.69%, respectively. Owing to its four-fold rotational symmetry, the structure exhibits excellent polarization insensitivity at normal incidence and good angular stability under TE-polarized oblique incidence. Physical mechanism analysis reveals that the low-frequency peak is dominated by the middle-closed ring with a noticeable capacitive interaction with the outer split ring; the mid-frequency peak is governed by the outer split ring and shows the most pronounced inter-resonator perturbation, with a significant inductive interaction involving the middle ring; and the high-frequency peak is led by the inner square ring with comparatively weak hybridization. For an analyte thickness of 16 µm, the three peaks exhibit linear red shifts as the refractive index n increases from 1.0 to 1.6, with sensitivities of 128.93 GHz/RIU, 234.11 GHz/RIU and 260.57 GHz/RIU, respectively, and R² > 0.99. The multi-band, high-linearity response provides multiple spectral readout channels, making the structure promising for label-free refractive-index sensing in biomedicine, chemical analysis and material characterization. This compact and polarization-insensitive design provides a useful platform for terahertz refractive-index sensing..

Keywords

Triple-band absorber, Refractive index sensor, Polarization insensitivity, Wide incident angle stability.

Submitted at: March 4, 2026
Accepted at: Oct. 5, 2026

Citation

JIANJUN LIU, JIANHUA LONG, JIAN LI, Triple-band terahertz metamaterial perfect absorber based on nested gold rings for high-performance refractive index sensing: a numerical investigation, Journal of Optoelectronics and Advanced Materials Vol. 28, Iss. 9-10, pp. 426-441 (2026)