Tutorial: Terahertz beamforming, from concepts to realizations

The terahertz range possesses significant untapped potential for applications including high-volume wireless communications, noninvasive medical imaging, sensing, and safe security screening. However, due to the unique characteristics and constraints of terahertz waves, the vast majority of these applications are entirely dependent upon the availability of beam control techniques. Thus, the development of advanced terahertz-range beam control techniques yields a range of useful and unparalleled applications. This article provides an overview and tutorial on terahertz beam control. The underlying principles of wavefront engineering include array antenna theory and diffraction optics, which are drawn from the neighboring microwave and optical regimes, respectively. As both principles are applicable across the electromagnetic spectrum, they are reconciled in this overview. This provides a useful foundation for investigations into beam control in the terahertz range, which lies between microwaves and infrared light. Thereafter, noteworthy experimental demonstrations of beam control in the terahertz range are discussed, and these include geometric optics, phased array devices, leaky-wave antennas, reflectarrays, and transmitarrays. These techniques are compared and contrasted for their suitability in applications of terahertz waves.Daniel Headland, Yasuaki Monnai, Derek Abbott, Christophe Fumeaux, and Withawat Withayachumnanku

Low-profile terahertz radar based on broadband leaky-wave beam steering

Date of publication December 1, 2016; date of current version January 12, 2017.We demonstrate short-range terahertz radar based on a leaky-wave antenna with a beam steering capability. As a proof of concept, we develop a microstrip-based periodic leakywave antenna driven by a vector network analyzer. By sweeping the frequency from235 to 325 GHz, beam steering from−23◦ to+15◦ across the broadside can be achieved with a nearly constant beam width of 4◦. Small target detection is demonstrated by locating a metal cylinder with a diameter of 12 mm placed 46–86 mm in front of the antenna with a mean error of 2.4 mm. The use of a leaky-wave antenna can pave the way for developing a low-loss, low-profile, and wide-aperture terahertz radar. Importantly, it can be integrated with a solid-state source and a detector. The proposed approach is particularly promising for use with emerging small devices such as drones or wearable devices, where millimeter-wave radar is not suitable in terms of the resolution and system footprint.Kosuke Murano, Issei Watanabe, Akifumi Kasamatsu, Safumi Suzuki, Masahiro Asada, Withawat Withayachumnankul, Toshiyuki Tanaka, and Yasuaki Monna

Dissipative corrections to particle spectra and anisotropic flow from a saddle-point approximation to kinetic freeze out

Lang C, Borghini N. Dissipative corrections to particle spectra and anisotropic flow from a saddle-point approximation to kinetic freeze out. The European Physical Journal C. 2014;74(7): 2955.A significant fraction of the changes in momentum distributions induced bydissipative phenomena in the description of the fluid fireball created inultrarelativistic heavy ion collisions are actually taking place when the fluidturns into individual particles. We study these corrections in the limit of alow freeze-out temperature of the flowing medium, and show that they mostlyaffect particles with a higher velocity than the fluid. For these, we deriverelations between different flow harmonics, from which the functional form ofthe dissipative corrections could ultimately be reconstructed from experimentaldata

Quantum Fluctuation Theorems

Recent advances in experimental techniques allow one to measure and control systems at the level of single molecules and atoms. Here gaining information about fluctuating thermodynamic quantities is crucial for understanding nonequilibrium thermodynamic behavior of small systems. To achieve this aim, stochastic thermodynamics offers a theoretical framework, and nonequilibrium equalities such as Jarzynski equality and fluctuation theorems provide key information about the fluctuating thermodynamic quantities. We review the recent progress in quantum fluctuation theorems, including the studies of Maxwell's demon which plays a crucial role in connecting thermodynamics with information.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum regime - Fundamental Aspects and New Directions", (Springer International Publishing, 2018

Experimental demonstration of reflectarray antennas at terahertz frequencies

Reflectarrays composed of resonant microstrip gold patches on a dielectric substrate are demonstrated for operation at terahertz frequencies. Based on the relation between the patch size and the reflection phase, a progressive phase distribution is implemented on the patch array to create a reflector able to deflect an incident beam towards a predefined angle off the specular direction. In order to confirm the validity of the design, a set of reflectarrays each with periodically distributed 360 × 360 patch elements are fabricated and measured. The experimental results obtained through terahertz time-domain spectroscopy (THz-TDS) show that up to nearly 80% of the incident amplitude is deflected into the desired direction at an operation frequency close to 1 THz. The radiation patterns of the reflectarray in TM and TE polarizations are also obtained at different frequencies. This work presents an attractive concept for developing components able to efficiently manipulate terahertz radiation for emerging terahertz communications.Tiaoming Niu, Withawat Withayachumnankul, Benjamin S.-Y. Ung, Hakan Menekse, Madhu Bhaskaran, Sharath Sriram, and Christophe Fumeau

Early collective expansion: Relativistic hydrodynamics and the transport properties of QCD matter

Relativistic hydrodynamics for ideal and viscous fluids is discussed as a tool to describe relativistic heavy-ion collisions and to extract transport properties of the quark-gluon plasma from experimentally measured hadron momentum spectra.Comment: Review article, 54 pages, 25 figure

IRMMW-THz 2015 - 40th International Conference on Infrared, Millimeter, and Terahertz Waves

We propose a leaky-wave antenna to generate circularly polarized highly directional terahertz beam using metamaterial scatters. A microstrip line is loaded with a series of complementary electric-LC and electric-LC resonators to generate respectively Ex and Ey components. The 900-phase difference and almost unity amplitude ratio of Ex and Ey are achieved by relative positioning of the resonators on and off the stripline and optimizing the gap size. Moreover, the phase front of the radiated wave can be adjusted to a specific direction by controlling the period of the resonator array. These highly directional planar antennas can be utilized in short-range THz communication, sensing and imaging applications

Dual circularly polarized series-fed microstrip patch array with coplanar proximity coupling

We demonstrate a concept of compact and highly efficient circular traveling wave series-fed microstrip patch array working at 10 GHz. The patch elements are excited by a microstrip line through coplanar proximity coupling. A dual-port feeding allows us to select the direction of the traveling waves and, consequently, the sense of circular polarization of the patches. Simultaneous feeding to both ports with proper amplitude and phase difference can result in radiated waves of arbitrary polarization. Owing to the circular array arrangement and the strong proximity coupling, the antenna exhibits a compact structure and achieves a high antenna efficiency of 90% with seven patches. Based on reciprocity, the antenna can readily be also utilized for polarimetry applications for which the signal amplitude at each port is proportional to the amplitude of each individual sense of polarization. Measured results of an antenna prototype successfully validate the concept.Shengjian Jammy Chen, Christophe Fumeaux, Yasuaki Monnai and Withawat Withayachumnanku

Terahertz plasmonic Bessel beamformer

Abstract not available.Yasuaki Monnai, David Jahn, Withawat Withayachumnankul, Martin Koch, and Hiroyuki Shinod