Freeze-Dried Carbon Nanotube Aerogels for High-Frequency Absorber Applications

Abstract

A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly porous carbon nanotube (CNT) aerogel prepared by a freeze-drying technique. CNT aerogel structures are shown to be good absorbers with a low reflection coefficient, less than -12 dB at 95 GHz. The reflection coefficient of the novel absorber is 3-4 times lower than that of commercial absorbers with identical geometry. Samples prepared by freeze-drying at -25 °C demonstrate resonance behavior, while those prepared at liquid nitrogen temperature (-196 °C) exhibit a significant decrease in reflection coefficient, with no resonant behavior. CNT absorbers of identical volume based on wet-phase drying preparation show significantly worse performance than the CNT aerogel absorbers prepared by freeze-drying. Treatment of the freeze-dried CNT aerogel with n- and p-dopants (monoethanolamine and iodine vapors, respectively) shows remarkable improvement in the performance of the waveguide embedded absorbers, reducing the reflection coefficient by 2 dB across the band.

Terahertz Birefringent Biomimetic Aerogels Based on Cellulose Nanofibers and Conductive Nanomaterials

“…The porous structure enhanced the interactions of MXene with the THz waves, leading to excellent THz shielding performance of the foams. Random cross-linked CNT and graphene aerogels also exhibited good THz absorption ability as efficient stealth materials due to the synergistic interactions of conducting carbon within the porous structure. , The conjunction of functional nanomaterials with a porous structure in 3D scaffolds is greatly promising for developing lightweight and high-performance THz devices. However, few attempts were made to implement these 3D porous architectures in creating controllable anisotropic porous microstructures for THz devices with high birefringence wherein anisotropy or orientation of the structure plays the key and essential role.…”

Superhydrophobic/Superoleophilic Polyacrylonitrile/Ag Aerogels for the High Efficient Oil/Water Separation and Sensitive Detection of Low‐Concentration Oily Sudan Dyes

“…In general, the as‐obtained aerogel through freeze‐dried process possesses porous structure. [ 34 ] The architecture of the aerogels contains many hierarchical pores, such as minor primary pores between tangled nanofibers and major secondary pores. [ 35 ] These hierarchical microstructure and nanostructure could be clearly observed in SEM images (Figures S4 and S5).…”

Ultra‐Wideband Integrated Graphene‐Based Absorbers for Terahertz Waveguide Systems

“…The bubble‐like structure of CNTs in a polymer matrix has successfully been used to form a CNT‐based absorber, with good performance for a frequency range of 8–16 GHz, [ 33 ] 5‐40 GHz, [ 34 ] and 75–110 GHz. [ 35 ] The performance of such materials above 110 GHz has not been reported to date. In addition, these materials may necessitate additional chemical treatments to improve their performance, [ 35 ] adding fabrication cost and complexity.…”