Propagation Characteristics Of Terahertz Wave Research Articles

Terahertz wave propagation characteristics in SMM-based three-dimensional plasma fluid

During the return to the atmosphere of a hypersonic vehicle in adjacent space, a plasma sheath forms on the surface of the vehicle, which blocks normal electromagnetic communications. The ‘blackout’ phenomenon caused by plasma sheaths has received much attention. This paper focuses on the American RAM-C vehicle as the research object, and utilizes the fluid simulation software USim to numerically simulate the pressure, temperature, and electron density under different flight conditions, and based on the simulation results, selects the appropriate electron density and plasma collision frequency, introduces the terahertz (THz) wave, and adopts the scattering matrix method (SMM) to study the propagation characteristics of the vertically incident non-uniform magnetized plasma with the terahertz wave. Among other things, the transmission characteristics of terahertz waves in the plasma are affected by the flight altitude and flight angle of attack of the vehicle. The conclusions indicate that the transmissivity of terahertz wave transmission in plasma increases, and the reflectivity and absorptance decrease with increasing flight altitude and flight angle of attack. Under the condition of controlling other flight parameters unchanged, the plasma frequency and collision frequency decrease with the increase of flight altitude. The larger the flight angle of attack is, the larger the plasma frequency and collision frequency are. The electron density on the wall surface of the vehicle was also tested, and it was found that the lowest electron density was found at the tail end of the leeward surface. This study can provide some theoretical references for mitigating the ‘blackout’ phenomenon of re-entry vehicles.

Plasma and Terahertz-Wave Propagation Characteristics in Atmospheric-Pressure Plasma Jet Under Different Operating Conditions

High-density plasma source device is of great significance for ground experiment verification of vehicle reentry communication. atmospheric-pressure plasma jet (APPJ), as a high-density plasma source, has received little attention in ground experiments on vehicle communications. In this article, terahertz (THz) wave propagation characteristics in APPJ are investigated by joint simulation of APPJ discharge and THz transport model and related experimental measurements. THz interferometer (THz-IF) system is used to diagnose the electron density and THz transmission characteristics of APPJ for the first time, and the measured results are in good agreement with the simulation results of a joint simulation model in this article and the measured results of THz time-domain spectroscopy (THz-TDS) system of other researchers. Sheath thickness and electron density produced by self-designed APPJ are highly matched with the plasma sheath environment of the HIFIRE-5b vehicle. Further analysis of the influence of different voltages and needle electrode radius on the THz transmission characteristics shows that the absorption effect plays a major role in THz-wave attenuation in APPJ, and the contribution of the collision effect almost disappears, which is completely consistent with the phenomenon observed in HIFIRE-5b vehicle. The joint simulation model and THZ-IF method developed in this article are of great significance for the ground test verification of reentry communication schemes.

Terahertz Wave Propagation Characteristics in Graded Teflon Based Solid-Core Photonic Crystal Fibre

In the past few years, photonic crystal fibre (PCF) in the Terahertz spectrum is drawing significant attention because of its multifaceted applications in high-speed data communication, spectroscopy, sensing, etc. The proposed PCF structure is based on a Teflon solid core surrounded by porous cladding. Teflon has been used as a background material because of its high flexibility and the possibility of making longer PCFs, which is capable of guiding waves in the THz region. The porous cladding consists of circular air-holes positioned hexagonally whose diameters increase with each subsequent layer keeping the pitch constant thus providing a graded-index profile. The diameters of air holes in each hexagonal layer are 1 mm, 1.2 mm and 1.5 mm respectively, maintaining a constant pitch of 2mm and a perfectly matched layer (PML) thickness of 3mm. We have examined the transmission characteristics of the proposed profile in the frequency range of 0.8 THz to 2.5 THz. The modal solution of the profile is solved using the Finite Element Method based on COMSOL Multiphysics version 5.5. Using the graded-index profile, we have obtained a large effective modal area of around 5.6 mm2 at 1 THz and a low confinement loss of 2.25 × 10−4 dB/km at the same frequency. Due to this large effective modal area, we get higher damage threshold and weaker non-linear effects, making it suitable for high power applications.

Terahertz Wave Propagation Characteristics on Rough Surfaces Based on Full‐Wave Simulations

AbstractTerahertz (THz) communications are considered as a critical technology for the future wireless communication. The THz band (0.1–10 THz) offers ultra‐wide bandwidths and promises to satisfy the need for ultra‐high‐speed wireless communication. Although propagation characterization is necessary for the THz system design and validation, the response mechanism between the surface roughness and the THz wave is rarely studied. According to the Rayleigh Criterion, most surfaces in a physical environment may be considered to be rough. Scattering on rough surfaces will play a significant role in the THz propagation. Due to the difficulty of practical measurements at the THz band, we use a full‐wave simulation method to study the propagation characteristics of scattering on rough surfaces. First, the Monte Carlo method is used to model rough surfaces with different root‐mean‐squared heights δ and correlation lengths l. Then, with full‐wave simulations, frequency dependency, incident angle dependency, material dependency, and surface size dependency are discussed. By changing the roughness of surfaces, scattering on different rough surfaces at 300 GHz are simulated. Based on a large number of simulation results, we investigate the effect of δ and l on scattering on rough surfaces. Afterward, the cross‐polarization discrimination of each case is analyzed and counted to evaluate the depolarization effect. This study shows that scattering can become a prominent propagation mechanism with the growth of roughness. Besides, the depolarization effect becomes much more severe for a rougher surface. Studying THz propagation characteristics on rough surfaces is critical to accurate THz channel modeling, which further supports the design and deployment of THz communication systems.

Propagation characteristics of terahertz wave in inductively coupled plasma.

Firstly, the electron density distribution of inductively coupled plasma (ICP) is measured by laser Thomson scattering (TS) method and the features of the ICP under the same experimental conditions are simulated by finite element method (FEM). The simulated results are in good agreement with the experimental results, which verifies the accuracy of the ICP generation simulation model. Secondly, the propagation characteristics of terahertz wave in ICP are measured by terahertz time domain spectroscopy (THz-TDS) and calculated by FEM according to the electron density distribution of ICP simulated in the first step above. The high consistency between the experimental and simulation results of terahertz wave propagation characteristics in ICP further proves the accuracy of terahertz wave transmission model in plasma and the feasibility of joint simulation with ICP generation simulation model.

Study on the Propagation Characteristics of Terahertz Waves in Dusty Plasma with a Ceramic Substrate by the Scattering Matrix Method.

The propagation characteristics of terahertz (THz) waves incident vertically into inhomogeneous and collisional dusty plasma with a ceramic substrate are studied using the scattering matrix method (SMM). The effects of the incident wave frequency and plasma parameters, such as the maximal electron density, dust particle density, dust particle radius and collision frequency, on the reflectance and transmittance of THz waves in the dusty plasma are discussed. In addition, the differences of the propagation properties in the dusty plasma, with and without ceramic substrate, are analyzed. Meanwhile, the differences of the propagation properties in dusty plasma and common plasma, respectively, with ceramic substrate are also compared. Simulation results show that the substrate and dust particles have significant influence on the propagation characteristics of THz wave in plasma sheath. Finally, the transmission increases with the increase of electron density, dust density, dust particle radius and collision frequency.

Propagation characteristics of terahertz wave in plasma sheath around air vehicle

In this paper, the plasma electron density and collision frequency are calculated based on the flow field simulation of RAM C-III air vehicle, and an inhomogeneous plasma model is established according to the calculation results. The effects of plasma density, plasma thickness, plasma collision frequency and external magnetic field on the propagation characteristics of terahertz wave in plasma are analyzed using scattering matrix method. The results show that the propagation loss increases with plasma electron density and plasma thickness, while the transmittance decreases first and then increases with the increasing of collision frequency. When an external magnetic field is applied, the propagation characteristics of the left-handed polarized terahertz wave will be improved, while for the right-handed polarized terahertz wave, the application of magnetic field induces an absorption peak, which shifts to high frequency range with the increasing of magnetic induction intensity. This work may make a contribution to solving the problem of communication blackout.

Terahertz wave propagation characteristics in plasma sheath around a hypersonic blunt cone

In this paper, the propagation characteristics of terahertz wave in the plasma sheath is analyzed theoretically, which is simulated and calculated on the basis of the air thermal chemical reactions around a hypersonic blunt cone model. According to the simulation results of the flow field distribution, the electron density of the plasma sheath is fixed through the 7 reacting species equilibrium constant method. The influence of Mach number and flying height on plasma sheath are discussed. And then the interaction model between terahertz wave and plasma sheath is studied by adopting the scattering matrix method. The results show that the plasma parameters are subject to the Mach number and flying height intensely. Moreover, the effects of applied magnetic field on left-hand and right-hand polarized terahertz wave propagation characteristics are considered. The external magnetic field can improve the penetration ability of left-handed polarized terahertz wave. These results demonstrate that terahertz wave has good potential in real-time communication and target detection of near space.

Propagation characteristics of terahertz wave in hypersonic plasma sheath considering high temperature air chemical reactions

In this work, the propagation characteristics of terahertz wave in the hypersonic plasma sheath is demonstrated and analyzed based on the realistic vehicle model and the high temperature air thermal chemical reactions. Based on the simulated flow field distribution around the hypersonic vehicle, the electron densities of the plasma sheath at different Mach numbers are calculated by adopting the equilibrium constant method of the 7-species reacting air model. And then the propagation model of terahertz wave in plasma sheath is established using the scattering matrix method. The calculated and simulated results show that the plasma electron density is strongly influenced by Mach number, and the higher frequency and smaller incident angle of terahertz wave are advantageous for a better transmittance and lower loss. Furthermore, the effects of an external magnetic field on the propagation characteristics of left-hand and right-hand polarized terahertz wave in plasma sheath are studied. The external magnetic field indeed reduces the transmission loss of the left-handed wave. This work promises that terahertz waves have good potential applications in the detection and the communication for the hypersonic vehicles in plasma sheath.

Effects of magnetized plasma on the propagation properties of obliquely incident THz waves

In this paper, the propagation of obliquely incident terahertz (THz) wave in a non-uniform magnetized plasma slab is investigated. The electron density and the collision frequency across the plasma are assumed to have a Gaussian profile. To deal with the non-uniform profile, the plasma slab is divided into a series of subslabs. For more accuracy, twice reflection between the interfaces of each subslab is considered, and the corresponding transmitted and reflected power are derived. Effects of collision frequency, magnetic field amplitude and incident angle on THz wave propagation characteristics are investigated. Specifically, the refraction angles in each subslab are presented. These simulation results are meaningful for the hypersonic flight communication.

Performance analysis of LDPC codes on OOK terahertz wireless channels**Project supported by the National Key Basic Research Program of China (Grant No. 2014CB339803), the National High Technology Research and Development Program of China (Grant No. 2011AA010205), the National Natural Science Foundation of China (Grant Nos. 61131006, 61321492, and 61204135), the Major National Development Project of Scientific Instrument and Equipment (Grant

Atmospheric absorption, scattering, and scintillation are the major causes to deteriorate the transmission quality of terahertz (THz) wireless communications. An error control coding scheme based on low density parity check (LDPC) codes with soft decision decoding algorithm is proposed to improve the bit-error-rate (BER) performance of an on-off keying (OOK) modulated THz signal through atmospheric channel. The THz wave propagation characteristics and channel model in atmosphere is set up. Numerical simulations validate the great performance of LDPC codes against the atmospheric fading and demonstrate the huge potential in future ultra-high speed beyond Gbps THz communications.

Studies of terahertz wave propagation in non-magnetized plasma

The space crafts, such as spaceship, space shuttle and so on, will face a famous blackout problem when they re-enter the earth's atmosphere at high velocity. The plasma sheath severely affects the propagation of the incident electromagnetic wave and causes severe electromagnetic wave attenuation, which results in the communication failures between the space crafts and the ground control center. It is important to study the properties of terahertz wave propagation in non-magnetized plasma, for using the terahertz wave communication is an alternative method to solve the reentry blackout problem. The terahertz wave propagation characteristics in non-magnetized plasma are studied in this paper. The variations of the terahertz wave propagation properties with the terahertz wave frequency, plasma density, plasma collision frequency and the thickness of the plasma are acquired. Some new phenomena are found i.e., there appears periodic oscillation on the reflectivity curve with the increase of terahertz wave frequency, and the period of oscillation is 0.03THz. The oscillation amplitude increases with the increase of terahertz frequency, decreases with the increase of plasma density, and increases with the increase of plasma collision frequency. The oscillation is attributed to the multiple reflections of the electromagnetic wave at the interfaces at z=0 and z=-d. The terahertz wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. Both the theoretical and experimental results indicate that using terahertz wave communication is an effective way to solve the reentry blackout problem.