Broad Frequency Range Research Articles

Effect of lanthanum oxide on the radiation-shielding, dielectric, and physical properties of lithium zinc phosphate glasses

This study looked at the shielding properties, physical properties, and dielectric spectroscopy of various lanthanum oxide concentrations based on (65-x) P2O5-15 Li2O–15ZnO– 5Bi2O3- xLa2O3 with x = 0.0, 1.0, 2.0, 3.0, and 4.0 mol% glasses. When La2O3 is added, the molar volume quantities fall but the density values increase. The sample with the designation La-4.0 (4.0 mol% La2O3 content) had the highest density observed, 3.2182 g/cm3. Monte Carlo simulations and the Phy-x/PSD software were used to determine the critical gamma radiation attenuation characteristics, particularly linear attenuation coefficients and mass attenuation coefficients of glass samples under investigation. The half-value layer, mean free path, effective atomic number and effective electron density were then examined across a wide energy range (0.015–15 MeV). The findings of the investigation showed that the addition of La2O3 decreased the half-value layer and mean free path while increasing the mass attenuation coefficient, effective atomic number, and effective electron density. The results indicate that the inclusion of La2O3 appears to improve that glass system's ability to deflect gamma and neutron radiation. Over a broad frequency range, the dielectric properties were measured. The dielectric constant (ε′), which is typically steadily decreased with the addition of lanthanum, indicates an increase in the degree of electrical stiffness inside the glass network. Among the samples examined, the glass sample La-4.0 is thought to possess the best properties for electronic packaging due to its maximum propagation speed and lowest dielectric constant.

Chaos control in cardiac dynamics: terminating chaotic states with local minima pacing.

Current treatments of cardiac arrhythmias like ventricular fibrillation involve the application of a high-energy electric shock, that induces significant electrical currents in the myocardium and therefore involves severe side effects like possible tissue damage and post-traumatic stress. Using numerical simulations on four different models of 2D excitable media, this study demonstrates that low energy pulses applied shortly after local minima in the mean value of the transmembrane potential provide high success rates. We evaluate the performance of this approach for ten initial conditions of each model, ten spatially different stimuli, and different shock amplitudes. The investigated models of 2D excitable media cover a broad range of dominant frequencies and number of phase singularities, which demonstrates, that our findings are not limited to a specific kind of model or parameterization of it. Thus, we propose a method that incorporates the dynamics of the underlying system, even during pacing, and solely relies on a scalar observable, which is easily measurable in numerical simulations.

Dielectric properties of honey-water solutions over broad frequency range

The dielectric constant (ε′) and dielectric loss (ε″) of pure honey (PH) and honey-water mixtures have been measured over 20 Hz − 20 GHz frequency range, at 26 °C using a precision LCR meter and a Vector Network Analyzer. It has been observed that as water proportion in honey increases, ε′ and ε″ increases over the given frequency range. The dielectric relaxation peak of ε″ for honey-water mixture in the microwave frequency range shifts towards relaxation peak of water as amount of water in honey increases. The normalized ε′/ε′PH ratio is found to increase with increase in water content in Honey, reaching up to 1000 over 20 Hz to 2 kHz. In frequency range from 500 MHz to 5 GHz, ε′/ε′PH ratio approaches a value of 10 times at 750 mg/g. Over 20 Hz to 2 MHz frequency range, ε″/ε″PH ratio approaches 100 times that of PH, but over frequency range from 200 MHz to 600 MHz the ratio ε″/ε″PH is found to decrease anomalously with increase in water content in PH. Further, over the frequency range from 8.2 GHz to 20 GHz the ε″/ε″PH ratio continuously increases with increase in water content.

Longitudinal-twist wave converter based on chiral metamaterials

Advances in material architectures have enabled endowing materials with exotic attributes not commonly available in the conventional realm of mechanical engineering. Twisting, a mechanism whereby metamaterials are used to transform static axial load into twist motion, is of particular interest to this study. Herein, computations based on the finite element method, corroborated by a theoretical approach derived from applying Lagrange’s equations to a monoatomic spring-mass system, are employed to explore the longitudinal-twist (L-T) conversion exhibited by a chiral tetragonal-beam metamaterial. Firstly, we perform an eigenvalue analysis taking into account the polarization states to highlight the contribution of the longitudinal mode in the L-T conversion. We contrast the twisting behavior of the chiral cell with that of other homogeneous medium, octagonal-tube, and non-chiral cells. Moreover, we demonstrate the influence of the cell’s chirality on the L-T conversion using both time-domain and frequency-domain studies. The findings indicate that at least a portion of the longitudinally propagating wave is transformed into twist throughout a broad frequency range and even quasi-totally converted at distinct frequencies.

Topology optimization of chiral metamaterials with application to underwater sound insulation

Chiral metamaterials have been proven to possess many appealing mechanical phenomena, such as negative Poisson’s ratio, high-impact resistance, and energy absorption. This work extends the applications of chiral metamaterials to underwater sound insulation. Various chiral metamaterials with low acoustic impedance and proper stiffness are inversely designed using the topology optimization scheme. Low acoustic impedance enables the metamaterials to have a high and broadband sound transmission loss (STL), while proper stiffness guarantees its robust acoustic performance under a hydrostatic pressure. As proof-of-concept demonstrations, two specimens are fabricated and tested in a water-filled impedance tube. Experimental results show that, on average, over 95% incident sound energy can be isolated by the specimens in a broad frequency range from 1 kHz to 5 kHz, while the sound insulation performance keeps stable under a certain hydrostatic pressure. This work may provide new insights for chiral metamaterials into the underwater applications with sound insulation.

Non-uniform polarization boosted electromagnetic wave absorption with high efficiency and a broad frequency range

3-Aminobenzene sulfonic acid (mASA) has been co-polymerized into polyaniline (PANI) surface layers of ferrite nano particles by oxidative polymerization method. The sulfonic group of mASA anchored into PANI molecular have been employed as a dopant of PANI to partially substitute the dissociative dopant, hydrochloric acid (HCl). Owing to the constrained local distribution of mASA in PANI, the non-uniform polarization of PANI has been successfully stimulated by sulfonic acid doping. This results in various scattering loss modes and refined impedance matching in the synthesized ferrite/PANI nano-composite, which contributes to excellent absorbing properties with a high reflection loss of −56.42 dB and a broad effective absorption bandwidth of 3.8 GHz. The exhibited performances in microwave absorption are superior to most of ferrite-related composites. The explored strategy provides a novel way to tailor microwave absorbing composites to enhance their comprehensive microwave absorbing properties.

A cryogenic forced oscillation apparatus to measure anelasticity of ice.

We have developed a new cryogenic uni-axial forced oscillation apparatus to measure the anelastic behavior of ice by adapting the design of a previous high-precision apparatus for use in low-temperature (<0 °C) conditions. With this new apparatus, Young's modulus and attenuation can be measured over a broad frequency range from 10-4 to 10Hz. We have performed calibration tests with standard materials (steel spring, stainless steel, and acrylic samples) under various conditions to assess the apparatus properties and correct the effects on the obtained raw data. Young's modulus and attenuation for an acrylic sample after all of the data corrections show good agreement with previously published values, demonstrating the validity of the data corrections and reliability of the obtained data. We further obtained a preliminary dataset of Young's modulus and attenuation for an ice polycrystalline sample under small median stress and small stress amplitude. The anelastic response was not strain amplitude-dependent, that is, the response is linear. Moreover, the attenuation data are consistent with the data measured for other polycrystalline materials under similarly small stress conditions in terms of the Maxwell frequency scaling, which is known as a scaling law applicable to linear anelasticity induced by the diffusionally accommodated grain boundary sliding mechanism. Although there is still room for improving the control of testing conditions, we show that the new forced oscillation apparatus is capable of systematic studies on the anelastic properties of ice, the subject of future studies.

A Contoured Controller Bode-Based Iterative Tuning Method for Multi-Band Power System Stabilizers

An iterative tuning method for multi-band power system stabilizers is proposed, which utilizes the contoured controller Bode (CCBode) plot. The typical multi-band power system stabilizer, PSS4B, is conceptualized as a series connection of two filters: a band-pass filter and a phase compensator. The tuning process involves a space searching approach for the phase compensator to ensure its phase–frequency response remains within acceptable bounds. Subsequently, the CCBode plot is employed to adjust the magnitude–frequency response of the band-pass filter, thereby enhancing stability performance across a broad frequency range. The method proposed can be applied to the parameter design of the multi-band power system stabilizer PSS4B in the power system to suppress the low-frequency oscillations of the local mode and inter-regional mode in the system. The effectiveness of this proposed method is demonstrated through case studies of the four -machine/two-area system and the North China Power Grid.

Resting state EEG in young children with Tuberous Sclerosis Complex.

Tuberous Sclerosis Complex (TSC) manifests behaviorally with features of autism, epilepsy, and intellectual disability. Resting state electroencephalography (EEG) offers a window into neural oscillatory activity and may serve as an intermediate biomarker between gene expression and behavioral manifestations. Such a biomarker could be useful in clinical trials as an endpoint or predictor of treatment response. However, seizures and antiepileptic medications also affect resting neural oscillatory activity and could undermine the utility of resting state EEG features as biomarkers in neurodevelopmental disorders such as TSC. This paper compares resting state EEG features in a cross-sectional cohort of young children with TSC (n=49, ages 12-37 months) to 49 age- and sex-matched typically developing controls. Within children with TSC, associations were examined between resting state EEG features, seizure severity composite score, and use of GABA agonists. Compared to matched typically developing controls, children with TSC showed significantly greater alpha and beta power in permutation cluster analyses iterated across a broad frequency range (2-50Hz). Children with TSC also showed significantly greater aperiodic offset after power spectra were parameterized using SpecParam into aperiodic and periodic components. Within children with TSC, greater seizure severity was significantly related to increased periodic peak beta power. Use of GABA agonists was also independently and significantly associated with increased periodic peak beta power; the interaction between seizure severity and GABA agonist use had no significant effect on peak beta power. The elevated peak beta power observed in children with TSC compared to matched typically developing controls may be driven by both seizures and GABA agonist use. It is recommended to collect seizure and mediation data alongside EEG data for clinical trials. These results highlight the challenge of using resting state EEG features as biomarkers in trials with neurodevelopmental disabilities when epilepsy and anti-epileptic medication are common.

Inverse design of ultrawideband one-dimensional metamaterial photonic filters using Riccati equation constrained gradient descent.

One-dimensional photonic wave devices exhibit a pivotal role in wave engineering. Despite their relative simplicity, designing 1D wave devices that implement complex functionalities over a broad frequency range is challenging and requires careful sculpting and multiple optimizations. This paper theoretically and experimentally demonstrates a new inverse design paradigm to achieve a desired broadband frequency response efficiently. Specifically, we calculate the required dielectric profile along the device using constrained gradient descent optimization to minimize the L 2 norm between the desired and actual responses. In each optimization step, we avoid the need to solve the complete set of Maxwell equations by using Riccati's equation or its discrete ancestor as the optimization constraint for calculating the local reflection coefficient. Using this approach, we design several unorthodox filters, such as dual-band narrowband bandpass filters located within a wideband bandstop and ultrawideband first and second-order differentiators. The technique produces excellent results for ultrawideband frequency ranges, with very low computational complexity and, remarkably, with a single trivial guess for the optimization starting point. We experimentally implemented the two differentiator designs in radio frequencies using electronic circuit elements that comprise a metamaterial transmission line structure.

Data-driven modeling of multi-stable origami structures: Extracting the global governing equation and exploring the complex dynamics

In recent years, multi-stable origami structures have garnered increasing attention for their applications in dynamic scenarios such as robotic arm motions, impact energy absorption, and spectrum gap regulation. Understanding the intricate working mechanisms and exploring the rich dynamics of these structures necessitate the development of dynamic models. However, existing dynamic modeling methods for origami structures are often cumbersome, and the resulting dynamic models often lack interpretability. To overcome these limitations, we propose a novel data-driven dynamic modeling approach based on B-spline Galerkin method and subset selection strategy. This approach directly captures the dynamics of multi-stable origami structures using measured data, eliminating the need for reliance on empirical or prior knowledge. To validate the effectiveness of the proposed approach, we first evaluate it on the Duffing system, which has explicit expressions, successfully reconstructing the governing equation. Subsequently, we apply this method to the dynamic modeling of the origami ball structure with tri-stability and the multi-cell stacked Miura-origami (SMO) structure with high dimensionality through simulation, showing favorable results. Finally, using experimental data collected from a bi-stable SMO structure prototype, we employ the proposed method to obtain a global model that can accurately predict different dynamic behaviors over a broad range of excitation frequencies, including intra-well periodic vibrations, inter-well periodic vibrations, and inter-well chaotic vibrations. Overall, our method showcases outstanding efficacy in formulating interpretable, manageable, and comprehensive dynamic models. It plays a pivotal role in delving into the intricate dynamics of multi-stable origami structures.

Elastic wave spin and unidirectional routing in thin rod systems

The unusual topology of elastic waves in continuum systems has been recently uncovered. Prominently, the spin of Rayleigh-Lamb waves has been experimentally observed and used to achieve the unidirectional wave propagation. In this work, the elastic wave spin in thin rod systems is theoretically predicted and experimentally observed, for all the three basic wave modes, i.e., the zero-order flexural, longitudinal and torsional modes. By elaborately building up the subwavelength chiral sources, the spin-momentum locking has been achieved for these three modes within broad frequency range. Interestingly and surprisingly, the spin-momentum locking occurs for flexural and longitudinal modes in both circular and non-circular thin rods; the spin-momentum locking for torsional modes only exits in non-circular thin rods, due to the warping effect in non-circular cross-section rods. Our results open up the door for elastic wave spin in thin rod systems, and provide general tips for the research on basic modes in diverse thin rods, based on either the continuum media or the artificial metamaterials in future.

Magnetic behavior of a laminated magnetic core in the presence of interlaminar faults: A simulation method based on fractional operators

Stacks of grain-oriented silicon steel (GO FeSi) laminations play a crucial role as magnetic cores of power transformers. These cores undergo degradation over time due to corrosion, thermal cycles, etc. Geometrical abnormalities and residual stress from manufacturing processes exacerbate these degradation processes. Edge burrs can form around cut edges and lead to InterLaminar Faults (ILFs). In a recent work, we described an innovative method for simulating dynamical GO FeSi lamination hysteresis cycles. This method can be applied without any change to a stack of electrically isolated laminations, like in a magnetic core. It is especially easy when the working conditions impose a homogeneous behavior (B-imposed conditions). The simulation technique combines the resolution of the magnetic diffusion equation and a fractional differential equation as material law, yielding excellent simulation results across a broad frequency range with only two parameters accounting for the dynamic contribution. This new article outlines the successful extension of this simulation method to consider ILFs and predict their impact on the performances. For this, lamination stacks were initially simulated under full short-circuit conditions. Then, we used linear combinations between responses from these stacks and flawless ones. The simulation successfully reproduced the experimental data obtained for one or three aligned ILFs on several conditions. Then it was used to predict the behavior of additional aligned ILFs and/or different numbers of laminations in the simulated stack.

Analysis of fusion alphas interaction with RF waves in D-T plasma at JET

This work studies the influence of radio frequency (RF) waves in the ion cyclotron resonance heating (ICRH) range of frequencies on fusion alphas during the recent JET D-T campaign. Fusion alphas from D-T reactions are created with energies of about 3.5 MeV and therefore have significant Doppler shifts enabling synergistic interactions between them and RF waves at a broad range of frequencies, including the ones foreseen for future fusion machines in ITER (Schneider et al 2021 Nucl. Fusion 61 126058) and SPARC (Creely et al 2020 J. Plasma Phys. 86 865860502). Resonant interactions between RF waves and alphas, also called synergistic effects, will modify the alpha distribution and ultimately will have an impact on alpha orbit losses and heating. Data from JET 3.43 T/2.3 MA pulses based on the hybrid scenario (Hobirk et al 2023 Nucl. Fusion; Hobirk et al 29th IAEA FEC23 Conf. (16–21 October 2023); Challis et al 48th EPS Conf. on Plasma Physics (27 June–1 July 2022) during the DTE2 campaign (Maggi et al 2023 Nucl. Fusion)) were used for the analysis in this study. The impact of synergistic effects on alpha orbit losses and alpha heating are assessed. The conclusions are based on the analysis of experimental data for fast alpha losses, i.e. measurements from neutral particle analyser (NPA), fast ion losses scintillator detector, Faraday cups (FCs), and TRANSP (Hawryluk et al 1980 Physics of Plasmas Close to Thermonuclear Conditions vol 1 (CEC) pp 19–46) simulations. Experimental data and TRANSP analysis indicates that there are indeed changes in the alpha distribution function (DF) due to interaction with RF waves. Data from the NPA show increased 4He flux in the range from a few hundred keV up to 800 keV for pulses with RF power, while TRANSP clearly shows modifications in the fast alpha DF for these energies. Data from the scintillator detector and the FCs were compared for pulses with and without ICRH power and versus cases with enhanced alpha losses due to MHD activity. The trends from these diagnostics consistently show no additional alpha losses due to interaction with RF waves. TRANSP predictions for the impact of ynergistic effects on alpha heating show up to a 42% increase in alpha electron heating and up to a 25% increase in alpha ion heating. These effects, however, become negligibly small, less than 1%, when alpha heating is compared to the total auxiliary heating power in the investigated JET pulses.

Double-panel metamaterial with multi-resonator for broadband sound insulation

Currently, double-layer panels are usually filled with damping and sound-absorbing materials, which can effectively reduce the intensity of sound waves and enhance the sound insulation capability in the mid to low frequency range. Although this method can improve the peak and valley values in sound insulation to a certain extent, it still struggles to meet stricter design standards and requirements. This paper proposes a double-layer metamaterial plate with multi-resonator (DLMPMR) to fulfill sound insulation requirements through modifications to the double-layer plate structure. Firstly, the mathematical model pertaining to the sound insulation of DLMPMR is derived utilizing on the transfer matrix method and subsequently verified by the finite element analysis approach. Secondly, the influence mechanism of diverse structural parameters on the sound insulation performance of DLMPMR is studied. It is explored that the sound transmission loss (STL) of DLMPMR can be improved by adjusting the structural parameters to enhance the resonance of the structure across a broader frequency range and shifting the resonance frequencies to lower ranges. Finally, the sound insulation capability of the structure is verified through the reverberant fully anechoic chamber. The results demonstrate that the structure exhibits acoustic performance surpassing the mass law in the range of 220-5000 Hz. The proposed metamaterial, owing to the light weight and thinness, demonstrates promising potential for various applications in noise control engineering.

Dielectrophoresis as an Adjunctive Technique for Fibroblast Cell Migration to Enhance Wound Closure

This study reports on DEP-based simulation and experimental validation of polystyrene (PS) beads and fibroblast cells for primary skin cell migration for enhancing wound closure. MyDEP software was used to calculate the numerical simulation of the Clausius-Mossotti factor (CMF). In order to examine particle trajectories based on input frequencies, the finite element technique (FEM) is used. The trajectories of PS beads and fibroblast cells were experimentally assessed to verify the impact of frequency applied on the polarisation of PS beads and fibroblast cells. The outcome illustrated the potential of employing FDEP to move particles and cells to regions of high and low electric field. Fibroblast cells exhibit negative dielectrophoresis (NDEP) at a broad range of frequencies. Thus, FDEP can be utilised for frequency optimisation to enhance wound closure.

Ultra-Compact 4-Port MIMO Antenna with Defected Ground Structure and SAR Analysis for 28/38 GHz 5G Mobile Devices

To tackle the challenge of keeping 5G mobile devices compact while supporting millimeter-wave bands, we've created an ultra-compact 4-port dual-band MIMO antenna with a defected ground structure (DGS). This design minimizes mutual coupling and covers a broad frequency range. Built on a Rogers TMM4 substrate with dimensions of 17.76×17.76 mm2, the antenna includes four planar patch antennas positioned perpendicularly at the corners. Each antenna operates at 28/38 GHz and features a rectangular patch with four rectangular slots and a full ground plane. The patches are separated by 0.5 λo, with the DGS further reducing mutual coupling. Both simulations and measurements indicate a significant reduction in mutual coupling (−39 to −60 dB), improving ECC, TARC, MEG, and DG. Time-domain and SAR analyses confirm the antenna's efficiency and its suitability for 5G devices.

Additively-Manufactured Broadband Metamaterial-Based Luneburg Lens for Flexible Beam Scanning

Multi-beam microwave antennas have attracted enormous attention owing to their wide range of applications in communication systems. Here, we propose a broadband metamaterial-based multi-beam Luneburg lens-antenna with low polarization sensitivity. The lens is constructed from additively manufactured spherical layers, where the effective permittivity of the constituting elements is obtained by adjusting the ratio of dielectric material to air. Flexible microstrip patch antennas operating at different frequencies are used as primary feeds illuminating the lens to validate the radiation features of the lens-antenna system. The proposed Luneburg lens-antenna achieves ±72° beam scanning angle over a broad frequency range spanning from 2 GHz to 8 GHz and presents a gain between 15.3 dBi and 22 dBi, suggesting potential applications in microwave- and millimeter-wave mobile communications, radar detection and remote sensing.

Experimental investigation of pore-filling substitution effect on frequency-dependent elastic moduli of Berea sandstone

SUMMARY Based on both forced oscillation and ultrasonic pulse transmission methods, we investigated solid pore infill influences on rock elastic moduli in a broad frequency range $[ {1 - 3000,\,\,{{10}^6}} ]$ Hz for different differential pressures. For a Berea sandstone sample, filled sequentially by solid (${22\,\,^{\rm{o}}}{\rm{C}}$), quasi-solid (${26\,\,^{\rm{o}}}{\rm{C}}$) and liquid (${34\,\,^{\rm{o}}}{\rm{C}}$) octadecane, a frequency-dependence was found for the Poisson's ratio, Young's modulus and bulk modulus, nevertheless, these elastic parameters were strongly suppressed by increasing pressures. Experimental measurements showed that shear wave velocity and modulus of solid-octadecane-filled samples are significantly larger than those of the dry and liquid-octadecane-filled ones, implying the potential stiffening effects related to solid infill in compliant pores. A three porosity structure model, which describes the solid stiffening effects related to equant, compliant and the intermediate pores with aspect ratios larger than those of compliant pores but much less than those of stiff pores, was used to compare against the experimentally measured elastic properties for octadecane pore infill, together with several other fluid/solid substitution theories. The agreement between experimental measurements and theoretical predictions is reasonably good for the sandstone tested, providing that the three porosity model can be applied for pressure- and frequency-dependent elastic moduli estimations for a viscoelastic pore-infill-saturated sandstone. Evaluating the combined squirt flow mechanism responsible for the observed moduli dispersion and attenuation is of great importance to reduce potential errors in seismic AVO inversion and 4-D seismic monitoring of gas-hydrate or bitumen-saturated reservoir, especially for reservoir rocks with complex microstructures and heterogeneous pore types.

Hyperbranched Vitrimer for Ultrahigh Energy Dissipation.

Polymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics. In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate-2-(4-ethenylphenyl)-5,5-dimethyl-1,3,2-dioxaborinane) P(HMA-co-ViCL) copolymers. The -type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high-performance HBV damping materials. We found that P(HMA-co-ViCL) 20k-40-60 HBV exhibited ultrahigh energy-dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials.