Frequency-dependent Properties Research Articles

Time-domain simulation of sound propagation through anisotropic porous media for room acoustic applications

Wave-based room acoustic simulations require accurate modeling of sound propagation in the presence of extended (bulk) reacting porous absorbers. The sound absorption in porous media is typically addressed by means of equivalent fluid models that provide frequency-dependent effective material parameters, such as density and bulk modulus. In the time domain, these frequency dependent properties result in the computation of convolution integrals, which is effectively handled via an auxiliary differential equations (ADE) method. In this work, we apply the time-explicit discontinuous Galerkin approach to modelling of sound propagation in anisotropic porous media (with an anisotropic equivalent fluid model) together with the ADE method. We demonstrate the importance of using the extended approach for porous media, where the sound absorption depends not only on the frequency and incident angle, but also on the travelling wave direction.

Iterative eigenvalue method coupled with RSM for structural acoustic analysis and optimization of the CLD-damped orthotropic steel deck

In the present work, an iterative eigenvalue method (IEM) is proposed and combined with the boundary element method (BEM) to perform the structural acoustical analysis of the orthotropic steel deck (OSD) damped with constrained layer damping (CLD), through which the frequency-dependent properties of the viscoelastic core can be accurately considered. Then, a series of hammer tests are carried out in a semi-anechoic chamber to verify the acoustic prediction method. It shows that the simulated structural noises basically agree with the test results, and the overall deviations at the field points M2 and M8 are merely 2.4 and 2.3 dB, respectively. Subsequently, taking the thicknesses of the damping layer and the constraining layer, as well as the material properties of the constraining layer as design variables, a central composite experiment is designed and combined with response surface methodology (RSM) to fit the relationship between analysis objectives and design variables. With the objective of minimizing the acoustic radiation power, a program for finding the optimal values of design variables is developed based on the interior penalty function method. Through iterative computations, the optimal points are numerically determined as t 1 = 2.3 mm and t 2 = 0.3 mm for the thicknesses of the damping layer and the constraining layer, respectively. Steel alloy is found to be the optimal material for the constraining layer. After optimizing CLD treatment, the overall acoustical power level can be reduced from 97.7 dB to 93.1 dB and the overall sound pressure levels (SPLs) at the field points M2 and M8 can be reduced from 89.2 dB to 83.5 and 76.9 dB to 70.3 dB, respectively, indicating that the optimization of CLD design parameters can significantly improve acoustic performance of the CLD-damped structures.

Synthesis and Characterization of CdS and Sr-Doped CdS Quantum Dots: Impedance Analysis for Nano-Tuned Electronic Applications

This study reports the synthesis and comprehensive characterization of cadmium sulfide (CdS) and strontium-doped CdS quantum dots (QDs) using a straightforward chemical precipitation method. N, N-Dimethylformamide served as the stabilizing agent, while specific metal precursors facilitated the formation of the nanostructures. The incorporation of strontium into the CdS matrix aimed to enhance the electronic properties of the quantum dots. Energy Dispersive X-ray Analysis (EDAX) confirmed the successful doping of Sr into the CdS QDs. X-ray Diffraction (XRD) analysis verified the high-crystallinity of the synthesized quantum dots, with the mean crystal sizes determined to be 3.18 nm for pure CdS and 3.99 nm for Sr-doped CdS (2mM and 4mM concentrations). Impedance spectroscopy was utilized to study the frequency-dependent electrical properties of the QDs at room temperature, revealing significant variations in impedance with frequency. The results demonstrated that both pure and Sr-doped CdS QDs exhibit capacitive admittance, which is indicative of their potential application in nano-tuned electronic devices. The ability to fine-tune the resonant frequency by controlling the size and doping level of the quantum dots presents a significant advantage for their use in advanced electronic applications. The study highlights the promising application of CdS and Sr-doped CdS quantum dots in the development of high-performance, frequency-tunable nanoscale electronic devices.

The effect of complex formation on the static and frequency-dependent nonlinear optical properties: A combined experimental and theoretical investigation

A novel mixed ligand Mn(II) complex of 6-Bromopyridine-2-carboxylic acid (6Brpca) and 4,4′-dimethyl-2,2′-dipyridyl has been prepared and structurally characterized using single-crystal X-ray diffraction. The spectroscopic properties were also analyzed by using FT-IR and UV–Vis spectral techniques. The coordination complexes having transition metal ions are known to have promising optical nonlinearity behavior. Therefore, B3LYP level density functional theory was used to investigate first- and second-order hyperpolarizabilities (β and γ) and provide a deep understanding of the relation between the structure and NLO properties. The calculations of frequency-dependent α, β, and γ at frequencies of ω = 0.0856252 and 0.0428126 au. for 6Brpca and Dmdpy ligands as well as Mn(II) complex have been also carried out using B3LYP/LanL2DZ level. Especially second harmonic generation (SHG) first and second hyperpolarizabilities (β(−2ω;ω,ω) and γ (−2ω;ω,ω,0)) parameters for Mn(II) complex have been calculated as 11448 × 10−30 and 680035 × 10−36 esu, respectively. It has been determined that there is a tremendous increase in β and γ parameters when 6Brpca and Dmdpy ligands coordinate to the high spin multiplicity Mn(II) ion. Theoretical calculations revealed that the large first- and second-order hyperpolarizabilities are caused by strong intramolecular charge transfer between the transition metal and the coordinated ligands. These results indicate that the the organometallic complex under investigation is valuable candidate for optoelectronic and photonic applications.

An investigation of the structure property relation of Na2MnWO6 for device application

This communication delves into the structural, microstructural, dielectric, impedance, modulus, and optical properties of the double-perovskite ceramic Na2MnWO6. Our X-ray diffraction study revealed a multiphase crystal structure in this ceramic, a result of high-temperature mixed-oxide synthesis. Morphological studies indicated a nearly uniform grain scattering and distribution with minimal spaces. The Maxwell-Wagner model, by addressing alternative polarisation mechanisms, studied the frequency-dependent dielectric properties. Our study of temperature-dependent dielectric permittivity identified a ferroelectric to paraelectric phase transition dielectric aberration. The material’s NTCR characteristic was determined using impedance analysis. Jonscher’s power law showed that the conduction mechanism follows the overlapping of large polaron tunnelling and correlated barrier hopping models, establishing the link between conductivity and frequency. Relaxation and conduction activation energies support electron hopping. UV spectroscopy revealed a band gap of 4.01 eV, and temperature-dependent resistance studies suggest a potential use in thermistors with due parameters. These findings significantly enhance our understanding of NMWO, paving the way for its potential uses in electronics and optics, owing to its unique structural, electrical, and optical features.

Model order reduction of time-domain acoustic finite element simulations with perfectly matched layers

This paper presents a stability-preserving model reduction method for an acoustic finite element model with perfectly matched layers (PMLs). PMLs are often introduced into an unbounded domain to simulate the Sommerfeld radiation condition. These layers act as anisotropic damping materials to absorb the scattered field, of which the material properties are frequency- and coordinate-dependent. The corresponding time-domain model size is often very large due to this frequency-dependent property and the number of elements needed per wavelength. Therefore, to enable efficient transient simulations, this paper proposes a two-step method to generate stable reduced order models (ROMs) of such systems. Firstly, the modified and stable version of PMLs is projected by a one-sided split basis, which gives a stable intermediate ROM. Secondly, the intermediate ROM is modified to satisfy the stability-preserving condition by applying the modal transformation. Applying any one-sided model order reduction method on this modified model leads to a stable and small ROM. This two-step method is further extended to account for the locally-conformal PML model by reformulating it in curvilinear coordinates, which works for arbitrary convex truncated domains. The proposed method is successfully verified by several numerical simulations.

Soundbox-based sound insulation measurement of composite panels with viscoelastic damping

Sound transmission loss (STL), an essential index for assessing the sound insulation performance of composite laminated structures, typically relies on experimental methods to measure. The soundbox method (SBM), a straightforward technique for measuring the STL, is sensitive to microphones’ positions. Within the framework of the Chebyshev-Ritz method, a semi-analytical vibro-acoustic model extended to composite laminated panels with viscoelastic damping (VED) is proposed for the first time. Based on the developed simplified layer-wise theory, the panel is modeled using three layers: the top face layer, the VED layer, and the bottom face layer. A closed cavity is added to the model as the soundbox enclosure used in actual measurements. By employing the Hamilton's principle, the governing equation for the coupling system is derived, and the vibration and internal acoustic responses of the coupling system are calculated. A discretization strategy is introduced to address the frequency-dependent properties of the VED layer, avoiding the need to reconstruct the stiffness matrix at each frequency. To obtain the STL of the panel, sound pressures at external measurement points are calculated based on the Rayleigh integral. The proposed model is validated against numerical results from finite element analyses. The influences of the microphone position inside and outside the cavity on the measured STL are studied. Furthermore, parametric studies over the microphones' positions are performed to enhance the SBM-based evaluation of the composite panel's sound insulation performance. The optimal locations for two internal microphones and one external microphone are recommended. Finally, experimental studies are carried out to guide the implementation of the SBM.

Sintering temperature dependent characterization of Ni nano ferrite with the optimization of frequency dependent properties

Ni ferrite is becoming a prominent candidate for high frequency applications. To find the best performance of Ni ferrite for high frequency devices, NiFe2O4 ferrites are synthesized by co-precipitation method at five distinct sintering temperatures (TS = 500 °C, 700 °C, 850 °C, 1000 °C, and 1200 °C). The structural properties of the synthesized samples are characterized by x-ray diffraction (XRD) with Rietveld refinement analysis. The grain formation of the ferrites is observed by field emission scanning electron microscopy (FESEM) and the gradual increase in grain size is noticed with the increment of sintering temperature. The frequency dependent properties are studied by an impedance analyzer. The real permeability values of the samples are stable in a wide frequency range (100 Hz to 100 MHz) and the imaginary permeability values are decreased at lower frequency region. It can be seen that the real part of magnetic permeability increases significantly with sintering temperature. The real and imaginary dielectric properties are reduced at the initial applied field and become constant at higher frequencies. The magnetic quality factor and dielectric quality factor are enhanced with the increase of sintering temperature. Frequency dependent properties confirm that these ferrites are strong candidates for potential high frequency applications. Finally, it is found that, comparatively a higher sintering temperature is better for permeability properties, and a lower sintering temperature is better for dielectric properties.

Exploring the ON/OFF nonlinear optical (NLO) response in tetracene-based chromophores: A DFT study on solvent and frequency-dependent NLO properties for switching applications

Tetracene-based nonlinear optical (NLO) materials are an ambient field of interest in optoelectronic technology. Inspired by this material, we theoretically designed D-D-A framework molecules (ZO and ZO-1 to ZO-16) with auxiliary donor and acceptor screening of solo tetracene linear surface and investigated their reactivity, electrical properties, solvent-dependent optical and ON/OFF NLO properties utilizing DFT simulations. The CPCM and IEFPCM model is used to examine how entire spectrum of medium polarity, ranging from less polar to more polar solvents (chloroform (ε = 4.71) < tetrahydrofuran (ε = 7.43) < DMSO (ε = 46.83 < water (ε = 78.36)) affect the optical absorption and NLO characteristics (βtot, αtot, and μtot) of suggested compounds (ZO and ZO-1 to ZO-16). Furthermore, natural bond orbital analysis (NBO) and topological analysis (MEP, ELF, and LOL) were used to explain the NLO results. Regarding the charge transfer robustness, ZO-9, a promising tetracene derivative, is identified as an appealing second-order NLO candidate, with the lowest energy gap (1.642 eV) and largest λmax (546.692 nm) among all investigated derivatives. Moreover, the solvent-dependent optical absorption spectrum shows that polar solvent (THF) alleviates the λmax from 273.081 nm to 707.511 nm in ZO-11. Similarly, solvent also influences the NLO properties in all designed compounds, especially in ZO-9, which displayed giant βtotal = 7.244 × 105 in chloroform, 8.640 × 105 in THF, 1.153 × 106 in DMSO, and 1.180 × 106 in water as well as in gas (1.993 × 105). Additionally, the results of the second harmonic generation (SHG) β(−2ω, ω, ω) and the electro-optical Pockels effect (EOPE) β(−ω,ω,0) computed at the frequencies of ω = 1064 nm (0.0428 au) and ω = 532 nm (0.0856 au) validates that all tetracene based derivatives are excellent NLO candidates for laser working condition and switching applications.

Floating-gate memristor based on a MoS2/h-BN/AuNPs mixed-dimensional heterostructure

Memristors have recently received substantial attention because of their promising and unique emerging applications in neuromorphic computing, which can achieve gains in computation speed by mimicking the topology of the brain in electronic circuits. Traditional memristors made of bulk MoO3 and HfO2, for example, suffer from a low switching ratio and poor durability and stability. In this work, a floating-gate memristor is developed based on a mixed-dimensional heterostructure comprising two-dimensional (2D) molybdenum disulfide (MoS2) and zero-dimensional (0D) Au nanoparticles (AuNPs) separated by an insulating hexagonal boron nitride (h-BN) layer (MoS2/h-BN/AuNPs). We find that under the modulation of back-gate voltages, the MoS2/h-BN/AuNPs device operates reliably between a high-resistance state (HRS) and a low-resistance state (LRS) and shows multiple stable LRS states, demonstrating the excellent potential of our memristor in multibit storage applications. The modulation effect can be attributed to electron quantum tunneling between the AuNP charge-trapping layer and the MoS2 channel. Our memristor exhibits excellent durability and stability: the HRS and LRS are retained for more than 104 s without obvious degradation and the on/off ratio is >104 after more than 3000 switching cycles. We also demonstrate frequency-dependent memory properties upon stimulation with electrical and optical pulses.

Determination of Frequency-Dependent Dynamic Properties of Rocks Using the Nonresonance Method

Determination of Frequency-Dependent Dynamic Properties of Rocks Using the Nonresonance Method

Frequency-Dependent Fatigue Properties of Additively Manufactured PLA.

Vibration-fatigue failure occurs when a structure is dynamically excited within its natural frequency range. Unlike metals, which have constant fatigue parameters, polymers can exhibit frequency-dependent fatigue parameters, significantly affecting the vibration resilience of 3D-printed polymer structures. This manuscript presents a study utilizing a novel vibration-fatigue testing methodology to characterize the frequency dependence of polymer material fatigue parameters under constant temperature conditions. In this investigation, 3D-printed PLA samples with frequency-tunable geometry were experimentally tested on an electro-dynamical shaker with a random vibration profile. Using the validated numerical models, the estimation of vibration-fatigue life was obtained and compared to the experimental results. Performing the numerical minimization of estimated and actual fatigue lives, the frequency-dependent fatigue parameters were assessed. In particular, the results indicate that the tested samples exhibit varying fatigue parameters within the loading frequency range of 250-750 Hz. Specifically, as the loading frequency increases, the fatigue exponent increases and fatigue strength decreases. These findings confirm the frequency dependence of fatigue parameters for 3D-printed polymer structures, underscoring the necessity of experimental characterization to reliably estimate the vibration-fatigue life of 3D-printed polymer structures. The utilization of the introduced approach therefore enhances the vibration resilience of the 3D-printed polymer mechanical component.

Computational insights into the static, solvent and frequency-dependent nonlinear optical properties of head-to-tail novel non-fullerene compounds for modern electro-optic applications

Addressing the growing demand of novel nonlinear optical (NLO) materials, hyper-rayleigh-scattering (HRS) in solution, static and frequency-dependent NLO properties of novel IsoIDTC-based derivatives (AFS1-AFS9) are computed at laser frequencies of 1064 nm and 532 nm to explore SHG β (−2ω, ω, ω) and EOPE β (−ω, ω, 0) for modern electro-optic applications. Structural, electrical, and NLO features were calculated using DFT, and TDDFT modeling, HRS, and DR measurement. The polar, non-polar solvent, and gas phase NLO properties show the highest linear polarizability of 8.92 × 102 a.u. (AFS8) in water, 9.68 × 102 a.u. (AFS5) in gas, and 9.56 × 102 a.u. (AFS) in benzene. AFS8 push-pulls exhibit the highest first hyper-polarizability (βtot) at 1.05 × 105 a.u. and 1.47 × 105 a.u. in gas and benzene solvent, respectively. The proposed chromophores showed substantial SHG and EOPE values at 532 nm and 1064 nm lasers compared toIDT, hence, allowed the successful synthesis of NLO materials for future cutting-edge optoelectronic applications.

Wykorzystanie metody radaru penetrującego grunt w badaniu gleby zanieczyszczonej węglowodorami w obszarze Navodari - Rumunia

Ground penetrating radar (GPR) is a very useful geophysical method for use in hydrogeologic and near-surface mapping studies. It can be used to study contaminants in groundwater, subsurface faulting, and underground cavities (natural or man-made), all of which pose potentially dangerous geological hazards. The GPR technique is similar in principle to seismic reflection and sonar techniques. The propagation of the radar signal depends on the frequency-dependent electrical properties of the ground.Electrical conductivity of the soil or rock materials along the propagation paths introduces significant absorptive losses which limit the depth of penetration into the earth formations and is primarily dependent upon the moisture content and mineralization present.Reflected signals are amplified, and transformed to the audio-frequency range, recorded, processed, and displayed. From the recorded display, subsurface features such as soil/ soil, soil/rock, and unsaturated/saturated interfaces can be identified. In addition, the presence of floating hydrocarbons on the water table, the geometry of contaminant plumes, and the location of buried cables, pipes, drums, and tanks can be detected. The GPR data are presented as a two-dimensional depth profile along a scanned traverse line in which the vertical axis is two-way travel time measured in nanoseconds. The location of hydrocarbon contamination in the ground using the GPR method is based mainly on information taken from reflected signals. In the cases investigated in Romania contaminated sites (Navodari area), such signals were very rarely recorded. A long time after spillage, contamination takes the form of plumes with different size and distribution, which depends on the geological and hydraulic properties of the ground. The survey discussed in this paper was carried out using the GPR system-Noggin with two antennas (250 and 500mHz) Data collected were processed using software(EKKO_Project™ GPR Data Analysis) to produce 2D radargram in time scale. The presence of contaminant plumes as well as the water table are observed in the GPR sections at depths approximately of 0.5 to 1.5 m. In the GPR section, the oil contaminated layer exhibits discontinuous, subparallel, and chaotic high amplitude reflection patterns. Promising results were also obtained in the GPR survey where three obvious reflection patterns representing the top sand-silt layer, oil-contaminated zone and, the underlying thick soft clay were detected in all 2D radargrams of the GPR traverse lines.

Dynamic topology optimization of two-phase viscoelastic composite structures considering frequency- and temperature-dependent properties under random excitation

This article proposes an efficient optimum design method of constrained layer damping (CLD) plates characterized by non-proportional damping subjected to random excitation. Considering frequency and temperature dependence, a two-phase viscoelastic composite material composed of stiffness-phase and damping-phase materials is used as the damping layer. The pseudo excitation and hybrid expansion methods are adopted to compute the random responses at the specified frequency intervals as the objective functions. The sensitivity analysis is performed through the adjoint vector method. The similarity index is defined to distinguish the various optimal layouts quantitatively. Several numerical examples clearly demonstrate the robustness and effectiveness of the proposed method, highlighting a remarkable improvement of over 60% in computational efficiency. Furthermore, it is proved that, when subjected to broadband random excitation, the damping materials' temperature- and frequency-dependent properties are critical factors in obtaining accurate vibration responses and desirable optimal layouts. The effects of the layer thicknesses and volume fractions of composite structures on topology optimization are also discussed. The results indicate that both layer thickness and volume fraction can change the mechanical properties of the composite structure and further affect the distribution characteristics of the damping material.

Tunable wave localization at the Dirac frequency in a metallic photonic crystal cavity

In this study, the two-dimensional (2D) triangular lattice metallic photonic crystals (PCs) in visible and infrared bands have been utilized to achieve light confinement at the Dirac frequency. Distinct from the traditional bandgap or total internal reflection cavity modes, the unique photonic localization mechanism leads to an unusual algebraic decay of state and a unique frequency located beyond any bandgaps. This investigation delves into the band structure analysis of 2D metallic PCs, specifically focusing on their distinctive features, such as photonic bandgaps and Dirac cones. The plane wave expansion (PWE) method, enhanced with a linearization technique, is employed for band structure calculations, considering both the frequency-dependent dielectric properties and the intrinsic lossy nature of metallic materials described by the Drude model. The study provides a comprehensive derivation of the PWE equations for metallic PCs and investigates their band characteristics under both TM and TE polarizations. Focusing on TM modes in triangular lattice metallic PCs, it reveals zero density of states (DOS) at K points of the Brillouin corner and the existence of Dirac cones with linearly dispersion and linearly vanishing DOS. The study extends to exploring localized modes at Dirac frequencies, employing a relativistic quantum mechanics approach analogous to graphene's charge carriers. Theoretical predictions are corroborated by numerical simulations, and the potential for tunable Dirac localized modes is highlighted. This research not only deepens the understanding of Dirac properties in graphene-like systems but also lays the groundwork for further exploration of the practical quasi-2D devices, which will provide assistance in the integration of micro- and nano- devices, especially in applications requiring long-range coupling, given the critical importance of optical cavities in contemporary optical technologies.

Highly dispersive transmission conditions for a conductive rods-based ultrathin bilayer metastructure

We experimentally demonstrate that the transmission of microwave electromagnetic fields through a bilayer metasurface (BMS) composed of thin conductive rods can abruptly change in a narrow frequency range. A theoretical analysis based on the coupled oscillator model is performed to reveal the physical mechanism behind the frequency-dependent properties of such a structure. Two conditions primarily facilitate the observed high dispersion in the BMS. The first one is the resonant interaction between the incident microwaves and rods, leading to the formation of surface standing waves. These waves with radial electric fields enable the coupling of the near-field of rods in structural layers. The second condition is the complex value of the coupling coefficient between rods of different owing to the delayed interaction process between them. The electromagnetic response here can be effectively controlled by varying the distance between layers and the dielectric properties of the interlayer medium.

Synthesis, Structural characterization and complex impedance analysis of a novel organic-inorganic hybrid compound based on Mercury (II) chloride

The organic-inorganic hybrid compounds are promising materials due to their electro-optical and semiconducting properties. In this study, a single crystal of (C6H16N)2[HgCl4] has been synthesized and characterized using single-crystal X-ray diffraction at room temperature, SEM/EDS and complex impedance spectroscopy. The crystal structure is centrosymmetric with the monoclinic system (P21/c space group). It consists of isolated tetrahedral anions [HgCl4]2− and protonated amines (C6H16N) +. SEM/EDS analyses proved the composition of the title compound. The frequency-dependent electrical and dielectric properties were analyses using complex impedance spectroscopy in the frequency range of 10−1 Hz – 1 MHz. The Nyquist plots (-Z’’ vs Z’) was characterized by the appearance of a single semicircle arc, indicating a non-Debye type relaxation process in the (C6H16N)2[HgCl4] material. The AC conductivity followed Jonscher law, and the variation of frequency exponent s with temperature suggested that non-overlapping small polaron tunneling (NSPT) is the dominant electrical transport mechanism. So, this work will be very beneficial to the further development of the (C6H16N)2[HgCl4] compound and its potential electrical applications.

Frequency-dependent dielectric properties of aromatic polyimides in the 25–330 GHz range

Frequency-dependent dielectric properties of aromatic polyimides in the 25–330 GHz range

Structural and dielectric characteristics of doped nickle oxide polyaniline composites

ABSTRACT The PANI-NiO composites were synthesized by employing an in situ chemical polymerization technique, with varying weight percentages of NiO dopant (PANI-5%NiO and PANI-10%NiO). Additionally, AC conductivity, dielectric constant and dielectric loss were investigated within a frequency range from 20 Hz to 1 MHz. XRD confirmed the phase purity and high crystallinity. SEM reveals the granular shape with a porous surface. In addition, the incorporation of NiO with different concentrations influences the composite’s dielectric properties. All samples exhibited frequency-dependent dielectric properties in line with the Maxwell–Wagner model. Notably, the AC conductivity of PANI-10% NiO composite increased as the frequency increased, this behaviour was certified with Jonscher’s power law. The I–V characteristics confirm the ohmic nature of all synthesized samples. Therefore, the potential of PANI and PANI-NiO composites, as efficient dielectric materials, has been explored and can be useful for device applications in diverse fields.