Abstract
Terahertz metamaterial biosensor is a label-free affinity sensor that enhances the strength of the local electromagnetic field. It is extremely sensitive to changes in the dielectric constant of the surrounding environment, thereby providing a new method of detecting micro or trace biological samples. In this work, a highly sensitive terahertz refractive index metamaterial absorber sensor for detecting the biological sample is proposed. The sensor consists of two concentric open metal rings and is a multimode resonator. With two independent adjustable operating bands in a frequency range of 0.7–2.5 THz, i.e. 1.079 THz and 2.271 THz, the sensor can observe different electromagnetic effects of the sample in the terahertz band. We evaluate the performance of terahertz sensors with indicators such as absorption characteristics and sensitivity. The sensor possesses the absorption higher than 99.9% in free space. In addition, the large Q value indicates that the sensor provides high frequency selectivity characteristics. Especially, the sensitivity of the sensor achieves 693.7 GHz/RIU, with a minimum refractive index change of 0.004 for the detection of biological samples, which provides good sensing performance. In the proposed sensor, a flexible material with low dielectric constant is used, which has the advantages of biocompatibility and portability and shows high stability at the 0°–60° oblique incidence angle and within 4% fabrication error. Moreover, the detection effectiveness of the sensor is verified by simulation experiments with ethanol-water mixtures. The sensor units designed in this paper have small interactions among them, work stably and are easily fabricated The sensor can significantly enhance the interaction between light and matter and has broad application prospects in terahertz high-sensitivity biosensing detection.
Highlights
We evaluate the performance of terahertz sensors using absorption characteristics and sensitivity
4) (School of Artificial Intelligence and Big Data, Henan University of Technology, Zhengzhou 450001)
Summary
6 μm 时,结构开始交叠,从图中可以看出,ƒ2 红移程度较大,约为 0.47 THz, 这主要是由于内外环之间的相消干涉引起的,当移动距离 8 μm 处,两环完全交. 叉,ƒ2 吸收强度断层式下降。内环沿 x 轴移动时的吸收特性曲线如图 6(b)所 示,ƒ2 变化明显,出现红移、频带展宽、吸收强度下降现象,交叉重叠部分吸收 谱变化较大,在 0.7~2.5THz 范围内只有一个谐振峰,由于检测样品对于每个谐. 6 μm 时,结构开始交叠,从图中可以看出,ƒ2 红移程度较大,约为 0.47 THz, 这主要是由于内外环之间的相消干涉引起的,当移动距离 8 μm 处,两环完全交. 叉,ƒ2 吸收强度断层式下降。内环沿 x 轴移动时的吸收特性曲线如图 6(b)所 示,ƒ2 变化明显,出现红移、频带展宽、吸收强度下降现象,交叉重叠部分吸收 谱变化较大,在 0.7~2.5THz 范围内只有一个谐振峰,由于检测样品对于每个谐. 对传感器性能影响更大。内环旋转一定角度,ƒ1 比较平稳,ƒ2 以旋转 180°为对称 轴,当内环从 0°旋转到 60°时,吸收强度逐渐下降,带宽逐渐变窄,并且在旋转. 60°时,ƒ2 消失;当内环从 60°旋转到 180°时,ƒ2 频带展宽,吸收先增强后降低, 考虑到传感器性能指标,本部分不适于传感检测。图 8(a)展示了内环旋转 60°. 为 36。外环以旋转 180°为对称轴,从 0°旋转到 90°的过程中,ƒ1 吸收强度下降, 带宽变窄至消失,ƒ2 带宽变宽甚至出现多峰情况,并且谐振峰不独立;从 90°旋 转到 180°过程中,ƒ1 吸收强度上升,带宽变宽,ƒ2 变化不稳定,此时,不适用于 传感检测,在复杂不定的检测环境中,可能会造成样品信号紊乱。. 外环开口间隙 g1 是设计中应该考虑的第二个因素,如果其他几何参数保持不变, g1 从 2 μm 增加到 5 μm,模拟的吸收光谱如图 9(b)所示,随着 g1 的增加,谐. 振频率 ƒ1 逐渐向高频移动。原因是 g1 的增加减小了等效电容 C1 及等效电感 L1, 因此,共振频率 ƒ1 最终随着 g1 的增加而增加。此外,共振频率还受线宽 w1 的 影响,w1 从 2 μm 变化到 5 μm 时,模拟并绘制相应的吸收谱,如图 9(c)所示, 共振频率 ƒ1 逐渐向高频移动,这是因为 w1 的增加会产生以下两个效应,一方 面,等效电感 L1 随着 w1 的增加而减小,谐振频率增大,另一方面,w1 的增大. 图 9 传感器几何参数变化吸收特性曲线。(a)外环半径 r1;(b)外环开口间隙 g1; (c)外环线宽 w1;(d)内环半径 r2;(e)内环开口间隙 g2;(f)内环线宽 w2. 两个透射峰,透射峰的半峰宽为 75.9 GHz、80.8 GHz,Q 值分别为 14.5、28.0, 均小于吸波体型 Q 值。这是由于金属反射板增强了入射能量在吸波器内部的相. 器表面覆盖 10 μm 厚不同折射率的分析物时,模拟并绘制对应的吸收特性曲线, 如图 11(a)所示,分析物折射率 n 从 1.3 变化到 1.8 时,两种谐振峰出现明显的. 11(b)所示,Δƒ2 明显大于 Δƒ1,通过线性拟合后,ƒ1、ƒ2 折射率灵敏度分别为 318.9 GHz/RIU、693.7 GHz/RIU,FOM 值分别为 6.5、9.8。许多物质折射率分布
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