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图1(a)为所设计结构的几何示意图,该结构是由两个带有单间隙的环形金属带交错重叠组成的,单元结构沿X、Y轴周期性地排列以形成阵列,每个单元结构的周期为200 μm×160 μm。仿真计算表明,当参数d从10 μm变化到30 μm时,谐振谷的Q值保持在8.5~9左右。因此笔者选择了d=10 μm来缩小超表面芯片的大小。优化后的几何参数如下:g=4 μm,w=5 μm,R=40 μm,d=10 μm。超表面通过单步光刻制造,随后通过热沉积镀上金膜。由金膜制成的图案(厚度为200 nm)附着在厚度为22 μm聚酰亚胺柔性衬底上。结构中的双磁矩模式被垂直于超表面平面(Z轴)入射的太赫兹波激发,其电场极化(Ey)沿间隙(Y轴)方向。
图 1 (a) 双磁矩环偶极子单元结构图;(b) 0.551 THz处的透射谱;(c) 双磁矩模式形成示意图;(d)多极子的远场散射功率
Figure 1. (a) Unit cell of dual torus toroidal structure; (b) Transmission spectrum at 0.551 THz; (c) Schematic diagram of toroidal dipole formation; (d) Far-field scattering power of multipole
利用CST微波工作室仿真工具,基于有限元法对结构进行了全波电磁仿真,并研究了双磁矩模式共振的机理。首先在单元上设置了沿X、Y轴方向的条件边界条件,沿Z轴方向设置了开放边界条件,计算了所设计的双磁矩模式的透射谱,如图1(b)所示。在0.551 THz处观察到明显的共振。为研究此共振的特性,笔者对其共振频率下的表面电流进行了数值模拟,如图1(c)所示。最左侧月牙型环路与右侧圆形开口谐振环路的表面电流分别以顺时针和逆时针的方向流动(蓝色箭头),产生方向相反的两个磁场,形成左侧首尾相连的闭合磁场,从而沿Y方向引起环形磁矩;由于镜像对称,最右侧月牙型环路与左侧圆形开口谐振环路的表面电流分别以逆时针和顺时针的方向流动(紫色箭头),形成的两个方向相反的磁场首尾相连,在右侧激发另一个环形磁矩。与大多数环偶极子超表面结构中单环形磁场模式相比,所设计的超表面支持新的双磁矩模式,从而可以进一步增强光与物质的相互作用。
结构的多极矩的远场散射功率计算公式为[18]:
$$ {{I}}=\frac{{2\omega }^{4}}{{3c}^{3}}{\left|{\overrightarrow{{P}}}_{x}\right|}^{2}+\frac{{2\omega }^{4}}{{3c}^{3}}{\left|{\overrightarrow{{M}}}_{z}\right|}^{2}+\frac{{2\omega }^{6}}{{3c}^{5}}{\left|{\overrightarrow{{T}}}_{y}\right|}^{2}+\frac{{\omega }^{6}}{{5c}^{5}}{\left|{Q}_{e}\right|}^{2}+\frac{{\omega }^{6}}{{20c}^{5}}{\left|{Q}_{m}\right|}^{2} $$ (1) 式中:第一项表示电偶极矩Px远场散射能量;第二项表示磁偶极矩Mz远场散射能量;第三项为环偶极矩Ty远场散射能量、第四项为电四极矩Qe远场散射能量;第五项为磁四极矩Qm远场散射能量。图1(d)给出了多极子的远场散射功率[19],通过计算电偶极子Px,磁偶极子Mz,环形偶极子Ty,总四极子Q(电四极子Qe和磁四极子Qm之和)的远场散射功率可以看出,在共振频率附近,电磁偶极子和电四极子都被强烈抑制,环偶极子占主导地位。
接下来,利用双磁矩结构仿真了两种检测方法:(1)直接将原油样品滴覆于结构表面上,即原油样品层与超表面结构无缝贴合;(2)在超表面结构上无缝贴合一张聚碳酸酯滤膜,随后将原油样品滴覆于滤膜上。这里假定原油样品的折射率为1.4[20]。对于超表面结构上27 μm的原油样品有(无)滤膜的情况进行了模拟,如图2(a)所示,传感器的灵敏度按照公式(2)计算,得:
$$S=|\partial f/\partial n|$$ (2) 根据理论仿真结果,当折射率n从1(空气)变化到1.4(原油)时,对于第1种检测方法,谐振频率f的漂移为54 GHz,计算出的灵敏度为135 GHz/RIU。而对于第2种检测方法,谐振频率漂移为49.2 GHz,计算出的灵敏度为123 GHz/RIU,由此可见,检测中引入滤膜对检测灵敏度产生的影响较小。图2(b)~(e)所示为图2(a)中4种情况下共振频点处的磁场图,4个频点处的磁场强度相差很小。由于滤膜可以有效保护高灵敏检测芯片不被原油污染,在下面的实验中利用滤膜上加原油样品的方法进行太赫兹测试及分析。
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根据所上述理论参数,加工后的芯片的部分结构的光学显微镜图像如图3(a)所示。笔者采用的实验装置为太赫兹时域光谱系统(Advantest TAS 7400)。芯片所测得的太赫兹光谱如图3(b)所示,所设计得结构得谐振峰的中心频率位于0.56 THz处,与仿真结果吻合,仿真与实验的误差主要来源于通过热沉积方法制造的金属谐振器粗糙边缘的散射损耗和柔性样品图案可能的不均匀性。
Terahertz dual torus toroidal sensing chip and its application in crude oil detection
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摘要: 原油样品中主要成分的快速检测及产地溯源对国防安全及生态环境等领域意义重大。现阶段的原油成分检测操作复杂、成本高且检测时间较长,无法满足对原油成分的快速检测及原油产地快速溯源的需求。文中结合高灵敏太赫兹检测芯片(基于双磁矩环偶极子)和时域太赫兹波谱系统,测试了不同产地原油样品的太赫兹光谱,发现芯片谐振峰频移呈现不同的规律。且对于原油中两个最主要的指标硫含量和残碳量,可分别根据它们的频移规律进行定量分析。实验数据计算表明:相同产地的原油的谐振频率平均值相对差值平均为4.63%,不同产地的原油的谐振频率平均值的相对差值平均为56.53%,可明显区分出原油的产地。设计的超表面芯片激发了电磁新模式,提供了一种高灵敏度的检测技术,可广泛应用于生物分子实时监测或探测化学物质(如原油)成分检测、产地溯源等领域。Abstract: The detection of the main components in crude oil samples and the origin traceability is of great significance to the fields of national defense security and ecological environment. At this stage, the measurement of crude oil composition are complicated, high-cost, and have long detection time, which cannot meet the demands of rapid detection of crude oil composition and traceability of the origin of crude oil. Combining with a highly sensitive terahertz detection chip (Based on dual torus toroidal effect) and terahertz time-domain spectroscopy system, the terahertz spectra of crude oil samples from different origins were measured in this paper, and it was found that the frequency shift of the chip resonant peak showed different rules. For two main indicators of sulfur content and residual carbon in crude oil, quantitative analysis can be carried out according to their unique frequency shifts. The calculation of experimental data shows that the relative difference of the average resonance frequency of crude oil from the same origin is about 4.63%, and the relative difference of the average resonance frequency of crude oil from different production areas is about 56.53%, which can clearly distinguish the origin of crude oil. The designed metasurface chip can excite new electromagnetic mode, providing a highly sensitive detection technology, which can be widely used in real-time monitoring of biomolecules or detection of chemical substances (such as crude oil) composition detection, origin traceability and other fields.
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Key words:
- dual torus toroidal /
- crude oil /
- terahertz /
- metasurface /
- high sensitivity
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图 6 (a) 实验透射谱图;(b) 混合物中全频移和单频移的关系柱状图;(c) 计算得到的硫含量频移点图及线性拟合图;(d) 计算得到的残炭含量频移点图及线性拟合图
Figure 6. (a) Experimental transmission spectrum; (b) Bar graph of the relationship between full frequency shift and single frequency shift in the mixture; (c) Frequency shift point diagram and linear fitting diagram of sulfur content; (d) Frequency shift point diagram and linear fitting diagram of residual carbon content
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[1] 吴考民, 王可中, 石鑫, 等. 含硫原油对输油管道的腐蚀性[J]. 油气储运, 2010, 29(008): 616-618. Wu K M, Wang K Z, Shi X, et al. Corrosivlty of sour crude on oil pipelines [J]. Oil & Gas Storage and T ransportation, 2010, 29(8): 616-618. (in Chinese) [2] 张嘉璇, 王萍, 韩玉萍, 等. 能量色散X射线荧光分析法测定石油焦硫含量的研究[J]. 分析仪器, 2009(06): 48-53. doi: 10.3969/j.issn.1001-232X.2009.06.014 Zhang J X, Wang P, Han Y P, et al. Determination of sulfur content in petroleum coke by energy-dispersive X-ray fluorescence spectrometry [J]. Analytical Instrumentation, 2009(6): 48-53. (in Chinese) doi: 10.3969/j.issn.1001-232X.2009.06.014 [3] 何世梅, 陈国华. WK-2B微库仑仪测定重质石油中的硫含量[J]. 石油化工, 2001(06): 467-470. doi: 10.3321/j.issn:1000-8144.2001.06.011 He S M, Chen G H. Determination of sulfur content in heavy oil with modified WK-2B type microcoulometer [J]. Petrochemical Technology, 2001(6): 467-470. (in Chinese) doi: 10.3321/j.issn:1000-8144.2001.06.011 [4] 王红, 文萍. 石油产品中残炭测定方法的对比[J]. 现代仪器, 2011, 17(03): 73-75. Wang H, Wen P. Determination method of carbon residue in petroleum products [J]. Modern Instrument, 2011, 17(3): 73-75. (in Chinese) [5] 丁丽, 丁茜, 叶阳阳, 等. 室内人体隐匿物被动太赫兹成像研究进展[J]. 中国光学, 2017, 10(01): 114-121+149. doi: 10.3788/co.20171001.0114 Ding L, Ding Q, Ye Y Y, et al. Overview of passive terahertz imaging systems for indoor concealed detection [J]. Chinese Optics, 2017, 10(1): 114-121+149. (in Chinese) doi: 10.3788/co.20171001.0114 [6] Chen L, Liao D G, Guo X G, et al. Terahertz time-domain spectroscopy and micro-cavity components for probing samples: A review [J]. Frontiers of Information Technology & Electronic Engineering, 2019, 20(5): 591-607. [7] 张雯, 雷银照. 太赫兹无损检测的进展[J]. 仪器仪表学报, 2008, 029(007): 1563-1568. Zhang W, Lei Y Z. Progress in terahertz nondestructive testing [J]. Chinese Journal of Scientific Instrument, 2008, 029(7): 1563-1568. (in Chinese) [8] 田璐, 赵昆. 太赫兹技术在石油领域的应用进展[J]. 现代科学仪器, 2011(06): 5-11. Tian L, Zhao K. Applications of terahertz technology in petroleum industry [J]. Modern Scientific Instruments, 2011(6): 5-11. (in Chinese) [9] 宝日玛, 赵昆, 田璐等. 原油超声处理的太赫兹时域光谱分析[J]. 现代科学仪器, 2013(02): 126-129. Bao R M, Zhao K, Tian L, et al. Analysis of THz time-domain spectroscopy in crude oil ultrasound treatment [J]. Modern Scientific Instruments, 2013(2): 126-129. (in Chinese) [10] 张莎莎, 丁继伟, 李俊毅等. 原油中硫含量的太赫兹时域光谱检测[J]. 现代科学仪器, 2013(04): 225-227. Zhang S S, Ding J W, Li J Y, et al. Measurement of sulfur content in crude oil using terahertz time-domain spectroscopy [J]. Modern Scientific Instruments, 2013(4): 225-227. (in Chinese) [11] 李俊毅, 赵昆, 田璐. 利用太赫兹技术研究重油燃料油标准物质中的微量硫含量[J]. 现代科学仪器, 2011(06): 16-18. Li J Y, Zhao K, Tian L. Investigation of sulfur contents in heavy oil reference materials by terahertz spectroscopic technique [J]. Modern Scientific Instruments, 2011(6): 16-18. (in Chinese) [12] 陈瀑, 李敬岩, 褚小立等. 拉曼和红外光谱快速评价原油性质的可行性比较[J]. 石油炼制与化工, 2016, 47(10): 98-102. doi: 10.3969/j.issn.1005-2399.2016.10.019 Chen P, Li J Y, Chu X L, et al. Feasibility study of crude oil rapid assay by Raman and infrared spectroscopy [J]. Petroleum Refining and Chemical Industry, 2016, 47(10): 98-102. (in Chinese) doi: 10.3969/j.issn.1005-2399.2016.10.019 [13] Zel’Dovich I B. Electromagnetic interaction with parity violation [J]. Sov Phys Jetp, 1958, 6(6): 1184-1186. [14] Gupta M, Savinov V, Xu N, et al. Sharp toroidal resonances in planar terahertz metasurfaces [J]. Advanced Materials, 2016, 28(37): 8206-8211. doi: 10.1002/adma.201601611 [15] Ahmadivand A, Gerislioglu B, Ahuja R, et al. Toroidal metaphotonics and metadevices [J]. Laser & Photonics Reviews, 2020, 14(11): 1900326. [16] Chen L, Xu N, Singh L, et al. Defect‐induced Fano resonances in corrugated plasmonic metamaterials [J]. Advanced Optical Materials, 2017, 5(8): 1600960. doi: 10.1002/adom.201600960 [17] Ahmadivand A, Gerislioglu B, Tomitaka A, et al. Extreme sensitive metasensor for targeted biomarkers identification using colloidal nanoparticles-integrated plasmonic unit cells [J]. Biomedical Optics Express, 2018, 9(2): 373-386. doi: 10.1364/BOE.9.000373 [18] Ahmadivand A, Gerislioglu B, Ramezani Z, et al. Attomolar detection of low-molecular weight antibiotics using midinfrared-resonant toroidal plasmonic metachip technology [J]. Physical Review Applied, 2019, 12(3): 034018. doi: 10.1103/PhysRevApplied.12.034018 [19] Ahmadivand A, Gerislioglu B, Ramezani Z, et al. Functionalized terahertz plasmonic metasensors: Femtomolar-level detection of SARS-CoV-2 spike proteins [J]. Biosensors and Bioelectronics, 2021,177: 112971. [20] Zhan H, Wu S, Bao R, et al. Qualitative identification of crude oils from different oil fields using terahertz time-domain spectroscopy [J]. Fuel, 2015, 143: 189-193. doi: 10.1016/j.fuel.2014.11.047 [21] 梁文杰, 阙国和, 陈月珠等. 我国原油减压渣油中镍、氮及残炭的分布[J]. 石油学报(石油加工), 1993(03): 1-9. Liang W J, Que G H, Chen Y Z, et al. Distribution of nickel, nitrogen and carbon residue of chinese vacuum residues [J]. Acta Petrolei Sinica(Petroleum Processing Section), 1993(3): 1-9. (in Chinese)