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Michele Tamagnone

Publications and source records attributed to Michele Tamagnone.

24 records · Page 2Linked to original sources
arXiv2014

Predicting input impedance and efficiency of graphene reconfigurable dipoles using a simple circuit model

An analytical circuit model able to predict the input impedance of reconfigurable graphene plasmonic dipoles is presented. A suitable definition of plasmonic characteristic impedance, employing natural currents, is used to for consistent modeling of the antenna-load connection in the circuit. In its purely analytical form, the model shows good agreement with full-wave simulations, and explains the remarkable tuning properties of graphene antennas. Furthermore, using a single full-wave simulation and scaling laws, additional parasitic elements can be determined for a vast parametric space, leading to very accurate modeling. Finally, we also show that the modeling approach allows fair estimation of radiation efficiency as well. The approach also applies to thin plasmonic antennas realized using noble metals or semiconductors.

physics.optics↗
arXiv2013

Fundamental limits and near-optimal design of graphene modulators and non-reciprocal devices

The potential of graphene for use in photonic applications was evidenced by recent demonstrations of modulators, polarisation rotators, and isolators. These promising yet preliminary results raise crucial questions: what is the optimal performance achievable by more complex designs using multilayer structures, graphene patterning, metal additions, or a combination of these approaches, and how can this optimum design be achieved in practice? Today, the complexity of the problem, which is magnified by the variability in graphene parameters, leaves the design of these new devices to time-consuming and suboptimal trial-and-error procedures. We address this issue by first demonstrating that the relevant figures of merit for the devices above are subject to absolute theoretical upper bounds. Strikingly these limits are related only to the conductivity tensor of graphene; thus, we can provide essential roadmap information such as the best possible device performance versus wavelength and graphene quality. Second, based on the theory developed, physical insight, and detailed simulations, we demonstrate how structures closely approaching these fundamental limits can be designed, demonstrating the possibility of significant improvement. These results are believed to be of paramount importance for the design of graphene-based modulators, rotators, and isolators and are also directly applicable to other 2-dimensional materials.

physics.optics↗
arXiv2013

Graphene Antennas: Can Integration and Reconfigurability Compensate for the Loss?

In this opening presentation we will first recall the main characteristics of graphene conductivity and electromagnetic wave propagation on graphene-based structures. Based on these observations and different graphene antenna simulations from microwave to Terahertz, we will discuss the issue of antenna efficiency, integration and reconfigurability, as function of the operation frequency range. While the applicability of graphene for antennas at microwave appears limited to particular cases where very low efficiency can be tolerated for integration or transparency purpose, the plasmonic nature of graphene conductivity at terahertz frequency allows unprecedented antenna properties and in particular efficient dynamic reconfiguration.

physics.optics↗
arXiv2012

Tunable Graphene Reflective Cells for THz Reflectarrays and Generalized Law of Reflection

A tunable graphene-based reflective cell operating at THz is proposed for use in reconfigurable-beam reflectarrays, or similarly to implement the so-called generalized law of reflection. The change in the complex conductivity of graphene when biased by an electric field allows controlling the phase of the reflected field at each element of the array. Additionally, the slow wave propagation supported by graphene drastically reduces the dimensions of the cell, which allows smaller inter-element spacing hence better array performance. An elementary cell is optimized and its scattering parameters computed, demonstrating a dynamic phase range of 300 degrees and good loss figure for realistic chemical potential variations. Finally, a circuit model is proposed and shown to very accurately predict the element response.

physics.optics↗
arXiv2012

Comment on 'Encoding many channels on the same frequency through radio vorticity: first experimental test'

We show that the public experiment held in Venice by F. Tamburini et al and reported in (2012 New J. Phys. 14 033001) can be regarded as a particular implementation of Multiple-Input Multiple-Output (MIMO) communications, hence bringing no advantages with respect to known techniques. Moreover, we explain that the use of a 'vortex' mode (orbital angular momentum OAM l = 1) at one of the transmit antennas is not necessary to encode different channels since only different patterns -or similarly different pointing angles- of the transmit antennas are required. Finally, we identify why this MIMO transmission allowed decoding of two signals despite being line-of-sight. This is due to the large separation between the receiving antennas, which places the transmit antennas in the near-field Fresnel region of the receiving 'array'. This strongly limits the application of this technique in practice, since, for a fixed separation between receiving antennas, the detectable signal power from any additional vortex mode decays at least as 1/r^4.

physics.optics↗