In this paper, a flexible compact antenna array operating in the 3.2-13 GHz which covers the standard Ultra-Wide Band (UWB) frequency range is presented. The design is aimed at integration within Multiple Input Multiple Output (MIMO) based flexible electronics for Internet of Things (IoT) applications. The proposed antenna is printed on a single side of a 50.8 μm Kapton Polyimide substrate and consists of two half-elliptical shaped radiating elements fed by two Coplanar Waveguide (CPW) structures. The simulated and measured results show that the proposed antenna array achieves a broad impedance bandwidth with reasonable isolation performance (S12 < -23 dB) across the operating bandwidth. Furthermore, the proposed antenna exhibits a low susceptibility to performance degradation caused by the effect of bending. The system's isolation performance along with its flexible and thin profile suggests that the proposed antenna is suitable for integration within flexible Internet of Things (IoT) wireless systems.
Using absorber-emitter modules, solar thermophotovoltaic (STPV) systems could potentially break through the Shockley-Queisser limit. Efficient spectral selectivity and high temperature endurance are the keys to this technology. In this paper, a high-efficiency selective absorber-emitter module based on refractory material nanostructures is designed for solar thermophotovoltaic applications. Our numerical simulations show that the proposed absorber-emitter module could provide a specified narrowband emission spectrum above the bandgap with optimal bandwidth, and its performance is robust and independent of incident angle and polarization. According to detailed balance calculations, over a broad range of module temperatures, the solar cell efficiency of our design could suprass the Shockley-Queisser limit by 41%.
A flexible fully textile-integrated bandstop frequency selective surface working at a central frequency of 3.75 GHz and presenting a 0.6 GHz bandwidth has been designed, manufactured and experimentally characterised. The frequency selective surface consists of a multilayered woven fabric whose top layer presents periodic cross-shaped conductive resonators, and due to its symmetries, its performance is largely independent of polarisation and angle of incidence. These properties make the prototype very interesting for shielding applications. The designed frequency selective surface is based on a layer-to-layer angle interlock 3D woven fabric. This technology provides the prototype with flexibility, portability and the possibility of manufacturing it in a large scale production by the use of existing industrial weaving machinery, in contrast to conventional frequency selective surfaces manufactured using rigid substrates. The proposed textile frequency selective surface has been simulated and experimentally validated providing good agreement between the simulations and measurements. The measured maximum attenuation has been found to be higher than 25 dB under normal incidence conditions.
nullA quasi-octave bandwidth arbitrary-angle compact waveguide twist using a single matching step is presented. The proposed twist, based on a single intermediate ridge waveguide section that broadens its mono-mode operation, exhibits a similar wave impedance to the rectangular waveguide connected to its ports thus facilitating the reflections minimization in an extended frequency range. An exemplary 45° twist has been manufactured in the 10 GHz to 19.3 GHz frequency range (~64%) for demonstration purposes. The measured data are in concordance with those predicted by the simulation. This result represents, to the authors' knowledge, today's state-of-the-art in terms of compactness and bandwidth performance.
This paper deals with uncertainty propagation applied to the analysis of crosstalk in printed circuit board microstrip traces. Complex interconnection networks generally are affected by many uncertain parameters and their point-to-point transfer functions are computationally expensive, thus making Monte-Carlo analyses rather inefficient. To overcome this situation, a metamodel is highly desirable. This paper presents a sparse and accelerated polynomial chaos approach, which proves to be well adapted for high-dimensional uncertainty quantification and well suited for the sensitivity analysis of crosstalk effects. We highlight the significant advantage of the advocated approach for the design of microstrip line networks of complex topology. In fact, we demonstrate how a small number of system simulations can help to quantify the statistics of the output variability and identify a reduced set of high-impact parameters.
This paper presents an imaging radar system for structural health monitoring (SHM) of wind turbine blades. The imaging radar system developed here is based on two frequency modulated continuous wave (FMCW) radar sensors with a high output power of 30 dBm. They have been developed for the frequency bands of 24,05 GHz-24,25 GHz and 33.4 GHz-36.0 GHz, respectively. Following the successful proof of damage detection and localization in laboratory conditions, we present here the installation of the sensor system at the tower of a 2 MW wind energy plant at 95 m above ground. The realization of the SHM-system will be introduced including the sensor system, the data acquisition framework and the signal processing procedures. We have achieved an imaging of the rotor blades using inverse synthetic aperture radar techniques under changing environmental and operational condition. On top of that, it was demonstrated that the front wall and back wall radar echo can be extracted from the measured signals demonstrating the full penetration of wind turbine blades during operation.
Recent years have witnessed an increasing interest in topological states of condensed matter systems, whose concepts have been also extended to wave phenomena. Especially at optical frequencies, several studies have reported applications of structured light exploiting topological transitions and exceptional points or lines, over which a field property of choice is undefined. Interesting properties of light beams with phase singularities (such as the creation, annihilation or motion of these topological points) have been observed in composite vortices
Polyomino-based arrays allow to efficiently exploit the available array area with a regular element lattice, yet exhibit a non-uniform distribution of their phase centers, leading to superior electronic scanning capabilities. Yet polyomino arrays are usually implemented via polyomino of equal order, leading to uniform amplitude distribution and poor side lobe levels. In this contribution, a tiling of polyominoes of different order is proposed to attain at the same time good scanning characteristics and side lobe level.
The Lienard-Wichert potentials show that radiation is caused by charge acceleration. The question arises about where charge acceleration occurs on the most basic of antennas, a center-fed, perfectly conducting dipole, for which there are two obvious causes. One is the feeedpoint exciting voltage that sets into motion an outward-propagating charge and current wave at light speed c in the medium. A second is at the dipole ends where the outgoing wave is totally reflected producing a change in charge speed of 2c. A third is the decreasing amplitude of the propagating wave with distance due to its partial reflection along the wire. That reflected charge also undergoes a speed change of 2c. This is the reason why the decay of current flowing along a straight wire antenna has been attributed as being due to radiation. Radiation caused by these and other kinds of charge acceleration due to resistive loads, right-angle bends, and radius steps are investigated. These phenomena are examined primarily in the time-domain where they are more observably separable in time and space than in the frequency domain. The current and charge induced on an impulsively excited wire antenna and its broadside radiated E-field are computed using a time-domain, integral-equation model. The computed results are used to derive a numerical relationship between the amount of accelerated charge and its radiated field. This relationship is denoted as an Acceleration Factor (AF) that is obtained for various charge-accelerating features of a generic wire object are normalized to that of the exciting source for comparison with their respect speed changes.
Objective: In this paper we present a study of a novel method to noninvasively monitor temperature noninvasively during thermotherapy, for instance, in cancer treatment using M-sequence radar technology. The main objective is to investigate the temperature dependence of reflectivity in UWB radar signal in gelatine phantoms using electrically small antennas. Methods: The phantom was locally heated up, and consequently changes of signal reflectivity were observed. Results: An approximate linear relationship between temperature change and reflectivity variations was formulated. To show the potential of this approach we used an M-sequence MIMO radar system. The system was tested on breast-shape phantom with local heating by circulating water of controlled temperature. For two dimensional imaging the Delay and Sum algorithm was implemented for two-dimensional imaging. Significance: The article is a study of temperature measurement using UWB radar system for possible usage in thermotherapy.