Frequency Range Research Articles

Influence of thickness, Si and SiO2/Si substrate interfaces upon magnetization dynamics in RF sputtered Fe3O4 thin films

The effect of film thickness (90–220 nm), Si and SiO2/Si substrate interfaces upon structural, micro-structural and dynamic magnetic properties of RF sputtered Fe3O4 films are investigated. Structural and micro-structural studies have confirmed the polycrystalline Fe3O4 growth with a α-Fe2O3 minority phase. A systematic grain growth with thickness suggests the presence of anti-phase boundary (APB) and corresponding competing magnetic interactions. The absence of Verwey phase transition and lower effective magnetization of 283–359 emu/cm3 are attributed to the APBs. The influence of APBs and impurity states upon the magnetization dynamics has been investigated with co-planar waveguide ferromagnetic resonance spectroscopy from 9 to 33 GHz frequency range. A higher Gilbert damping of ∼0.016 is noted for Fe3O4/Si films as compared to the lower damping of ∼0.002–0.004 for Fe3O4/SiO2/Si interfaces. Further, inhomogeneity, intrinsic Gilbert damping and two-magnon scattering contributions to the damping parameter are evaluated and discussed.

Study of a cubic cavity resonator for gravitational waves detection in the microwave frequency range

The direct detection of gravitational waves (GWs) of frequencies above MHz has recently received considerable attention. In this work, we present a precise study of the reach of a cubic cavity resonator to GWs in the microwave range, using for the first time tools allowing to perform realistic simulations. Concretely, the boundary integral—resonant mode expansion (BI-RME) 3D method, which allows us to obtain not only the detected power but also the detected voltage (magnitude and phase), is used here. After analyzing three cubic cavities for different frequencies and working simultaneously with three different degenerate modes at each cavity, we conclude that the sensitivity of the experiment is strongly dependent on the polarization and incidence angle of the GW. The presented experiment can reach sensitivities up to 1×10−19 at 100 MHz, 2×10−20 at 1 GHz, and 6×10−19 at 10 GHz for optimal angles and polarizations, and where in all cases we assumed an integration time of Δt=1 ms. These results provide a strong case for further developing the use of cavities to detect GWs. Moreover, the possibility of analyzing the detected voltage (magnitude and phase) opens a new interferometric detection scheme based on the combination of the detected signals from multiple cavities. Published by the American Physical Society 2024

Sonoluminescence: Photon production in time-dependent analog systems

Sonoluminescence is a well-known laboratory phenomenon where an oscillating gas bubble in the appropriate environment periodically emits a flash of light in the visible frequency range. In this work, we study the system in the framework of analog gravity. We model the oscillating bubble in terms of analog geometry and propose a nonminimal coupling prescription of the electromagnetic field with the geometry. The geometry behaves as an analogous oscillating time-dependent background in which repeated flux of photons are produced in a wide frequency range through parametric resonance from quantum vacuum. Due to our numerical limitation, we could reach the frequency up to ∼105 m−1. However, we numerically fit the spectrum in a polynomial form including the observed frequency range around ∼107 m−1. Our current analysis seems to suggest that parametric resonance in analog background may play a fundamental role in explaining such phenomena in the quantum field theory framework. Published by the American Physical Society 2024

A bifunctional metamaterial with broadband properties of absorption and linear-to-linear polarization conversion

This paper proposes, measures, and investigates a bifunctional metamaterial capable of achieving absorption and reflective linear-to-linear polarization conversion simultaneously, which both exhibit the characteristics of broadband. The unit cell consists of a metal pattern with resistors, a dielectric plate, an air layer, and a metal backplate. The simulation results demonstrate that the designed metamaterial acquires over 90% absorption in the microwave band of 6.5–9.3 GHz. Within the frequency range of 12.7 GHz–17.2 GHz, the polarization conversion rate exceeds 90%, effectively converting y-polarized incident waves into x-polarized reflected waves. The experimental results align with the simulation data. The surface current and electric field distributions are utilized to analyze the absorption and polarization conversion phenomena. This bifunctional metamaterial exhibits potential application in radar imaging, enhancing data transmission rates, and wireless communication.

Dual-functional pentamode metamaterial with water-like and topological transmission properties

In this paper, a water-like pentamode metamaterial (PM) with a single metallic material is designed and the topological edge-state transmission properties of elastic waves in the PM are thoroughly investigated. Numerical results indicate that by introducing structural perturbation into PM, the Dirac point degeneracy at K-point can be opened and topological band inversion can be generated. Topological edge states are also obtained by organizing PM structural units, which are robust to defects such as bending and cavities. In addition, it also has the mimics water in acoustic properties over a wide frequency range, i.e. it exhibits transparency when surrounded by water. Therefore, it will have both good transmission efficiency and acoustic stealth performance when used as an underwater waveguide. The dual-functional PM proposed in this study provides theoretical guidance for designing underwater stealth acoustic waveguides.

Wearable flexible Kapton-graphene electromagnetic sensors

This research is dedicated to the development of a new technology for a quick diagnosis of virial virus, using electromagnetic technology facilitated by either a Rectangular Patch Resonator (RPR) or a Wearable Flexible Sensor (WFS) designed for non-invasive viral disease detection, including Nano-virus, and macro-virus. These devices is tailored for a precise and non-invasive detection of a wide array of viruses. To enhance diagnostic precision, an electromagnetic sensor was meticulously explored and simulated, to be capable of detecting and identifying even the most minuscule viruses. Employing numerical modeling with a focus on the 10 GHz to 20 GHz frequency range. We hold a strong sense of optimism regarding this sensor's potential for non-invasive virus detection. Extensive simulations conducted throughout this study have underscored the WFS's selectivity across all viruses, boasting an exceptional limit of detection and sensitivity. Moreover, the WFS exhibited the capability to distinguish between varying infection percentages, each corresponding to a distinct reflection pattern.

Contact acoustic nonlinearity and damping properties of completely free vibrating curved and delaminated CFRP plates

This study reports an experimental investigation on the effect of plate curvature and circular inter-ply delamination on the completely free vibration properties of carbon fiber reinforced polymer (CFRP) plates. Impact tests on wire suspended plates were performed and variations in measured natural frequencies and modal damping are reported. Delamination clapping type contact acoustic nonlinearity (CAN) was observed in the presence of a series of higher harmonics in the vibration spectrum. These higher harmonics consisted of five to seven equally distanced peaks grouped in a frequency range of around the double of odd mode M (5,0). Modal damping was highly sensitive to delamination which caused a 33% average increase in damping loss factors. Odd mode M (3,0) was the most affected with an average increase of 51% in damping loss factor, explained by the delamination location relative to the wavelength of that mode shape. Natural frequencies were less sensitive to delamination, on average decreasing 1.0% in flat plates and increasing 3.1% in curved plates. The modal frequencies calculated from embedded fiber optic sensor (FOS) or electrical resistance strain gauge signals agreed with finite element modeling (FEM) to within a 3.1% difference for all modes considered. The damping loss factors deducted from suspended plate tests were consistent with complementary results from dynamic mechanical analysis (DMA). The measured delamination clapping CAN and its related influence on damping can serve to enhance structural health monitoring (SHM) methods.

Study on mode properties of GaAs based hybrid plasmonic terahertz waveguide

Abstract The Terahertz (THz) field is emerging with the goal of addressing the critical challenges associated with achieving high data rates and rapid communication. In this study, a hybrid plasmonic THz waveguide has been designed and analyzed operating in 2.5-3.5 THz frequency range. The waveguide is constructed using GaAs (Gallium Arsenide) as the high refractive index core, surrounded by AlAs (Aluminium Arsenide), Ag (Silver) and placed on an HDPE (high-density polyethylene) substrate. Graphene is strategically positioned between HDPE layer to enhance light confinement. The mode properties of the designed waveguide that have been simulated using multiphysics simulations of finite element method shows unique characteristics. The observations of the simulated results at 2.5 to 3.5 THz, shows the effective refractive index of 3.79, effective mode area of 1.88 mm2, birefringence of 0.2, dispersion of 0.10 ps/THz/cm, mode field diameter of 15.8 mm, beat length of 123 mm, confinement loss 1.79 x 10-9 mm-1 has been obtained. These features make the proposed waveguide suitable for applications in photonic integrated circuits for THz communications.

Enhancing motor impedance measurements: broadening the spectrum from low to high frequencies

Three-phase induction motors serve as critical parts in various industrial applications, lauded for their high energy efficiency and notable power density. Obtaining their broadband impedance information is paramount for analyzing conducted emissions, evaluating overvoltage ringing, and assessing motor health status. Nonetheless, conventional methods for motor impedance measurements typically rely on Kelvin clip leads or extension cables, which are effective only in a relatively low-frequency region (i.e. below 1 MHz). This paper presents an improved approach to extend the measurable spectrum from low to high frequencies, up to 120 MHz. The proposed method develops a series of fixture adapters to enable seamless interconnection between the terminals of an induction motor and the coaxial ports of an impedance analyzer. The parasitics introduced by these adapters are identified using boundary-element analysis, and their impacts are minimized based on the de-embedding concept. Experimental results affirm the accuracy and effectiveness of the proposed method for four types of motor impedances (i.e. single-phase, phase-to-ground, common-mode, and differential-mode) across a broad frequency range from 100 Hz to 120 MHz. Moreover, the inaccuracy of motor impedance measurements at high frequencies (i.e. above 1 MHz) using conventional methods, including Kelvin clip leads and extension cables, is also demonstrated.

Miniaturized and High Volumetric Energy Density Power Supply Device Based on a Broad-Frequency Vibration Driven Triboelectric Nanogenerator.

The widespread vibration is one of the most promising energy sources for IoT and small sensors, and broad-frequency vibration energy harvesting is important. Triboelectric nanogenerators (TENGs) can convert vibration energy into electrical energy through triboelectricity and electrostatic induction, providing an effective solution to the collection of broad-frequency vibration energy. Also, the power supply in constrained and compact spaces has been a long-standing challenge. Here, a miniaturized power supply (MPS) based on a broad-frequency vibration-driven triboelectric nanogenerator (TENG) is developed. The size of the MPS is 38 mm × 26 mm × 20 mm, which can adapt to most space-limited environments. The TENG device is optimized through theoretical mechanical modeling for the external stimuli, it can efficiently harvest vibrational energy in the frequency range of 1-100 Hz and has a high output power density of 134.11 W/cm3. The developed device demonstrates its practical application potential in powering small electronics like LEDs, watches, and timers.

Experimental investigation of the polarity-switching process with different bipolar ionic liquid thruster operating frequencies

The bipolar ionic liquid thruster employs ionic liquid as a propellant to discharge positively and negatively charged high-energy particles under an alternating current (AC) power source, effectively suppressing electrochemical reaction and ensuring charge neutrality. Determining an optimal AC supply power source frequency is critical for sustained stable thruster operation. This study focuses on the emission characteristics of the ionic liquid thruster under varied AC conditions. The AC power supply was set within the frequency range of 0.5–64 Hz, with eight specific frequency conditions selected for experimentation. The experimental results indicate that the thruster operates steadily within a voltage range of ±1470 to ±1920 V, with corresponding positive polarity current ranging from 0.41 to 4.91 μA and negative polarity current ranging from −0.49 to −4.10 μA. During voltage polarity switching, an emission delay occurs, manifested as a prominent peak signal caused by circuit capacitance characteristics and a minor peak signal resulting from liquid droplets. Extended emission test was conducted at 16 Hz, demonstrating approximately 1 h and 50 min of consistent emission before intermittent discharge. These findings underscore the favorable impact of AC conditions within the 8–16 Hz range on the self-neutralization capability of the ionic liquid thruster.

Synchronous averaging with sliding narrowband filtering for low-speed bearing fault diagnosis

The health condition of low-speed rolling bearing, such as the main bearing in wind turbines which bears the heavy dead weight and operates under variable speeds, has a big impact on the safe operation of the machinery. Therefore, damage detection of low-speed bearings plays a key role in the health management of large-scale rotating machinery. However, in popular vibration based bearing damage detection algorithms, due to the fact that the additional vibration features incurred by the low-speed operated bearing damage are typically weak in amplitude and low in frequency contents, the additional responses caused by damage are difficult to be isolated by conventional algorithms. Especially, in the cases of variable speed operations, the smearing effect caused by Fourier transform makes it more difficult to extract the damage features by spectrum analysis based methods. To deal with these issues, we developed a damage detection procedure specially designed for bearings operated at low and variable speeds. According to the dynamic properties of the vibration signals incurred by a low-speed bearing with damage, an envelope analysis method based on synchronous averaging with sliding narrow band-pass filters is designed and developed for extracting damage features in the low frequency range. The fundamental theory used in the method is derived first. Then, a damage detection signal processing procedure is constructed based on the elaborated theory. The feasibility and advantages of the proposed methodology are validated by numerical simulations as well as the measured data from a wind turbine field example.

Viscous Mechano‐Electric Response of Ferroelectric Nematic Liquid

AbstractDirect viscous mechano‐electric response is demonstrated for a room‐temperature ferroelectric nematic liquid, which combines large spontaneous electric polarization with 3D fluidity. The mechano‐electric transduction is observed in the frequency range 1 −200 Hz via a simple demonstrator device. The liquid is placed into a deformable container with electrodes and the electric current induced by both periodic and irregular actuation of the container is examined. The experiments reveal a rich interplay of several distinct viscous mechano‐electric phenomena, where both shape deformations and material flow cause changes in the electric polarization structure of a ferroelectric nematic liquid. The results show that the mechano‐electric features of the material promise a considerable applicative perspective spanning from sensitive tactile sensors to energy harvesting devices.

Effect of Bentonite on the Electrical Properties of a Polylactide-Based Nanocomposite.

In this paper, a novel polylactide-based nanocomposite with the addition of bentonite as a filler, Fusabond, and glycerine as a compatibilizer and plasticizer, were prepared and investigated. Four samples with different contents of bentonite (1, 5, 10, and 15 wt.%), as well as three samples without fillers, were prepared with an easily scalable method: melt blending. The electrical properties of all prepared samples were investigated with broadband dielectric spectroscopy in the frequency range between 0.1 Hz and 1 MHz. Measurements were conducted at nine temperatures between 293.15 and 333.15 K (20 to 60 °C) with steps of 5 K. It was found that the increase in the content of bentonite in polylactide has a significant effect on the electrical properties of the prepared nanocomposites.

Giant magneto-photoluminescence at ultralow field in organic microcrystal arrays for on-chip optical magnetometer

Optical detection of magnetic field is appealing for integrated photonics; however, the light-matter interaction is usually weak at low field. Here we observe that the photoluminescence (PL) decreases by > 40% at 10 mT in rubrene microcrystals (RMCs) prepared by a capillary-bridge assembly method. The giant magneto-PL (MPL) relies on the singlet-triplet conversion involving triplet-triplet pairs, through the processes of singlet fission (SF) and triplet fusion (TF) during radiative decay. Importantly, the size of RMCs is critical for maximizing MPL as it influences on the photophysical processes of spin state conversion. The SF/TF process is quantified by measuring the prompt/delayed PL with time-resolved spectroscopies, which shows that the geminate SF/TF associated with triplet-triplet pairs are responsible for the giant MPL. Furthermore, the RMC-based magnetometer is constructed on an optical chip, which takes advantages of remarkable low-field sensitivity over a broad range of frequencies, representing a prototype of emerging opto-spintronic molecular devices.

Design and Simulation of High-Power Planar Čerenkov Oscillators with Two-Dimensional Distributed Feedback in the Subterahertz Frequency Range

Design and Simulation of High-Power Planar Čerenkov Oscillators with Two-Dimensional Distributed Feedback in the Subterahertz Frequency Range

Near-zero thermal expansion ZrW2O8/SiO2f wave-transparent composites: Interfacial anti-debonding structures based on polymeric films

The thermal stability of fiber-optic gyroscopes (FOGs) limits their application in harsh environments. This work utilized the unique water-retention properties of hyaluronic acid and the low-temperature cold sintering process combined to fabricate near-zero thermal expansion ZrW2O8/SiO2f composites with thermal resistance. Based on this novel process, the interface debonding of the composites is effectively suppressed and the mechanical and thermal properties of the composites are significantly improved (flexural strength increased by 69.47 %). Moreover, the interface anti-debonding structure reduces the interfacial polarization and reflection loss of the composites, and enhances the wave-transparent properties in the 2–18 GHz frequency range, with a minimum reflection loss of −0.21 dB. Furthermore, the interface anti-debonding structure of the composite provides creep resistance with enhanced sintering densities (increased by 13.61 %). Simultaneously, the composites achieve a controllable coefficient of thermal expansion (CTE) by regulating the liquid phase content and reach near-zero CTE (−0.246 × 10−6 °C−1 [30–300 °C]). Finally, finite element analysis and thermal shock experiments show that the anti-debonding interfacial structure has excellent thermal resistance, and the densest ZrW2O8/SiO2f composites exhibit the best thermal resistance due to minimal thermal strain during thermal shock, which is expected to meet the requirements of FOGs applications.

Large-scale engineered meta-barriers for attenuation of seismic surface waves

This study evaluates the performance of large-scale meta-barriers in attenuating seismic surface waves and transportation-induced vibrations in the most disastrous frequency range of 0–30 Hz. By developing analytical and three-dimensional numerical models, it evaluates the properties of the proposed meta-barrier and presents their effects on the attenuation range. Moreover, it discusses a simplified mass-spring-mass model of the meta-barrier, demonstrating that the attenuation range of a unit cell can be approximated using this model. The proposed design consists of three-dimensional two-layers (3D-2C) unit cells arranged periodically with different configurations to be placed between the wave source and structure. Specifically, the meta-barriers can be arranged gradually (periodic spacing along the length), widening the attenuation range to block nearly 85% of the most devastating waves using typically arranged stacked unit cells and triangular-like arrangement (double wedge). The results show that a typical stacked unit cells reflect the incoming waves towards the source, while using the double wedge design, the surface wave can be converted to bulk wave, thereby reducing the risk to the surroundings. Moreover, the study validates the attenuation range using three-dimensional time history analysis subjected to an artificial wavelet (Ormsby wavelet) and three actual seismic records (1975 Oroville, 1984 Bishop, and 2001 Anza time histories).

Simulation‐Guided Design of Gradient Multilayer Microwave Absorber with Tailored Absorption Performance

AbstractFlexible microwave absorber (MAR), vital in advanced applications such as wearable electronics and precision devices, are highly valued for their lightweight, exceptional electromagnetic waves (EWs), and ease of fabrication. However, optimizing the electromagnetic parameters of microwave absorption materials (MAMs) to enhance absorption ability and expand effective absorption broadband (EAB, reflection loss (RL) <−10 dB) is a considerable challenge. Herein, a permittivity‐attenuation evaluation diagram (PAED) is constructed using parameter scanning based on the Materials Genome Initiative to determine the ideal electromagnetic parameters and thickness, optimize absorption efficiency, and obtain highly efficient absorbers. Guided by the PAED, a multilayer MAR consisting of a “matching‐absorption‐reflection layer” and a dielectric loss gradient aligned with the direction of EWs propagation is developed. This design significantly enhances the EWs penetration and ensures effective absorption, attributed to the well‐matched impedance and attenuation characteristics. As anticipated, the microwave absorption of the absorber (density = 0.063 g cm−3) is optimized, with an RL of −34 dB at d = 4 mm and an EAB covering the entire X‐band (8.2–12.4 GHz). This study presents a novel approach for establishing a material database for MAMs and developing high‐performance absorbers characterized by thinness, lightness, broad operational frequency range, and robust absorption capacity.

Left-handed metamaterial based on circular split ring (CSRR) resonator for microwave sensing Application

This paper presents a new metamaterial structure specifically designed to operate in the L, S, and C frequency bands. It is characterized by a small unit cell size of 15mm × 15 mm. The metamaterial's electromagnetic properties are thoroughly examined, utilizing FR-4 substrate material and copper circular split ring resonators (CSRRs). The Computer Simulation Technology (CST) software uses the finite integration technique (FIT) to precisely model the effective parameters over a frequency range of 0–6 GHz. In simulations and experiments, the structure demonstrates negative refractive index, effective permittivity, and effective permeability. The electric and magnetic field distributions within the unit cell are accurately characterized using vector fields. In addition, the equivalent circuit is simulated and depicted using ADS software, with comparisons drawn between the measured data and the simulated data. The experimental validation, conducted using six varying thicknesses of FR4 materials, verifies the resemblance between the simulated and the measured transmission coefficients. Moreover, the effective medium ratio (EMR) of the metamaterial is calculated to be 12.74, indicating its promising capabilities for microwave sensing applications. The examination of the sensor model uncovers such metrics as quality factors, frequency detection resolution (FDR) values, and sensitivities, all of which enhance our comprehension of the material's performance. This discovery has the potential to advance the development of sensing metamaterials, which could significantly impact various applications and enhance research in the field.