Graphene is an ideal 2D material system bridging electronic and photonic devices. It also breaks the fundamental speed and size limits by electronics and photonics, respectively. Graphene offers multiple functions of signal transmission, emission, modulation, and detection in a broad band, high speed, compact size, and low loss. Here, we have a brief view of graphene based functional devices at microwave, terahertz, and optical frequencies. Their fundamental physics and computational models were discussed as well.

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Graphene based functional devices: A short review

Exceptional advancement has been made in the development of graphene optical nanoantennas. They are incorporated with optoelectronic devices for plasmonics application and have been an active research area across the globe. The interest in graphene plasmonic devices is driven by the different applications they have empowered, such as ultrafast nanodevices, photodetection, energy harvesting, biosensing, biomedical imaging and high-speed terahertz communications. In this article, the aim is to provide a detailed review of the essential explanation behind graphene nanoantennas experimental proofs for the developments of graphene-based plasmonics antennas, achieving enhanced light-matter interaction by exploiting graphene material conductivity and optical properties. First, the fundamental graphene nanoantennas and their tunable resonant behavior over THz frequencies are summarized. Furthermore, incorporating graphene-metal hybrid antennas with optoelectronic devices can prompt the acknowledgment of multi-platforms for photonics. More interestingly, various technical methods are critically studied for frequency tuning and active modulation of optical characteristics, through in situ modulations by applying an external electric field. Second, the various methods for radiation beam scanning and beam reconfigurability are discussed through reflectarray and leaky-wave graphene antennas. In particular, numerous graphene antenna photodetectors and graphene rectennas for energy harvesting are studied by giving a critical evaluation of antenna performances, enhanced photodetection, energy conversion efficiency and the significant problems that remain to be addressed. Finally, the potential developments in the synthesis of graphene material and technological methods involved in the fabrication of graphene-metal nanoantennas are discussed.

A Review on the Development of Tunable Graphene Nanoantennas for Terahertz Optoelectronic and Plasmonic Applications

A pattern-reconfigurable, low-profile, efficient, electrically small, near-field resonant parasitic (NFRP), Huygens source antenna is presented. The design incorporates both electric and magnetic NFRP elements. The electric ones are made reconfigurable by the inclusion of a set of p-i-n diodes. By arranging these electric and magnetic NFRP elements properly, a set of three Huygens sources are attained, each covering a 120° sector. Pattern reconfigurability is obtained by switching the diodes on or off; it encompasses the entire 360° azimuth range. A prototype was fabricated and tested. The numerical and experimental studies are in good agreement. The experimental results indicate that in each of its instantaneous states at $f_{0} = 1.564$ GHz, the antenna provides uniform peak realized gains, front-to-back ratios, and radiation efficiencies, respectively, as high as 3.55 dBi, 17.5 dB, and 84.9%, even though it is electrically small: $ka = 0.92$ , and low profile: $0.05~\lambda _{{\mathbf {0}}}$ .

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Low-Profile, Electrically Small, Huygens Source Antenna With Pattern-Reconfigurability That Covers the Entire Azimuthal Plane

An annular dielectric resonator (DR) antenna (DRA) is implemented for THz applications. A silicon made DR is loaded with graphene disk for obtaining the tunability in the frequency response. The physical parameters of silicon annular DR can be set to obtain the resonance at any frequency in the lower THz band and can be tuned by changing the chemical potential of graphene nano-disk placed at the top of the DR. The response of antenna is preserved after changing the chemical potential of graphene. The higher order hybrid electromagnetic mode is excited in the antenna structure. The proposed research work provides a way to implement the antenna for THz frequency with high gain around 3.8 dBi and radiation efficiency in the range 72 − 75%.

Tunable Terahertz Dielectric Resonator Antenna

A reconfigurable graphene antenna is designed and numerically analyzed. The antenna structure contains a radiating graphene patch and non-radiating graphene ring. The operating frequency of the antenna can be tuned by applying the gate voltage on the graphene patch. This proximity coupled antenna structure operates with the [Formula: see text] mode. In this configuration, the field is distributed in the form of horizontal magnetic dipole. The application of gate voltage at the periphery of graphene ring converts the field configuration to the form of the vertical electric dipole. Thus, the mode of operation of the antenna is changed to [Formula: see text] Consequently, the radiation pattern of the antenna can be steered in different directions as per the location of the applied gate voltage at the periphery of the graphene ring.

Reconfigurable graphene antenna for THz applications: a mode conversion approach.

The concept and analysis of a graphene-metal beam-reconfigurable terahertz (THz) loop antenna are presented. The hybrid graphene-metal implementation is proposed to combine (i) dynamic surface conductivity tunability using different DC bias voltages and (ii) high radiation efficiency enabled by metal. The loop antenna which employs an artificial mu-negative transmission line provides the horizontally polarised omnidirectional radiation. The graphene-metal loop around the centre ring acts as a reflector. Changing the DC bias of different position of graphene to control the position of resonance can effectively adjust the beam direction. The proposed concept and achieved performance, computed using realistic material parameters, are extremely promising for beam scanning at THz frequencies.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/el.2015.4435

Yongle Wu

Papers

Circular beam-reconfigurable antenna base on graphene-metal hybrid