image: Figure | (Carbon-Based Advanced Manufacturing) Working principle of Printing THz Metasurfaces Using Carbon Materials. a, Flowchart of the carbon-based additive manufacturing method. b, Carbon-based materials: carbon black, graphene, graphene oxide. c, Carbon-based ink preparation process. d, Schematic of syringe. e, Schematic of dual-mode printing system. f, Schematic of 3D direct-write printing. g, Structures of the metasurface absorbers. h, Structure of the metasurface filter.
Credit: Cheng Gong et al.
Terahertz band lies between microwave and infrared spectra, is recognized as a critical frequency band for next-generation 6G communication, high-resolution sensing, non-destructive testing and other fields. As planar optical devices composed of artificial subwavelength microstructures, terahertz metasurfaces enable flexible modulation of terahertz wave amplitude, phase and polarization, making them core components of new-generation terahertz systems. Nevertheless, conventional metasurface fabrication heavily relies on sophisticated processes such as photolithography and electron beam lithography. These techniques feature high costs and complicated workflows, and are incapable of large-area, low-cost mass production on flexible substrates. This greatly hinders the translation of terahertz metasurface technology from laboratory research to practical applications.
In a new paper published in Light: Advanced Manufacturing, a team of scientists, led by Professors Cheng Gong and Shengjiang Chang from the Institute of Modern Optics, Nankai University, China, and co-workers have developed a dual-mode additive manufacturing technique that enables direct printing fabrication of terahertz metasurfaces using carbon-based nanocomposites. This technique integrates the complementary merits of high-precision electric-driven jet printing and high-viscosity extrusion printing. The jet printing mode shapes delicate resonant microstructures with a measured minimum linewidth of 55 μm, sufficient to construct subwavelength resonant units operating in the terahertz band. The extrusion printing mode operates simply and rapidly without high voltage, preserving intrinsic material properties and suiting large-area coating and thick-film fabrication. The research group systematically optimized the electrical and rheological properties of carbon-based composite inks as well as printing parameters to guarantee appropriate conductivity and printability of printed patterns. On this basis, two terahertz absorbers and one terahertz filter were fabricated on diverse flexible substrates (PET and paper) and experimentally characterized. Measurement results reveal that the device performances match simulation designs closely, and favorable frequency stability is maintained even under bending deformation.
This study verifies the feasibility of carbon-based additive manufacturing for fabricating terahertz metasurface devices. Its core innovation lies in bypassing the multi-step procedures of traditional photolithography and realizing an integrated "design-to-print" manufacturing paradigm, which drastically reduces fabrication complexity and cost barriers of devices. Meanwhile, the inherent flexibility and chemical stability of carbon materials make the devices inherently compatible with flexible and wearable applications. The tunability of ink formulations also provides ample room for flexible design of resonant frequency bands. Furthermore, this technology imposes almost no restrictions on substrate selection, opening up a new route for heterogeneous integration of terahertz metasurfaces with flexible electronics, biosensors and other systems.
Scientists summarized the core idea of this technology:
“We tried a method of directly' printing' terahertz functional devices with carbon-based nano-materials, which made the manufacture of super-surfaces as simple as printing pictures.”
"With this technology, terahertz metasurface devices are expected to be integrated into flexible terminal equipment at extremely low costs in the future, offering plug-and-play photonic solutions for integrated 6G communication and sensing, wearable health monitoring, on-line industrial non-destructive testing and other scenarios," the scientists predicted. With continuous upgrades in printing precision and ink systems, this technology can be extended to higher frequency bands. Combined with machine learning-aided inverse design, it will usher in a new era of "on-demand printing" for terahertz photonics.
Journal
Light: Advanced Manufacturing
Article Title
Carbon-based manufacturing for flexible terahertz metasurfaces