The recent growth of terahertz (THz) applications has sparked interest in the design of novel electromagnetic structures for this frequency regime. One of the structures is the THz absorber, used in sensing and imaging applications. Metamaterial based designs are commonly used to achieve the desired absorption characteristics. Absorbers whose spectra can be tuned by changing the temperature are a subclass in the broad family of THz absorbers that are used for temperature sensing. In the beginning years, single band temperature tunable absorbers were designed, and at present the focus has shifted to the design of multi-band temperature tunable absorbers. Absorbers with six tunable bands have already been proposed. In this paper an octa-band temperature tunable terahertz metamaterial absorber is proposed, whose unit cell consists of four orthogonally placed tapered triangular structures connected by a ring resonator on top of an InSb dielectric substrate. At 210K it is observed that the structure's absorption spectra are: 98.7% at 1.026 THz, 79.5% at 1.245 THz, 90.4% at 1.301 THz, 95.2% at 1.442 THz, 97.44% at 1.585 THz, 96.4% at 1.644 THz, 97.1% at 1.756 THz, and 90.4% at 2.071 THz. The temperature sensitivities of the proposed structure in eight of its absorption bands are 10.3 GHz/K, 8.22 GHz/K, 7.96 GHz/K, 7.02 GHz/K, 6.44 GHz/K, 6.17 GHz/K, 5.5 GHz/K, and 3.2 GHz/K, respectively. Thus, the proposed design can have practical applications in terahertz temperature sensing applications.
2. Veselago, V. G., "The electrodynamics of substances with simultaneously negative values of ε and μ," Uspekhi Fizicheskikh Nauk, Vol. 10, No. 4, 509-514, 1968.
3. Grant, J., I. J. H. Mccrindle, and D. R. S. Cumming, "Multi-spectral materials: Hybridisation of optical plasmonic filters, a mid infrared metamaterial absorber and a terahertz metamaterial absorber," Optics Express, Vol. 24, 3451-3463, 2016.
4. Ramakrishna, S. A. and T. M. Grzegorczyk, Physics and Application of Negative Refractive Index Materials, CRC Press, Boca Raton, 2008.
5. Landy, N. I., S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, "Perfect metamaterial absorber," Physics Review Letters, Vol. 100, 207402, 2008.
6. Siegel, P. H., "Terahertz technology," IEEE Transactions on Microwave Theory and Techniques, Vol. 50, No. 3, 910-928, Mar. 2002.
7. Tonouchi, M., "Cutting-edge terahertz technology," Nature Photonics, Vol. 1, No. 2, 97-105, 2007.
8. Yen, T. J., et al., "Terahertz magnetic response from artificial materials," Science, Vol. 303, 1494-1496, 2004.
9. Rhee, J. Y., Y. J. Yoo, K. W. Kim, Y. J. Kim, and Y. P. Lee, "Metamaterial-based perfect absorbers," Journal of Electromagnetic Waves and Applications, Vol. 28, No. 13, 1541-1580, 2014.
10. He, X. Y., X. Zhong, F. T. Lin, and W. Z. Shi, "Investigation of graphene assisted tunable terahertz metamaterials absorber," Optic Materials Express, Vol. 6, No. 2, 331-342, 2016.
11. Xiong, H., Q. Ji, T. Bashir, and F. Yang, "Dual-controlled broadband terahertz absorber based on graphene and dirac semimetal," Optics Express, Vol. 28, No. 9, 13884-13894, 2020.
12. Hu, F., et al., "Design of a tunable terahertz narrowband metamaterial absorber based on an electrostatically actuated MEMS cantilever and split ring resonator array," Journal of Optics, Vol. 15, No. 5, 055-101, 2013.
13. Wang, B. X., X. Zhai, G. Z.Wang, W. Q. Huang, and L. L.Wang, "Frequency tunable metamaterial absorber at deep-subwavelength scale," Optic Materials Express, Vol. 5, 227-235, 2015.
14. Castorina, G., L. Di Donato, A. F. Morabito, T. Isernia, and G. Sorbello, "Analysis and design of a concrete embedded antenna for wireless monitoring applications," IEEE Antennas and Propagation Magazine, Vol. 58, No. 6, 76-93, 2016.
15. Wang, B. X. and G. Z. Wang, "Temperature tunable metamaterial absorber at THz frequencies," Journal of Materials Science: Materials in Electronics, Vol. 28, No. 12, 1-7, 2017.
16. Song, Z. Y., K. Wang, J. W. Li, and Q. H. Liu, "Broadband tunable terahertz absorber based on vanadium dioxide metamaterials," Optics Express, Vol. 26, No. 6, 7148-7154, 2018.
17. Oszwalldowki, M. and M. Zimpel, "Temperature dependence of intrinsic carrier concentration and density of states effective mass of heavy holes in InSb," Journal of Physics and Chemistry of Solids, Vol. 49, 1179-1185, 1988.
18. Li, Z. Z., C. Y. Luo, G. Yao, J. Yue, J. Ji, J. Q. Yao, and F. R. Ling, "Design of a concise and dual-band tunable metamaterial absorber," Chinese Optics Letters, Vol. 14, No. 10, 102303, 2016.
19. Li, W., D. Kuang, F. Fan, S. Chang, and L. Lin, "Subwavelength B-shaped metallic hole array terahertz filter with InSb bar as thermally tunable structure," Applied Optics, Vol. 51, No. 21, 7098-7102, 2012.
20. Zou, H. and Y. Cheng, "Design of a six-band terahertz metamaterial absorber for temperature sensing application," Optical Materials, Vol. 88, 674-679, 2019.
21. Verma, V. K., et al., "An octaband polarization insensitive terahertz metamaterial absorber using orthogonal elliptical ring resonators," Plasmonics, Vol. 15, No. 1, 75-81, 2020.