This article presents the analysis of the electromagnetic (EM) properties of a novel metamaterial (MM) array in the microwave frequency range. The background for this work is the rapid development of portable devices with low individual energy consumption for the so-called “Internet of Things” (IoT) and the demand for energy harvesting from the environment on a micro scale through harvesters capable of powering billions of small receivers globally. The main goal of this work was to check the potential of the novel MM array structure for EM energy harvesting. The proposed MM array was analyzed in the CST Studio simulation environment. This resulted in the determination of the substitute average EM parameters (absorption, reflection, and transmission) of the MM array. Then, the MM array was manufactured, and the simulation results of the MM array parameters were experimentally validated in a microwave waveguide test system. Based on this conclusion, a prototype of the microwave MM absorber, together with an RF/DC converter, was designed and manufactured for harvesting EM energy from the environment. The system’s energy efficiency was evaluated, and its potential application in energy harvesting technology was appraised. Using a microwave horn antenna, the EM energy harvesting efficiency of the prototype was evaluated. It was about 50% at a microwave frequency of about 2.6 GHz. This may make the prototype attractive as an EM energy harvester or bolometric sensor.

The most likely intentional high-power electromagnetic (EM) interference, threatening the operation of technologically advanced electronic infrastructure, will have the forms of sub- and nanosecond ultra-wideband (UWB) pulses, several hundred nanosecond pulses of attenuated sinusoids, and sub- and microsecond sinusoidal pulses. The protection of electronic objects against high-power EM pulses is provided by different types of metal enclosure shields with technological apertures, inside which sensitive electronic objects can be placed. These technological apertures allow external EM interference to penetrate into the enclosure, making the EM shielding imperfect. The EM protection against the EM pulses has been mainly assessed based on the so-called shielding effectiveness (SE) parameters. The SE parameters (SE^e and SE^m for the electric and magnetic fields, respectively) are useful for designing and comparing EM shields. In relatively small shielding enclosures, which have recently become the subject of interest, the SE parameters have been studied for relatively long transient EM interference, longer than 150 ns, i.e., for the EM pulses whose duration is much longer than the time that the pulse takes to pass the small enclosure. In this work, we dealt with an ultrashort transient interference pulse, the duration of which was much shorter than the pulse transit time through the enclosure. The intentional high-power EM subnanosecond UWB pulse is an example of such a pulse. For such an ultrashort pulse, we studied the EM shielding performance of a small size enclosure numerically (W:H:D = 455 mm:50 mm:463 mm) with aperture (W:H = 80 mm:30 mm). The ultrashort EM interference pulse of a Gaussian distribution of the electric and magnetic fields with amplitudes of 10⁶ V/m and 2.68·10³ A/m, respectively, applied in this study, had a duration of 0.0804 ns (FWHM). This means that the high-power EM interference pulse was about 18 times shorter than the time that it takes to pass the enclosure (equal to about 1.5 ns). Our numerical simulations of the subnanosecond high-power EM interference of the interior of the enclosure with aperture were performed in the time domain using the commercial code CST Microwave Studio. First of all, the time-domain simulations resulted in 2D and 3D images and 2D vector maps of the electric and magnetic fields, which visualized the temporal and spatial development of the EM field in the enclosure with aperture caused by the incident subnanosecond high-power EM interference. The development of the associated electric and magnetic fields proceeded in two phases: first in the form of EM waves and later as an interference pattern, traveling forth and back between the front and rear enclosure walls. Due to the energy loss through the aperture, suffered by the traveling EM field and the tendency of the EM field to be evenly distributed over time throughout the entire enclosure, the amplitudes of the EM field decreased about 30 times within 90 ns. Despite the energy loss, the EM field developed in the enclosure existed at least 1000 times longer than the subnanosecond duration of the incident EM pulse (i.e., at least 90 ns as demonstrated by the numerical calculation). Apart from the EM field development visualization, the time-domain simulation enabled easy tracking of the temporal behavior of the EM field in selected points in the enclosure. Such tracking showed that each point in the enclosure was passed by a series of subnanosecond EM pulses, called internal EM pulses, over a relatively long time (at least over the simulation duration of 90 ns). This means that over 90 ns, the points in the enclosure were repeatedly influenced by the series of about 500 subnanosecond internal EM pulses. The amplitudes of many of these pulses were only (3–5) times lower than that of the incident EM pulse. Despite the lower amplitudes, these internal pulses may cause severe EM interference inside the enclosure. This shows a substantial change in the nature of the EM interference caused by a subnanosecond high-power EM plane wave when a given point is not shielded (a single interference of the subnanosecond strong EM pulse) and when a given point is shielded by the enclosure with aperture (a repetitive interference of subnanosecond weaker EM pulses). With the time dependence of the EM field amplitudes obtained from the time-domain calculation at a selected point in the enclosure, it is easy to determine the SE^e and SE^m at that point as a function of time. In this way, evaluation of the local SE^e and SE^m (for selected points in the enclosure) can be performed. Moreover, the 2D and 3D images and 2D vector maps calculated in the time domain for a given time enabled easy calculation of the SE^e and SE^m maps for various times. Such maps, shown for the first time in this paper, give a more global view of the shielding properties of the enclosure with an aperture. This all shows the advantages of the use of the time-domain approach for studying EM shielding in the case of ultrashort EM interferences.

Due to the increase in the threat of attacks with high-power electromagnetic (EM) pulses, there is great interest in metallic enclosures with high shielding effectiveness (SE). Necessary technological apertures in these enclosures reduce their effectiveness. Understanding the penetration and internal propagation of the high-power EM pulses into an apertured enclosure is fundamental to assessing the EM SE of the enclosure. In the present paper, results of the numerical simulations of development of the EM field in a shielding enclosure with aperture after the interference of a subnanosecond high-power EM plane wave pulse of the parallel polarization (having the duration of 0.3558 ns and the amplitudes of the electric and magnetic fields of 10⁶ V/m and 2.6 × 10³ A/m, respectively) are presented. The results obtained include 3D and 2D images , vector maps of the EM field developed inside the enclosure, and time-varying distributions of the electric charges formed on the inner walls of the enclosure. They revealed the mechanism of formation of the EM field inside the enclosure caused by the subnanosecond high-power parallelly polarized EM pulse. The EM field formed in the enclosure with aperture has the form of the electric and magnetic field interference structures. They are a superposition of the incident EM pulse field, which entered the enclosure through the aperture in the way described by the geometrical (ray) optics, the electric field generated by the electric charges formed on the aperture edges and inner sides of the walls of the enclosure, and the magnetic field generated by the surface current formed on the aperture edges and on the inner walls of the enclosure. The amplitudes of the electric and magnetic fields of the strongest EM interference structures decrease non-monotonically to about 0.7 × 10⁵ V/m and 200 A/m at t = 5 ns. We found that the points in the enclosure are subjected to the disturbance of a long series of subnanosecond EM pulses, which we have called internal EM pulses. The amplitudes of these internal pulses are lower than those of the incident EM pulse. Nevertheless, they can pose a severe EM hazard inside the enclosure due to their large number (about 900 internal pulses in 30 ns). This means a fundamental change in the character of the EM disturbance caused by the subnanosecond pulse when the enclosure with aperture is used as a shield.

A proper assessment of the shielding effectiveness of an enclosure with aperture under subnanosecond transient interference requires a better understanding of the coupling and development mechanisms of the EM field induced inside the enclosure. In this paper, the results of a numerical study of the temporal and spatial development of the electromagnetic (EM) field in a shielding enclosure with aperture after transient interference caused by a subnanosecond high-energy EM plane wave pulse are presented. The interference pulse had Gaussian distribution of the electric and magnetic fields with amplitudes of 10⁶ V/m and 2.68·10³ A/m, respectively. The maximum pulse power density was 2.68 GW/m². The novelty of this study was 2D and 3D images, which visualized the temporal and spatial build-up of electric and magnetic fields in the shielding enclosure within 90 ns after the transient interference. This is 58 times longer than the time needed by any EM wave to travel the distance between the front and rear walls of the enclosure. The presented images, showing the EM field morphology over a relatively long period of time, were crucial for understanding the EM field build-up process inside the shielding enclosure with aperture. They revealed the existence of two unknown phases of the EM field build-up in the enclosure with aperture. We call these two phases the wave phase and the interference phase. In the wave phase, the EM field is generated in the form of so-called primary and secondary wave pulses, traveling towards the enclosure rear wall. In the interference phase, the EM field has the form of temporally and spatially varying pulse-like interference (size-limited) patterns of the associated electric and magnetic fields. The EM field induced in the enclosure is long-lasting compared to the interference pulse duration. The amplitudes of the electric and magnetic fields decreased about threefold in 5 ns and 30-fold in 90 ns, thus exhibiting a severe EM hazard for much longer than the external interference duration. For a long period of time, the highest EM field amplitudes would change their locations in the enclosure, which makes it difficult to assess the shielding effectiveness on the basis of classical definitions. The existence of the long-lasting temporally and spatially varying EM field induced in the enclosure with aperture by the subnanosecond transient interference, visualized in detail in this paper, confirms that a new definition and measurement methods of shielding effectiveness under transient conditions are needed. The obtained results provide a source of data that can be useful when working on the introduction of time-domain parameters to evaluate the transient shielding effectiveness in the case of the ultrashort EM interference.

Metamaterials are artificially structured composite media with a unique electromagnetic (EM) response that is absent from naturally occurring materials, which appears counterintuitive and aggravates traditional difficulties in perceiving the behavior of EM waves. The aim of this study was to better understand the interaction of EM waves with metamaterials by virtual visualizing the accompanying physical phenomena. Over the years, virtual visualization of EM wave interactions with metamaterials has proven to be a powerful tool for explaining many phenomena that occur in metamaterials. In this study, we performed virtual visualization of the interaction of an EM plane wave with a split-ring resonator (SRR) metamaterial structure, employing CST Studio software for modeling and comprehensive simulations of high-frequency EM fields of 3D objects. The SRR structure was designed to have its magnetic resonance at the frequency f = 23.69 GHz, which is of interest for antennas supporting wireless microwave point-to-point communication systems (e.g., in satellite systems). Our numerical calculations of the coefficients of absorption, reflection, and transmission of the EM plane wave incident on the SRR structure showed that the SRR structure totally reflected the plane EM wave at the magnetic resonance frequency. Therefore, we focused our research on checking whether the results of numerical calculations could be confirmed by visualizing the total reflection phenomenon on the SRR structure. The performed vector-field visualization resulted in 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period, which demonstrated the existence of characteristic features of the total reflection phenomenon when the EM plane interacted with the studied SRR, i.e., no EM field behind the SRR structure and the standing electric and magnetic waves before the SRR structure, thus, confirming the numerical calculations visually. For deeper understanding the interaction of the EM plane wave with the SRR structure of reflection characteristics at the magnetic resonance frequency f = 23.69 GH, we also visualized the SRR structure response at the frequency f = 21 GHz, i.e., at the so-called detuned frequency. As expected, at the detuned frequency, the SRR structure lost its metamaterial properties and the obtained 2D vector maps of the electric and magnetic fields around the SRR structure during the wave period showed the transmitted EM wave behind the SRR structure and no EM (fully) standing waves before the SRR structure. The visualizations presented in this study are both unique educational presentations to help understand the interaction of EM plane waves with the SRR structure of reflection characteristics at the magnetic resonance and detuned frequencies.