Search query: Terahertz wave intelligent reflection surface material

Related papers:

abstract: We measured complex refractive indices of materials that transmitted well in the terahertz (THz) range using a tunable, monochromatic pulsed THz wave source and a high sensitivity semiconductor detector. This approach is based on simple monochromatic transmission power measurements. Contrast enhancement by refractive index cladding was employed to measure the complex refractive indices. The experimental results were in good agreement with previously reported values. These results suggested that our approach could be used to quickly analyze material properties, such as surface roughness, and to determine the complex refractive indices of liquids or gases. In addition, as an application of the findings obtained here, we applied an anti reflection polymer film to the silicon prism that served as an output coupler of the THz wave source. The film reduced surface reflection by 25%
author_names: Yoshio Wada

Yoshiharu Urata

Hiroshi Ito

Yasuhiro Higashi
title: Measuring material parameters using a tunable monochromatic terahertz wave source.
venue: Applied optics
year: 2020

abstract: This letter focuses on the secure transmission for an intelligent reflecting surface (IRS) assisted millimeter wave (mmWave) and terahertz (THz) system, in which a base station (BS) communicates with its destination via an IRS, in the presence of a passive eavesdropper. To maximize the system secrecy rate, the transmit beamforming at the BS and the reflecting matrix at the IRS are jointly optimized with transmit power and discrete phase shift constraints. It is first proved that the beamforming design is independent of the phase shift design under the rank one channel assumption. The formulated non convex problem is then converted into two subproblems, which are solved alternatively. Specifically, the closed form solution of transmit beamforming at the BS is derived, and the semidefinite programming (SDP) based method and element wise block coordinate descent (BCD) based method are proposed to design the reflecting matrix. The complexity of our proposed methods is analyzed theoretically. Simulation results reveal that the proposed IRS assisted secure strategy can significantly boost the secrecy rate performance, regardless of eavesdropper's locations (near or blocking the confidential beam)
author_names: Jingping Qiao

Mohamed-Slim Alouini
title: Secure Transmission for Intelligent Reflecting Surface Assisted mmWave and Terahertz Systems
venue: IEEE Wireless Communications Letters
year: 2020

abstract: Recent techniques utilizing reflectarrays or novel metamaterial based surfaces to control wireless propagation environments have attracted great attention. While most solutions focus on sub 6 GHz wireless channel to assist in throughput enhancement, these intelligent surfaces have significant potentials in combating the transmission distance limitation and solving the non line of sight transmission problems for the millimeter wave (30 300 GHz) and Terahertz band (0.3 10 THz) where signal propagation is significantly attenuated in the atmosphere. The Ultra Massive MIMO (UM MIMO) communication framework has been proposed in such frequency bands, which relies on the plasmonic antenna arrays to realize different operation modes, including anomalous reflection, transmission and reception, among others. In this paper, a joint beamforming scheme is developed based on fractional programming optimization to maximize the spectral efficiency under practical consideration of energy constraints of the UM MIMO communication platform. Numerical results are presented to show the performance comparison with existing solutions.
author_names: Shuai Nie

Ian F Akyildiz
title: Beamforming in Intelligent Environments based on Ultra Massive MIMO Platforms in Millimeter Wave and Terahertz Bands
venue: ICASSP 2020 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)
year: 2020

abstract: There was no appropriate antireflection coating material for organic nonlinear optical (NLO) crystal used for terahertz wave generation; therefore, it was difficult to reduce Fresnel's reflection loss of laser power used to excite the emitter crystal until we found that an amorphous polymer "Cytop" was applicable. Here, we demonstrate enhanced terahertz (THz) wave generation from an organic NLO crystal using a coating made from Cytop. With the Cytop coating, surface reflection losses of the excitation light were minimized, resulting in a significant improvement in THz wave generation over a wide frequency range.
author_names: Hirohisa Uchida

Chisa Koyama

Takeshi Takagi

Peibin Wang

Takayuki Kamei

Saroj R Tripathi

Kodo Kawase

Kei Takeya
title: Enhanced Terahertz Wave Generation from Cytop Antireflection Coated DAST Crystal
year: 2020

abstract: Millimeter wave (30 300 GHz) and Terahertz band communications (0.3 10 THz) are envisioned as key wireless technologies to satisfy the demand for Terabit per second (Tbps) links in the 5G and beyond eras. The very large available bandwidth in this ultra broadband frequency range comes at the cost of a very high propagation loss, which combined with the low power of mm wave and THz band transceivers limits the communication distance and data rates. In this paper, the concept of intelligent communication environments enabled by Ultra Massive MIMO platforms is proposed to increase the communication distance and data rates at mm wave and THz band frequencies. An end to end physical model is developed by taking into account the capabilities of novel intelligent plasmonic antenna arrays which can operate in transmission, reception, reflection and waveguiding, as well as the peculiarities of the mm wave and THz band multi path channel. Based on the developed model, extensive quantitative results for different scenarios are provided to illustrate the performance improvements in terms of both achievable distance and data rate in Ultra Massive MIMO environments.
author_names: Shuai Nie

Josep Miquel Jornet

Ian F Akyildiz
title: Intelligent Environments Based on Ultra massive Mimo Platforms for Wireless Communication in Millimeter Wave and Terahertz Bands
venue: ICASSP 2019 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)
year: 2019

abstract: Recently, terahertz (THz) communication has drawn considerable attention as one of the promising technologies for the future wireless communications owning to its ultra wide bandwidth. Nonetheless, one major obstacle that prevents the actual deployment of THz lies in its inherent huge attenuation. Intelligent reflecting surface (IRS) and multiple input multiple output (MIMO) represent two effective solutions for compensating the large pathloss in THz systems. In this paper, we consider an IRS aided multi user THz MIMO system with orthogonal frequency division multiple access, where the sparse radio frequency chain antenna structure is adopted for reducing the power consumption. The objective is to maximize the weighted sum rate via jointly optimizing the hybrid analog/digital beamforming at the base station and reflection matrix at the IRS. {Since the analog beamforming and reflection matrix need to cater all users and subcarriers, it is difficult to directly solve the formulated problem, and thus, an alternatively iterative optimization algorithm is proposed. Specifically, the analog beamforming is designed by solving a MIMO capacity maximization problem, while the digital beamforming and reflection matrix optimization are both tackled using semidefinite relaxation technique. Considering that obtaining perfect channel state information (CSI) is a challenging task in IRS based systems, we further explore the case with the imperfect CSI for the channels from the IRS to users. Under this setup, we propose a robust beamforming and reflection matrix design scheme for the originally formulated non convex optimization problem. Finally, simulation results are presented to demonstrate the effectiveness of the proposed algorithms.
author_names: Wanming Hao

Gangcan Sun

Ming Zeng

Zhengyu Zhu

Zheng Chu

Octavia A Dobre

Pei Xiao
title: Robust Design for Intelligent Reflecting Surface Assisted MIMO OFDMA Terahertz Communications
venue: ArXiv
year: 2020

abstract: This paper describes terahertz (THz) wave generation within forbidden bands in polar crystals, focusing on the A1 phonon modes in lithium niobate. This material exhibits two negative permittivity frequency ranges at 7.4 12.7 THz and 18.8 25.6 THz for the lowest and highest A1 modes, respectively. Exploiting the finite difference time domain simulations, we demonstrate that both the surface phonon modes can be radiative with a structured grating. Fourier analyses of the radiative fields reveal the relevant peaks in the spectrum as well as the dispersion relations. Our results provide a novel method for coherent THz wave sources at unexplored THz frequencies.
author_names: Jun-ichi Shikata

Seigo Ohno

Hiroaki Minamide
title: Terahertz wave generation from surface phonons at forbidden frequencies of lithium niobate
venue: IEICE Electron. Express
year: 2020

abstract: A ray tracing method based on the geometrical optics and physical optics approximation is proposed for calculation of the scattering from rough metal surface with rough coating in terahertz regime. Geometrical optics is utilized to describe the wave propagation concerning the reflection and transmission, whereas physical optics is applied to obtain the scattering fields by equivalent currents on the surfaces. The method provides a reliable treatment of scattering from rough layers involving identical/different roughness. The scattering predictions of the rough layers are compared to the multilevel fast multipole algorithm (MLFMA) to demonstrate the efficiency and accuracy of the proposed method. Once validated, we use the method to carry out a sensitivity study of the bistatic radar scattering cross section to variations in layer parameters of interest in terahertz coating target detection, such as the roughness of the coating and metal surface, thickness of the coating layer.
author_names: Rui Wang

Guangbin Guo

Lixin Guo
title: Study of the Terahertz Wave Scattering From Metal Surface Coated by Rough Lossy Coating Based on a Ray Tracing Modeling
venue: IEEE Access
year: 2019

abstract: This paper provides indoor reflection, scattering, transmission, and large scale path loss measurements and models, which describe the main propagation mechanisms at millimeter wave and Terahertz frequencies. Channel properties for common building materials (drywall and clear glass) are carefully studied at 28, 73, and 140 GHz using a wideband sliding correlation based channel sounder system with rotatable narrow beam horn antennas. Reflection coefficient is shown to linearly increase as the incident angle increases, and lower reflection loss (e.g. stronger reflections) are observed as frequencies increase for a given incident angle. Although backscatter from drywall is present at 28, 73, and 140 GHz, smooth surfaces (like drywall) are shown to be modeled as a simple reflected surface, since the scattered power is 20 dB or more below the reflected power over the measured range of frequency and angles. Partition loss tends to increase with frequency, but the amount of loss is material dependent. Both clear glass and drywall are shown to induce a depolarizing effect, which becomes more prominent as frequency increases. Indoor propagation measurements and large scale indoor path loss models at 140 GHz are provided, revealing similar path loss exponent and shadow fading as observed at 28 and 73 GHz. The measurements and models in this paper can be used for future wireless system design and other applications within buildings for frequencies above 100 GHz.
author_names: Yunchou Xing

Ojas Kanhere

Shihao Ju

Theodore Ted S Rappaport
title: Indoor Wireless Channel Properties at Millimeter Wave and Sub Terahertz Frequencies
venue: 2019 IEEE Global Communications Conference (GLOBECOM)
year: 2019

abstract: In this paper, we propose and numerically demonstrate a new way to realize superfocusing of terahertz waves via the spoof surface plasmons (SSP) With the assist of a modified subwavelength metallic grating, a near field rapid oscillation can be formed, originating from the Fabry Perot resonances due to the reflection of SSP waves at terminations. We show that the field pattern of oscillation on textured metallic surface can be engineered by adjusting groove width and grating number. This produces a desired modulation of phase and amplitude for the radiationless electromagnetic interference (REI) focusing. The effective focusing depth through the corrugated metal is evaluated by the full width half maximum (FWHM) beamwidth. At the situation of third order Fabry Perot resonance, the FWMH reaches up to 0.069l at a distance of 0.1l, improving the beamwidth by more than 540% compared with a single slit. The FWHM is optimized to 0.06l as the order of Fabry Perot resonance becomes seven, leading to the superfocusing metric of 1.67. On the basis of this, we further show the focusing ability can be held on the ultra thin metallic grating. Two dimensional subwavelength focusing behavior is also numerically verified. Our study may extend the working distance of sensing and super resolution imaging devices at terahertz frequency.
author_names: Tie-Jun Huang

Jiang-Yu Liu

Li-Zheng Yin

Feng-Yuan Han

Pu-Kun Liu
title: Superfocusing of terahertz wave through spoof surface plasmons.
venue: Optics express
year: 2018