Search Results (276)

This study represents a first step toward improving the repeatability, reproducibility, and accuracy of a process designed to enhance dynamic water structuring. We aim is to investigate the optical reflectivity of a watery magnesium chloride solution treated with electromagnetic waves, we employ a novel methodology derived from human plethysmography (PPG) with three wavelengths spanning the visible and infrared spectra. We measured the reflectance of 17 flasks at 536 nm, 660 nm, and 940 nm before and after treatment, first using the succussion method (control) and second using a 50 Hz signal. The observed variability was acceptable, with repeatability errors below 0.15% and reproducibility errors below 3.5% across all wavelengths before and after treatment. Out of 51 samples dynamically structured using the succussion method, we obtained two false negatives, while one false negative was recorded out of 51 samples dynamically structured using the electromagnetic (EM) method. PPG appears to be a relevant sensor, as it correctly detected dynamically structured water in 99 out of 102 cases, using either the succussion or electromagnetic method. Our results show significant differences in reflectance (supposedly correlated with water’s structured status) at 536 nm between dynamically structured and dynamic non-structured samples (p < 0.001). Future improvements will include a validation protocol against gold-standard spectrophotometry with a larger sample size. Full article

This study employed a hydrothermal method to prepare V-doped MoS₂. The influence of varying filler ratios (30 wt%, 40 wt%, 50 wt%) on its absorption properties was analyzed. For annealing studies, a precursor powder with a 40 wt% filler ratio was heat-treated at 600 °C for 2 h. The results obtained through characterization and testing indicate that the unannealed 40 wt% filler sample demonstrates superior absorption performance, with minimum reflection loss (RL_min) of −32.24 dB, an effective absorption bandwidth (EAB) of 4.40 GHz, and 99.9% electromagnetic (EM) wave attenuation. However, upon subjecting the sample with a 40 wt% filling ratio to annealing treatment, a notable decrease in impedance matching degree was observed, and regions with impedance matching values close to 1 were no longer present. Consequently, it can be concluded that at a filling ratio of 40 wt%, the sample’s excellent attenuation coefficient in conjunction with its good impedance matching collectively contribute to its superior comprehensive absorption performance. Full article

In this paper, we propose a novel evaluation method to assess the strength of electromagnetic (EM) waves in a specific area by analyzing the propagation environment at a radar testing site. To analyze the propagation environment of the radar test site, this evaluation method performs precise modeling of actual structures such as buildings and terrain. The calculated received power is then converted into electric field strength to compare with the reference threshold level (61 V/m). The electric field during the radar operation is examined by changing two scenarios: one is when the transmitter (Tx.) is directed toward the receiver (Rx.), and the other is when the Tx. is misaligned. In particular, it may increase the electric field strength near the Tx. system when Tx. and Rx. are misaligned. To reduce the impact of EM waves, we conducted a comparison based on the installation of absorbers. The results indicate that the received electric field shows attenuation rates of 39.47% in the X-band and 39.35% in the Ku-band, achieved with a 1 m absorber. In addition, the theoretical and average measured received powers of −61.9 dBm and −62.03 dBm, respectively, show good agreement with the simulated result of −64.64 dBm. This measurement procedure exhibits high accuracy when compared with theoretical and simulation results. These results demonstrate the reliability of the propagation environment analysis using the proposed integrated simulation model. Full article

As a significant geological hazard in large–scale engineering construction, deep subsurface voids demand effective and precise detection methods. Cross–hole radar tomography overcomes depth limitations by transmitting/receiving electromagnetic (EM) waves between boreholes, enabling the accurate determination of the spatial distribution and EM properties of subsurface cavities. However, conventional inversion approaches, such as travel–time/attenuation tomography and full–waveform inversion, still face challenges in terms of their stability, accuracy, and computational efficiency. To address these limitations, this study proposes a deep learning–based imaging method that introduces the concept of travel–time fingerprints, which compress raw radar data into structured, low–dimensional inputs that retain key spatial features. A large synthetic dataset of irregular subsurface cavity models is used to pre–train a UNET model, enabling it to learn nonlinear mapping, from fingerprints to velocity structures. To enhance real–world applicability, transfer learning (TL) is employed to fine–tune the model using a small amount of field data. The refined model is then tested on cross–hole radar datasets collected from a highway construction site in Guizhou Province, China. The results demonstrate that the method can accurately recover the shape, location, and extent of underground cavities, outperforming traditional tomography in terms of clarity and interpretability. This approach offers a high–precision, computationally efficient solution for subsurface void detection, with strong engineering applicability in complex geological environments. Full article

A causal electromagnetic (EM) metasurface is backed by a lossless substrate and partially absorbs obliquely incoming rays. The integral of the absorbed power along the entire frequency axis is analytically evaluated, and the obtained sum rules indicate the global absorption by such a generic configuration. The beneficial influence of the plasma frequency and damping factor on the total absorbance score as well as the opposite effect of the angle of excitation, is noted. An overall lossless behavior at the incidence direction where the propagating waves into the substrate turn into evanescent is identified, once the magnetic field is parallel to the interface. The reported results can be useful in the tailoring of spectrally dependent absorption by a whole class of planar structures and, accordingly, in the forward and inverse design of lossy photonic metasurface setups. Full article

Ti-based MXenes such as Ti₃C₂T_X and Ti₂CT_X have attracted considerable attention because of their superior electromagnetic interference (EMI) shielding effectiveness compared to other EMI shielding materials, especially for high electromagnetic (EM) wave absorption. In this study, we investigated the microstructural changes produced by heat treatment and their effect on the EMI shielding properties of Ti-based MXenes. Ti₃C₂T_X and Ti₂CT_X films were prepared using vacuum filtration and annealed at temperatures up to 300 °C. The microstructures and chemical bonding properties of these heat-treated Ti₃C₂T_X and Ti₂CT_X films were analyzed, and the EMI shielding effectiveness was measured in the X-band and THz frequency range. The porous Ti₃C₂T_X film showed higher EM absorption than that calculated using the transfer matrix method. On the other hand, the Ti₂CT_X films had a more densely stacked structure and lower EM absorption. As the heat treatment temperature increased, Ti₃C₂T_X developed a more porous structure without significant changes in its chemical bonding. Its EM absorption per unit of thickness increased up to 6 dB/μm, while the reflectance remained constant at less than 1 dB/μm after heat treatment. This suggested that the heat treatment of Ti-based MXenes can increase the porosity of the film by removing residual organics without changing the chemical bonds, thereby increasing electromagnetic shielding through absorption. Full article

In this article, a miniaturized frequency-selective surface (FSS)-based electromagnetic shield is investigated for EMI mitigation in the X-band. The FSS comprises a convoluted conducting loop designed over an FR-4 substrate. It operates at 10 GHz X-band frequency and offers an effective shielding of at least 33 dB. It reveals rejection bandwidths of 26% for the TE and TM wave modes at normal incidence. Moreover, it accomplishes polarization-insensitive and angularly stable spectral responses owing to its structural symmetry and compact size. In addition, an equivalent circuit model (ECM) and a finite prototype of the shield are developed to verify EM simulations. A comparison of the results indicates that the FSS offers wide angular stability and excellent shielding performance, which makes it a suitable candidate for applications requiring targeted EMI mitigation. Full article

This paper presents an on–off power control technique for galvanically isolated dc–dc converters, which implements a feedback control loop for power regulation on the same isolation transformer used for power transfer. To this aim, the power oscillator is controlled with a PWM scheme, and the control signal is transmitted through the galvanic barrier by using an ASK modulation that acts on the secondary winding of the isolation transformer. The key building block of the proposed architecture is a PLL that allows the reconstruction of the PWM control signal when the power oscillator is turned off and data transmission is disabled. The effectiveness of the proposed power control architecture is validated by designing an isolated dc–dc converter based on a thick polyimide transformer. It complies with reinforced isolation while addressing the power requirements of applications such as low-power sensor interfaces, medical devices, and housekeeping power, e.g., gate drivers or controllers for power converters. At a 20 V output voltage, 110 mW isolated output power is delivered. The dc–dc converter also provides PWM power regulation against PVT variations. Full article

The increasing demand for high-frequency applications and the widespread use of electromagnetic (EM) waves in communication systems necessitate the development of effective electromagnetic interference (EMI) shielding materials. This study investigates the structural and shielding effectiveness properties of novel polyaniline (PANI)-based NiO/ZnNb₂O₆ composites for sub-8 GHz applications. NiO and ZnNb₂O₆ were synthesized via conventional solid-state reactions and combined with PANI to form composites with varying compositions. X-ray diffraction (XRD) confirmed the successful formation of single-phase NiO and ZnNb₂O₆, while scanning electron microscopy (SEM) revealed well-defined microstructures, contributing to enhanced shielding efficiency. Shielding effectiveness (SE) measurements were performed across the 0–8 GHz frequency range using a vector network analyzer. Among the compositions tested, the epoxy-based NiO-ZnNb₂O₆ (75–25% by weight) with a 1:1 PANI ratio exhibited the highest SE value of −41.16 dB (decibels) at 6.24 GHz, demonstrating superior attenuation of EM waves. The observed shielding efficiency is attributed to multiple reflection effects, dipole interactions, and the conductive network formed by PANI. These findings highlight the potential of NiO/PANI/ZnNb₂O₆ composites as cost-effective, high-performance EMI shielding materials for next-generation microwave communication and electronic applications. Further optimization and hybridization approaches are recommended to enhance performance for broader frequency bands. Full article

Carbon nanotube-based nanocomposites are being increasingly utilized in materials for electromagnetic shielding purposes due to their exceptional electrical and mechanical properties. The current study optimizes a simple procedure to prepare multi-wall carbon nanotubes (MWCNTs)-based hydrogel nanocomposites out of water, gelatin, and glycerol. The content ratio of each component in the hydrogel composite is carefully selected to optimize the dielectric properties over the electromagnetic (EM) wave frequency of 0.5 to 20 GHz. The hydrogel nanocomposites were prepared with MWCNT concentrations ranging from 0.1 to 0.9 wt%. The dispersion of MWCNTs in the nanocomposites was investigated and confirmed using a scanning electron microscope (SEM). The dielectric parameters, including the real dielectric constant ${\epsilon }^{\prime }$, imaginary dielectric constant ${\epsilon }^{″}$, and tangent loss tan $\delta$ along with the DC and AC electrical conductivity (${\sigma }_{DC}$,${\sigma }_{AC}$) were investigated. The study shows a significant enhancement in the dielectric parameters of the prepared nanocomposites as the MWCNT concentration is increased. The shielding effectiveness (SE) of the hydrogel nanocomposites against electromagnetic waves in the frequency range from 1.7 to 6.0 GHz is investigated and found to be enhanced as the concentration of MWCNTs and frequency have increased. The shielding effectiveness of the prepared hydrogel nanocomposites ranges from 10 dB to 26 dB, equivalent to shielding of 90% and more than 99% of incident radiation, respectively. Full article

Where and at what altitudes electromagnetic wave ducts within the atmosphere are likely to occur is important for a variety of communication and military applications. We examined the modified refractivity profiles and wave duct characteristics derived from nearly 50,000 observed upper air soundings obtained over four years from seven tropical and subtropical islands, as well as middle latitude sites at four US coastal locations, three sites near the Great Lakes, and four US inland sites. Across all location types, elevated ducts were found to be more common than surface-based ducts, and the median duct thicknesses were ~100 m. There was a weak correlation between duct thickness and strength and, essentially, no correlation between the duct strength and duct base height. EM ducts more frequently occurred at the tropical and subtropical island locations (~60%) and middle latitude coastal locations (70%) as compared to the less than 30% of the time that occurred at the Great Lake and US inland sites. The tropical and subtropical island sites were more likely than the other location types to have ducts at altitudes higher than 2 km, which is above the boundary layer height. Full article

This study presents an innovative Dual-Band Frequency Selective Surface (FSS) designed for LTE applications, offering an effective solution for minimizing Passive Inter-Modulation (PIM) in contemporary wireless communication systems at the base station. The proposed passband FSS filter is designed to deliver optimal dual-band filtering characteristics with consistent stability over incidence angles up to 80°. Corresponding to antenna systems requirements, the proposed method gives resonant frequencies at 1.9 and 2.1 GHz which operate in the LTE band with bandwidths of 40 and 60 MHz, respectively. Moreover, the proposed design is analyzed to establish the optimal range for each resonant frequency by examining the parametric effects. The suggested FSS-based filter consists of a single-layer structure with the dimension of the unit cell of 0.33${\lambda }_1$ × 0.33${\lambda }_1$ where ${\lambda }_1$ is the wavelength of low frequency, which delivers desired reflection and transmission coefficients using RT/Duroid 5880 with a thickness of 0.508 mm. The designed filter is validated through measurements of a fabricated prototype, demonstrating its practicality and performance. Simulations carried out with Equivalent Circuit Modeling (ECM) are demonstrated by measurements from a constructed 4 × 4 array prototype, showing a robust alignment with experimental findings. This work emphasizes an asymmetric FSS design that improves frequency selectivity and angular stability for the desired LTE dual band and also depicts the future possibilities for tuneable models and broader applications to meet the demands of modern wireless communication. Full article

An electromagnetic (EM) absorber-embedded Ka-band double-layer tapered slot antenna (DLTSA) is proposed in this work. The EM absorber is placed on both sides of the tapered radiating slots as a means of achieving the reduced monostatic radar cross section (RCS) at the X-band. A conventional tapered slot antenna (TSA) with EM absorbers at the same position suffers from the distorted current distribution from the feedline to the radiating slots and causes a degraded radiation performance with a tilted beam. In contrast, the DLTSA with EM absorbers maintains the impedance and radiation characteristics of the antenna without the EM absorbers, while achieving the reduced monostatic RCS for the cross-polarized incident wave. The functionality of the reduced RCS is verified with the 4-by-4 DLTSA array design. The 4-by-4 array prototype with FGM-125 EM absorbers is matched at the Ka-band with a 14.7 dBi boresight gain at 35 GHz. The monostatic RCS is measured in an indoor environment, showing 6.5 dB monostatic RCS reduction at the X-band on average, verifying the computed expectations. This work validates the possible use of EM absorbers at the front side of a missile seeker composed of end-fire radiating elements. Full article

In this paper, a novel dual-band metasurface filter (MSF) designed for accurately differentiating pulse waves (PWs) and continuous waves (CWs) is proposed, which is based on a complementary cross resonator (CSR) structure adhered on a dielectric substrate integrated with a capacitive nonlinear circuit. The unit cell of the designed dual-band MSF comprises two identical CSR structures: one of the capacitive nonlinear circuits is configured in parallel with a capacitor (C₁) within one CSR structure. These structures loaded with nonlinear circuits are fabricated on a dielectric substrate. The simulation outcomes reveal that, for normally incident CWs with an input power of 10 dBm, the transmittance of the designed dual-band MSF reaches as high as 97.1% at 2.0 GHz and 93.9% at 3.45 GHz. In contrast, when it comes to 50 ns short PWs, the transmittance remains consistently below 6% throughout the entire frequency range from 1 GHz to 5 GHz. In addition, the transmittance of the dual-band MSF for normally incident PWs increases significantly as the pulse width widens at the aforementioned two discrete frequencies. The ensuing simulation data corroborates that within the input power range of −15 to 15 dBm, the transmittance difference between CWs and PWs of the dual-band MSF first rises and then falls as the input power increases. Specifically, when the input power is specified as 10 dBm and the angle of oblique incidence ranges from 0° to 60°, in the context of TE and TM modes, the transmittance of CWs exceeds 80% around both 2.0 GHz and 3.45 GHz, while that of PWs remains below 15%. Finally, the effects of resistance and capacitance on the transmittance of the dual-band MSF for the incident PWs and CWs are also studied. The dual-band MSF proposed herein showcases its potential applications in wireless communication as well as in the realm of anti-electromagnetic interference. The electromagnetic (EM) waveform modulation in the frequency band of 1–5 GHz has great development prospects in low-frequency working fields such as radar antennas and EM protection. Full article

This paper examines the potential for shielding against electromagnetic (EM) radiation in traditional buildings. The primary objective is to evaluate how effectively these buildings can reduce the intensity of the electric field from external sources, while also identifying the factors that influence this reduction, such as geometry, structure, and the characteristics of EM waves. Measurements were conducted on the transmission parameter S₂₁, which indicates how EM waves propagate through the walls of residential buildings constructed using traditional methods. The buildings analyzed were made from wood, rammed earth, raw bricks blended with straw (known in Croatian as ćerpič), and baked bricks, which served as the reference material. During the measurements, conditions such as the thickness, humidity, and temperature of both the walls and the surrounding environment were carefully controlled. The buildings represented traditional construction styles typical of Croatia and most of Central and Eastern Europe. The results indicate that structures made from rammed earth and raw bricks with added straw significantly decrease the transmission of EM wave energy compared to those made from wood and baked bricks. It is important to note that the walls of wood buildings were considerably thinner than those made from the other materials tested. Additionally, both the moisture content and thickness of the walls contributed significantly to reducing transmission parameters. These findings support the use of these traditional materials for constructing environmentally friendly buildings, while also suggesting the need for further architectural design and testing. Since this research does not cover all types of traditionally constructed buildings—such as stone houses, wicker structures, and dugouts—future studies will aim to expand this investigation to include a broader variety of traditional building styles. Full article