Synchronization in Networks of Hindmarsh-Rose Neurons

Synchronization is deemed to play an important role in information processing in many neuronal systems. In this work, using a well known technique due to Pecora and Carroll, we investigate the existence of a synchronous state and the bifurcation diagram of a network of synaptically coupled neurons described by the Hindmarsh-Rose model. Through the analysis of the bifurcation diagram, the different dynamics of the possible synchronous states are evidenced. Furthermore, the influence of the topology on the synchronization properties of the network is shown through an exampl

First demonstration of machine-designed ultra-flat, low-cost directive antenna

In this paper, we present a fully automated procedure for the direct design of a novel class of single‑feed flat antennas with patterning of a conductive surface. We introduce a convenient surface discretization, based on hexagonal cells, and define an appropriate objective function, including both gain and input matching requirements. The reference geometry is constituted by a very thin, single feed‑point square panel. It features a backing metal plate (“ground”) and a top conductive layer, which is automatically patterned to achieve the desired radiation and input matching properties. The process employs an evolutionary algorithm combined with a boundary element electromagnetic solver. By applying this method, we designed an antenna tailored to the 2.4 GHz ISM frequency band, with a size of 24 cm × 24 cm , i.e., 2 × 2 wavelengths and an height of 4 mm, or 0.03 wavelengths. Measured data confirmed the expected high gain (13 dBi), with a remarkable aperture efficiency (higher than 50%, including losses), thus validating the proposed approach

Entire-Domain Spectral Basis Functions for the Efficient Design of Metasurface Antennas of Circular Shape

This paper offers an efficient numerical approach to optimizing the design of large circular planar Metasurfaces (MTSs) antennas based on specially varying impedance profiles. Div-conforming spectral basis functions on the whole antenna are defined. The goal is to reduce the number of unknowns, to lead to a well-conditioned system, and to speed up the multiple solutions needed by an automatic optimization code. We consider the overall numerical complexity of the scheme and show its advantages in optimization applications

Current Based Automated Design of Realizable Metasurface Antennas With Arbitrary Pattern Constraints

We present a 3-D method to numerically design a realizable metasurface, which transforms a given incident field into a radiated field that satisfies mask-type (inequality) constraints. The method is based on an integral equation formulation, with local impedance boundary condition (IBC) approximation. The procedure yields the spatial distribution of the impedance, yet the process involves the synthesis of the equivalent current only. This current is constrained to correspond to a realizable surface impedance, i.e., passive, lossless, and with reactance values bounded by practical realizability limits. The current-based design avoids any solution to the forward problem, and the impedance is obtained from the synthesized current only at the end of the process. The procedure is gradient-based, with the gradient expressed in closed form. This allows handling large metasurfaces, with full spatial variability of the impedance in two dimensions. The method requires no a priori information, and all relevant operations in the iterative process can be evaluated with O(N log N) complexity. Application examples concentrate on the case of on-surface excitation and far-field (FF) pattern specifications; they show designs of circular and rectangular metasurface antennas of 20 wavelengths in size, with pencil- and shaped-beam patterns, and for both circular and linear polarizations

Automated Synthesis of Metasurface Antennas

This paper proposes an algorithm for the automated design of metasurface antennas. From the knowledge of an objective radiation field and of an incident field, it allows to synthesize the required surface impedance on the radiating aperture. A scalar impedance boundary condition is employed in the integral equation formulation of the electromagnetic problem. The approach is entirely numerical, based on an iterative algorithm able to enforce both physical and feasibility constraints. This procedure was applied to the design of a leaky-wave antenna at 30 GHz and a circular metasurface antenna at 17 GHz. The results showed a good performance compared to a reference analytical design