Wave Transmission Spectra Research Articles

Effect of probe structure on wave transmission spectra of microwave cutoff probe

Effect of probe structure on wave transmission spectra of microwave cutoff probe

Magnonic notch filter based on spin wave caustic beams

Here, we study a magnonic crystal made of low-damping yttrium iron garnet that utilizes pseudo-caustic spin wave beams generated from subwavelength square well features arranged in a two-dimensional array. The lattice symmetry and the angle between the caustic beam propagation direction and the applied magnetic field were tailored to optimize the interaction of spin waves with the engineered defects. A prominent, narrow 3 MHz feature with large rejection efficiency is observed in the spin wave transmission spectrum that could be useful as a narrowband notch filter, and time- and space-resolved Brillouin light scattering (BLS) measurements suggest that both caustic interference and edge effects may contribute to this notch feature. Furthermore, the BLS measurements show that caustics are generated efficiently at the laser ablated wells, and by tuning the frequency by 30 MHz, the caustic beam angles and, hence, the details of how the spin wave caustics hit the ablated wells change sufficiently to add and remove caustic beams, which can be used to create additional device functionality. The generation and conversion of caustic beams show promise for applications that require directional energy transport and for magnonic devices.

Novel hybrid-controlled graded metamaterial beam for bandgap tuning and wave attenuation

In this paper, a tunable functionally graded metamaterial beam is designed for flexural wave attenuation by integrating piezomagnetic shunt damping system and inertial amplification mechanism. The proposed piezomagnetic shunt damping system is a complex mechanic–magnetic–electrical coupling system, which aims to transform and consume the vibration energy through local resonance to form a bandgap with tunable and strong wave attenuation ability. Based on Timoshenko beam theory, the wave equation and transmission spectrum of the metamaterial beam are derived by using transfer matrix method. The theoretical results are compared with the numerical simulation results. The results show that the resonance characteristics of piezomagnetic shunt circuit lead to negative group velocity and strong wave attenuation(−30 dB) at frequency defined by inductance and capacitance in shunt circuit. In varying frequency regimes, the coupled bandgap width can be maximized to 1925 Hz by tuning the external capacitance and coil turns. The superposition of double attenuation peaks caused by inertial amplification mechanism and local resonance coupling can be generated in the bandgap, allowing wave attenuation up to −94 dB. Subsequently, the attenuation capability of locally resonant bandgap can be significantly enhanced without changing the frequency by introducing the negative resistance into shunt circuit. Furthermore, the initiation and termination frequencies of bandgap can be flexibly designed by important material and structural parameters. This work is expected to provide valuable research ideas for the application of advanced intelligent materials in the field of vibration and noise reduction.

Periodic and quasi-periodic one-dimensional extrinsically magnetized photonic crystals with robust photonic bandgaps.

The study of light wave transmission spectra for a one-dimensional extrinsic multilayered photonic structure is investigated by using the transfer matrix method. The photonic transmission properties of the proposed structure are analyzed for the different values of the external magnetic field, incident angles in terms of standard and oblique, and the electron concentrations of the electromagnetic wave propagation through the extrinsic quasi-periodic and periodic photonic structures. Robust and wider PBGs have appeared for several kinds of quasi-sequences. The increase in electron concentration strengthens the PBG, though it is highly affected by the collision frequency. Furthermore, various PBGs in the terahertz frequency ranges are significantly influenced by the physical entities. The terahertz region's optical bandpass filters can be fabricated using the proposed framework. We also demonstrate that this proposed quasi-periodic multilayered architecture can be supplely controllable photonic crystals with positionable versions of the aforementioned features.

One-Dimensional Phononic Crystals: A Simplified Platform for Effective Detection of Heavy Metals in Water with High Sensitivity.

Recently, the pollution of fresh water with heavy metals due to technological and industrial breakthroughs has reached record levels. Therefore, monitoring these metals in fresh water has become essentially urgent. Meanwhile, the conventional periodic one-dimensional phononic crystals can provide a novel platform for detecting the pollution of heavy metals in fresh water with high sensitivity. A simplified design of a defective, one-dimensional phononic crystals (1D-PnC) structure is introduced in this paper. The sensor is designed from a lead-epoxy multilayer with a central defect layer filled with an aqueous solution from cadmium bromide (CdBr2). The formation of a resonant peak through the transmittance spectrum is highly expected. This study primarily aims to monitor and detect the concentration of cadmium bromide in pure water based on shifting the position of this resonant peak. Notably, any change in cadmium bromide concentration can affect the acoustic properties of cadmium bromide directly. The transfer matrix method has been used to calculate the transmission spectra of the incident acoustic wave. The numerical findings are mainly based on the optimization of the cadmium bromide layer thickness, lead layer thickness, epoxy layer thickness, and the number of periods to investigate the most optimum sensor performance. The introduced sensor in this study has provided a remarkably high sensitivity (S = 1904.25 Hz) within a concentration range of (0-10,000 ppm). The proposed sensor provides a quality factor (QF), a resolution, and a figure of merit of 1398.51752, 48,875,750 Hz, and 4.12088 × 10-5 (/ppm), respectively. Accordingly, this sensor can be a potentially robust base for a promising platform to detect small concentrations of heavy metal ions in fresh water.

A high-sensitivity liquid concentration-sensing structure based on a phoxonic crystal slot nanobeam

A high-sensitivity liquid concentration-sensing structure based on a phoxonic crystal slot nanobeam with gradient cavities is presented and its sensing properties are investigated using the finite element method. The proposed sensing structure, which can be made from either isotropic or anisotropic materials, can have excellent sensing properties that are designed via geometric optimization. We investigate the influences of various solution concentrations on electromagnetic and elastic wave transmission spectra. The results demonstrate that the introduction of gradient cavities can enable the system to avoid lattice mutation and reduce energy loss, thereby concentrating light and sound energy in the slot and holes, enhancing interactions between the electromagnetic and elastic waves, and improving sensitivity. It is worth noting that the sensing characteristics are related to the electric field distribution in the light sensor. That is, the sensitivity is better when more electric energy is distributed in the liquid-filled slot and holes. The sensitivity can reach 238.1 nm/RIU. The acoustic sensing properties are related to the solid–liquid interaction. This is especially true for the modal sensing characteristics, where the acoustic energy is concentrated on the solid–liquid interface. Therefore, greater interaction strength implies better sensitivity. The acoustic sensitivity can reach 3167 kHz/ms−1. The proposed structure provides acoustic and optical cross-checks for different types of solutions. This helps us to improve sensing accuracy and reduce sensing uncertainty.

Propagation properties of spin wave in Co2FeAl Heusler alloy ultrathin films

We report an investigation of spin wave propagation in ion beam sputtered Co2FeAl Heusler alloy thin film on Si(100) substrate. The spin wave transmission spectra measured at fixed frequencies by sweeping the external applied magnetic field were used to estimate technologically relevant spin wave propagation parameters. The spin wave group velocity was found at 6.1 km s−1 with an attenuation length larger than 7 μm. The Gilbert damping parameter was estimated to be 0.019. The frequency dependency of the group velocity decreased with increasing frequency and the attenuation length increased at low frequencies while started to decrease at larger frequencies. The amplitude of non-reciprocity also decreased with increasing frequency. The propagation parameters presented were also independently verified by time-resolved propagating spin wave spectroscopy.

Evanescent waves attenuation and stiffness enhancement of viscoelastic locally resonant metamaterials by nanofiller addition- a multi-scale k(ω) based modeling

A CNT-modified viscoelastic locally resonant metamaterial (LRM) is investigated to study the complex dispersion curve, loss factor, wave transmission spectra, and effective stiffness. The dispersion curve analysis is based on the Bloch theorem applied to the nanocomposite LRM (NLRM) equations of motion and solving the resulting eigenvalue problem by the finite element method. The transmission spectra is obtained by COMSOL Multiphysics software. Due to the material viscoelasticity, multi-scale frequency-dependent homogenization of the nanocomposite is performed within the k(ω) framework which is systematically presented. The CNTs are added to the host LRM to enhance its stiffness without a significant increase in density. Hence, the impedance mismatch between the host nanocomposite and the coated cores is increased which affects the complex branch of NLRM, and shifts the imaginary part of the wave number to greater values without considerable change in its real part. So, the NLRM loss factor is increased which leads to lower wave transmission. Therefore, the NLRM exhibits simultaneously higher stiffness and loss factor with respect to ordinary LRMs. The effective stiffness of the CNT/host nanocomposite and the complex LRM dispersion curve and attenuation diagram are validated by experimental and numerical results, respectively. A parametric study is conducted to consider the effects of the CNT volume fraction (CNTVF), aspect ratio (AR), aggregation state and the CNT/host interface properties. Results show that the CNTVF and AR have the most influential effects on the NLRM properties. The CNT aggregation state is detrimental to the NLRM stiffness and wave attenuation properties too.

In situ millimeter wave spectroscopy of microplasma within a photonic crystal

Microplasma generated within a millimeter wave (MMW) photonic crystal (PhC) is analyzed by direct measurement of the electron density and the wave transmission spectra (S21) of the crystal. A continuous wave (cw) drive frequency of 43.66 GHz maintains plasma, while a low power frequency sweep (43.5–44.1 GHz) simultaneously probes the wave transmission in the presence of microplasma. Rotational gas temperature and electron density are measured from the CH emission spectrum and the Stark broadening of the Hβ atomic transition. The permittivity of the plasma depends on the electron density. As higher cw power and argon gas pressure increase the electron density in the PhC vacancy, the resonant frequency of the PhC shifts upward in accordance with the measured electron density and plasma permittivity. As the PhC obscures the central core of the microplasma, we present a simple diffusion model that approximates the electron density distribution within the microplasma. The diffuse electron density is then used in a numerical model for S21(ω). The measured and modeled transmission spectra can only be reconciled using the diffusion density gradient of the microplasma, thus resolving previous discrepancies observed when using simplified, abrupt-boundary plasma models.

Reconfigurable locally resonant surface acoustic demultiplexing behavior in ZnO-based phononic crystal

We present the design and numerical investigation of a reconfigurable and miniature locally resonant surface acoustic wave demultiplexer based on a ZnO pillar phononic crystal, for the first time. Hollow cylinder line defects are used as waveguides, due to their good structural controllability over the local resonant waveguiding frequency and bandwidth. Two local resonant surface acoustic waveguides are designed and simulated as the output channels of the demultiplexer, and the shear-horizontal wave transmission spectra are calculated for each channel individually. The designed radio frequency demultiplexing output channels support frequencies of 4.14 GHz and 4.28 GHz, with respective bandwidths of 40 MHz and 60 MHz, while their spatial separation is just about 800 nm. In order to achieve a reconfigurable output characteristic, the effect of acoustoelectric interaction in piezoelectric semiconductors is numerically simulated in this study. The acoustoelectric interaction causes an additional stiffness in ZnO that can be released by adding extra charge carriers, i.e., increasing conductivity, thus changing the effective elasticity of the ZnO structures and the guiding frequencies of the output channels. Two output frequencies show red shifts of about 100 MHz and 150 MHz by extremely increasing the conductivity of ZnO structures from 0.01 S/m to 100 S/m.

Surface anisotropy induced spin wave nonreciprocity in epitaxial La0.33 Sr0.67 MnO3 film on SrTiO3 substrate

Spin wave propagation in perovskite La0.33 Sr0.67 MnO3 films epitaxially grown on a SrTiO3 substrate of (001) orientation was investigated using an all electrical spin wave spectroscopy technique. The spin wave nonreciprocity in amplitude, resonance frequency, and group velocity of the transmission spectra were observed. The origin of the spin-wave nonreciprocity is attributed to the out-of-plane surface anisotropy, with a value of 1.3 mJ/m2 at the interface with the substrate, as extracted from the theoretical model. The magnetic field dependence of the frequency shift is attributed to the perpendicular surface anisotropy. The important role of the surface anisotropy in the spin wave nonreciprocity was further confirmed by the angle dependent measurements of the spin wave transmission spectra.

Glycine sensor based on 1D defective phononic crystal structure

Phononic crystals (PnCs) provide an innovative platform for sensing biomaterials. In this work, we introduce a defective 1D-PnC from lead-epoxy multilayer with a central defect layer filled with glycine. The transmission spectra of the incident acoustic wave are calculated numerically by the transfer matrix method. The working principle of this sensor is to sense how much change occurs in the concentration of glycine. Any change in glycine concentration affects the acoustic properties of glycine directly. Thereby the central resonance frequency in the transmission spectrum shifted. In this study, we firstly made optimization for the type of the structure (symmetric/asymmetric), the number of periods, the glycine layer thickness, and glycine concentration to get the best sensor performance. The proposed sensor provided high sensitivity (S = 969.973 kHz) over just a molar ratio range 0–0.383 mol/L. Moreover, we calculated other performance parameters such as the quality factor, which reached a maximum value of 13,497, sensor resolution of 3.49 × 105 Hz, and figure of merit of 4.2. Based on the obtained results, this sensor has many merits such as it is designed from low cost materials, the ease of fabrication, high sensitivity, and absence of any electronic component in its design.

Improving sound insulation in low frequencies by multiple band-gaps in plate-type acoustic metamaterials

According to the mass law, low-frequency sound attenuation is very difficult in engineering because the mass and space of structures are usually limited. In this paper, we propose a plate-type acoustic metamaterial with good sound insulation in low-frequency ranges. By attaching multilayered rubber and metal cylinders on a thin plate, multiple flexural wave band-gaps at low-frequency ranges are obtained. The band structures and eigenmodes are elucidated by finite element calculations. Both the flexural wave transmission spectra and the sound transmission loss are investigated. The results show that the obtained multiple band-gaps lead to more than one sound insulation peak at low frequencies. The geometrical parameter effects on the band-gap frequencies are discussed. By combining cells with different geometrical parameters, the formed supercell can improve the low-frequency sound insulation efficiency and introduce much more variety. The results in this paper will be useful for sound and vibration control in engineering applications.

Love waves dispersion by phononic pillars for nano-particle mass sensing

We present a design of a pillared phononic crystal based structure for Love wave manipulation to achieve high mass sensitivity. The structure is made of phononic micro-pillars constructed by stacking tungsten and SiO2 layers, distributed on a substrate designed for Love wave propagation. The multilayered pillar allows the creation of bandgaps, which leads to the existence of resonant modes where the elastic energy is confined within the SiO2 free surface layer of the pillar. We study particularly a resonant mode where this layer exhibits torsional mechanical motion which can only be excited by shear horizontal surface waves. We show that Love wave interaction with the torsional mode gives rise to a sharp attenuation in the surface wave transmission spectrum with a high quality factor. We also study the variation of the mass sensitivity of the system by evaluating the resonant mode's frequency shift induced by a mass perturbation using two theoretical approaches: a perturbation theory based approximation and a numerical method. The system presents very promising mass sensitivity which provides an interesting approach to increase the detection performance of Love wave based bio-sensors.

In-plane elastic wave propagation in nanoscale periodic layered piezoelectric structures

Wave propagation in nanoscale piezoelectric structures is much more complex than in macro-sized elastic structures. This study is devoted to the analysis of in-plane elastic waves propagating normally and obliquely in nanoscale periodic layered piezoelectric structures. The equations of wave motion which take both the piezoelectric effect and the nanoscale size-effect into account are solved numerically. The transfer matrix method based on the nonlocal piezoelectric continuum theory is used to calculate the localization factor which characterizes the band structures. Additionally, the wave transmission spectra are also computed by the stiffness matrix method. The piezoelectric effect (i.e., the piezoelectric constants) and the size-effect (i.e., R, the influences of the ratio of the internal to external characteristic lengths) on the cut-off frequency and the wave propagation characteristics are discussed in details. The influence of the mode conversion on band-gaps and the influence of R on the mode conversion are analyzed.

Wave properties of shallow-layer semiconductor–insulator medium in the presence of magnetic field

Expressions for effective permittivity of a periodic semiconductor–insulator structure with both n- and p-type semiconductor layers are derived in the approximation of shallow-layer medium. Dispersion relations are obtained for the TM wave that is controlled by external magnetic field with allowance for different propagation directions of the wave relative to the periodicity axis of the structure. Specific features of the transmission spectrum of wave are revealed for a layer of shallow-layer medium with finite thickness at several ratios of layer thicknesses in the period of structure.

Flexural vibration bandgaps in local resonance beam with a novel two-degree-of-freedom local resonance system

In this paper, an elastic metamaterial beam with a novel two-degree-of-freedom local resonator is investigated theoretically, and the dispersion relation is calculated by using transfer matrix (TM). In order to confirm the existence of band gaps, the transmission spectrum of flexural wave are also studied by using finite element method. The formation mechanism of the flexural vibration bandgaps (FVBGs) are further analyzed by studying the displacement fields of the eigenmodes at the band-gap edges. At last, the evolution of the dispersion relations with the increasing of the distance from the one side rubber to the center of the local resonance mass are discussed in detail, and the effects of the outside diameter of the Cu ring and the equivalent stiffness k of the rubbers on the FVBGs are also investigated. Through the above analysis, we can draw the following conclusions, due to the unequal of the torques provided by the two rubbers, two different rotational vibrations of local resonance mass with two different local resonance frequencies are introduced in the local resonance system, thus the elastic metamaterial beam shows two FVBGs at low frequencies. The theoretical results are in good agreement with the numerical results. The magnitude of torques introduced in the local resonance system can obviously affect the locations of the FVBGs. With the asymmetry decreasing, the frequency region of the first FVBG moves to the higher value, while that of the second FVBG tends to the lower value, and when the two torques are equal, the two FVBGs coupled into one wider gap. For the elastic metamaterial beam with heavy resonance mass and weak rubbers is appropriate to obtain a lower band gap, and the total width of the FVBGs becomes wider. However, it does just the opposite under the condition of the case with light Cu ring and strong rubbers, but the total width of the band gaps also becomes wider. The propagation properties of the flexural wave in the designed local resonance beam can potentially be used to control and insulate vibration at low-frequency range and the unequal distances between the two rubbers to the center of the local resonance mass provide possibilities to expand the application of the beams for the vibration control in the needed frequency ranges.

Anti-plane transverse waves propagation in nanoscale periodic layered piezoelectric structures

In this paper, anti-plane transverse wave propagation in nanoscale periodic layered piezoelectric structures is studied. The localization factor is introduced to characterize the wave propagation behavior. The transfer matrix method based on the nonlocal piezoelectricity continuum theory is used to calculate the localization factor. Additionally, the stiffness matrix method is applied to compute the wave transmission spectra. A cut-off frequency is found, beyond which the elastic waves cannot propagate through the periodic structure. The size effect or the influence of the ratio of the internal to external characteristic lengths on the cut-off frequency and the wave propagation behavior are investigated and discussed.

20721 テラヘルツ時間領域分光法を用いた再生軟骨の非侵襲評価

When bringing regenerated cartilage into practical use, due to its piece-to-piece property difference, non-invasive evaluation should be developed before implantation. We intended to achieve non-invasive assessment of articular cartilage by applying terahertz technology. The purpose of this research is to clarify the relation between terahertz spectra and cartilage characteristics such as mechanical strength, extracellular matrix structure. In this paper, by applying dielectric analysis to transmission spectra of terahertz wave, we clarified slow relaxation strength of water molecular, which can be corresponding to the amount of free water in cartilage. The amount of free/bound water in cartilage is one of the factors that decide the mechanical properties of cartilage. To verify cartilage characteristics, we performed mechanical test and determined the amount of extracellular matrix. A comparison between slow relaxation strength and cartilage characteristics shows that terahertz technology can be one way of measuring water status and its characteristics.

Characterization of Radome Materials Comprising LTCC-Derived FSS on a Quartz Glass Plate

Frequency selective surfaces (FSS) and recent metamaterials (MTM) have shown unique electromagnetic characteristics and are of potential benefits for radome applications. To make the radomes/windows high-temperature resistant, the substrates of the frequency selective surfaces or metamaterials should be made of ceramic/glass-based materials of a low dielectric constant and a low loss tangent. However, fabricating ceramic/glass-based FSS or MTM is always challenging. In this paper, a constrained low-temperature co-fired ceramic (LTCC) technique was used to produce quartz glass-based radome material consisting of a frequency selective surface (FSs) layer embedded in a surface laminate. Due to the constrained sintering shrinkage, the geometry and the dimensions of the unit cells of the FSs were not subjected to significant variations and thus the measured electromagnetic (EM) wave transmission spectra matched those of the computer simulation results quite well. This preliminary work marks the beginning of our long-term efforts toward the goal of achieving high-temperature resistant, highly electromagnetic wave transparent, as well as carefullydesigned and fabricated radome materials.