由於兆赫波(THz)技術的快速發展，同時也需要進一步探索兆赫波系統各種應用的前瞻性，相關的元件及設備將不可或缺。為了尋找最適合用於兆赫波技術的材料，在本研究中選用3D列印常用的材料分別為Acrylonitrile butadiene styrene(ABS)、Polyamide(PA)、Poly Lactic Acid(PLA)及光固化樹脂，將其分別與不同重量百分比的陶瓷粉末混合，並藉由量測兆赫波時域光譜(THz-TDS)觀察在不同添加比例陶瓷粉末時吸收係數與折射率的改變。
本實驗嘗試固定高分子粉末探討改變添加陶瓷粉末比例對兆赫波光學特性的影響。以PLA、PA粉末和光固化樹脂為基底分別混和10 wt%、20 wt%、30 wt %、40 wt%和50 wt%石英粉末，隨著添加的石英粉末比例提高，吸收係數會隨之下降，折射率也隨之提升；其中添加50 wt%石英粉末的樣品降低最多吸收係數，提升最多的折射率。
為探討高分子材料添加不同陶瓷粉末後，其兆赫波光學常數的改變，本研究固定以ABS粉末為基底，混合不同陶瓷粉末。此部分分為兩組實驗，一組實驗使用鍛燒稻殼灰質(RHA)還原的SiO2，探討不同溫度製備的RHA其兆赫波光學特性的差異。本研究將ABS粉末混合50 wt%不同溫度製備的稻殼灰質樣品量測兆赫波時域光譜。另一組實驗則將ABS粉末分別與鍛燒1000℃前後Al2O3、SiO2、ZrSiO4和石英粉末混合，在0.5 THz時，混合50 wt%鍛燒後的Al2O3粉末樣品有最低的吸收係數3.40，在1 THz時，混合50 wt%鍛燒後的石英粉末樣品有最低的吸收係數9.17。混合50 wt% ZrSiO4粉末有最高的折射率，在0.5和1 THz時分別為1.81和1.80。
為實現將陶瓷粉末添加於3D列印材料之中，在分析各3D列印技術的優缺點後，選用以光固化之技術製作透鏡。依據兆赫波時域光譜量測的結果，考量其可列印性及列印後的表面粗糙度，最後以光固化樹脂混合30 wt% Al2O3為材料來設計與製作兆赫光學透鏡。本研究分別製作了直徑50 mm焦距50 mm和100 mm的平凸透鏡，並以VDI公司開發的商用成套系統量測自製透鏡的聚焦效果與光斑大小，量測結果顯示其透鏡具有聚焦功能且符合焦距較短的透鏡光通過後發散較快的趨勢。以刀口法量測光斑大小，焦距50 mm的透鏡x方向的直徑為4.08 mm，y方向為3.89 mm；焦距100 mm的透鏡x方向直徑則為4.24 mm，y方向為4.05 mm。因此，添加陶瓷粉末於3D列印材料為提升折射率及降低吸收係數有效的方式，且可應用於3D列印技術，改善以3D列印技術製作THz的元件效能。

With the rapid development of terahertz (THz) technology comes the need to further explore the prospects for various applications of THz systems. For further study, components and equipment involving are indispensable. In order to find out the most suitable material for THz technology, we selected some common materials for different 3D printing techniques—acrylonitrile butadiene styrene (ABS), polyamide (PA), polylactic acid (PLA), and light-curable resin. After mixing each material with a ceramic powder of a different weight percentage, we observed the change in absorption coefficients and refractive indices of the mixtures by THz time-domain spectroscopy (THz-TDS).
In this study, the impact of different percentage of a ceramic powder added in polymer powders on the optical characters of THz was tested. The base polymer powders including PLA, PA and light-curable resin were mixing with 10 wt%, 20 wt%, 30 wt %, 40 wt% , and 50 wt% of quartz powder. With higher percentage of quartz powder, the absorption coefficient became significantly lower following with higher refractive index. Hence, among all the samples, the powder mixture with 50 wt% quartz powder had the lowest absorption coefficient and highest refractive index.
In order to explore the changes of optical constant of THz caused by different ceramic powders, we used a single polymer material, ABS powder, as base mixing with various ceramic powders. In this part, two sets of experiment were conducted. In the first set of the experiment, 50 wt% SiO2 (rice husk ash, RHA burnt at different temperatures) mixed with ABS powder were applied to find out the impact of RHA on the THz-TDS. The other experiment mixed Al2O3, SiO2, ZrSiO4 and quartz powder burnt at 1000 ℃ with ABS base. At 0.5 THz, the powder mixture with 50 wt% Al2O3 sample had the lowest absorption coefficient, 3.40. At 1.0 THz, the lowest absorption coefficient (9.17) was from the sample with 50 wt% quartz powder. Among all the samples, the mixture with 50 wt% ZrSiO4 powder had the highest refractive index at both 0.5 and 1.0 THz which were 1.81 and 1.80.
After analyzing the advantages and disadvantages of each 3D printing techniques, the lens created by light curing techniques was selected. According to the results of THz-TDS and considering the printability and surface roughness after printing, the material we chose to design and 3D print was 30 wt% Al2O3 mixed with photocurable resin. The 50mm diameter plane-convex lenses with a focal length of 50mm and 100mm were produced in this study and the focusing effects and spot-size were measured by measuring system developed by VDI. Based on the tested results, the lenses have focus function and the trends of speedy divergence of light corresponding with the characters of those lenses with shorter focus. Using the knife edge method to measure the spot size, the lens with a focal length of 50 mm has a diameter of 4.08 mm in the x-direction and 3.89 mm in the y-direction; the lens with a focal length of 100 mm has a diameter of 4.24 mm in the x-direction and 4.05 mm in the y-direction. Since mixing ceramics powders into materials is an effective way to increase refractive indices and decrease absorption coefficients, this method could be applied to 3D printing technology to enhance the efficiency of 3D-printed THz components.

1. T. S. Rappaport, Y. Xing, O. Kanhere, S. Ju, A. Madanaya, A. Manday, A. Alkhateeb, and G. C. Trichopoulos, "Wireless communications and applications above 100 GHz: opportunities and challenges for 6G and beyond," IEEE Access 7, 78729-78757(2019).
2. Z. Zhang, Y. Xiao, Z. Ma, M. Xiao, Z. Ding, X. Lei, G. Karagiannidis and P. Fan, "6G wireless networks: vision, requirements, architecture, and key technologies," IEEE Vehicular Technology Magazine 14, 28-41 (2019).
3. S. Wang, T. Yuan, E. Walsby, R. Blaikie, S. Durbin, D. Cumming, J. Xu, and X. Zhang, "Characterization of T-ray binary lenses," Optics Letters 27, 1183-1185 (2002).
4. M. Komlenok, B. Volodkin, B. Knyazev, T. Kononenko, V. Kononenko, V. Konov, V. Soifer, V. Pavel'ev, K. Tukmakov, and Y. Choporova, "Fabrication of a multilevel THz fresnel lens by femtosecond laser ablation," Quantum Electronics 45, 933-936 (2015).
5. M. Sypek, M. Makowski, E. Hérault, A. Siemion, A. Siemion, J. Suszek, F. Garet, and J. L. Coutaz, "Highly efficient broadband double-sided Fresnel lens for THz range," Optics Letters 37(12), 2214–2216 (2012).
6. A. Moazami, M. Hashemi and N.C. Shirazi, "High efficiency tunable graphene-based plasmonic filter in the THz frequency range," Plasmonics, 14(2), 359-363 (2019).
7. M. Nagel, A. Marchewka, and H. Kurz, "Low-index discontinuity terahertz waveguides," Optics Express 14, 9944-9954 (2006).
8. S. Atakaramians, S. Afshar, T. Monro, and D. Abbott, "Terahertz dielectric waveguides," Advances in Optics and Photonics 5, 169-215 (2013).
9. D. Chen, and H. Chen, "A novel low-loss Terahertz waveguide: Polymer tube," Optics Express 18, 3762-3767 (2010).
10. C. F. Hsieh, C. S. Yang, F. C. Shih, R. P. Pan, and C. L. Pan, "Liquid-crystal-based magnetically tunable terahertz achromatic quarter-wave plate," Optics Express 27(7), 9933–9940 (2019).
11. X. P. Dong, J. R. Cheng, F. Fan, S. T. Xu, X. H. Wang, and S. J. Chang, "Wideband sub-THz half-wave plate using 3D-printed low-index metagratings with superwavelength lattice," Optics Express 27(1), 202-211 (2019).
12. A. Squires, E. Constable, and R. Lewis, "3D printed terahertz diffraction gratings and lenses," Journal of Infrared, Millimeter, and Terahertz Waves 36(1), 72–80 (2015).
13. D. Jahn, M. Weidenbach, J. Lehr, L. Becker, F. Beltrán-Mejía, S. F. Busch, J. C. Balzer, and M. Koch, "3D printed terahertz focusing grating couplers," Journal of Infrared, Millimeter, and Terahertz Waves 38(6), 708–716 (2017).
14. J. M. Seifert, G. G. Hernandez-Cardoso, M. Koch, and E. Castro-Camus, "Terahertz beam steering using active diffraction grating fabricated by 3D printing," Optics Express 28(15), 21737 (2020).
15. S. Atakaramians, S. Afshar, H. Ebendorff-Heidepriem, M. Nagel, B. Fischer, D. Abbott, and T. Monro, "THz porous fibers: design, fabrication and experimental characterization," Optics Express 17, 14053-14062 (2009).
16. K. Nielsen, H. Rasmussen, A. Adam, P. Planken, O. Bang, and P. Jepsen, "Bendable, low-loss topas fibers for the terahertz frequency range," Optics Express 17, 8592-8601 (2009).
17. J. Anthony, R. Leonhardt, S. Leon-Saval, and A. Argyros, "THz propagation in kagome hollow-core microstructured fibers," Optics Express 19, 18470-18478 (2011).
18. M. Hoy, "3D printing: making things at the library," Medical Reference Services Quarterly 32, 93-99 (2013).
19. J. Banks, "Adding value in additive manufacturing: researchers in the united kingdom and europe look to 3D printing for customization," IEEE Pulse 4, 22-26 (2013).
20. Q. Yan, H. Dong, J. Su, J. Han, B. Song, Q. Wei and Y. Shi, "A review of 3D printing technology for medical applications," Engineering 4, 729-742 (2018).
21. J. Lee, H. Kim, J. Choi and I. Lee, "A review on 3D printed smart devices for 4D printing," International Journal of Precision Engineering and Manufacturing-Green Technology 4, 373-383 (2017).
22. S. Joshi and A. Sheikh, "3D printing in aerospace and its long-term sustainability," Virtual and Physical Prototyping 10, 175-185 (2015).
23. M. Sakin and Y. Kiroglu, "3D printing of buildings: construction of the sustainable houses of the future by BIM," Energy Procedia 134, 702-711 (2017).
24. S. Busch, M. Weidenbach, M. Fey, F. Schäfer, T. Probst and M. Koch, "Optical properties of 3D printable plastics in the THz regime and their application for 3D printed THz optics," Journal of Infrared, Millimeter, and Terahertz Waves 35, 993-997 (2014).
25. W. Furlan, V. Ferrando, J. Monsoriu, P. Zagrajek, E. Czerwińska and M. Szustakowski, "3D printed diffractive terahertz lenses," Optics Letters 41, 1748 (2016).
26. J. Suszek, A. Siemion, M. S. Bieda, N. Blocki, D. Coquillat, G. Cywinski, E. Czerwinska, M. Doch, A. Kowalczyk, N. Palka, A. Sobczyk, P. Zagrajek, M Zaremba, A. Kolodziejczyk, W. Knap, and M. Sypek, "3-D-printed flat optics for THz linear scanners," IEEE Transactions on Terahertz Science and Technology. 5(2), 314–316 (2015).
27. B. Zhang, Y.X. Guo, Q. Guo, L. Wu, K.B. Ng, H. Wong, Y. Zhou, and K. Huang, "Dielectric and metallic jointly 3D-printed mm wave hyperbolic lens antenna," IET Microwaves Antennas Propagation 13(11), 1934-1939, (2019).
28. Y. Yang, L. Niu, Z. Yang, and Jinsong Liu, "Measuring the topological charge of terahertz vortex beams with a focal hyperbolic lens," Applied Optics 59(15), 4685-4691 (2020).
29. L.D. van Putten, J. Gorecki, E. Numkam Fokoua, V. Apostolopoulos, F. Poletti, "3D-printed polymer antiresonant waveguides for short-reach terahertz applications," Applied Optics 57(14), 3953–3958 (2018).
30. J. Yang, J. Zhao, C. Gong, H. Tian, L. Sun, P. Chen, L. Lin and W. Liu, "3D printed low-loss THz waveguide based on kagome photonic crystal structure," Optics Express 24, 22454-22460 (2016).
31. S. Pandey, B. Gupta and A. Nahata, "Terahertz plasmonic waveguides created via 3D printing," Optics Express 21, 24422-24430 (2013).
32. A. K. Klein, J. Hammler, C. Balocco and A. J. Gallant, "Machinable ceramic for high performance and compact THz optical components," Optical Materials Express 8(7), 1968-1975 (2018).
33. M. Naftaly and R. Miles, "Terahertz beam interactions with amorphous materials," R.E Naftaly et al. (eds), Terahertz Frequency Detection and Identification of Materials and Objects, Springer, 107-122 (2007).
34. J. R. Middendorf, D. A. LeMaster, M. Zarepoor and E. R. Brown1, "Design of multi-order diffractive THz lenses," in 2012 37Th International Conference on Infrared, Millimeter, And Terahertz Waves (2012).
35. E. Walsby, S. Wang, J. Xu, T. Yuan, R. Blaikie, S. Durbin, X. Zhang and D. Cumming, "Multilevel silicon diffractive optics for terahertz waves," Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 20, 2780-2783 (2002).
36. B. Scherger, M. Scheller, C. Jansen, M. Koch and K. Wiesauer, "Terahertz lenses made by compression molding of micropowders," Applied Optics 50, 2256-2262 (2011).
37. R. Piesiewicz, C. Jansen, S. Wietzke, D. Mittleman, M. Koch, and T. Kürner, "Properties of building and plastic materials in the THz range," International Journal of Infrared and Millimeter Waves 28, 363-371 (2007).
38. N. Duangrit, B. Hong, A. Burnett, P. Akkaraekthalin, I. Robertson, and N. Somjit, "Terahertz dielectric property characterization of photopolymers for additive manufacturing," IEEE Access 7, 12339-12347 (2019).
39. X. Chen, J. Han, W. Zhang, and L. Zhang, "Silica‐based ceramic core for aviation applications: Facile pore filling and flexural strength improvement," Interational Journal of Applled Ceramic Technology 16(6), 2181-2189 (2019).
40. E. N. Kablov, D. V. Grashchenkov, N. V. Isaeva, S. S. Solntsev, and V. G. Sevast’yanov, "Glass and ceramics based high-temperature composite materials for use in aviation technology," GLASS CERAM+. 69(3-4), 109-112 (2012).
41. J. Li, and G.W. Hastings, "Oxide bioceramics: inert ceramic materials in medicine and dentistry," Handbook of biomaterial properties 339-352 (2016).
42. S.M. Barinov, "Calcium phosphate-based ceramic and composite materials for medicine," Russian Chemical Reviews 79(1), 13 (2010).
43. S. Balasubramanian, B. Gurumurthy, "Biomedical applications of ceramic nanomaterials: a review," Internstional Journal of Pharmaceutical Sciences and Research 8(12), 4950-4959 (2017).
44. P. Pálvölgyi, D. Sebők, I. Szenti, E. Bozo, H. Ervasti, O. Pitkänen, J. Hannu, H. Jantunen, M. Leinonen, S. Myllymäki, A. Kukovecz and K. Kordas, "Lightweight porous silica foams with extreme-low dielectric permittivity and loss for future 6G wireless communication technologies," Nano Research 14, 1450-1456 (2021).
45. S. Busch, M. Weidenbach, J. Balzer and M. Koch, "THz optics 3D printed with TOPAS," Journal of Infrared, Millimeter, and Terahertz Waves 37, 303-307 (2015).
46. J. Sun and F. Hu, "Three‐dimensional printing technologies for terahertz applications: A review," International Journal of RF and Microwave Computer-Aided Engineering 30, (2019).
47. Thorlabs.com. 2022. PTFE Plano-Convex Lenses. [online] Available at: <https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1627> [Accessed 27 July 2022].
48. Batop.de. 2022. THz lenses. [online] Available at: <https://www.batop.de/products/terahertz/THz-parts/THz-parts.html> [Accessed 30 July 2022].
49. Y.A. Wei, "Magnetically tunable terahertz phase modulator based on the ferrofluid," National Taiwan Normal University, Master, 202008.
50. F. Alves, D. Grbovic, B. Kearney, N.V. Lavrik, and G. Karunasiri, "Bi-material terahertz sensors using metamaterial structures," Optics Express 21(11), 13256-13271 (2013).
51. V. Spagnolo, P. Patimisco, R. Pennetta, A. Sampaolo, G. Scamarcio, M. Vitiello and F. Tittel, "THz Quartz-enhanced photoacoustic sensor for H2S trace gas detection," Optics Express 23, 7574 (2015).
52. S. Yoshida, E. Kato, K. Suizu, Y. Nakagomi, Y. Ogawa and K. Kawase, "Terahertz sensing of thin poly (ethylene Terephthalate) film thickness using a metallic mesh," Applied Physics Express 2, 012301 (2009).
53. L. Valzania, P. Zolliker and E. Hack, "Coherent reconstruction of a textile and a hidden object with terahertz radiation," Optica 6, 518 (2019).
54. K. Ajito, Y. Ueno, H. Song, E. Tamechika and N. Kukutsu, "Terahertz chemical imaging of molecular networks for pharmaceutical applications," ECS Transactions 35, 157-165 (2019).
55. M. Kemp, P. Taday, B. Cole, J. Cluff, A. Fitzgerald and W. Tribe, "Security applications of terahertz technology," Terahertz for Military and Security Applications, 44-52, (2003).
56. M. Mumtaz, A. Mahmood, S. D. Khan, M. A. Zia, M. Ahmed, and I. Ahmad, "Investigation of dielectric properties of polymers and their discrimination using terahertz time-domain spectroscopy with principal component analysis," Applied Spectroscopy 71(3), 456–462 (2017).
57. E. Jung, H.-J. Choi, M. Lim, H. Kang, H. Park, H. Han, B.-H. Min, S. Kim, I. Park, and H. Lim, "Quantitative analysis of water distribution in human articular cartilage using terahertz time-domain spectroscopy," Biomedical Optics Express 3(5), 1110–1115 (2012).
58. K. M. Mølster, T. Sørgård, H. Laurell, C. Canalias, V. Pasiskevicius, F. Laurell, and U. Österberg, "Time-domain spectroscopy of KTiOPO4 in the frequency range 0.6-7.0 THz," OSA Continuum 2(12), 3521–3538 (2019).
59. A. J. Seeds, H. Shams, M. J. Fice, and C. C. Renaud, "Terahertz photonics for wireless communications," Journal of Lightwave Technology 33(3), 579–587 (2015).
60. W. Yang and Y. S. Lin, "Tunable metamaterial filter for optical communication in the terahertz frequency range," Opt. Express 28(12), 17620-17629 (2020).
61. H. Shams, M. J. Fice, K. Balakier, C. C. Renaud, F. van Dijk, and A. J. Seeds, "Photonic generation for multichannel THz wireless communication," Optics Express 22(19), 23465–23472 (2014).
62. V. Mazzanti, L. Malagutti and F. Mollica, "FDM 3D printing of polymers containing natural fillers: A review of their mechanical properties," Polymers 11, 1094 (2019).
63. R. Matsuzaki, M. Ueda, M. Namiki, T. Jeong, H. Asahara, K. Horiguchi, T. Nakamura, A. Todoroki and Y. Hirano, "Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation," Scientific Reports 6, (2016).
64. R. Singh, A. Gupta, O. Tripathi, S. Srivastava, B. Singh, A. Awasthi, S.K. Rajput, P. Sonia, P. Singhal, K.K. Saxena "Powder bed fusion process in additive manufacturing: an overview," Materials Today Proceedings 26, 3058-3070 (2020)
65. C. Vyas, G. Poologasundarampillai, J. Hoyland and P. Bartolo, "3D printing of biocomposites for osteochondral tissue engineering," Biomedical Composites 261-302 (2017).
66. P. Robles Martinez, A. Basit and S. Gaisford, "The history, developments and opportunities of stereolithography," 3D Printing of Pharmaceuticals 55-79 (2018).
67. A. Bagheri and J. Jin, "Photopolymerization in 3D printing," ACS Applied Polymer Materials 1, 593-611 (2019).
68. M. Pagac, J. Hajnys, Q. Ma, L. Jancar, J. Jansa, P. Stefek and J. Mesicek, "A review of vat photopolymerization technology: materials, applications, challenges, and future trends of 3D printing," Polymers 13, 598 (2021).
69. N. Nguyen, C. Bowland and A. Naskar, "A general method to improve 3D-printability and inter-layer adhesion in lignin-based composites," Applied Materials Today 12, 138-152 (2018).
70. C. Kuo, L. Liu, W. Teng, H. Chang, F. Chien, S. Liao, W. Kuo and C. Chen, "Preparation of starch/ acrylonitrile-butadiene-styrene copolymers (ABS) biomass alloys and their feasible evaluation for 3D printing applications," Composites Part B: Engineering 86, 36-39 (2016).
71. A. Torrado Perez, D. Roberson and R. Wicker, "Fracture surface analysis of 3D-printed tensile specimens of novel ABS-Based Materials," Journal of Failure Analysis and Prevention 14, 343-353 (2014).
72. S. Selvamani, M. Samykano, S. Subramaniam, W. Ngui, K. Kadirgama, G. Kanagaraj and M. Idris, "3D printing: Overview of ABS evolvement," AIP Conference Proceedings, 2059(1),020041 (2019).
73. T. Letcher and M. Waytashek, "Material property testing of 3D-printed specimen in PLA on an entry-level 3D printer," in 2014 International Mechanical Engineering Congress And Exposition , 1-8 (2014).
74. M. Jamshidian, E. Tehrany, M. Imran, M. Jacquot and S. Desobry, "Poly-lactic acid: Production, applications, nanocomposites, and release studies," Comprehensive Reviews in Food Science and Food Safety 9, 552-571 (2010).
75. V. Mazzanti and F. Mollica, "Rheological behavior of wood flour filled poly (lactic acid): Temperature and concentration dependence," Polymer Composites 40, E169-E176 (2017).
76. S. Wojtyła, P. Klama and T. Baran, "Is 3D printing safe? Analysis of the thermal treatment of thermoplastics: ABS, PLA, PET, and nylon," Journal of Occupational and Environmental Hygiene 14, D80-D85 (2017).
77. X. Zhang, W. Fan and T. Liu, "Fused deposition modeling 3D printing of polyamide-based composites and its applications," Composites Communication 21, 100413 (2020).
78. Y. Jia, H. He, X. Peng, S. Meng, J. Chen and Y. Geng, "Preparation of a new filament based on polyamide-6 for three-dimensional printing," Polymer Engineering & Science 57, 1322-1328 (2017).
79. C. Cai, W. Tey, J. Chen, W. Zhu, X. Liu, T. Liu, L. Zhao and K. Zhou, "Comparative study on 3D printing of polyamide 12 by selective laser sintering and multi jet fusion," Journal of Materials Processing Technology 288, 116882 (2021).
80. J. Colla, R. Vickers, M. Nancarrow and R. Lewis, "3D printing metallised plastics as terahertz reflectors," Journal of Infrared, Millimeter, and Terahertz Waves 40, 752-762 (2019).
81. X. Chen, J. Han, W. Zhang, and L. Zhang, C. Liu, "Silica‐based ceramic core for aviation applications: Facile pore filling and flexural strength improvement," International Journal of Applied Ceramic Technology 16(6), 2181-2189 (2019).
82. E. N. Kablov, D. V. Grashchenkov, N. V. Isaeva, S. S. Solntsev, and V. G. Sevast’yanov, "Glass and ceramics based high-temperature composite materials for use in aviation technology," Glass and ceramics. 69(3-4), 109-112 (2012).
83. J. Li, and G.W. Hastings, "Oxide bioceramics: inert ceramic materials in medicine and dentistry," Handbook of biomaterial properties 339-352 (2016).
84. S.M. Barinov, "Calcium phosphate-based ceramic and composite materials for medicine," Russian Chemical Reviews 79(1), 13 (2010).
85. P. S. Pálvölgyi, D. Sebők, I. Szenti, E. Bozo, H. Ervasti, O. Pitkänen, J. Hannu, H. Jantunen, M. E. Leinonen, S. Myllymäki, A. Kukovecz and K. Kordas, " Lightweight porous silica foams with extreme-low dielectric permittivity and loss for future 6G wireless communication technologies," Nano Research 14, 1450-1456 (2021).
86. Y. Ko, W. Kwon and Y. Kim, "Development of Al2O3–SiC composite tool for machining application," Ceramics International 30, 2081-2086 (2004).
87. A. Senthil Kumar, A. Raja Durai and T. Sornakumar, "The effect of tool wear on tool life of alumina-based ceramic cutting tools while machining hardened martensitic stainless steel," Journal of Materials Processing Technology 173, 151-156 (2006).
88. J. Houska, J. Blazek, J. Rezek and S. Proksova, "Overview of optical properties of Al2O3 films prepared by various techniques," Thin Solid Films 520, 5405-5408 (2012).
89. Y. Kim, M. Yi, B. G. Kim and J. Ahn, "Investigation of THz birefringence measurement and calculation in Al2O3 and LiNbO3," Applied Optics 50(18), 2906-2910 (2011).
90. J. Ornik, M. Sakaki, M. Koch, J. Balzer and N. Benson, "3D Printed Al2O3 for Terahertz Technology," IEEE Access 9, 5986-5993 (2021).
91. G. Komandin, V. Nozdrin, A. Gavdush, A. Pronin, O. Porodinkov, I. Spektor, V. Sigaev, A. Mikhailov, G. Shakhgildyan, V. Ulitko and D. Abdullaev, "Effect of moisture adsorption on the broadband dielectric response of SiO2-based nanoporous glass," Journal of Applied Physics 126, 224303 (2019).
92. C. Davies, J. Patel, C. Xia, L. Herz and M. Johnston, "Temperature-dependent refractive index of quartz at terahertz frequencies," Journal of Infrared, Millimeter, and Terahertz Waves 39, 1236-1248 (2018).
93. R. Ghosh, "A review study on precipitated silica and activated carbon from rice husk," Journal of Chemical Engineering & Process Technology 4(4), 1-7, (2013).
94. R. Madrid, C.A. Nogueira, F. Margarido, "Production and characterisation of amorphous silica from rice husk waste," Proceedings 4th International Conference on Engineering for Waste and Biomass Valorisation, September 10–13, 2012 – Porto, 4, (2012).
95. V. Della, I. Kühn and D. Hotza, "Rice husk ash as an alternate source for active silica production," Materials Letters 57, 818-821 (2002).
96. A. Proctor, "X-ray diffraction and scanning electron microscope studies of processed rice hull silica," Journal of the American Oil Chemists' Society 67, 576-584 (1990).
97. R. Mittal, S. Chaplot, R. Parthasarathy, M. Bull and M. Harris, "Lattice dynamics calculations and phonon dispersion measurements of zircon, ZrSiO4," Physical Review B 62, 12089-12094 (2000).
98. Musyarofah, R. Nurlaila, N. Muwwaqor, M. Saukani, A. Kuswoyo, Triwikantoro and S. Pratapa, "Phase study of SiO2-ZrO2 composites prepared from polymorphic combination of starting powders via a ball-milling followed by calcination," Journal of Physics: Conference Series 817, 012033 (2017).
99. L. Sun and K. Gong, "Silicon-based materials from rice husks and their applications," Industrial & Engineering Chemistry Research 40(25), 5861-5877 (2001)
100. T. Brabec, C. Spielmann, P. Curley and F. Krausz, "Kerr lens mode locking," Optics Letters 17, 1292 (1992).
101. D. Strickland and G. Mourou, "Compression of amplified chirped optical pulses," Optics Communications 55, 447-449 (1985).
102. H. Yi. Peng, C. S. Yang, Y. A. Wei, Y. C. Ruan, Y.C. Hsu, C. F. Hsieh and C. P. Cheng, "Terahertz complex refractive index properties of acrylonitrile butadiene styrene with rice husk ash and its possible applications in 3D printing techniques," Optical Materials Express 11, 2777 (2021).
103. C. S. Yang, C. Lin, R. Pan, C. Que, K. Yamamoto, M. Tani, and C. Pan, "The complex refractive indices of the liquid crystal mixture E7 in the terahertz frequency range," Journal of the Optical Society of America B 27, 1866-1873 (2010)
104. Y. Battie, A. En Naciri, W. Chamorro and D. Horwat, "Generalized effective medium theory to extract the optical properties of two-dimensional nonspherical metallic nanoparticle layers," The Journal of Physical Chemistry C 118, 4899-4905 (2014).
105. W. Ke, M. Miao, B. Liu, Q. Wu and T. Liu, "Structural characteristics and properties of polylactic acid (PLA) and cellulose triacetate (CTA) fibers for heat-not-burn (HNB) cigarettes," IOP Conference Series: Earth and Environmental Science 719, 042044 (2021).
106. N. Song, H. Pan, X. Hou, S. Cui, L. Shi and P. Ding, "Enhancement of thermal conductivity in polyamide-6/graphene composites via a “bridge effect” of silicon carbide whiskers," RSC Advances 7, 46306-46312 (2017).
107. Coursehero.com. 2022. Course Hero. [online] Available at: <https://www.coursehero.com/study-guides/boundless-physics/lenses/> [Accessed 27 July 2022].
108. S. Genieva, S. Turmanova, A. Dimitrova, and L. Vlaev, "Characterization of rice husks and the products of its thermal degradation in air or nitrogen atmosphere," Journal of Thermal Analysis and Calorimetry 93(2), 387-396 (2008).
109. V. Ulitko, A. Zotov, A. Gavdush, G. Katyba, G. Komandin, I. Spektor, I. Shmytko, G. Emelchenko, I. Dolganova, M. Skorobogatiy, V. Kurlov, V. Masalov and K. Zaytsev, "Nanoporous SiO2 based on annealed artificial opals as a favorable material platform of terahertz optics," Optics Mater. Express 10(9), 2100-2133 (2020).
110. T. Suzuki, K. Takayama, S. Yamauchi, Y. Imai, and M. Tonouchi, "Measurement of water absorption coefficient using terahertz time-domain spectroscopy," 2009 34th International Conference on Infrared, Millimeter, and Terahertz Waves (2009).
111. Batop.de. 2022. [online] Available at: <https://www.batop.de/products/terahertz/THz-parts/data-sheet/TPX-D50.8-f100.pdf> [Accessed 27 July 2022].
112. X. D. Yang, J. X. Shao, S. H. Liao, J. Y. Tan, J. Zhou, Y.W. Jiang, "Investigation on measuring beam width of the gaussian beam by knife-edge method," Laser & Lnfrared 39(8), 829-831(2009).
113. A. Sadeqi, H. Rezaei Nejad, R. Owyeung and S. Sonkusale, "Three dimensional printing of metamaterial embedded geometrical optics (MEGO)," Microsystems &amp; Nanoengineering 5, (2019).