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Periodic structures have gained attention in the research community since they show attenuation zones in their frequency response, called bandgaps. In this paper, the interactions of two mechanisms of bandgap formation in mono-coupled periodic structures are examined, i.e., Bragg scattering and local resonators. With reference to longitudinal elastic waves, an analytical study is carried out to describe in detail the formation of bandgaps. Local resonators are implemented via piezoelectric inserts shunted with a resonating electrical circuit for which a non-traditional model is needed since the study concerns higher frequencies with respect to those of the subwavelength regime. Design maps and tuning formulas are developed not only for the case of infinite structures, but also for the finite case, highlighting the role of the number of unit cells and that of resonances in the attenuation zones. Among the possible tuning strategies of local resonators, it is shown that the mutual influence between elastic and electric parameters is able to produce a wider attenuation zone, bridging Bragg scattering bandgaps thanks to the effect of local resonators. The analytical findings of this paper are validated with numerical results in an example application. [ABSTRACT FROM AUTHOR]

Piezoelectric metamaterials with inductance shunt circuits connected to the transducers have attractive potential for guiding and attenuating elastic waves. However, it is challenging to evaluate their wave attenuation capability experimentally because the signals of transmitted waves within the bandgap have extremely small amplitudes and are submerged in noise. The present paper reports a method for revealing the wave attenuation features of a piezoelectric metamaterial beam by taking advantage of the physical correlation between the excitation and the transmitted and incident waves. Correlations between the excitation and the measured waves are calculated in real time to eliminate noise. It is demonstrated that wave attenuation features within the bandgap can be recovered from noise with an amplitude that is 69.1 dB larger than that of the transmitted wave. The transmission diagram is presented, and wave attenuation of up to −50.7 dB can be observed. Also, the correlation-based signal processing procedure is effective for illustrating the resistance-load-based wave attenuation behavior of the piezoelectric metamaterial beam. This method can be extended to the experimental analysis of many other types of metamaterials and phononic crystals. [ABSTRACT FROM AUTHOR]

Slow electrons (with energy below 10 eV) play an important role in nature and technology. For instance, they are believed to initiate solubility change in extreme ultraviolet resists. Depending on their mobility, such secondary electrons can lead to image blur and degradation of patterning resolution. Hence, it is important to characterize the transport of slow electrons by measuring parameters such as the effective attenuation length (EAL). We present a technique that allows for prompt characterization of EAL in polymer films. In this experiment, slow electrons are generated in a substrate upon absorption of x-ray photons. The attenuation of electron flux by a polymer film is measured as a function of film thickness, allowing for the determination of EAL for slow electrons. We illustrate this method with poly(hydroxy styrene) and poly(methyl metacrylate) films. Furthermore, we propose an improvement for this technique that would enable the measurement of EAL as a function of electron kinetic energy. [ABSTRACT FROM AUTHOR]

Stealth technology plays an important role in modern military conflicts, and because of its many practical advantages, plasma stealth technology has gained a lot of attention. In this paper, we describe our study of the reflection and absorption characteristics of waves propagating in multilayer plasma slabs. Our results show that positive effects on the attenuation can be obtained by optimizing the plasma parameters and by increasing the number of plasma layers. We also found that multilayer plasma slabs can effectively widen absorption bands, especially for low frequency bands. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new multi-resonator metamaterial (MRM) for attenuating impact stress waves. Theoretical analyses show that the MRM has wider bandgaps than those of a single-resonator metamaterial (SRM) and a dual-resonator metamaterial (DRM), and numerical studies are conducted to compare the performances of the MRM, SRM, and DRM in mitigating impact forces. The influences of the number of unit cells, the spring stiffnesses, and the resonator masses on the mitigation of impact force are analyzed by studying a one-dimensional impact wave model. In addition, the calculation results of a three-dimensional crash model clearly confirm the outstanding features of the MRM, which can provide a thin and light structure with a wider attenuation region of the frequency spectrum and a better mitigation effect of the impact force. [ABSTRACT FROM AUTHOR]

Ducts with membranes in their sidewalls have been used for noise control due to their remarkable ability to reflect sound waves at low frequencies. To obtain a broader attenuation band, combining several membranes is one possible way, which leads to yet another branch of engineering called phononic crystals or acoustic metamaterials. This study analyzes sound wave propagation and attenuation in a duct with periodic membranes embedded in its sidewalls. For each cell, an analytical, fully coupled vibro-acoustic model is proposed via energy formulation, and then the interference among multiple membrane cells is treated using the cell transfer matrix. Our study provides an efficient means to predict, and eventually optimize, the acoustic bandgap structure. Results from the current model fit well with those simulated using a two/three-dimensional finite element method. The 2D membrane with free lateral edges was found to perform almost as well as its 1D counterpart. Moreover, a better bandgap can be achieved via coupling of resonance and Bragg reflection. The effects of periodic distance and membrane tension force on the bandgap structure are then discussed and analyzed to determine their appropriate parameters. Some optimal designs are implemented through artificial disorder, which shows promising potential in attenuating bandwidth expansion compared with the original periodic configuration. [ABSTRACT FROM AUTHOR]

A Green function-based analytic solution of pressure diffusive wave motion is introduced for investigating the transient pressure response in fluid saturated matrix-fracture media. One-dimensional solutions are presented for a time-harmonically forced problem with internal damping and are used to analyze the propagation and attenuation of pressure pulse in a semi-infinite spatial domain. The concise form of the solutions simplifies the calculation of pressure diffusion with arbitrary forcing functions at fixed boundaries. It indicates that the periodically forced function with internal damping has remarkable effects on pressure diffusion-wave motions. It is found that the characteristic delay-frequency separates the pressure diffusion-wave domain into matrix-dominated, transition, and fracture-dominated zones. The Green functions could physically predict any transient response of pressure fluctuations due to hydro-fracturing in geological reservoirs given proper physical parameters. [ABSTRACT FROM AUTHOR]

Acoustic liners, consisting of a perforated panel affixed to a honeycomb core with a rigid back plate, are widely used for noise attenuation purpose. In this study, by exploiting inhomogeneous impedance properties, we report an experimental and numerical study on a liner-type acoustic metasurface, which possesses the functionality of both reflected wave manipulation and sound energy attenuation simultaneously. To realize the inhomogeneous acoustic impedance, an acoustic metasurface constructed by varying-depth acoustic liners is designed and fabricated. The reflected sound pressure fields induced by the metasurface are obtained in both experiments and simulations. A complete characterization of this metasurface is performed, including the effects of depth gradient, incident angle, and incident frequency. Anomalous reflection, apparent negative reflection, and conversion from an incident wave to a surface wave with strong energy dissipation are achieved by the structure. Moreover, our proposed structure can overcome the single frequency performance limitation that exists in conventional metasurfaces and performs well in a broadband frequency range. The proposed acoustic metasurface offers flexibility in controlling the direction of sound wave propagation with energy dissipation property and holds promise for various applications of noise reduction. [ABSTRACT FROM AUTHOR]

In this paper, we propose a general design concept for acoustic metamaterials that introduces a ubiquitous synergetic behavior into the design procedure, in which the structure of the design is driven by its functional requirements. Since the physical properties of the widely used, resonanttype metamaterials are mainly determined by the eigenmodes of the structure, we first introduce the design concept through the modal displacement distributions on two typical plate-type structures. Next, by employing broadband sound attenuations that involve both the insulation and absorption as the typical targets, two synergetic coupling behaviors are systematically revealed among the dense resonant modes and multi-cell. Furthermore, through plate-type multiple-cell structures assembled from nine oscillators, the design is shown to realize strong broadband attenuations with either the average sound transmission loss (STL) below 2000 Hz higher than 40 dB or the absorption approximately 0.99 in the range of 400-700 Hz wherein the average absorption below 800 Hz remains higher than 0.8. Finally, two multi-cell plate-type samples are fabricated and then used experimentally to measure the STLs in support of the proposed synergetic coupling design method. Both the computational and experimental results demonstrate that the proposed synergetic design concept could effectively initiate a design for metamaterials that offer a new degree of freedom for broadband sound attenuations. [ABSTRACT FROM AUTHOR]

The spin-Hall effect induced modification of the attenuation of propagating exchange-mode spin waves (SWs) is studied micromagnetically and analytically in heavy-metal/ferromagnet bilayers. Micromagnetic simulations of spin-wave propagation in Pt/NiFe show that at a relatively low current density of ~6×1011 A/m2, Gilbert damping is exactly balanced by the spin-Hall torque and long-distance SW transmission is possible. An analytical model is developed to explain the micromagnetic results and relate the current density to the characteristic attenuation length. The results suggest that the spin Hall effect can be used as an effective means to control the attenuation length of propagating spin waves in nanostructures. [ABSTRACT FROM AUTHOR]

A new analytical technique, time-of-flight prompt gamma-ray analysis, has been developed at the Japan Proton Accelerator Research Complex. In order to apply it to accurate elemental analysis, a set of Fe and Au reference samples were measured to examine the several factors which affect the number of detected events. It was found that major contributing factors included attenuations of neutrons and gamma rays in the sample, live-time fraction and signal pile-up correction. A simulation model was built for the estimation of neutron and gamma-ray attenuations. A simple empirical formula was proposed to calculate the signal pile-up correction factor. The whole correction method has proven to be accurate and reliable. [ABSTRACT FROM AUTHOR]

In this paper, we design a low-reflection coaxial tunable attenuator with a maximum attenuation of -50 dB by use of zero refractive index metamaterial. Almost no reflection is observed from input port of the proposed structure, due to the easily accessible impedance matching derived from the use of zero refractive index metamaterial. The relationship between attenuation and the air gap width can be well described by an equivalent circuit model. Interestingly, the ratio of input to output voltage is linearly related to the gap width due to the eliminated fringing capacitance by zero-refraction metamaterial, which makes it easy to achieve accurate calibration of the proposed attenuator. The low reflection and linear relationships enable the proposed attenuator to hold promising potential for practical applications. [ABSTRACT FROM AUTHOR]

Verification of future warhead-dismantlement treaties will require detection of certain warhead attributes without the disclosure of sensitive design information, and this presents an unusual measurement challenge. Neutron spectroscopy—commonly eschewed as an ill-posed inverse problem—may hold special advantages for warhead verification by virtue of its insensitivity to certain neutron-source parameters like plutonium isotopics. In this article, we investigate the usefulness of unfolded neutron spectra obtained from organic-scintillator data for verifying a particular treaty-relevant warhead attribute: the presence of high-explosive and neutron-reflecting materials. Toward this end, several improvements on current unfolding capabilities are demonstrated: deuterated detectors are shown to have superior response-matrix condition to that of standard hydrogen-base scintintillators; a novel data-discretization scheme is proposed which removes important detector nonlinearities; and a technique is described for re-parameterizing the unfolding problem in order to constrain the parameter space of solutions sought, sidestepping the inverse problem altogether. These improvements are demonstrated with trial measurements and verified using accelerator-based time-of-flight calculation of reference spectra. Then, a demonstration is presented in which the elemental compositions of low-Z neutron-attenuating materials are estimated to within 10%. These techniques could have direct application in verifying the presence of high-explosive materials in a neutron-emitting test item, as well as other for treaty verification challenges. [ABSTRACT FROM AUTHOR]

A methodology is worked out to retrieve the numerical values of all the main parameters of the six-dimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from the ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propagation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60K for the wave propagating along the [110] direction, for both the longitudinal and the shear modes, the latter with two polarizations along the [001] and [1̄10] axes, respectively. We show that these anomalies are due to the ultrasound relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the experimental findings is based on the T2g ⊗ (eg + t2g) JTE problem including the linear and the quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis, we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states. To our knowledge, such a based-on-experimental-data numerical reconstruction of the APES of a JTE problem in the five-dimensional space of all active tetragonal and trigonal displacements has not been reported before. [ABSTRACT FROM AUTHOR]

A mechanism has been established for pressure diffusion waves in dual-porosity media. Pressure diffusion waves are heavily damped with relatively low velocities and short wavelengths. The characteristic frequency dominates the attenuation behavior of pressure diffusions and separates wave fields into two asymptotic regimes: relaxed and unrelaxed. Characteristic delay times control the pressure diffusion between the matrix and the fractures. The transition zones in wavelength and attenuation peak shift toward high frequencies when the characteristic delay time decreases. In contrast, the transition zones in both phase and group velocity shift toward low frequencies as the characteristic time of the delay increases. In a spatially dependent diffusivity field, the pressure diffusion waves in dual-porosity media obey an accumulation-depletion law. [ABSTRACT FROM AUTHOR]

A pyrotechnic system consisting of donor/acceptor pair separated by a gap relies on shock attenuation characteristics of the gap material and shock sensitivity of the donor and the acceptor charges. Despite of its common use, a numerical study of such a pyrotechnic train configuration is seldom reported because proper modeling of the full process requires precise capturing of the shock wave attenuation in the gap prior to triggering a full detonation of a high explosive and accurate description of the high strain rate dynamics of the explosively loaded inert confinements. We apply a hybrid particle level-set based multimaterial hydrocode with reactive flow models for pentolite donor and heavily aluminized cyclotrimethylene-trinitramine as the acceptor charge. The complex shock interaction, a critical gap thickness, an acoustic impedance, and go/no-go characteristics of the pyrotechnic system are quantitatively investigated. [ABSTRACT FROM AUTHOR]

An original approach for designing a one dimensional phononic crystal strip with an ultra-wide band gap is presented. The strip consists of periodic pillars erected on a tailored beam, enabling the generation of a band gap that is due to both Bragg scattering and local resonances. The optimized combination of both effects results in the lowering and the widening of the main band gap, ultimately leading to a gap-to-midgap ratio of 138%. The design method used to improve the band gap width is based on the flattening of phononic bands and relies on the study of the modal energy distribution within the unit cell. The computed transmission through a finite number of periods corroborates the dispersion diagram. The strong attenuation, in excess of 150 dB for only five periods, highlights the interest of such ultra-wide band gap phononic crystal strips. [ABSTRACT FROM AUTHOR]

An aerocraft with the surface, inlet and radome covered large-area inductive coupled plasma (ICP) can attenuate its radar echo effectively. The shape, thickness, and electron density (Ne) distribution of ICP are critical to electromagnetic wave attenuation. In the paper, an air all-quartz ICP generator in size of 20 x 20 x 7 cm³ without magnetic confinement is designed. The discharge results show that the ICP is amorphous in E-mode and ring-shaped in H-mode. The structure of ICP stratifies into core region and edge halo in H-mode, and its width and thickness changes from power and pressure. Such phenomena are explained by the distribution of RF magnetic field, the diffusion of negative ions plasma and the variation of skin depth. In addition, the theoretical analysis shows that the Ne achieves nearly uniform within the electronegative core and sharply steepens in the edge. The Ne of core region is diagnosed by microwave interferometer under varied conditions (pressure in range of 10-50 Pa, power in 300-700 W). Furthermore, the electromagnetic wave attenuation measurements were carried out with the air ICP in the frequencies of 4-5 GHz. The results show that the interspaced ICP is still effective to wave attenuation, and the wave attenuation increases with the power and pressure. The measured attenuation is approximately in accordance with the calculation data of finite-different time-domain simulations. [ABSTRACT FROM AUTHOR]

We demonstrate that the phenomenon of slow sound propagation associated with its inherent dissipation (dispersion + attenuation) can be efficiently used to design sound absorbing metamaterials. The dispersion relation of the wave propagating in narrow waveguides on one side of which quarter-wavelength resonators are plugged with a square lattice, whose periodicity is smaller than the wavelength, is analyzed. The thermal and viscous losses are accounted for in the modeling. We show that this structure slows down the sound below the bandgap associated with the resonance of quarter-wavelength resonators and dissipates energy. After deriving the effective parameters of both such a narrow waveguide and a periodic arrangement of them, we show that the combination of slow sound together with the dissipation can be efficiently used to design a sound absorbing metamaterial which totally absorbs sound for wavelength much larger than four times the thickness structure. This last claim is supported by experimental results. [ABSTRACT FROM AUTHOR]

Attenuation of short stress pulses under different levels of precompression was investigated in a one-dimensional strongly nonlinear discrete metamaterial assembled using alternating steel disks and toroidal Nitrile O-rings. The results were compared with the numerical modeling. A double power-law is used to describe the nonlinear interaction between the disks due to the compression of rubber O-rings. The dispersion behavior caused by the periodic arrangement of elements is contributing to the attenuation of pulse, but could not explain the experimental observations. It was explained by taking into account the nonlinear viscous behavior of O-rings. The numerical simulations were able to predict the dependence of the signal speed on the precompression force, a significant decrease of the pulse width with the precompression and the attenuation of the leading positive pulse, the latter of major significance in the protection against impact. This strongly nonlinear dissipative metamaterial has a potential for attenuation of dynamic loading and allows an enhanced tunability of signal speed and degree of attenuation. [ABSTRACT FROM AUTHOR]

Silver nanoparticles were produced by nanosecond pulsed-laser ablation at 1064 nm of Ag in pure water. These experiments were performed using an alternative ablation cell design where a cylindrical shaped Ag target was horizontally irradiated, while the liquid was stirred by a stir rod coaxially arranged to the target. The repeatability of the generated colloids properties (extinction and size distribution) is assessed by statistical tools. The colloids properties prepared under stationary liquid are found to be unpredictable, while they are highly repeatable at high stirring speed. At the same time, electronic microscopy examinations of the irradiated Ag targets revealed that the width of the laser-machined grooves exponentially decays in stationary liquid and almost linearly under high stirring speed as the ablation proceeds. In the latter case, the decay rate was found to be constant from one experiment to the other, while it was not repeatable stationary liquid. We show that the decay of the groove width is due to an attenuation of the laser energy reaching the target surface due to the formation of a more or less dense NPs layer in front of the target as the ablation proceeds. Using the ablation time-dependence of the groove width, we can quantify the attenuation factor of the laser energy with exposure time. Finally, the relationship between the laser energy attenuation, stirring speed, and repeatability of the colloids properties is interpreted and discussed in terms of mass transfer. [ABSTRACT FROM AUTHOR]

Waves in magnetic systems often show nonreciprocal propagation, where the properties of a wave depends on whether it is travelling in a forward or reversed direction. This fundamental property is used in devices such as isolators, which often use a transverse electric (TE) polarized wave. In this paper, we study propagation of electromagnetic waves in small microstrip waveguides where the wave propagates at an arbitrary angle with respect to the magnetization direction. The angle allows mixtures of TE and transverse magnetic (TM) modes. This has distinct benefits, allowing the nonreciprocity typically found in TE modes, but also allowing propagation of low frequency TM modes, which do not have a cut-off frequency. Our calculations, using Barium hexaferrite as the magnetic material, show significant nonreciprocity and isolation are possible. Differences in attenuation above 75 dB/cm are found for these mixed-polarization waves for propagation angles of about 40°. We study nonreciprocal propagation as a function of propagation angle and other material parameters for both primarily TM and primarily TE modes. [ABSTRACT FROM AUTHOR]

Current radiographic methods are limited in their ability to determine the presence of nuclear materials in containers or composite objects. A central problem is the inability to distinguish the attenuation pattern of high-density metals from those with a greater thickness of a less dense material. Here, we show that spectrally sensitive detectors can be used to discriminate plutonium from multiple layers of other materials using a single-view radiograph. An inverse algorithm with adaptive regularization is used. The algorithm can determine the presence of plutonium in simulated radiographs with a mass resolution per unit area of at least 0.07 g cm-2. [ABSTRACT FROM AUTHOR]

We present an acoustic study of relaxor ferroelectrics with magnetic ordering PbFexB1-xO3 (B = Nb, Ta, W) in the wide temperature range from 100 to 750K as well as relaxor PbMg1/3Nb2/3O3 at temperatures from 300 to 750 K. The longitudinal and transverse acoustic wave velocity and attenuation have been measured by the ultrasonic pulse-echo technique at frequencies of 5 and 10MHz. The strong anomalies observed in the longitudinal sound velocity and attenuation versus temperature are correlated with a temperature range of the coexistence of relaxor ferroelectric and antiferromagnetic states. Attenuation peaks have been observed at distinctive temperatures for relaxors, i.e., at TB (Burns temperature) and T* (an additional distinctive temperature). Fluctuations of the polar nanoregion boundaries are considered as the source of the acoustic anomalies. [ABSTRACT FROM AUTHOR]

The attenuation and the absorption of silver halide crystal and fibers in the mid-IR were measured. The absorption coefficients of silver halide crystals, deformed crystals, and fibers were measured by laser calorimetry at several different wavelengths in the near-IR and the mid-IR. The absorption coefficients of the fibers were higher than those of the deformed crystals and these were higher than those of the un-deformed crystals. We suggest that the absorption behavior is best described by a weak absorption tail. The total attenuation in fibers was measured using the cut back method. The scattering values were calculated by subtracting the absorption coefficients from the total attenuation coefficients. The scattering in the silver halide fibers was ascribed to pores of estimated size of 0.7 µm. We showed that the main contribution to the attenuation of fibers in the mid-IR range was due to scattering and suggested that reducing the scattering will dramatically improve the transmission of silver halide fibers in the mid-IR. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a bidirectional optical switch based on electrowetting. Four rectangular polymethyl methacrylate substrates are stacked to form the device and three ITO electrodes are fabricated on the bottom substrate. A black liquid droplet is placed on the middle of the ITO electrode and surrounded by silicone oil. When we apply a voltage to one ITO electrode, the droplet stretches and moves in one direction and a light beam is covered by the stretched droplet, while the droplet yields a space to let the original blocked light pass through. Due to the shift of the droplet, our device functions as a bidirectional optical switch. Our experiment shows that the device can obtain a wide optical attenuation from ∼1 dB to 30 dB and the transmission loss is ∼0.67 dB. The response time of the device is ∼177 ms. The proposed optical switch has potential applications in variable optical attenuators, electronic displays, and light shutters. [ABSTRACT FROM AUTHOR]

The work considers the depth evaluation of ground penetrating radar (GPR) surveys using the attenuation factor of electromagnetic radiation in a medium. A method of determining the attenuation factor of low-conductive non-magnetic soils is developed based on the results of direct measurements of permittivity and conductivity of soils in the range of typical frequencies of GPR. The method relies on measuring the shift and width of the resonance line after a soil sample is being placed into a tunable cavity resonator. The advantage of this method is the preservation of soil structure during the measurement. [ABSTRACT FROM AUTHOR]

Oncogenesis and metastasis of tumor are difficult to detect during the clinic therapy. To explore the optical properties of tumorigenesis and metastasis in nasopharyngeal carcinoma (NPC), we assessed the NPC cell lines 5-8F and 6-10B by optical coherence tomography (OCT): first, the OCT images of the two different types of cell pellets were captured. Second, by fitting Beer's law to the averaged A-scans in these OCT datasets, the attenuation coefficients (μt) of the cells were extracted. The median attenuation coefficients (interquartile range (IQR)) of 5-8F and 6-10B were 6.79 mm-1 (IQR 6.52 to 7.23 mm-1) versus 8.06 mm-1 (IQR 7.65 to 8.40 mm-1), respectively (p < 0.01, df = 39). Subsequently, the results were compared with those obtained by polarization sensitive OCT, which further confirmed that the quantitative OCT analysis (by μt) could differentiate the oncogenesis and metastasis NPC cell lines in real time non-invasively. [ABSTRACT FROM AUTHOR]

Acoustic streaming of ink particles inside a water microdroplet generated by a surface acoustic wave (SAW) has been studied numerically using a finite volume numerical method and these results have been verified using experimental measurements. Effects of SAW excitation frequency, droplet volume, and radio-frequency (RF) power are investigated, and it has been shown that SAW excitation frequency influences the SAW attenuation length, lSAW, and hence the acoustic energy absorbed by liquid. It has also been observed that an increase of excitation frequency generally enhances the SAW streaming behavior. However, when the frequency exceeds a critical value that depends on the RF power applied to the SAW device, weaker acoustic streaming is observed resulting in less effective acoustic mixing inside the droplet. This critical value is characterised by a dimensionless ratio of droplet radius to SAW attenuation length, i.e., Rd/lSAW. With a mean value of Rd/lSAW ≈ 1, a fast and efficient mixing can be induced, even at the lowest RF power of 0.05 mW studied in this paper. On the other hand, for the Rd/lSAW ratios much larger than ∼1, significant decreases in streaming velocities were observed, resulting in a transition from regular (strong) to irregular (weak) mixing/flow. This is attributed to an increased absorption rate of acoustic wave energy that leaks into the liquid, resulting in a reduction of the acoustic energy radiated away from the SAW interaction region towards the droplet free surface. It has been demonstrated in this study that a fast and efficient mixing process with a smaller RF power could be achieved if the ratio of Rd/lSAW ≤ 1 in the SAW-droplet based microfluidics. [ABSTRACT FROM AUTHOR]

One of the outstanding challenges in phononic crystals and acoustic metamaterials development is the ability to tune their performance without requiring structural modifications. We report on the experimental demonstration of a tunable acoustic waveguide implemented within a two-dimensional phononic plate. The waveguide is equipped with a periodic array of piezoelectric transducers which are shunted through passive inductive circuits. The resonance characteristics of the shunts lead to strong attenuation and to negative group velocities at frequencies defined by the circuits' inductance. The proposed waveguide illustrates the concept of a controllable acoustic logic port or of an acoustic metamaterial with tunable dispersion characteristics. [ABSTRACT FROM AUTHOR]

We studied thermal fluctuations in magnetoresistance (MR) signals originating from geometrically confined magnetic walls (GCMWs) of nanometer size. To this end, we developed a novel numerical simulation method which quantitatively evaluates the magnitude of thermal fluctuations in MR signals of magnetic nanostructures. Using the method, we first investigated the case when the twist angle Θ between the magnetization in a fixed layer and that in a free layer is 180°. We found that the thermal fluctuations of the magnetic structure of the 180° GCMW do not induce any crucial fluctuations in the MR signal because there is no significant difference among the MR values of the magnetic structures caused by the thermal fluctuations. We next investigated the dependence on the twist angle Θ of thermal fluctuations in MR signals. Since the GCMW is stabilized by decreasing Θ from 180°, the standard deviation (SD) of the MR signal is reduced with decreasing Θ. On the contrary, the SD/M ratio (M is the mean of the MR signal) monotonically increases with decreasing Θ because the attenuation of the mean value of MR is faster than that of the standard deviation. We also found that the SD/M ratio was not large for any of the temperatures (from 300 to 600 K) and twist angles (from 90° to 180°) we examined. The maximum value of the ratio, which was obtained when T = 600 K and Θ = 90°, was about 13%. This result indicates that thermal fluctuations do not cause significant noise in MR devices that utilize GCMWs of nanometer size. [ABSTRACT FROM AUTHOR]

The results of the studies of the propagation of plane harmonic waves and vibrations in an isotropic, elastic solid layer with atomic point defects (interstitial atoms, vacancies, and electron-hole pairs) generated by a pulsed laser beam are presented. The study is based on coupled evolution equations for the elastic displacement of the medium and atomic defect density fields. The defect dynamics are governed by the strain-stimulated generation, diffusion, and annihilation processes. The frequency equations corresponding to the symmetric and antisymmetric elastic-concentration modes of vibration of the layer are obtained. Some limiting cases and special cases of the frequency equations are considered and a procedure for determining the phase velocity and the attenuation (or amplification) constants is discussed. [ABSTRACT FROM AUTHOR]

Spinel ferrite flakes Ni0.97-xZnxCo0.03Fe2O4 with x=0.5 and 0.65 are prepared for use as fillers in electromagnetic composites. The composites with the flaky fillers exhibit greatly enhanced high-frequency and attenuation properties. The complex permeability, μ0′ and μmax″, is enhanced by about 500%-700%, and the relative attenuation bandwidth WR is increased by 300%-440%, as compared to those for composites with conventional spherical fillers. WR achieves 90% of the theoretically maximum relative bandwidth. The composites with the spinel ferrite flaky fillers are powerful and potential candidates as electromagnetic attenuation materials with ultrabroad bandwidth at microwave L, S, and C bands. [ABSTRACT FROM AUTHOR]

The total cross section has been measured for the electron induced dissociation of trimethyl (methylcyclopentadienyl) platinum (IV) [MeCpPt(IV)Me3], a Pt precursor often used in focused electron beam induced processing (FEBIP), for incident electron energies ranging between 3–3 keV. Measurements were performed for the precursor in the adsorbed state under ultrahigh vacuum conditions. The techniques used in this study were temperature programmed desorption, x-ray photoelectron spectroscopy and mass spectrometry. Two surfaces were used in these experiments, amorphous carbon overlayers containing embedded Pt atoms (a:C-Pt), formed by the electron decomposition of the Pt precursor, and atomically clean Au. The results from these three experiments revealed a comparatively low total cross section at 8 eV (4.2±0.3×10-17 cm2 on the a:C-Pt and 1.4±0.1×10-17 cm2 on the Au) that increases with increasing incident electron energy, reaching a maximum at around 150 eV (4.1±0.5×10-16 cm2 on the a:C-Pt and 2.3±0.2×10-16 cm2 on the clean Au), before decreasing at higher incident electron energies, up to 3000 eV. Differences in the measured cross sections between Au and a:C-Pt surfaces demonstrate that the substrate can influence the reaction cross section of adsorbed species. Temperature programmed desorption was also used to measure the adsorption energy of MeCpPt(IV)Me3, which was found to depend on both the substrate and the adsorbate coverage. The work in this paper demonstrates that surface science techniques can be used to quantitatively determine the total cross section of adsorbed FEBIP precursors for electron induced dissociation as a function of incident electron energy. These total cross section values are necessary to obtain quantitatively accurate information from FEBIP models and to compare the reaction efficiencies of different precursors on a quantitative basis. [ABSTRACT FROM AUTHOR]

Thin polycrystalline aluminum (1050 and 6061-T6 alloys) samples were shocked to 4 GPa to examine elastic wave attenuation not observed in thicker samples (1–10 mm). Using laser interferometry in plate impact experiments, particle velocity histories were obtained for 0.08–1 mm thick samples, thinned from bulk material. Unlike past work on thicker samples, thin 1050 Al samples reveal large and rapidly attenuating elastic wave amplitudes, indicating a time-dependent elastic-plastic response. Extrapolation of measured elastic wave amplitudes to larger sample thicknesses agrees well with previously observed amplitudes for thicker 1050 and 1060 Al samples. Thus, all of the results for relatively pure polycrystalline Al can be reconciled into a single consistent picture: elastic wave attenuation, due to time-dependent elastic-plastic response, is confined to material close to the impact surface. In contrast to the 1050 Al results, thin 6061-T6 Al samples reveal an elastic wave amplitude of ∼0.7 GPa with no attenuation, in quantitative agreement with previous results for thick 6061-T6 Al samples. The lack of elastic wave attenuation even in thin samples suggests that elastic wave amplitudes in shocked 6061-T6 Al are governed by different plastic deformation mechanisms than those for shocked pure Al. [ABSTRACT FROM AUTHOR]

Solution processed n-channel organic field-effect transistors based on [6,6]-phenyl C61 butyric acid methyl ester with high mobility and low contact resistance are reported. Ca, Au, or Ca capped with Au (Ca/Au) was used as the top source/drain electrodes. The devices with Ca electrodes exhibit excellent n-channel behavior with electron mobility values of 0.12 cm2/V s, low threshold voltages (∼2.2 V), high current on/off ratios (105–106) and subthreshold slopes of 0.7 V/decade. By varying the channel lengths (25–200 μm) in devices with different metal/semiconductor interfaces, the effect of channel length scaling on mobility is studied and the contact resistance is extracted. The width-normalized contact resistance (RCW) for Au (12 kΩ cm) is high in comparison to Ca (7.2 kΩ cm) or Ca/Au (7.5 kΩ cm) electrodes at low gate voltage (VGS=10 V). However, in the strong accumulation regime at high gate voltage (VGS=30 V), its value is nearly independent of the choice of metal electrodes and in a range of 2.2–2.6 kΩ cm. These devices show stable electrical behavior under multiple scans and low threshold voltage instability under electrical bias stress (VDS=VGS=30 V, 1 h) in N2 atmosphere. [ABSTRACT FROM AUTHOR]

Porous Fe3O4/Fe/SiO2 core/shell nanorods were fabricated, in which the diameter of the pores was 5–30 nm. The magnetic and electromagnetic properties were investigated. The temperature dependent magnetic measurements showed that these nanorods were ferromagnetic with a Verwey temperature of 129 K. The electromagnetic data indicated that effective complementarities between the dielectric loss and the magnetic loss were realized, suggesting that they have excellent electromagnetic wave absorption properties. Thus the porous core/shell nanorods could be used as a kind of candidate absorber. [ABSTRACT FROM AUTHOR]

The properties of prismatic dislocation loops, generated by radiation in metals, have remained elusive for decades, and recent advances in computational capabilities as well as transmission electron microscopy have renewed interest in their study. Acoustic and elastic waves could become an interesting, nonintrusive, probe to this end, as they have for other dislocation configurations. What then are the characteristics of elastic wave scattering that would be sensitive to a prismatic loop signature? In this paper, we report the scattering cross section for an elastic wave by a prismatic dislocation loop. It differs in significant ways from the analog quantity in the case of pinned dislocation segments, the most significant being the polarization of the scattered wave. The properties of a coherent wave traveling through an elastic medium filled with randomly placed and randomly oriented such loops are also reported. At long wavelengths, the effective wave velocity and attenuation coefficients resemble those for a similar case with pinned dislocation segments. [ABSTRACT FROM AUTHOR]

A perfect matching chart is designed to obtain the matching frequency fm and the matching thickness tm of electromagnetic (EM) attenuation material. Based on the chart, the relationship between matching parameters (fm and tm) and high-frequency dynamic parameters [μ′(f), μ″(f), and ε′(f)] are studied for Ni0.97-xZnxCo0.03Fe2O4 (NiZnCo) spinel ferrites with x=0.5 and 0.65. At tm, the spinel ferrites exhibit excellent EM attenuation characteristics with low reflectivity and broad bandwidth at very high frequency and ultrahigh frequency bands. [ABSTRACT FROM AUTHOR]

Attenuation of the x rays and ¿ rays in the 22Ti, 41Nb, 69Tm, 70Yb, and 71Lu elements have been measured with special emphasis for the x ray energies (Ein) in lower vicinity of the K shell ionization threshold (BK) of the element. The incident photon beam is obtained from decay of the 55Fe, 241Am, and 57Co radioisotopes, and fluorescence of the 23V, 70Yb, 71Lu, 74W, 76Os, and 90Th targets excited by the x rays and ¿ rays from the radioisotopes. The measurements were performed using energy dispersive setups involving Ge detectors. The measured attenuation coefficients agree with the available theoretical values except at the photon energies with (BK-Ein) less than or nearly equal to the K-shell width (¿K), where significant positive deviations as large as factor of 2 have been observed. In view of reliability of the available theoretical cross sections for the photoionization and the photon scattering processes, the magnitude of positive alteration at the photon energy in lower vicinity of the ionization threshold is attributed to the K shell resonant Raman scattering (RRS) process and the corresponding cross sections have been deduced. Possible matrix effects in the energy dispersive x ray spectrometry due to RRS are also discussed. [ABSTRACT FROM AUTHOR]

The attenuation (ATT) of hydrogen plasma in carbon nanotubes, grown by iron-catalyzed high-pressure carbon monoxide disproportionate process, is investigated. The effects of the incident wave, the electron density, the collision frequency, the thermal frequency, and the cyclotron frequency on the ATT of the microwave are discussed. Moreover, the impacts of thermal frequency and cyclotron frequency on the ATT are investigated separately. Numerical results indicate that position of the ATT peak and the ATT level depend on the incident frequency, the electron density, the collision frequency, the thermal frequency, and the cyclotron frequency. The results show that the cyclotron frequency highly influences the ATT level. In contrast, the shift frequency is more affected by the thermal frequency. The ATT is more sensitive at the middle band of incident frequency. [ABSTRACT FROM AUTHOR]

A model is developed for a parallel-plate waveguide formed by graphene. The graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula. Maxwell’s equations are solved for the model fields guided by the graphene layers. It is shown that despite the extreme thinness of its walls, a graphene parallel-plate waveguide can guide quasi-transverse electromagnetic modes with attenuation similar to structures composed of metals, while providing some control over propagation characteristics via the charge density or chemical potential. Given the interest in developing graphene electronics, such waveguides may be of interest in future applications. [ABSTRACT FROM AUTHOR]

The characterization of bounded roughened surfaces before applying adhesive joint, in order to detect poor cohesive and adhesive properties, remains difficult. Earlier studies based on analysis of surface wave (Rayleigh waves or Scholte waves) are not really adapted to the characterization of such surfaces. Guided acoustic waves, i.e., Lamb waves, turn out to be the best adapted kind of waves to characterize this roughness when plates are bounded together. It is the aim of this paper to provide analytical and experimental approaches to analyze the behavior of Lamb waves propagating inside plates with a rough surface (small perturbations). First, experimental results of the attenuation effects are given on roughened glass plates. Second, the attenuation factor of the Lamb wave in an anisotropic rough solid plate is calculated through a complex analytical model of the dispersion equation which accounts for the effect of the power spectrum density of the rough profile (including the effect of the statistical roughness parameters). [ABSTRACT FROM AUTHOR]

This paper aims at providing analytical and numerical approaches to analyze the behavior of guided waves (Lamb-type waves) propagating inside plates with a rough surface considered here as distributed small perturbations. A physical interpretation of the attenuation phenomenon of the propagating mode generated by the source (mode coupling) is provided for an ideal rough plate (fluid plate) using an analytical model available in the literature. This analytical model is validated using a numerical method. The obtained results on periodically corrugated surfaces of fluid plates emphasize the role played by the spatial period and the modal coupling. They serve also as results for interpreting the effect due to randomly rough surfaces in solid plates, notably the effect of the power spectrum density of the rough profile (including the effect of the statistical roughness parameters mentioned in Part I). The results obtained experimentally and theoretically, for the attenuation factor of the main Lamb wave, are found close to one another. [ABSTRACT FROM AUTHOR]

This effort investigates surface-preparation methods to enhance dynamic surface-property measurements of shocked metal surfaces. To assess the ability of making reliable and consistent dynamic surface-property measurements, the amount of material ejected from the free surface upon shock release to vacuum (ejecta) was monitored for shocked Al-1100 and Sn targets. Four surface-preparation methods were considered: Fly-cut machine finish, diamond-turned machine finish, polished finish, and ball rolled. The samples were shock loaded by in-contact detonation of HE PBX-9501 on the front side of the metal coupons. Ejecta production at the back side or free side of the metal coupons was monitored using piezoelectric pins, optical shadowgraphy, and x-ray attenuation radiography. [ABSTRACT FROM AUTHOR]

A method for the determination of acoustic impedance, time of flight, and attenuation of an immersed thin linear-viscoelastic layer on a substrate of infinite extent is proposed as the transfer functions of the normally incident ultrasonic reflected signals are given. Utilizing the derived analytical expressions related to the measured data, three parameters can be determined without considering the acoustic impedance of the substrate and giving the initial guesses and the corresponding convergence zones. The measurement relations between the layer properties and the three parameters are theoretically derived. The method stability against the experimental noises is numerically investigated. [ABSTRACT FROM AUTHOR]

In laser shock processing, overlays are used to enhance peak pressures and prolong pulse widths of laser shock waves. The overlay usually has three types: rigid, flexible, and liquid overlays. In this paper, some mathematical models are constructed to analyze the process of laser-induced shock waves and pressure attenuations of the shock waves. The analyses indicate that the peak pressure of shock waves depends on the deformation amount of the overlays and the pressure attenuations depend on the deformation speed of the overlays, while the deformation amount and deformation speed are determined by the density and thickness of the overlays. Besides, for the rigid overlay, the elastic modulus must be taken into account in addition to its density and thickness. Furthermore, the reflected waves from the overlays enhance the shocking effects of laser-induced shock waves. Therefore, the rigid overlays are superior to the flexible and liquid overlays. [ABSTRACT FROM AUTHOR]

A kind of fiber-optic modulation-depth-tunable modulator is developed in this paper. In this modulator, a magnetic fluid is used as the cladding of the drawn fiber, which attenuates the evanescent field when the light is guided in the fiber. Because the attenuation depends on the strength of the applied external magnetic field, the emergent light intensity from the fiber is modulated with the change of the magnetic field strength. The response times, i.e., the span for the light intensity to reach the final steady value from the time when the magnetic field is turned on or off, are evaluated quantitatively. [ABSTRACT FROM AUTHOR]

Thin V2O3 films were deposited on a piezoelectric substrate by electron-beam evaporation. Surface acoustic waves were generated by interdigital transducers. The attenuation and sound velocity were investigated from 260 to 10 K, providing an insight into the temperature-dependent electrical, dielectrical, and elastic properties of V2O3 at the metal-to-insulator transition. [ABSTRACT FROM AUTHOR]

Using surface acoustic wave (SAW) to drive droplets on a piezoelectric chip is a distinctive microfluidic technique developed recently. In the previous research, uniform interdigital transducers (IDTs) were used to radiate SAW amplitude and move the droplets within the same delay line simultaneously. In this paper, we employ slanted finger interdigital transducers (SFITs) to replace uniform IDTs. The merit is that we can move individual droplets at will by varying the frequency. This is because SAW amplitude profile actuated by a SFIT is not uniform along the aperture. The position of the maximum amplitude can be changed by adjusting the input frequency. In addition, we apply the coupling-of-modes model to simulate the amplitude profile and the frequency response of SFITs. Since the transmitted SAW intensity is strongly attenuated by the liquid when SAW hits the droplet, we can use the measured frequency response to detect the position of the droplet and verify the validity of the proposed method; we fabricated a SFIT on an Y128X-LiNbO3 substrate coated with hydrophobic film. The experimental results show good agreement with those predicted by the simulations. We note that the proposed method can further be used to construct a multichannel microfluidic chip. [ABSTRACT FROM AUTHOR]