Sinuous Antenna for UWB Radar Applications.

In this paper, the recent progress on sinuous antennas is detailed, focusing the attention on the antenna geometry, dielectric structure, and miniaturization techniques. In the first part, we introduce the basic principles of the frequency-independent antenna, in particular the self-complementary and log-periodic geometries, as well as the antenna geometries, all characterized in terms of angles. The operating principles, main advantages, system design considerations, limits, and challenges of conventional sinuous antennas are illustrated. Second, we describe some technical solutions aimed to ensure the optimal trade-off between antenna size and radiation behavior. To this aim, some special modification of the antenna geometry based on the meandering as well as on the loading with dielectric structures are presented. Moreover, the cavity backing technique is explained in detail as a method to achieve unidirectional radiation. Third, we present a new class of supershaped sinuous antenna based on a suitable merge of the 2D superformula and the sinuous curve. The effect of the free parameters change on the antenna arm geometry as well as the performance improvement in terms of directivity, beam stability, beam angle, gain, and radiating efficiency are highlighted.

Experimental and Numerical Study of Electroporation Induced by Long Monopolar and Short Bipolar Pulses on Realistic 3D Irregularly Shaped Cells.

In this article, the reversible electroporation induced by rectangular long unipolar and short bipolar voltage pulses on 3D cells is studied. The cell geometry was reconstructed from 3D images of real cells obtained using the confocal microscopy technique. A numerical model based on the Maxwell and the asymptotic Smoluchowski equations has been developed to calculate the induced transmembrane voltage and pore density on the plasma membrane of real cells exposed to the pulsed electric field. Moreover, in the case of the high-frequency pulses, the dielectric dispersion of plasma membranes has been taken into account using the second-order Debye-based relationship. Several numerical simulations were performed and we obtained suitable agreement between the numerical and experimental results.

Nonlinear Dispersive Model of Electroporation for Irregular Nucleated Cells.

In this work, the electroporation phenomenon induced by pulsed electric field on different nucleated biological cells is studied. A nonlinear, non-local, dispersive, and space-time multiphysics model based on Maxwell's and asymptotic Smoluchowski's equations has been developed to calculate the transmembrane voltage and pore density on both plasma and nuclear membrane perimeters. The irregular cell shape has been modeled by incorporating in the numerical algorithm the analytical functions pertaining to Gielis curves. The dielectric dispersion of the cell media has been modeled considering the multi-relaxation Debye-based relationship. Two different irregular nucleated cells have been investigated and their response has been studied applying both the dispersive and non-dispersive models. By a comparison of the obtained results, differences can be highlighted confirming the need to make use of the dispersive model to effectively investigate the cell response in terms of transmembrane voltages, pore densities, and electroporation opening angle, especially when irregular cell shapes and short electric pulses are considered. Bioelectromagnetics. 2019;40:331-342. © 2019 Wiley Periodicals, Inc.

Radiation hardened high-power Er3+/Yb3+-codoped fiber amplifiers for free-space optical communications.

The radiation responses of different high-power erbium/ytterbium-codoped fiber amplifiers (HP-EYDFA) have been investigated up to 100 krad (SiO2) dose levels. These devices are able to deliver 20 W of signal output power at 1565 nm by pumping at 915 nm (43 W) radiation tolerant (Er/Yb) or radiation hardened (ErYbCe) active few mode fibers; these performances are needed for free-space communications between low-orbit satellites and ground transceivers. X-ray irradiation results show that, thanks to a positive influence of the photo- and thermal-bleaching phenomena associated with such high-power operating conditions, the gain degradation levels of HP-EYDFA based on radiation hardened fibers remain below 6% after 100 krad at an accelerated dose rate of 3.4 rad/s.

Modeling of Electroporation Induced by Pulsed Electric Fields in Irregularly Shaped Cells.

During the past decades, the poration of cell membrane induced by pulsed electric fields has been widely investigated. Since the basic mechanisms of this process have not yet been fully clarified, many research activities are focused on the development of suitable theoretical and numerical models. To this end, a nonlinear, nonlocal, dispersive, and space-time numerical algorithm has been developed and adopted to evaluate the transmembrane voltage and pore density along the perimeter of realistic irregularly shaped cells. The presented model is based on the Maxwell's equations and the asymptotic Smoluchowski's equation describing the pore dynamics. The dielectric dispersion of the media forming the cell has been modeled by using a general multirelaxation Debye-based formulation. The irregular shape of the cell is described by using the Gielis' superformula. Different test cases pertaining to red blood cells, muscular cells, cell in mitosis phase, and cancer-like cell have been investigated. For each type of cell, the influence of the relevant shape, the dielectric properties, and the external electric pulse characteristics on the electroporation process has been analyzed. The numerical results demonstrate that the proposed model is an efficient numerical tool to study the electroporation problem in arbitrary-shaped cells.

Design of mid-infrared amplifiers based on fiber taper coupling to erbium-doped microspherical resonator.

A dedicated 3D numerical model based on coupled mode theory and solving the rate equations has been developed to analyse, design and optimize an optical amplifier obtained by using a tapered fiber and a Er³âº-doped chalcogenide microsphere. The simulation model takes into account the main transitions among the erbium energy levels, the amplified spontaneous emission and the most important secondary transitions pertaining to the ion-ion interactions. The taper angle of the optical fiber and the fiber-microsphere gap have been designed to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare earth doped region. In order to reduce the computational time, a detailed investigation of the amplifier performance has been carried out by changing the number of sectors in which the doped area is partitioned. The simulation results highlight that this scheme could be useful to develop high efficiency and compact mid-infrared amplifiers.

Optimization of pump absorption in MOF lasers via multi-long-period gratings: design strategies.

Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rare-earth-doped core of microstructured fiber lasers, are illustrated. Three kinds/configurations of optical couplers have been designed and compared as examples of the different design strategies which can be followed. Their effectiveness to enhance the performance of an ytterbium-doped, double cladding, microstructured optical fiber laser has been accurately simulated. They consist of a suitable cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core region. The characteristics of the MLPG couplers have been simulated via a homemade computer code based on both rate equations and an extended coupled mode theory. The proposed MLPG couplers seem particularly useful in the case of low rare-earth concentration but, even for a middle-high ytterbium concentration, as N(Yb)=5×10(25) ions/m(3), the slope efficiency S can be increased up to 20%, depending on the fiber length.

Design of a dielectric applicator for microwave heating.

In this paper the design of a handheld light applicator for microwave heating is presented. The applicator is made of an array of resonant longitudinal slots cut on a broad wall of a rectangular waveguide, and it is covered by a cylindrical lens made of Plexiglas with a permittivity of 2.53. The geometrical optics approach is used as initial approximation to establish the lens profile. It allows for the shaping of the slotted waveguide's radiation pattern into a desired output pattern in the transversal plane. Three-dimensional simulation results show that the applicator performance can be improved at 2.45 GHz by using a homogeneous dielectric lens.

Analysis of microwave thermal treatment of antique books with metallic insets.

The electromagnetic and thermal analyses of a mode-stirred chamber designed for the heat treatment of antique and precious books are proposed. In particular, the electromagnetic and thermal perturbations due to the presence of metallic insets inside the treated material (paper) are investigated. The temperature measurement results obtained by thermography and by temperature fiber-optic sensor are also reported. Finally, metallic shields are experimentally demonstrated to prevent the overheating of the treated material and the consequent damage of the antique tomes.