Abstract-A flexible ultra-wideband terahertz absorber based on vertically aligned carbon nanotubes

Dongyang Xiao, Minmin Zhu, Leimeng Sun, Chun Zhao, Yurong Wang, Edwin Hang Tong Teo, Fangjing Hu, Liangcheng Tu

https://pubs.acs.org/doi/10.1021/acsami.9b14428

Ultra-wideband absorbers have found wide applications in wireless communications, energy harvesting and stealth applications. Herein, with the combination of experimental and theoretical analyses, we develop a flexible ultra-wideband terahertz (THz) absorber based on vertically aligned carbon nanotubes (VACNTs). Measured results show that the proposed absorber is able to work efficiently within the entire THz region (e.g., 0.1 to 3.0 THz), with an average power absorptance of >98% at normal incidence. The absorption performance remains very high over a wide incident angle up to 60 degree More importantly, our devices can function normally, even after being bent up to 90 degree or after 300 times of bending. The total thickness of the device is about 360 μm, which is only 1/8 of the wavelength for the lowest evaluated frequency of 0.1 THz. The new insight into the VACNT materials paves the way for applications such as radar cross-section reduction, electromagnetic interference shielding and flexible sensing due to the simplicity, flexibility, ultra-wideband operation and large-scale fabrication of the device.

Abstract-Three‐dimensional printing technologies for terahertz applications: A review

Jingye Sun, Fangjing Hu,

https://onlinelibrary.wiley.com/doi/abs/10.1002/mmce.21983

Three‐dimensional (3D) printing technologies enables fast prototyping of complex 3D objects with ever improving printing qualities. To date, 3D printing has been found useful in areas such as manufacturing, industrial design, aerospace, dental and medical industries, and many others. In this article, we review recent advances of 3D printing technologies for terahertz (THz) applications. Different 3D printing technologies and printable materials are first discussed and compared. 3D‐printed THz components and devices, which are categorized as waveguides/fibers, antennas, and quasi‐optical components, are further demonstrated. It is found that the performances and functionalities of 3D‐printed THz devices have been greatly enhanced, while the operating frequencies have been increased from the lower end of THz range to over 1 THz region. With further development of novel materials and printing techniques, it is believed that 3D printing technologies will play an important role in the realization of THz components for efficient control and manipulation of THz waves.

Abstract-Wafer-scale vertically aligned carbon nanotubes for broadband terahertz wave absorption

Leimeng Sun, Minmin Zhu, Chun Zhao, Peiyi Song, Yurong Wang, Dongyang Xiao, Huafeng Liu, Siu HonTsang, Edwin HangTong Teo, Fangjing Hu, Liangcheng Tu,

https://www.sciencedirect.com/science/article/pii/S0008622319307985

Materials with high and broadband absorption characteristics in the terahertz (THz) range are desirable for many applications. In this paper, we propose, fabricate and experimentally demonstrated a wafer-scale vertically aligned carbon nanotube (VACNT) array for broadband THz wave absorption. The effects of VACNT parameters on the absorption performance are investigated within the THz and infrared spectra using the Maxwell-Garnett theory, revealing that the absorption in the THz range can be greatly enhanced by suitable selections of the length, volume fraction and vertical misalignment of CNTs. A VACNT array with an average CNT length of $\sim$600 μm is fabricated on a 4-inch silicon substrate. Experimental results measured by a THz time-domain spectroscopic system show an average power absorptance of $\sim$98% from 0.3 to 2.5 THz, and agree well with the numerical modelling. This device can be used as a cost-effective near-perfect absorber across the THz and infrared regions for thermal emission and imaging, electromagnetic interference shielding, stealth and energy harvesting applications.

Abstract-An Ultra-Wideband THz/IR Metamaterial Absorber Based on Doped Silicon

Huafeng Liu, Kai Luo,  Shihao Tang,  Danhua Peng, Fangjing Hu,  Liangcheng Tu

https://www.mdpi.com/1996-1944/11/12/2590

Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to far-infrared regimes, having an average power absorption of ∼95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband absorption are attributed to the combined effects of multiple cavities modes formed by silicon resonators and bulk absorption in the doped silicon substrate, as confirmed by simulated field patterns and calculated diffraction efficiency. This ultra-wideband absorption is polarization insensitive and can operate across a wide range of the incident angle. The proposed absorber can be readily integrated into silicon-based photonic platforms and used for sensing, imaging, energy harvesting and wireless communications applications in the THz/IR range

Abstract-Ultra-wideband THz/IR Metamaterial Absorber based on Doped Silicon

Huafeng Liu, Kai Luo, Danhua Peng, Fangjing Hu, Liangcheng Tu

https://arxiv.org/abs/1809.09400

Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to mid-infrared, having an average power absorption of >95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband absorptions are attributed to the combined effects of multiple cavities modes formed by silicon resonators and bulk absorption in the substrate, as confirmed by simulated field patterns. This ultra-wideband absorption is polarization insensitive and can operate across a wide range of the incident angle. The proposed absorber can be readily integrated into silicon-based platforms and is expected to be used in sensing, imaging, energy harvesting and wireless communications systems.

Abstract-Predicting Atmospheric Attenuation Under Pristine Conditions Between 0.1 and 100 THz

Jingye Sun,  Fangjing Hu,  Stepan Lucyszyn

Calculated color map of mean band transmittance against frequency and fractional bandwidth for horizontal path links at sea level, using predictions from LBLRTM at 296 K over a 1 km path length

http://ieeexplore.ieee.org/document/7736955/

This multidisciplinary paper reports on a research application-led study for predicting atmospheric attenuation, and tries to bridge the knowledge gap between applied engineering and atmospheric sciences. As a useful comparative baseline, this paper focuses specifically on atmospheric attenuation under pristine conditions, over the extended terahertz spectrum. Three well-known simulation software packages (`HITRAN on the Web', MODTRAN®4, and LBLRTM) are compared and contrasted. Techniques used for modeling atmospheric attenuation have been applied to investigate the resilience of (ultra-)wide fractional bandwidth applications to the effects of molecular absorption. Two extreme modeling scenarios are investigated: horizontal path links at sea level and Earth-space path links. It is shown by example that a basic software package (`HITRAN on the Web') can give good predictions with the former, whereas sophisticated simulation software (LBLRTM) is required for the latter. Finally, with molecular emission included, carrier-to-noise ratio fade margins can be calculated for the effects of line broadening due to changes in macroscopic atmospheric conditions with sub-1-THz ultra-narrow fractional bandwidth applications. Outdoors can be far from pristine, with additional atmospheric contributions only briefly introduced here; further discussion is beyond the scope of this paper, but relevant references have been cited.