Broad Frequency Domain Research Articles

Selective-wavelength perfect infrared absorption in Ag@ZnO conical metamaterial structure

We present a new selective Metamaterial Perfect Absorber (MPA) consisting of zinc oxide embedded silver (Ag@ZnO), designed for applications in infrared stealth technology. The numerical simulation included a wide frequency range from 1 to 1000 THz and shows that the design MPA structure presented two absorption peaks at the desired wavelengths of 1.7 µm and 6.5 µm. The absorptivity of both peaks reached approximately 93.1% and 93.5%. The first peak at 1.7 µm decreases the scattering of IR laser beams from the surface of the MPA structure and also lowers the infrared tracks that could direct laser-guided devices to its specific target. On the other hand, the second peak reduces the surface heat wave. The suggested MPA (Ag@ZnO) structure is activated by a plane wave using a full wave vector and a broad frequency domain solution. In the framework of computer simulation technology (CST) Microwave Studio, uses both Finite-Difference-Time-Domain (FDTD) and Finite-Element-Method (FEM) techniques to predict the optical behavior of the proposed MPA structure. Both peaks achieved a high value of absorptivity due to the simultaneous excitation of the electric and magnetic dipole at resonance wavelength.

Effective broadband electromagnetic wave absorption performance of nano-Fe3O4 magnetic fluid-modified resin geopolymer by metamaterial with a novel patterned structure

It is challenging to achieve high-strength absorption and effectively broaden the absorbing bandwidth when using conventional flat microwave-absorbing cementitious materials. To address this challenge and achieve excellent microwave-absorptive performance, this study proposes a novel two-layered periodic stepped absorbing structure (PSAS) composed of a mixture of nano-Fe3O4 magnetic fluid and a resin geopolymer. Additionally, the incident angle-dependent absorption performance, the impact of geometrical parameters, and the shape of the unit cell were investigated. The results demonstrate that the absorption of the designed metamaterial absorber exceeds 90% in the total frequency range of 2–18 GHz. A mean reflection value of −18.3 dB was obtained in this study. The outstanding absorption performance of PSAS results from the cooperative effect of multiple λ/4 resonances and edge diffraction effects, which improve the impedance matching to the level of the free space in a broad frequency domain. Combining the effect of electromagnetic field regulation with metamaterial structure, the ultra-broadband absorption can be significantly enhanced by adjusting the geometrical parameters of the unit cell for absorption resonance.

Highly Reliable Multicomponent MEMS Sensor for Predictive Maintenance Management of Rolling Bearings.

In the field of vibration monitoring and control, the use of low-cost multicomponent MEMS-based accelerometer sensors is nowadays increasingly widespread. Such sensors allow implementing lightweight monitoring systems with low management costs, low power consumption and a small size. However, for the monitoring systems to provide trustworthy and meaningful data, the high accuracy and reliability of sensors are essential requirements. Consequently, a metrological approach to the calibration of multi-component accelerometer sensors, including appropriate uncertainty evaluations, are necessary to guarantee traceability and reliability in the frequency domain of data provided, which nowadays is not fully available. In addition, recently developed metrological characterizations at the microscale level allow to provide detailed and accurate quantification of the enhanced technical performance and the responsiveness of these sensors. In this paper, a dynamic calibration procedure is applied to provide the sensitivity parameters of a low-cost, multicomponent MEMS sensor accelerometer prototype (MDUT), designed, developed and realized at the University of Siena, conceived for rolling bearings vibration monitoring in a broad frequency domain (from 10 Hz up to 25 kHz). The calibration and the metrological characterization of the MDUT are carried out by comparison to a reference standard transducer, at the Primary Vibration Laboratory of the National Institute of Metrological Research (INRiM).

Improved experimental setup to reach a broad frequency domain in local electrochemical impedance spectroscopy measurements

We report a new experimental setup enabling local electrochemical impedance spectroscopy (LEIS) measurements over a wide frequency range, including the low frequency domain. First, an improved signal treatment was performed using a potential shifter to minimize the DC component of the measured potential, allowing for the local AC potential to be probed using an ideal electrochemical system. Then, a unique, three-electrode LEIS probe was implemented to study the influence of radial and lateral contributions on the LEIS response. The radial LEIS response is highest when the LEIS probe is positioned in the middle of the gold electrode substrate, whereas the lateral LEIS response is similar in both measured regions. Both experimental modifications were implemented to study the LEIS response over a corroding aluminum substrate, for which reliable results are obtained in the low frequencies. These tools could be used in future LEIS studies in other fields that require time-sensitive measurements.

New equipment for high-accuracy laboratory measurements of spectral induced polarization of rock samples in the time- and frequency domains: Testing of laboratory multifunction potentiostat-galvanostat

The spectral induced polarization (IP) technique is widely used in prospecting and applied geophysics and allows remote assessment of porosity, mineralogical composition, textural and structural features of rocks, and chemical composition of the saturating fluid. The nature of the IP phenomenon in rocks is still not fully understood; therefore, much attention is paid to laboratory IP measurements on rock/ore samples carried out in the time (TDIP) and frequency (FDIP) domains. The intensity of the polarization effect can be low in rocks. Reliable IP measurements on rock samples in a broad time or frequency domain require tailored high-precision equipment.This paper presents the first experience of using the multifunctional electrochemical P-40× potentiostat-galvanostat instrument for high-precision laboratory measurement of spectral induced polarization (SIP) on rock samples. The advanced capabilities of the P-40× allowed us to implement a fully automated TDIP and FDIP measurement technology.The difference between the P-40× and specialized equipment for IP measurements in the time domain lies in recording of TDIP signals (full wave) of current and voltage without processing. A code has been developed for processing the observed TDIP signals. It suppresses harmonic and non-harmonic interference signals and the drift of potential electrodes and calculates IP parameters. The code and proposed algorithm for processing TDIP signals were successfully tested on synthetic signals contaminated by noise components of various origins and data from laboratory IP measurements on rock samples.We also compared the TDIP and FDIP measurements obtained with the P-40× and specialized equipment AIE-2 (TDIP) and SIP Fuchs III (FDIP), which have been used for high-precision laboratory measurements of IP for many years. We run our experiments with such test materials as RC circuit, ore carbonatite samples, and sand. Here we demonstrate that the IP data obtained with the P-40× and specialized equipment are identical.

Chasing the high-resolution mapping of rotational and strain FRFs as receptance processing from different full-field optical measuring technologies

Thanks to the recent advances in digital vision systems, a question might arise about where the full-field optical and contactless methods can bring modern design procedures. An answer lies on the methodologically detailed comparison of the results, processed from different full-field optical techniques, in exploring consistent and high-resolution maps of rotational and strain FRFs that is done through this paper.Great exertions were first put in thoroughly testing a thin aluminium plate, in its real dynamics as a lightweight structure with broad frequency band dynamics and high modal density, in a unique comparative set-up, to obtain Receptance FRF maps of displacements-over-force by means of 3 different full-field optical techniques (SLDV, DIC, ESPI). There resulted superior quality Receptance maps in a broad and dense frequency domain, with high-resolution and continuity-wise consistent mapping at each frequency line.This paper exploits the here detailed robust numerical differentiation and signal processing in order to calculate the Impedance-based models of rotational and strain FRFs. Especially for DIC and for ESPI, both rarely used on many frequency lines, the fully populated FRFs for rotations and strains are a clear novelty, with rotational Coherence functions as added quality assessment features.The systematic comparison of the results obtained in the same location of the sample, by means of spatial and frequency domain metrics, is possible because of the proposed pointwise procedure, permitting the first numerical matching assessment of the 3 optical technologies on these awaited experiment-based quantities, as the full-field rotational and strain FRFs.

A Multi-Scale Study of Water Dynamics under Confinement, Exploiting Numerical Simulations in Relation to NMR Relaxometry, PGSE and NMR Micro-Imaging Experiments: An Application to the Clay/Water Interface.

Water mobility within the porous network of dense clay sediments was investigated over a broad dynamical range by using 2H nuclear magnetic resonance spectroscopy. Multi-quanta 2H NMR spectroscopy and relaxation measurements were first performed to identify the contributions of the various relaxation mechanisms monitoring the time evolution of the nuclear magnetisation of the confined heavy water. Secondly, multi-quanta spin-locking NMR relaxation measurements were then performed over a broad frequency domain, probing the mobility of the confined water molecules on a time-scale varying between microseconds and milliseconds. Thirdly, 1H NMR pulsed-gradient spin-echo attenuation experiments were performed to quantify water mobility on a time-scale limited by the NMR transverse relaxation time of the confined NMR probe, typically a few milliseconds. Fourthly, the long living quantum state of the magnetisation of quadrupolar nuclei was exploited to probe a two-time correlation function at a time-scale reaching one second. Finally, magnetic resonance imaging measurements allow probing the same dynamical process on time-scales varying between seconds and several hours. In that context, multi-scale modelling is required to interpret these NMR measurements and extract information on the influences of the structural properties of the porous network on the apparent mobility of the diffusing water molecules. That dual experimental and numerical approach appears generalizable to a large variety of porous networks, including zeolites, micelles and synthetic or biological membranes.

Physio-Chemical Properties and Dielectric Behavior of As-Grown Manganese Oxide (γ-Mn2O3) Nanoparticles

Semiconducting metal oxide nanostructured materials are demonstrating efficient use and functional properties in devices. Manganese oxide (Mn2O3) is one of the smart semiconductor metal oxides. The hydrothermal method was found suitable to prepare γ-Mn2O3 nanoparticles. The nanostructural characterization using various advanced tools confirmed the purity and polymorph of the as-prepared γ-Mn2O3 nanoparticles. Optical analyses exposed the presence of a possible dual-band-gap in γ-Mn2O3 nanoparticles. A strong blue shift of 1.3 eV estimates the activation energy (Ea) of the nanoparticles. Furthermore, γ-Mn2O3 nanoparticles were used as dielectrics to explore the dielectric response of the material in a broad frequency domain (50 Hz–30 MHz). The dielectric spectroscopy analyses revealed the regular value of the dielectric constant (∼ 9) in the high-frequency domain, the low value of the tangent loss (0.05 ≤ tanδ ≥ 1.34), the frequency power law-dependent ac conductivity, the occurrence of single dielectric relaxation process of relaxation time 160 μs, and a non-Debye-type relaxation behavior in the γ-Mn2O3 nanoparticles. The properties assessed here indicate the functional-behavior and prospective application of the γ-Mn2O3 nanoparticles in devices.

Dynamic Modeling and Structural Optimization of a Bistable Electromagnetic Vibration Energy Harvester

A novel bistable electromagnetic vibration energy harvester (BEMH) is constructed and optimized in this study, based on a nonlinear system consisting mainly of a flexible membrane and a magnetic spring. A large-amplitude transverse vibration equation of the system is established with the general nonlinear geometry and magnetic force. Firstly, the mathematical model, considering the higher-order nonlinearities given by nonlinear Galerkin method, is applied to a membrane with a co-axial magnet mass and magnetic spring. Secondly, the steady vibration response of the membrane subjected to a harmonic base motion is obtained, and then the output power considering electromagnetic effect is analytically derived. On this basis, a parametric study in a broad frequency domain has been achieved for the BEMH with different radius ratios and membrane thicknesses. It is demonstrated that model predictions are both in close agreement with results from the finite element simulation and experiment data. Finally, the proposed efficient solution method is used to obtain an optimizing strategy for the design of multi-stable energy harvesters with the similar flexible structure.

Review on Multi-scale Structural Design of Submarine Stealth Composite

Research on the acoustic stealth structures of submarines primarily strives for low frequency, pressure resistance, and broad frequency domain absorption. The high-quality acoustic stealth coating on submarines is a complicated Multi-scale and multi-component structure, which consists of numerous macro-structures, such as acoustic air-filled cavities, laminated structures, filling components, and micro-phase structures. However, more information regarding how these components with different anechoic mechanisms obtain good results through synergistic work and how their absorption frequencies superpose effectively to realize acoustic stealth in a broad frequency domain is necessary. Understanding these mechanisms is essential to design a novel anechoic structure in a broad frequency domain. Thus, in this paper, research concerning these mechanisms was reviewed. In addition, the design methods and anechoic mechanism of anechoic structures were discussed for different levels, and the primary concerns in this field were summarized. Several suggestions were made for further research.

Uncertainty quantification in computational linear structural dynamics for viscoelastic composite structures

This paper deals with the analysis of a stochastic reduced-order computational model in computational linear dynamics for linear viscoelastic composite structures in the presence of uncertainties. The computational framework proposed is based on a recent theoretical work that allows for constructing the stochastic reduced-order model using the nonparametric probabilistic approach. In the frequency domain, the generalized damping matrix and the generalized stiffness matrix of the stochastic computational reduced-order model are random matrices. Due to the causality of the dynamical system, these two frequency-dependent random matrices are statistically dependent and are linked by a compatibility equation induced by the causality of the system, involving a Hilbert transform. The computational aspects related to the nonparametric stochastic modeling of the reduced stiffness matrix and the reduced damping matrix that are frequency-dependent random matrices are presented. A dedicated numerical approach is developed for obtaining an efficient computation of the Cauchy principal value integrals involved in those equations for which an integration over a broad frequency domain is required. A computational analysis of the propagation of uncertainties is conducted for a composite viscoelastic structure in the frequency range. It is shown that the uncertainties on the damping matrix have a strong influence on the observed statistical dispersion of the stiffness matrix.

Optical temperature sensing using a new thermographic phosphor

The luminescence emission of a new thermographic phosphor based on Chromium(III)-doped yttrium aluminum borate (Cr3+:YAB) has a strong temperature dependence, which makes this material well suited for temperature sensing. In this work the luminescence emission decay was investigated in great detail in a broad temperature range, both in time and frequency domain. The results obtained with these two measuring techniques, which are consistent, are used to determine the optimal design parameters for sensor development. The high sensitivity which is thus achievable, together with the high stability of the material, demonstrate that this phosphor is very suitable for the design of a sensitive, low-cost, and robust contactless temperature sensor. Due to the insensitivity of the sensing properties to the immobilization matrix, this material can be easily incorporated in the most appropriate matrix depending on the application.

Calibration independent estimation of optical constants using terahertz time‐domain spectroscopy

ABSTRACTA novel calibration independent technique that simultaneously determines the optical constants and material thickness with high accuracy, using the transmission and the reflection measurements, is proposed. A generalized closed form expression is derived to calculate the optical constants in terms of the measured transmitted and the reflected signals. The proposed measurement technique is noniterative, self‐calibrated, and independent of prior knowledge of the sample thickness. To validate the proposed technique, two different samples, viz., Gallium arsenide and Silicon, are considered during the numerical simulation. The result shows that the proposed technique provides highly accurate material parameters over a broad frequency domain and also recovers the information of the material thickness. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1861–1864, 2015

Contactless measurement of alternating current conductance in quantum Hall structures

We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.

Accurate determination of terahertz optical constants by vector network analyzer of Fabry–Perot response

We present a method based on a Fabry-Perot model to efficiently and accurately estimate optical constants of wafer samples in transmission-only measurements performed by a vector network analyzer (VNA). The method is demonstrated on two separate wafer samples: one of silicon and the other of polymethylmethacrylate. Results show that the method can not only acquire optical constants accurately and simply over a broad frequency domain but also overcome the limitations of calculation for dispersive and lossy materials to which existing methods are susceptible, such as those based on VNA-driven quasi-optical transmissometers and terahertz time-domain spectrometry.

Frequency characteristic analysis on acoustic emission of mortar using cement-based piezoelectric sensors

Acoustic emission (AE) monitoring was conducted for mortar specimens under three types of static loading patterns (cubic-splitting, direct-shear and pull-out). Each of the applied loading patterns was expected to produce a particular fracture process. Subsequently, the AEs generated by various fracture or damage processes carried specific information on temporal micro-crack behaviors of concrete for post analysis, which was represented in the form of detected AE signal characteristics. Among various available characteristics of acquired AE signals, frequency content was of great interest. In this study, cement-based piezoelectric sensor (as AE transducer) and home-programmed DEcLIN monitoring system were utilized for AE monitoring on mortar. The cement-based piezoelectric sensor demonstrated enhanced sensitivity and broad frequency domain response range after being embedded into mortar specimens. This broad band characteristic of cement-based piezoelectric sensor in frequency domain response benefited the analysis of frequency content of AE. Various evaluation methods were introduced and employed to clarify the variation characteristics of AE frequency content in each test. It was found that the variation behaviors of AE frequency content exhibited a close relationship with the applied loading processes during the tests.

On the constitutive modeling of reinforced rubber in a broad frequency domain

AbstractA constitutive model for the numerical simulation of rubber behavior in a wide frequency range is presented. The combination between the well known Simo's viscoelastic model and a pseudo‐elastic approach enables for the modeling of inelastic effects at low frequencies, such as nonlinear elasticity, hysteretic behavior, and damage (Mullins effect). The constitutive formulation is derived in detail with an aim of the finite element implementation. Because mechanical response at high frequencies is usually characterized by complex modulus, the developed viscoelastic damage model is extended to high‐frequency analysis. A key idea is the decomposition of the deformation gradient into linear and nonlinear part. The nonlinear part is associated with inelastic deformations established at low frequencies, while the linear contribution plays an important role for dynamic analysis at high frequencies. As a result, the steady‐state response of rubber at a certain static deformation is evaluated and consequently leads to the numerical solution for complex modulus. The computational efficiency of the proposed model can be seen from a good agreement with experimental data.

Constitutive Modeling of Rubber Behavior with an Application to Dynamics of Rolling Tires

AbstractMechanical response of technical rubbers is described by nonlinear elastic deformation, damage and hysteretic behavior under quasi‐static cyclic loading conditions, while dynamic stiffening and viscous effects are predominant for high frequency analysis. For the computation of the vibration of rolling tires, a material description incorporating all of these effects is needed. A constitutive model for filled rubbers under low frequency excitation is presented. A good agreement between the computational results and experimental data is also presented here. Furthermore, an idea to extend the constitutive model into a broad frequency domain is suggested through the uncoupled kinematic response in linear and nonlinear part. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamic macroscopic heterogeneities in a flexible linear polymer melt

This article describes shear-experiments on flexible linear polymer melts (polystyrene) with molecular weights (4,000 and 17,500 g/ mol ) lower than that of critical entanglement. The technique used is a shear piezoelectric rheometer, enabling the complex shear-modulus to be measured in a broad frequency domain (ranging from a few hundredths Hz to some kHz), for weak imposed strains (∼10 −4), and for thicknesses between 15 and 100 μm . The results obtained show that the behavior of the shear modulus progressively shifts from a liquid-type behavior to a solid-type as sample-thickness decreases from 100 to 15 μm . This unexpected change in behavior, which is only observed for strong anchoring conditions of the polymer on the substrate, indicates the presence of macroscopic heterogeneities (elastic clusters). We show that these clusters are associated with the glass transition and suggest that they are due to long-range density-fluctuations which are frozen as a result of their ultra-slow relaxation times and thus display an elastic response.

Broad bandwidth frequency domain instrument for quantitative tissue optical spectroscopy

Near-infrared (NIR) optical properties of turbid media, e.g., tissue, can be accurately quantified noninvasively using methods based on diffuse reflectance or transmittance, such as frequency domain photon migration (FDPM). Factors which govern the accuracy and sensitivity of FDPM-measured optical properties include instrument performance, the light propagation model, and fitting algorithms used to calculate optical properties from measured data. In this article, we characterize instrument, model, and fitting uncertaintics of an FDPM system designed for clinical use and investigate how each of these factors affects the quantification of NIR absorption (μa) and reduced scattering (μs′) parameters in tissue phantoms. The instrument is based on a 500 MHz, multiwavelength platform that sweeps through 201 discrete frequencies in as little as 675 ms. Phase and amplitude of intensity modulated light launched into tissue, i.e., diffuse photon density waves (PDW), are measured with an accuracy of ±0.30° and ±3.5%, while phase and amplitude precision are ±0.025° and ±0.20%, respectively. At this level of instrument uncertainty, simultaneous fitting of frequency-dependent phase and amplitude nonlinear model functions derived from a photon diffusion approximation provides an accurate and robust strategy for determining optical properties from FDPM data, especially for media with high absorption. In an optical property range that is characteristic of most human tissues in the NIR (5×10−3<μa<5×10−2 mm−1, 0.5<μs′<2 mm−1), we theoretically and experimentally demonstrate that the multifrequency, simultaneous-fit approach allows μa and μs′ to be quantified with an accuracy of ±5% and ±3%, respectively. Although exceptionally high levels of precision can be obtained using this approach (<1% of the estimated absorption and scattering values), we show that the absolute accuracy of optical property measurements is highly dependent on specific factors associated with instrument performance, model function relevance, and details of the fitting strategy used to calculate μa and μs′.