傳統兆赫波感測器受限於堅硬的基板，導致其無法靈活地運用於穿戴科技感測。本研究探索一種可彎曲三維人造週期結構在兆赫波頻段的穿透特性和感測應用，該結構包含金屬鍍膜-介電質複合編織網(metal-coated polymeric woven mesh, MCWM)以及全金屬編織網(metal woven mesh, MWM)進行分析。基於有限元素方法對不同幾何和金屬鍍膜參數之編織網結構進行數值模擬和分析其穿透特性。模擬結果顯示:編織網結構之尺寸改變顯著影響MCWM或MWM人造結構的穿透特徵頻率，其頻譜特徵波長正比於單元晶胞孔洞寬度或其週期，揭露入射兆赫波透過和單元晶胞結構共振，將能量轉變為局域的表面電漿波，和二維場型圖結果一致。此外，研究MCWM結構中的金屬性質改變對光學穿透頻譜影響:包含表面金屬鍍膜之導電度和金屬覆蓋介電質表面比例；發現當導電度或覆蓋比例增加，不但令等效金屬介電係數升高，導致共振頻率藍移；亦使集膚深度縮減和強化異常穿透現象(extraordinary optical transmission, EOT)，導致共振峰穿透強度增強。而研究MCWM結構中不同介電係數編織網對光學穿透頻譜影響結果顯示:當折射率遞增，使共振頻率紅移。以上模擬的光學穿透特性和實驗結果皆有良好的一致性，顯示此MCWM和MWM三維人工結構分別可作為頻率可調帶通和高通濾波器，其共振頻率可經由結構幾何參數調整。基於局域兆赫電漿場集中金屬-介電質表面對周圍介質環境敏感之特性，我們將上述兩種人造結構應用於厚度和折射率感測。模擬結果顯示隨著介電物質之填充厚度、覆蓋厚度以及折射率遞增，MWM結構的靈敏度皆比MCWM的表現還要優異。另外，縮小單元晶胞尺寸使表面電漿場之局域化現象越突出和強化EOT，導致特徵共振頻率飄移更敏感於分析物介質的微小變化，因此感測靈敏度優於大尺寸晶胞。本研究之三維編織網人造週期結構，對未來6G通訊和通感結合(ISAC)的穿戴科技具備高度的應用潛力。

Traditional terahertz sensors are limited by rigid substrates, preventing their flexible application in wearable sensing technology. This study explores the transmission characteristics and sensing applications of a flexible, three-dimensional artificial periodic structure in the THz frequency band, which includes a metal-coated polymeric woven mesh (MCWM) and a metal woven mesh (MWM). Based on the finite element method, numerical simulations and analyses of the transmission characteristics were conducted on woven mesh structures with different geometries and metal coating parameters.
The simulation results indicate that altering the size of the woven mesh structure significantly affects the transmission characteristic frequency of the artificial MCWM or MWM structures. The characteristic spectral wavelength is proportional to the unit cell aperture or its period, revealing that the incident THz waves resonate with the unit cell structure, converting energy into localized surface plasmon waves. The simulation results are consistent with the two-dimensional field pattern results. Furthermore, the study investigates the impact of changing metal properties in the MCWM structure on the optical transmission spectrum, including the conductivity of the surface metal coating and the ratio of metal coverage on the dielectric surface. The results show that increasing the conductivity or coverage ratio not only leads to a higher equivalent metal permittivity, which causes a blueshift in the resonance frequency, but also reduces the skin depth and strengthens the extraordinary optical transmission (EOT), ultimately increasing the transmission intensity at the resonance peak. Additionally, examining the effect of woven meshes with different dielectric constants in the MCWM structure on the optical transmission spectrum revealed that an increasing refractive index causes a redshift in the resonance frequency. The simulated optical transmission characteristics mentioned above show excellent agreement with experimental results, demonstrating that these three-dimensional artificial MCWM and MWM structures can serve as tunable bandpass and high-pass filters, with their resonance frequencies being adjustable via structural geometric parameters.
Based on the characteristic that localized terahertz plasmon fields concentrated on the metal-dielectric interface are highly sensitive to the surrounding dielectric environment, we applied these artificial MCWM and MWM structures to thickness and refractive index sensing. Simulation results demonstrate that as the filling thickness, covering thickness, and refractive index of the dielectric material increase, the sensitivity of the MWM structure consistently surpasses that of the MCWM. Moreover, reducing the unit cell size makes the localization of the surface plasmon field more prominent and enhances EOT, causing the characteristic resonance frequency shift to be more sensitive to subtle changes in the analyte medium. Therefore, structures with smaller unit cells exhibit superior sensing sensitivity compared to those with larger unit cells. The three-dimensional woven mesh artificial periodic structure presented in this study holds high application potential for future wearable technology in 6G communications and integrated sensing and communications (ISAC).

[1] F. A. Jenkins, H. E. White, and D. G. Burkhard, "Fundamentals of optics, 4," McGraw-Hill, New York, p.232-235 (2001).
[2] A. G. Davies, E. H. Linfield, and M. B. Johnston, "The development of terahertz sources and their applications," Physics in Medicine & Biology 47, 3679 (2002).
[3] T. Hasebe, Y. Yamada, and H. Tabata, "Label-free THz sensing of living body-related molecular binding using a metallic mesh," Biochemical and biophysical research communications 414, 192-198 (2011).
[4] P. H. Siegel, "Terahertz technology in biology and medicine," IEEE transactions on microwave theory and techniques 52, 2438-2447 (2004).
[5] D. Dragoman, and M. Dragoman, "Terahertz fields and applications," Progress in quantum electronics 28, 1-66 (2004).
[6] D. M. Mittleman, "Twenty years of terahertz imaging," Optics express 26, 9417-9431 (2018).
[7] W. L. Chan, J. Deibel, and D. M. Mittleman, "Imaging with terahertz radiation," Reports on progress in physics 70, 1325 (2007).
[8] Y.-W. Huang, T.-F. Tseng, C.-C. Kuo et al., "Fiber-based swept-source terahertz radar," Opt. Lett. 35, 1344-1346 (2010).
[9] W. Jiang, Q. Zhou, J. He et al., "Terahertz communications and sensing for 6G and beyond: A comprehensive review," IEEE Communications Surveys & Tutorials 26, 2326-2382 (2024).
[10] C. Tan, S. Wang, S. Li et al., "Cancer diagnosis using terahertz-graphene-metasurface-based biosensor with dual-resonance response," Nanomaterials 12, 3889 (2022).
[11] C.-H. Feng, and C. Otani, "Terahertz spectroscopy technology as an innovative technique for food: Current state-of-the-Art research advances," Critical reviews in food science and nutrition 61, 2523-2543 (2021).
[12] L. Sun, L. Zhao, and R.-Y. Peng, "Research progress in the effects of terahertz waves on biomacromolecules," Military medical research 8, 1-8 (2021).
[13] R. Balu, H. Zhang, E. Zukowski et al., "Terahertz spectroscopy of bacteriorhodopsin and rhodopsin: similarities and differences," Biophysical journal 94, 3217-3226 (2008).
[14] M. Naftaly, N. Vieweg, and A. Deninger, "Industrial applications of terahertz sensing: State of play," Sensors 19, 4203 (2019).
[15] W. Zhang, Y. Tang, A. Shi et al., "Recent developments in spectroscopic techniques for the detection of explosives," Materials 11, 1364 (2018).
[16] M. O. AlNabooda, R. M. Shubair, N. R. Rishani et al., "Terahertz spectroscopy and imaging for the detection and identification of illicit drugs," 2017 Sensors networks smart and emerging technologies (2017).
[17] Z. Ma, Z. Geng, Z. Fan et al., "Modulators for terahertz communication: The current state of the art," Research (2019).
[18] M. Z. Chowdhury, M. Shahjalal, S. Ahmed et al., "6G Wireless Communication Systems: Applications, Requirements, Technologies, Challenges, and Research Directions," IEEE Open J. Commun. Soc. 1, 957-975 (2020).
[19] S. M. Kanan, O. M. El-Kadri, I. A. Abu-Yousef et al., "Semiconducting metal oxide based sensors for selective gas pollutant detection," Sensors 9, 8158-8196 (2009).
[20] M. L. Larramendy, W. e. El‐Rifai, and S. Knuutila, "Comparison of fluorescein isothiocyanate‐and Texas red‐conjugated nucleotides for direct labeling in comparative genomic hybridization," Cytometry: The Journal of the International Society for Analytical Cytology 31, 174-179 (1998).
[21] H. Ozaki, and L. W. McLaughlin, "The estimation of distances between specific backbone-labeled sites in DNA using fluorescence resonance energy transfer," Nucleic acids research 20, 5205-5214 (1992).
[22] B. H. Stuart, "Infrared spectroscopy: fundamentals and applications, 1," John Wiley & Sons, Hoboken, p.137-163 (2004).
[23] L. Xie, Y. Yao, and Y. Ying, "The application of terahertz spectroscopy to protein detection: a review," Applied Spectroscopy Reviews 49, 448-461 (2014).
[24] Q. Wang, and W.-M. Zhao, "A comprehensive review of lossy mode resonance-based fiber optic sensors," Optics and Lasers in Engineering 100, 47-60 (2018).
[25] F. Chiavaioli, D. Santano Rivero, I. Del Villar et al., "Ultrahigh sensitive detection of Tau protein as Alzheimer's biomarker via microfluidics and nanofunctionalized optical fiber sensors," Advanced Photonics Research 3, 2200044 (2022).
[26] F. Esposito, L. Sansone, A. Srivastava et al., "Label-free detection of vitamin D by optical biosensing based on long period fiber grating," Sensors and Actuators B: Chemical 347, 130637 (2021).
[27] M. Hangyo, M. Tani, and T. Nagashima, "Terahertz time-domain spectroscopy of solids: a review," International journal of infrared and millimeter waves 26, 1661-1690 (2005).
[28] M. Seo, and H. R. Park, "Terahertz biochemical molecule‐specific sensors," Advanced Optical Materials 8, 1900662 (2020).
[29] M. Osawa, "Near-field optics and surface plasmon polaritons, 1," Springer, Berlin, p.163-187 (2006).
[30] V. I. Slyusar, "Metamaterials on antenna solutions," International conference on antenna theory and techniques, 19-24 (2009).
[31] V. Veselago, "The electrodynamics of substances with simultaneously negative values of and," Usp. fiz. nauk 92, 517-526 (1967).
[32] K. Modi, P. Kachhadiya, J. M. Rathod et al., "Low-Cost Metamaterial Loaded Microstrip Antenna for Defense Applications," Open Journal of Antennas and Propagation 09, 1-10 (2021).
[33] J. B. Pendry, A. Holden, W. Stewart et al., "Extremely low frequency plasmons in metallic mesostructures," Physical review letters 76, 4773 (1996).
[34] J. B. Pendry, A. Holden, D. Robbins et al., "Low frequency plasmons in thin-wire structures," Journal of Physics: Condensed Matter 10, 4785 (1998).
[35] J. B. Pendry, A. J. Holden, D. J. Robbins et al., "Magnetism from conductors and enhanced nonlinear phenomena," IEEE Transactions on Microwave Theory and Techniques 47, 2075-2084 (1999).
[36] D. Sievenpiper, M. Sickmiller, and E. Yablonovitch, "3D wire mesh photonic crystals," Physical Review Letters 76, 2480 (1996).
[37] D. R. Smith, W. J. Padilla, D. Vier et al., "Composite medium with simultaneously negative permeability and permittivity," Physical review letters 84, 4184 (2000).
[38] D. R. Smith, D. Vier, N. Kroll et al., "Direct calculation of permeability and permittivity for a left-handed metamaterial," Applied Physics Letters 77, 2246-2248 (2000).
[39] O. A. Abdelraouf, Z. Wang, H. Liu et al., "Recent advances in tunable metasurfaces: materials, design, and applications," ACS nano 16, 13339-13369 (2022).
[40] Y. Zhang, J. Duan, B. Zhang et al., "A flexible metamaterial absorber with four bands and two resonators," Journal of Alloys and Compounds 705, 262-268 (2017).
[41] S. Walia, C. M. Shah, P. Gutruf et al., "Flexible metasurfaces and metamaterials: A review of materials and fabrication processes at micro-and nano-scales," Applied Physics Reviews 2 (2015).
[42] T. W. Ebbesen, H. J. Lezec, H. Ghaemi et al., "Extraordinary optical transmission through sub-wavelength hole arrays," nature 391, 667-669 (1998).
[43] H. Ghaemi, T. Thio, D. e. a. Grupp et al., "Surface plasmons enhance optical transmission through subwavelength holes," Physical review B 58, 6779 (1998).
[44] M. Navarro‐Cía, V. Pacheco‐Peña, S. A. Kuznetsov et al., "Extraordinary THz transmission with a small beam spot: The leaky wave mechanism," Advanced Optical Materials 6, 1701312 (2018).
[45] Q. Wang, B. Gao, M. Raglione et al., "Design, fabrication, and modulation of THz bandpass metamaterials," Laser & Photonics Reviews 13, 1900071 (2019).
[46] Y. Gou, Y. Xuan, and Y. Han, "Investigation on spectral properties of metal–insulator–metal film stack with rectangular hole arrays," International Journal of Thermophysics 32, 1060-1070 (2011).
[47] C. Sabah, and H. Roskos, "Effect of the metallization on the resonances of THz fishnet metamaterials," Journal of the European Optical Society-Rapid publications 7, 12005 (2012).
[48] X. He, and H. Lu, "Graphene-supported tunable extraordinary transmission," Nanotechnology 25, 325201 (2014).
[49] C. Sabah, M. D. Thomson, F. Meng et al., "Terahertz propagation properties of free-standing woven-steel-mesh metamaterials: Pass-bands and signatures of abnormal group velocities," Journal of Applied Physics 110 (2011).
[50] B. R. You, J. Y. Lu, P. L. Chen et al., "Highly Transparent and Polarization-Maintained Terahertz Plasmonic Metamaterials Based on Metal-Wire-Woven Hole Arrays: Fundamentals and Characterization of Transmission Spectral Peaks," Materials 15, 20 (2022).
[51] B. R. You, R. Iwasa, P. L. Chen et al., "Specularly-Reflected Wave Guidance of Terahertz Plasmonic Metamaterial Based on the Metal-Wire-Woven Hole Arrays: Functional Design and Application of Transmission Spectral Dips," Materials 16, 17 (2023).
[52] J. Y. Lu, P. L. Chen, and B. You, "Terahertz Plasmonic Sensor Based on Metal-Insulator Composite Woven-Wire Mesh," Biosensors-Basel 12, 21 (2022).
[53] H. Raether, "Surface Plasmons on Smooth and Rough Surfaces and on Gratings, 1," Springer, Berlin, p.91-116 (2006).
[54] R. Ulrich, "Far-infrared properties of metallic mesh and its complementary structure," Infrared Physics 7, 37-55 (1967).
[55] C.-C. Chen, "Transmission through a conducting screen perforated periodically with apertures," IEEE Transactions on Microwave Theory and Techniques 18, 627-632 (1970).
[56] H.-T. Chen, W. J. Padilla, J. M. Zide et al., "Active terahertz metamaterial devices," Nature 444, 597-600 (2006).
[57] H.-T. Chen, W. J. Padilla, M. J. Cich et al., "A metamaterial solid-state terahertz phase modulator," Nature photonics 3, 148-151 (2009).
[58] Y. Chassagneux, R. Colombelli, W. Maineult et al., "Electrically pumped photonic-crystal terahertz lasers controlled by boundary conditions," Nature 457, 174-178 (2009).
[59] H. T. Chen, J. F. O'Hara, A. K. Azad et al., "Manipulation of terahertz radiation using metamaterials," Laser & Photonics Reviews 5, 513-533 (2011).
[60] S. Rossel, W. Zhang, H. A. Hafez et al., "Efficient terahertz optical filtering with large-area all-metal and polymer-metal woven wire meshes," Optics Express 31, 19076-19088 (2023).
[61] S. Rossel, W. Zhang, H. A. Hafez et al., "Plasmonic mode coupling in three-dimensional metallic wire terahertz metamaterials," Optics Express 33, 32320-32332 (2025).
[62] J. Y. Lu, C. Y. Chen, and B. R. You, "A dual-function tunable terahertz multiband bandpass filter based on PET woven-wire meshes with conductive coating surfaces," Results in Physics 56, 107225 (2024).
[63] R. Yahiaoui, A. C. Strikwerda, and P. U. Jepsen, "Terahertz plasmonic structure with enhanced sensing capabilities," IEEE Sensors Journal 16, 2484-2488 (2016).
[64] Simulia, "CST Studio Suite Electromagnetic and Multiphysics Simulation Software," Simulia, Rhode Island (2025).
[65] J. Jog, "Crystallization of polyethylene terephthalate," Journal of Macromolecular Science, Part C: Polymer Reviews 35, 531-553 (1995).
[66] V. Rogalin, I. Kaplunov, and G. Kropotov, "Optical materials for the THz range," Optics and Spectroscopy 125, 1053-1064 (2018).
[67] S. Pandey, S. C. Liu, B. Gupta et al., "Self-referenced measurements of the dielectric properties of metals using terahertz time-domain spectroscopy via the excitation of surface plasmon-polaritons," Photonics Res. 1, 148-153 (2013).
[68] A. K. Azad, Y. G. Zhao, W. L. Zhang et al., "Effect of dielectric properties of metals on terahertz transmission subwavelength hole arrays," Opt. Lett. 31, 2637-2639 (2006).
[69] M. A. Ordal, L. Long, R. J. Bell et al., "Optical properties of the metals al, co, cu, au, fe, pb, ni, pd, pt, ag, ti, and w in the infrared and far infrared," Applied optics 22, 1099-1119 (1983)
[70] C. W. Chen, Y. C. Lin, C. H. Chang et al., "Frequency-Dependent Complex Conductivities and Dielectric Responses of Indium Tin Oxide Thin Films from the Visible to the Far-Infrared," IEEE J. Quantum Electron. 46, 1746-1754 (2010).
[71] S. A. Maier, "Plasmonics: Fundamentals and Applications, 1," Springer, Berlin, p.5-11 (2007).
[72] I. S. Association, "IEEE Standard for Validation of Computational Electromagnetics Computer Modeling and Simulations," IEEE Std. 1597.1-2022, 1-52 (2022).
[73] B. E. Saleh, and M. C. Teich, "Fundamentals of photonics, 3," John Wiley & Sons, Hoboken, p.914-926 (2019).
[74] D. Liu, and T. Hattori, "Sharp resonances in terahertz free-standing three-dimensional metallic woven meshes," Optics Express 28, 30174-30186 (2020).
[75] H. A. Bethe, "Theory of diffraction by small holes," Physical review 66, 163 (1944).
[76] K. A. Willets, and R. P. Van Duyne, "Localized surface plasmon resonance spectroscopy and sensing," Annu. Rev. Phys. Chem. 58, 267-297 (2007).
[77] D. Halliday, R. Resnick, and J. Walker, "Fundamentals of physics, 10," John Wiley & Sons, Hoboken, p.1047-1052 (2013).
[78] D. J. Griffiths, "Introduction to electrodynamics, 3," Prentice Hall, New Jersey, p.58-64 (1999).
[79] H. Asif, and R. Sahin, "Tunable extraordinary optical transmission for integrated photonics," Applied Physics B 131, 37 (2025).
[80] A. K. Azad, J. F. O'Hara, R. Singh et al., "A Review of Terahertz Plasmonics in Subwavelength Holes on Conducting Films," IEEE J. Sel. Top. Quantum Electron. 19, 16 (2013).
[81] A. S. Saadeldin, M. F. O. Hameed, E. M. Elkaramany et al., "Highly sensitive terahertz metamaterial sensor," IEEE Sensors Journal 19, 7993-7999 (2019).
[82] H. Yao, H. Mei, W. Zhang et al., "Theoretical and experimental research on terahertz metamaterial sensor with flexible substrate," IEEE Photonics Journal 14, 1-9 (2021).
[83] R. Zhao, Q. Niu, Y. Zou et al., "A terahertz metasurface biosensor based on electromagnetically induced transparency for fingerprint trace detection," Journal of Materials Chemistry C 12, 6106-6113 (2024).
[84] X. Hu, G. Xu, L. Wen et al., "Metamaterial absorber integrated microfluidic terahertz sensors," Laser & Photonics Reviews 10, 962-969 (2016).