1,721,126 research outputs found
Nanoscale ferroelectrics for advanced electronics and microwave applications [Guest Editorial]
No full textRadio-Frequency Nanoelectronics: a new Paradigm in Electronic Systems Design
No full textOwing to the new qualitative and quantitative improvements that nanotechnology allows, nanoelectronics has the potential to introduce a paradigm shift in electronic systems design similar to that of the transition from vacuum tubes to semiconductor technology. Since many nano-scale devices and materials exhibit their most interesting properties at radiofrequencies (RF), nanoelectronics represent an enormous and yet largely undiscovered opportunity for the microwave engineering community, which can utilize its established body of modelling, design and measurement techniques with the aim to bridge the gap between nano-science and a new generation of extremely integrated devices, circuits and systems, for a broad range of applications and operating frequencies covering the radiofrequency (RF) spectrum, through the microwave region, and up to the optical region. In this contribution, examples of recent achievements in new nanotechnology-based radio-frequency devices and systems are presented. This is done, in particular, by focusing the areas of carbon-based and terahertz nanoelectronic
General constraints on the propagation of complex waves in closed lossless isotropic waveguides
No full textComplex propagation in linear time-invariant lossless isotropic closed waveguides is a theoretically intriguing subject. Complex modes are also practically important in the characterization of discontinuities as they contribute in pairs with complex conjugate (c.c.) propagation constants to local power storage. By the systematic application of Lorentz's reciprocity theorem, we derive the constraints linking complex propagation constant, Poynting's integral, and electromagnetic energy storage per unit length. Previously known conditions are recovered, and novel constraints on the exchange power between the two components of the pairs are derived. It is emphasized that existing relationships individually derived by different methods and scattered in the literature, as well as novel ones, are derived from a single fundamental theorem. This set of constraints is believed to pose the tightest necessary conditions so far for the existence of complex waves
Modal and Numerical Analysis of the TM-Passing Property of Laminated Cladding
No full textAn accurate investigation of an integrated optical polariser has been presented. The transverse magnetic (TM)-passing property for an asymmetrical slab with anisotropic cladding that behaves as negative or positive uniaxial crystal has been evaluated. After a modal analysis, the polarisation of the electromagnetic (EM) field is evaluated by means of transmission line matrix-integral equation (TLMIE) method which performs a 3D full-wave modelling of the structure (i) including dielectric losses and (ii) for different slant angle of the laminated cladding. The TLMIE method permits to maximise the TM-passing property for a single-mode channel with anisotropic claddin
Far-Field Radiation of Optical Fibers with Tapered End
No full textIn this paper, an accurate model of the far-field radiation of a tapered optical fiber, which is widely used in communication optics and biomedical tomography, is presented. The authors first analyze the far field that is radiated from the normally cut fiber then extend the model to a fiber with a tapered end by considering the different phase contributions of the emitted rays. The proposed technique shows the effects of the cut with a view of obtaining a high efficiency both in coupling and radiation pattern characteristic
Accurate analysis and modeling of laminated multilayered 3-D optical waveguides
No full textThe theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional waveguide, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMIE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMIE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation mode
A full-wave time-dependent Schrödinger equation approach for the modeling of asymmetric transport in geometric diodes
No full textDesign and modeling of geometric diodes can be really challenging as it requires a rigorous quantum analysis at the nanoscale, accurate enough to capture the asymmetric behavior of charge transport. In this paper, we present a full-wave Time-Dependent Schrödinger Equation (TDSE) approach to model coherent transport in a two-dimensional geometric diode defined by an asymmetric taper of the domain where the charges are confined. The proposed solution clearly shows asymmetric transport, and provides a description of the rectification behavior in response to a parametric change. In general, the above model can account for even more complex geometries in order to optimize diodes performance
Current-Voltage Characterization of Multi-Port Graphene Based Geometric Diodes for High-Frequency Electromagnetic Harvesting
Full text linkIn this contribution, geometric diodes based on graphene patterned with spatial asymmetry have been studied, starting from tight-binding numerical approximation in a self-consistent framework, to verify their potential for electromagnetic (e. m.) harvesting. We report a detailed analysis of coherent charge transport and provide some figures of merit with respect to e. m. rectification, such as, for instance, the asymmetry of the dark current-voltage characteristics. The most important achievement of this work is given by the accurate analysis of the main key physical/geometric parameters that affect the nonlinear response of the diodes, for different configurations and geometries. Owing to the Scattering Matrix approach, introduced elsewhere for coherent transport calculation, it was possible to cascade asymmetric discontinuities and simulate large structures (more than 100K atoms) in a modular fashion. In this way, simulation at the atomistic level can be brought up to the device level to provide guidelines for design and fabrication, in view of practical applications related to clean-energy harvesting/rectification up to infrared and solar-light frequencies
Self-Consistent and Full-Wave Analysis of Carbon-Nanotube Matrices for Multi-Channel Charge Confinement
No full textThis paper reports a theoretical characterization of carbon nanotubes matrices using a full-wave undulatory description of charge carriers, self-consistent with external and self-generated potentials. The effect of nanotubes coupling on charge and current confinement is described, by a new in-house simulation toolkit that can easily solve for 3D arrays of packed nanotubes, possibly multi-wall, in a multi-band framework. The availability of such a tool could be of crucial importance in view of the multiplicity of nanotechnology applications of CNT arrays as sensors, field effect transitors, quantum dots, interconnects and antennas
- …
