MAC-Oriented Programmable Terahertz PHY via Graphene-based Yagi-Uda Antennas

Graphene is enabling a plethora of applications in a wide range of fields due to its unique electrical, mechanical, and optical properties. In the realm of wireless communications, graphene shows great promise for the implementation of miniaturized and tunable antennas in the terahertz band. These unique advantages open the door to new reconfigurable antenna structures which, in turn, enable novel communication protocols at different levels of the stack. This paper explores both aspects by, first, presenting a terahertz Yagi-Uda-like antenna concept that achieves reconfiguration both in frequency and beam direction simultaneously. Then, a programmable antenna controller design is proposed to expose the reconfigurability to the PHY and MAC layers, and several examples of its applicability are given. The performance and cost of the proposed scheme is evaluated through full-wave simulations and comparative analysis, demonstrating reconfigurability at nanosecond granularity with overheads below 0.02 mm$^{2}$ and 0.2 mW.Comment: Accepted for presentation in IEEE WCNC '1

Study of hybrid and pure plasmonic terahertz antennas based on graphene guided-wave structures

Graphene is a unique material for the implementation of terahertz antennas due to extraordinary properties of the resulting devices, such as tunability and compactness. Existing graphene antennas are based on pure plasmonic structures, which are compact but show moderate to high losses. To achieve higher efficiency with low cost, one can apply the theory behind dielectric resonator antennas widely used in millimeter-wave systems. This paper presents the concept of hybridization of surface plasmon and dielectric wave modes. Then, via an analysis of one-dimensional structures, a comparison of the potential capabilities of pure and hybrid plasmonic antennas is performed from the perspectives of radiation efficiency, tunability, and miniaturization. Additionally, the impact of the quality of graphene upon the performance of the compared structures is evaluated. On the one hand, results show that hybrid structures deliver high gain with moderate miniaturization and tunability, rendering them suitable for applications requiring a delicate balance between the three aspects. On the other hand, pure plasmonic structures can provide higher miniaturization and tunability, yet with low efficiency, suggesting their use for application domains with high flexibility requirements or stringent physical constraints.Author's final draf

Integrated graphene patch antenna for communications at THz frequencies

Graphene is an attractive material for communications in the THz range due to its ability to support surface plasmon polaritons. This enables a graphene antenna to be smaller in size than its metallic counterpart. In addition, the possibility to control the graphene conductivity during operation by an applied bias leads to the tunability of the resonant frequency of graphene antennas. Graphene-based antennas integrated into transceivers working at THz frequencies may lead to faster and more efficient devices. In this work, we design and simulate a graphene patch antenna that can be integrated into transceivers by through-substrate vias. The tuning of the resonant frequency is also studied by simulations.This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement N° 863337.Peer ReviewedPostprint (author's final draft

High Photocurrent in Gated Graphene-Silicon Hybrid Photodiodes

Graphene/silicon (G/Si) heterojunction based devices have been demonstrated as high responsivity photodetectors that are potentially compatible with semiconductor technology. Such G/Si Schottky junction diodes are typically in parallel with gated G/silicon dioxide (SiO$_2$)/Si areas, where the graphene is contacted. Here, we utilize scanning photocurrent measurements to investigate the spatial distribution and explain the physical origin of photocurrent generation in these devices. We observe distinctly higher photocurrents underneath the isolating region of graphene on SiO$_2$ adjacent to the Schottky junction of G/Si. A certain threshold voltage (V$_T$) is required before this can be observed, and its origins are similar to that of the threshold voltage in metal oxide semiconductor field effect transistors. A physical model serves to explain the large photocurrents underneath SiO$_2$ by the formation of an inversion layer in Si. Our findings contribute to a basic understanding of graphene / semiconductor hybrid devices which, in turn, can help in designing efficient optoelectronic devices and systems based on such 2D/3D heterojunctions.Comment: 25 pages, 5 figure

Terahertz Dielectric Resonator Antenna Coupled to Graphene Plasmonic Dipole

This paper presents an efficient approach for exciting a dielectric resonator antenna (DRA) in the terahertz frequencies by means of a graphene plasmonic dipole. Design and analysis are performed in two steps. First, the propagation properties of hybrid plasmonic onedimensional and two-dimensional structures are obtained by using transfer matrix theory and the finite-element method. The coupling amount between the plasmonic graphene mode and the dielectric wave mode is explored based on different parameters. These results, together with DRA and plasmonic antenna theory, are then used to design a DRA antenna that supports the $TE_{y}^{112}$ mode at 2.4 THz and achieves a gain (IEEE) of up to 7 dBi and a radiation efficiency of up 70%. This gain is 6.5 dB higher than that of the graphene dipole alone and achieved with a moderate area overhead, demonstrating the value of the proposed structure.Comment: Accepted for presentation at EuCAP 201

Optimizing the Optical and Electrical Properties of Graphene Ink Thin Films by Laser-annealing

We demonstrate a facile fabrication technique for graphene-based transparent conductive films. Highly flat and uniform graphene films are obtained through the incorporation of an efficient laser annealing technique with one-time drop casting of high-concentration graphene ink. The resulting thin films are uniform and exhibit a transparency of more than 85% at 550 nm and a sheet resistance of about 30 k{\Omega}/sq. These values constitute an increase of 45% in transparency, a reduction of surface roughness by a factor of four and a decrease of 70% in sheet resistance compared to unannealed films.Comment: 18 pages, 4 figure

Graphene-based Wireless Agile Interconnects for Massive Heterogeneous Multi-chip Processors

The main design principles in computer architecture have recently shifted from a monolithic scaling-driven approach to the development of heterogeneous architectures that tightly co-integrate multiple specialized processor and memory chiplets. In such data-hungry multi-chip architectures, current Networks-in-Package (NiPs) may not be enough to cater to their heterogeneous and fast-changing communication demands. This position paper makes the case for wireless in-package nanonetworking as the enabler of efficient and versatile wired-wireless interconnect fabrics for massive heterogeneous processors. To that end, the use of graphene-based antennas and transceivers with unique frequency-beam reconfigurability in the terahertz band is proposed. The feasibility of such a nanonetworking vision and the main research challenges towards its realization are analyzed from the technological, communications, and computer architecture perspectives.Comment: 8 pages, 4 figures, 1 table - Accepted at IEEE Wireless Communications Magazin

Black sheep (on the great white way).

Gift of Dr. Mary Jane Esplen.Piano vocal [instrumentation]Not long ago they were happy children [first line]The black sheep roam on the great white way [first line of chorus]E flat major [key]Andante con moto [tempo]Popular song [form/genre]Woman, lights, skyscrapers [illustration]Publisher's advertisement on front inside cover & back cover [note