This paper describes a new design and an optimization framework for a four-band antenna to be used in wireless sensor networks. The antenna is designed to operate effectively in two open frequency bands (ISM—Industrial, Scientific, Medical), 2.4 GHz and 5.8 GHz, as well as in two bands allocated for the fifth-generation (5G) cellular networks, 0.7 GHz and 3.5 GHz. Our initial design was developed using the trial and error approach, modifying a circular disc monopole antenna widely used in ultra wideband (UWB) systems. This initial design covered the three upper bands, but impedance matching within the 700 MHz band was unsatisfactory. The antenna performance was then improved significantly using an optimization algorithm that applies a bi-objective fully-Paretian approach to its nine-parameter geometry. The optimization criteria were impedance matching and radiation efficiency. The final design exhibits good impedance matching in all four desired bands with the Voltage Standing Wave Ratio (VSWR) value below 2 and radiation efficiency of 88%. The simulated antenna performance was verified experimentally.

Magnetically coupled resonant circuits have been utilized in radio engineering for many years. Recently, these circuits have found new applications, particularly in supplying low- and medium-power devices through medium-range wireless power transmission technology based on magnetic resonance coupling. There is also a growing need to analyze magnetically coupled resonant circuits in the design of metamaterials, which exhibit specific electromagnetic properties within certain frequency bands. This paper provides a coherent and concise overview of the phenomena associated with magnetically coupled resonant circuits. The results encompass numerous established relations as well as new ones. They can be helpful in the design phase of magnetically coupled resonant circuits. The outcomes include equations for determining the coupling resonant frequencies and some parameters of resonance curves. These analytical results are accompanied by 3D and cross-sectional (contour) graphs for better visualization. Moreover, a lumped-element circuit model that includes magnetically coupled resonant circuits is proposed for the resonators used in metamaterials. Formulas for resonant frequencies are derived in the specific case of exciting such resonators. To validate the accuracy of the derived equations, the analytical results are compared with simulations from SPICE (IsSPICE4 ver. 8.1) and COMSOL 5.4 software, which are widely used tools for circuit analysis and electromagnetic simulations. The results of these comparative analyses indicate that the assumptions employed in the analytical solutions introduce only tiny errors.

In this paper an optimization method of a dual-band wearable antenna is presented. The antenna geometry is described with 8 geometrical parameters that are automatically adjusted with the use of a evolutionary algorithm to obtain the impedance matching of antenna located in the proximity of a human body. The antenna has been designed to operate in the ISM band which covers the frequency range of 2.4-2.5 GHz and 5.7-5.9 GHz. Within the optimization procedure the direct problem is solved by full wave finite-difference time-domain method to calculate the antenna impedance matching used in the objective function. As the first approach the optimization algorithm was firstly executed in an 8-dimensional parameter space. Subsequently the optimization algorithm was modified so it could start from the reduced set of parameters and then dynamically increase the dimension of the design variable space following the prescribed hierarchy of the parameters. The latter variant of the optimization procedure gave a better solution of the design problem with less computational effort.

This paper reviews the work that has been done in the past 10 years at the Lodz University of technology about the visualization and the quantification of phenomena related to degradation processes (i.e. stress corrosion cracking in stainless steel, fatigue crack in titanium alloys) in engineering materials as well as granular flow in silos using X-ray imaging (i.e. radiography and (micro)tomography). Besides presenting the experimental protocols, the paper also presents the image processing strategies that have been applied to enable the extraction of characteristic parameters from the volumetric images.