The use of massive Multiple-Input Multiple-Output (MIMO) systems is becoming progressively feasible, as well as progressively important, as the carrier frequency increases. Terahertz (THz) frequencies lead to smaller-sized RF components including antennas, so that even antenna arrays with a large number of antennas have a reasonable form factor while providing large beamforming gain and multi-user MIMO (MUMIMO) capability. However, the THz propagation mechanisms differ in various ways from previously explored channels. In fact, reflections by a rough surface and diffuse scattering mechanisms are the most critical features contributing to spatial and temporal dispersion at THz frequencies. For this study, first, we develop a hybrid modeling approach of 3D ray-tracing simulations in a realistic office room at 300 GHz and 350 GHz to obtain estimates of the impact of surface roughness on the channel capacity which depends on generic channel characteristics. Then, the indoor multipath propagation and its impact on massive MIMO channels considering smooth and rough surfaces are investigated by employing the Beckmann-Kirchhoff (B-K) model. Finally, channel capacities of indoor THz massive MIMO channels with different surface roughnesses for both line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios are calculated. Though based on modeling results, the scattering properties of materials can favorably be exploited to maximize spatial multiplexing gains, especially in LoS scenarios.

The problem of wave propagation and scattering at terahertz (THz) frequencies has become increasingly important, in particular for accurate modeling of future indoor wireless communication channels. The reflective properties of indoor materials with different surface roughness and dielectric constants are important to explore diffuse scattering for accurate channel modeling. First and foremost, a terahertz Swissto12 system is adopted to obtain the first ever transmission measurements for a wide choice of indoor material groups, such as wood, plastic , and brick at frequencies from 750 GHz to 1.1 THz using up-conversion (frequency-domain) method. Both the reflection ( $S_{11}$ , $S_{22}$ ) and transmission coefficients ( $S_{12}$ , $S_{21}$ ) are measured using this novel and noninvasive electromagnetic technique. The inversion method based on Kramers–Kronig (K-K) relations is then applied to convert the calibrated scatter data into intrinsic material properties (i.e., refractive index, permittivity, absorption coefficient). Then, the surface topography of rough material samples is acquired using surface measurement instruments. Further, the optically smooth $(\sigma _{h} /\lambda \ll 1)$ materials are assorted as most to least rough based on Rayleigh roughness factor. Lastly, the ray tracer considering the Rayleigh-Rice (R-R) scattering model is employed to obtain the maximum achievable reflected paths of the above-mentioned indoor material samples at 300 GHz followed by their experimental validation.

The channel in the terahertz (THz) band is extremely frequency selective. This study demonstrates a ray‐tracing method for modelling short‐range propagation channels at THz band. The propagation response of sounding bandwidth and centre frequency on power delay profile (PDP) is investigated in five spectral windows with relatively low attenuations and higher available bandwidths which could possibly offer terabit‐per‐second links also. In this approach, a very detailed non‐cubic three‐dimensional model of an ultra‐broadband indoor realistic office environment has been drawn up. Furthermore, the frequency‐dependent standard electrical parameters for the common building materials were taken from the literature. The transmitter (Tx) and the receiver (Rx) are 10 m apart in line‐of‐sight scenario with exactly same height of 1.5 m above the floor. The simulations were performed using 25 dBi horn antennas at the transmitter and receiver sides, respectively, to combat high path loss. These frequency‐dependent horn antennas were designed for the respective five spectral windows. Meanwhile, the corresponding channel impulse response of multipath components with spatial and temporal information such as angle of arrival, angle of departure and time of arrival has been captured to derive PDP models. Up to four reflections (i.e. fourth order) have been considered in the modelling process.

In this paper, new concepts for continuous 24/7 real-time monitoring of plants and insects with miniaturized terahertz (THz) systems are described and experimentally tested. Thus, for the first time, small-scale insights into the instantaneous plant health but also in their long-term growth can be obtained. Using such compact THz systems, e.g. water uptake, insect infestation and the behavior of pollinators (i.e. honey bees) and pests can be measured dynamically and non-invasively at virtually any position in the close biotope surrounding them. In addition to general understanding, this can be used to optimize crop yield and reduce resource consumption as well as for identifying characteristics of insect-plant interactions induced by potential environmental stressors. Given such holistic a approach, the proposed concepts may provide a significant advancement in environmental monitoring technology.

In recent years, terahertz (THz) systems have become an increasingly popular area of research thanks to their unique properties such as extremely high data rates towards Tb/s, submillimeter localization accuracy, high resolution remote sensing of materials, and remarkable advances in photonics and electronics technologies. This article traces the progress of THz measurements, antennas and simulations, from historical milestones to the current state of research and provides an outlook on the remaining challenges.

The scattering phenomenon caused by rough surfaces has a dominant role in shaping the reflected field at terahertz (THz) frequencies, both in specular and non-specular directions. Most surfaces in nature are randomly rough, and the surface height obeys a certain statistical distribution. A Gaussian probability density function (PDF) for height distribution is often considered, and the correlation length is assumed to be longer than the wavelength. However, a clear understanding of how changing these assumptions affect the angular distribution of the scattered field is still lacking. In the first part of this work we investigate via microscopic measurements the statistical distribution of realistic indoor materials, and its deviation from the assumed normal distribution. After that, the influence of non-Gaussianity on the specular reflection in the low THz region is shown analytically. In the second part, a measurement campaign of diffuse scattering, caused by structured statistically-controlled surfaces, is reported. The correlation length assumption has been proven experimentally and via full-wave simulation to affect the diffuse scattering by rough samples, when the other statistical parameters are kept without changes.