The realm of sustainable technologies and metamaterials represents a vibrant field of inquiry, and, upon closer examination, a fascinating correlation emerges. Metamaterials, being artificially engineered substances, exhibit diverse characteristics, depending on their specific composition. Remarkably, they hold immense potential in various sustainability-driven applications, such as energy harvesting, purification, and noise control. For instance, a straightforward approach involves the implementation of electromagnetic metamaterial absorbers in energy harvesting systems. As the scope of environmental concerns continues to expand, this proposed solution demonstrates its universal applicability, addressing a growing number of environmental challenges.

The purpose of this paper was to investigate the influence of fabrication process uncertainty on terahertz metasurface quality. The focus was on the effect of metasurface fabrication inaccuracy on resonances. To the best of our knowledge, this is the first paper to study the effect of the metasurface fabrication process on its resonant frequency. The terahertz split ring resonator-based metasurface is under consideration. Using a numerical model, the influence of the uncertainty of various geometrical parameters obtained during the fabrication process (mainly layer deposition, photolithography, and etching processes) is analyzed according to the resonance of the designed metasurface. The influence of the following parameters causes a shift of resonant frequencies of the considered metasurface: etching deviation e, metallization thickness tAl and SiO2 layer thickness tSiO2. The quality of the metasurface affected by the variations of obtained geometrical parameters was determined by the deviation of resonant frequency Δfr. The developed numerical model was verified by THz-TDS (terahertz time-domain spectroscopy) measurements of the fabricated structure.

The paper presents the evaluation of thin dielectric layers using a tunable split-ring resonator-based metasurface in the THz frequency range. Tunable unit cells of a metasurface allow its resonant frequency variation using some external excitation. This can be done in various ways. In this work, the behavior of such a metasurface is investigated by monitoring the resonant frequency value when the unit cell geometry is changed. Such behavior is utilized for the quality evaluation of a thin dielectric layer placed in vicinity of a metasurface. A change in dielectric permittivity noticeably affects the resonant frequency of a metasurface. In order to examine the state of the material under test, finite element method simulations were made for a 15 µm thin layer. As a result, the approximation-based relations between resonant frequencies (obtained for various geometries of structural element—in tunability range) and dielectric parameters of the examined material were derived. These relations carry more information than in the case of just one resonant frequency (the case of a non-tunable metasurface) and can be utilized for permittivity evaluation.

Until now, strain gauges, fiber optic sensors, magnetic sensors, and piezoelectric sensors have been used for strain measurements. In recent years, the idea of using microstrip antennas in strain measurement applications has emerged. One of the key requirements for deformation sensors is the ability to mount them on small-size elements (therefore the size of these sensors is crucial). The possible way to miniaturize microstrip sensors is the application of appropriate patch geometry, e.g. fractal geometry. In this article application of various fractal patch geometries in microstrip strain sensors were investigated. All sensors were designed for the same operating frequency ${f}_{\textbf {r}} =2.725$ GHz and on the same laminate. This approach showed how the influence of a specific geometry affects the sensitivity and the transducer size. The Sierpinski carpet, the Sierpinski triangle, the Sierpinski curve, and the combination of the Koch curve and the Sierpinski carpet were used to obtain the fractal geometry and miniaturize the sensor dimensions. They have been compared with the widely used rectangular patch. Numerical and experimental analyzes for the proposed sensors were carried out. The best solution to this problem was to use a combination of the Koch curve and the Sierpinski carpet. This fractal geometry, compared to a rectangular patch, enables the reduction of the patch size by 70% while reducing the sensitivity by 26%.

Strain is a crucial assessment parameter in structural health monitoring systems. Microstrip sensors have been one of the new types of sensors used to measure this parameter in recent years. So far, the strain directionality of these sensors and the methods of miniaturization have been studied. This article proposes the use of a single cell metamaterial as a resonator of the microstrip sensor excited through the microstrip line. The proposed solution allowed for significant miniaturization of the microstrip sensor, with just a slight decrease in sensitivity. The proposed sensor can be used to measure local deformation values and in places with a small access area. The presented sensor was validated using numerical and experimental methods. In addition, it was compared with a reference (rectangular geometry) microstrip sensor.