Abstract-Secrecy performance of terahertz wireless links in rain and snow

 

Rong Wang, Yu Mei, Xiangzhu Meng, Jianjun Ma, 

https://www.sciencedirect.com/science/article/abs/pii/S1878778921000119

Wireless communication technique operating at terahertz (THz) frequencies is regarded as the most potential candidate for future wireless networks due to its wider frequency bandwidth and higher directionality when compared with that employing radio frequency (RF) and millimeter waves (mmWaves). It has been proved that the high directionality owned by THz wireless links could help to reduce the possibility of eavesdropping attacks at physical layer. However, for outdoor applications in adverse weathers (such as water fog, dust fog, rain and snow), scattering and absorption effects suffered by a THz link due to weather particles and gaseous molecules could degrade its secrecy performance seriously. In this work, we present theoretical investigations on physical layer security of a point-to-point THz link in rain and snow with a potential eavesdropper locating outside of the legitimate link path. Signal degradation due to rain/snow, gaseous attenuation and beam divergence are included in a theoretical model to estimate the link performance. Secrecy capacity of the link with carriers at 140, 220 and 340 GHz is calculated and compared. We find that the rain/snow intensity, carrier frequency and receiver sensitivity could affect the secrecy performance and their influence on insecure region and maximum safe data transmission rate is discussed and summarized.

Abstract-3D direct writing of terahertz metamaterials based on TbFeO3 dielectric ceramics

Applied Physics Letters

Xinxi Zeng, Rong Wang, Xiaoqing Xi, Bo Li,  Ji Zhou

https://aip.scitation.org/doi/abs/10.1063/1.5035123

The integration of terahertz waves with metamaterials has become a key goal in modern photonics. In this work, we designed grating-structured metamaterials and face-centered-cubic (fcc) metamaterials based on TbFeO3 dielectric ceramics and built these materials using 3D direct writing technology. To simulate the behavior of the designed TbFeO3 metamaterials, the dielectric constant of TbFeO3 dielectric ceramic materials was determined. The desired strong electric and magnetic resonances were excited in the designed TbFeO3 metamaterials. The grating-structured metamaterials showed increased polarization-dependent transmittance as the line spacing decreased, while the fcc metamaterial showed a deep transmission dip at low frequencies and an electromagnetically induced increase in transmittance at higher frequencies. An increase in the electrical resistance contributed to the increase in the transmission properties of the fcc TbFeO3 metamaterial as its temperature decreased, while a reduction in the dielectric constant of TbFeO3 simultaneously caused a blueshift in this metamaterial. When combined with 3D direct writing technology, TbFeO3, with its high dielectric constant and low loss characteristics, represents an inexpensive and promising step towards the production of the next generation of low-cost, easy-to-fabricate, all-dielectric metamaterials.

Abstract-A Modularized and Switchable Component for Flexible Passive Device: Terahertz Photonic Crystals with Fine‐Tuning

Jiannan Gao, Rong Wang, Qian Zhao, Bo Li, Ji Zhou,




https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201800384?af=R

In this work, tunable terahertz photonic crystals (PCs) used as modularized and switchable components in flexible passive device are designed and prepared. Flexible woodpile structures created by the direct‐writing technology with a composite ink system composed of barium strontium titanate nanoparticles and polydimethylsiloxane are immersed in 5CB liquid crystals (LCs), where the orientation of LC molecule is modulated by the external magnetic field. Each of these can work in terahertz wavelength with specific position and depth of the dips in the transmittance spectra due to different geometries as well as having the ability of fine‐tuning. Experiments show that the photonic gaps of these PCs can cover from 0.2 to 0.3 THz, as well as about 7.5% fine tunability of photonic gap appearing with the orientation change of the magnetic field. More interestingly, the dips of photonic gaps keep the same position but become deeper with the increase of layer, an ability to realize another dimensional switchover. This work demonstrates that efficient terahertz PCs with different geometry parameters could be dynamically tuned by the orientation of magnetic field and it can open a universal approach to shrinking the size of device and rapid manufacturing in a large throughput.

Abstract-Creation of 3D terahertz photonic crystals by the direct writing technique with a TiO2 sol-gel ink

Rong Wang, Weiyi Yang, Pengfei Zhu, Shuang Gao, Bo Li, Qi Li

http://onlinelibrary.wiley.com/doi/10.1111/jace.15347/abstract

Three-dimensional TiO2 woodpile terahertz photonic crystals with feature size less than 100 μm were created by the direct writing technique with a TiO2 sol-gel ink. With proper heat treatment, the rheological properties of the TiO2 sol-gel ink were modulated to meet the requirement to construct 3D-TPCs with feature size less than 100 μm by the direct writing technique. Well-crystallized rutile TiO2 3D-TPCs were obtained by the calcination process to provide the required high refractive indices, while the lattice periods of these TiO2 3D-TPCs could be changed to tune their terahertz properties. With the increase of the lattice period, a shift of their THz photonic band gap peaks towards the lower frequency was observed in both the simulated and experimental investigations.

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Abstract-Direct Writing of Flexible Barium Titanate/Polydimethylsiloxane 3D Photonic Crystals with Mechanically Tunable Terahertz Properties

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600977/full

Mechanically flexible 3D terahertz photonic crystals (3D-TPCs) are created by the direct-writing technology with a composite ink system composed of polydimethylsiloxane (PDMS) and barium titanate (BaTiO3) nanoparticles. The direct-writing technology allows an easy creation of complex 3D structures with designed geometry, while the refractive indices of the composite ink can be modulated by varying the content of BaTiO3 nanoparticles. Thus, 3D-TPCs with different terahertz properties are obtained by the direct-writing technology. More interestingly, these 3D-TPCs demonstrate a unique tunable terahertz property under external force field due to their mechanical flexibility from the PDMS matrix of the composite ink. Thus, their terahertz property is responsive to external force fields reversibly, which can find novel applications in terahertz technology and other related technological applications

Abstract-Electromagnetic resonant properties of metal-dielectric-metal (MDM) cylindrical microcavities

Hang Heng, Rong Wang

http://link.springer.com/article/10.1007/s13320-017-0379-3

Optical metamaterials can concentrate light into extremely tiny volumes to enhance their interaction with quantum objects. In this paper, a cylindrical microcavity based on the Au-dielectric-Au sandwiched structure is proposed. Numerical study shows that the cylindrical microcavity has the strong ability of localizing light and confining 103–~104–fold enhancement of the electromagnetic energy density, which contains the most energy of the incoming light. The enhancement factor of energy density G inside the cavity shows the regularities as the change in the thickness of the dielectric slab, dielectric constant, and the radius of gold disk. At the normal incidence of electromagnetic radiation, the obtained reflection spectra operate in the range from 4.8 μm to 6 μm and with the absorption efficiency C (C=1–Rmin), which can reach 99% by optimizing the structure’s geometry parameters, and the dielectric constant. Due to the symmetry of the cylindrical microcavities, this structure is insensitive to the polarization of the incident wave. The proposed optical metamaterials will have potential applications in the surface enhanced spectroscopy, new plasmonic detectors, bio-sensing, solar cells, etc.