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Abstract A key challenge in millimeter-wave and terahertz wireless networks is blockage of the line-of-sight path between a base station and a user. User and environmental mobility can lead to blockage of highly directional beams by intervening people or objects, yielding link disruptions and poor quality of service. Here, we propose a solution to this problem which leverages the fact that, in such scenarios, users are likely to be located within the electromagnetic near field of the base station, which opens the possibility to engineer wave fronts for link maintenance. We show that curved beams, carrying data at high bit rates, can realize a link by curving around an intervening obstacle. We develop a model to analyze and experimentally evaluate the bandwidth limitations imposed by the use of self accelerating beams. We also demonstrate that such links employ the full aperture of the transmitter, even those portions which have no direct line of sight to the receiver, emphasizing that ray optics fails to capture the behavior of these near-field wave fronts. This approach, which is ideally suited for use at millimeter-wave and terahertz frequencies, opens vast new possibilities for wave front management in directional wireless networks. 

Abstract Wireless systems are facing increasing pressure due to the growing demand for data transmission. One potential solution to this problem is to shift communication frequencies toward the terahertz (THz) spectrum. However, this requires the development of new components that can efficiently process signals at these high frequencies and transmit them via highly directional beams. In this study, a novel approach is proposed to achieving efficient THz signal processing by combining two existing technologies: photonic crystals and leaky‐wave antennas. Incorporating a 2D photonic crystal inside a leaky‐wave waveguide allows to manipulate the wave vector of the guided wave in unique ways, which in turn impacts the far‐field radiation pattern emitted through the leaky‐wave aperture. The device fabrication uses 3D printing of alumina and allows for convenient and scalable manufacturing. Through numerical simulations and experiments, free‐space data transmission at rates of few hundred Mbps at a carrier frequency of 101.2 GHz is demonstrated. The findings illustrate the feasibility of photonic crystal‐based leaky‐wave antennas and lay the groundwork for the development of compact and high‐performance components for THz wireless communication systems. 

Abstract As the need for higher data rates for communication increases, the terahertz (THz) band has drawn considerable attention. This spectral region promises a much wider bandwidth and the transmission of large amounts of data at high speeds. However, there are still challenges that need to be addressed before the THz telecommunications technology hits the consumer market. One of the recurring concerns is that THz radiation is greatly absorbed by atmospheric water-vapor. Although many studies have presented the attenuation of THz signals under different atmospheric conditions, these results analyze specific temperature or humidity values, leaving the need for a more comprehensive analysis over a wider range of climate conditions. In this work, we present the first study of the attenuation of THz radiation over a broad range of temperatures and humidity values. It is worth noticing that all of our measurements have been undertaken at atmospheric pressure unlike many previous studies where the pressure was not kept constant for various temperatures. Furthermore, we extend our analysis beyond the impact of absolute humidity on the bit error rate in THz communications. We also discuss the refractivity of the atmosphere, examining its variations across different temperatures and humidity levels. THz propagation is studied using two different measurement systems, a long-path THz time-domain spectrometer as well as a quasi-optic setup with vector network analyze. We also compare the results with the ITU-R P.676-13 propagation model. We conclude that the attenuation at the absorption peaks increases linearly with water content and has no dependence on the temperature, while the refractive index, away from absorption lines, namely at 300 GHz shows a sub-linear increase with humidity. 

Transcending the capabilities of traditional architectures, metasurfaces offer nearlimitless control over the fundamental electromagnetic properties of wireless signals, presenting new opportunities for wireless communication. However, they also bring forth unprecedented security challenges, particularly for millimeter-wave and sub-THz wireless backhaul links employed for many critical functions, such as financial trading on Wall Street. In this article, we expose a new category of aerial ''MetaSurface-in-the-Middle'' attacks, wherein an adversary armed with an on-drone metasurface, MetaFly, can intercept wireless backhaul links with an almost imperceptible trace. Strikingly, such adversarial metasurfaces can be fabricated in minutes using standard office items like a foil sheet and a laminator. The attack is implemented and experimentally evaluated in both a large indoor atrium and outdoor rooftops in a large metropolitan area, demonstrating the adversary's ability to establish a secondary diffraction beam for eavesdropping while maintaining minimal impact on legitimate communication. 

We demonstrate a wireless security application to protect the weakest link in phone-to-phone communication, using a terahertz metasurface. To our knowledge, this is the first example of an eavesdropping countermeasure in which the attacker is actively misled.