Propagation Characteristics Of Surface Waves Research Articles

Laser ultrasonic inspection for mechanical properties of materials at high temperature

The measurement of mechanical properties of high-temperature resistant materials at high temperatures is particularly critical, and laser ultrasonic non-destructive testing technology is a prospective approach for measuring mechanical properties in high-temperature environments. Laser ultrasonic propagation models are constructed by finite element analysis, which reveals the effects of different excitation mechanisms on acoustic velocity measurements. It is found that the shear wave in the main propagation direction is hardly detected, and the distinction between shear waves and surface waves in the time domain signal is difficult. Based on the conclusions, the relationships between surface waves, longitudinal waves, and mechanical properties of materials are established by theoretical derivation. According to the propagation characteristics of surface waves and longitudinal waves, the eccentricity detection scheme of the same side and the concentricity detection scheme of the opposite side are, respectively, designed. The velocities of surface waves and longitudinal waves are measured, considering the thermal expansion coefficient and density changes with temperature. The mechanical properties of materials at different temperatures (25–1000 °C) are successfully calculated, and the experimental results are well in accordance with the reference values. It gives a reliable basis for efficient measurement of mechanical properties of materials at high temperatures.

Efficient Recursive Convolution Schemes for the Accurate FDTD Modeling of Graphene Interband Contribution via Complex Conjugate Pairs

The accurate time-domain numerical modeling of graphene surface conductivity due to the interband contribution is presented in this paper. Initially, the lower frequency limit for the interband conductivity inclusion is studied, highlighting that even in the far-infrared regime it should not be ignored. Then, a precise vector-fitting technique is utilized to decompose the analytical conductivity function into complex conjugate pairs. Every pair is connected to a complex surface current, while the frequency dispersion is evaluated via a proper recursive convolution scheme. Finally, a straightforward algebraic manipulation is conducted to eliminate the complex terms from the update equations of the electromagnetic components, concerning the finite-difference time-domain (FDTD) algorithm. The precision and efficiency of the proposed methodology are thoroughly validated by comparing the numerically extracted surface wave propagation characteristics to those obtained in terms of analytical expressions.

Complex Mode Dispersion Characteristics of Dielectric Loaded Radially Thick Helix

In this article, a generalized analytical and computational numerical theory, for both the guided and leaky modes, has been developed to investigate the dispersive behavior of dielectric-loaded radially thick helix (DLRTH). The complex root finding Muller iterative algorithm is used to compute the normalized phase and attenuation constants. A unique way has been adopted for the classification of HE and EH hybrid modes present in the proposed structure, and based on that, for the first time, we report that this structure shows physical leaky and trapped surface wave propagation characteristics. Furthermore, in the guided mode, it is seen that both slow wave (SW) and backward wave (BW) exist due to the inherently skewed boundary of the helical geometry. The parametric study of helix radius and pitch angle as well as dielectric constant gives optimized parameter values, which help in designing the proposed structure in the desired mode and at the desired frequencies. Moreover, it is reported that pitch angle aids in controlling and figuring out the leaky mode bandwidth. The analytical cum numerical MATLAB results are successfully verified using CST Microwave Studio computational analysis and are found to be in good agreement. The improved characteristic equations for guided mode find practical applications in the design and performance evaluation of the SW structure (SWS) for the phase delay applications. The leaky mode will find application for beam scanning helical antennas.

A mathematical modelling of multiphysics-based propagation characteristics of surface wave in piezoelectric - hydrogel layer on an elastic substrate

This paper presents a mathematical modelling of a novel multiphysics (electro-mechanic coupling) problem of the shear wave propagation in laminated structures (piezoelectric - hydrogel - elastic substrate) using the wave mode method while finding the general solution for each medium. A dynamic mechanical equilibrium equation (for transverse deflection) and Maxwell equation (for electric potential) are solved in a coupled manner over each domain resulting a general closed-form solution. A specific analytical solution is then obtained enforcing the boundary conditions at the top of piezoelectric layer and the interface continuity requirements between each layer and the elastic half-space. A novel approach, to uncouple the coupled equations, is presented resulting in a final systematic solution. The effect of x coordinate (thickness) on the field variables is carefully examined for the electrically open and short cases. The jump in the stress and electric displacement components (causing delamination due to shearing mode of fracture) is present across all the interfaces due to the different bulk material constants. The key contribution of the current work is demonstrating the influence of fixed-charge concentration inside the hydrogel layer on the shear wave propagation. The present study thus provides a new concept for adjusting and controlling the elastic wave propagation in the composite structures, and provides a proper theoretical understanding of wave propagation in the damage tolerance-based design of piezotronics devices.

Implementation of the surface thickness on additively manufactured parts for estimation of the loading location

Additive manufacturing (AM) technology has been used for the creation of complex parts in different industries. The addition of defect detection and load sensing capabilities to these products can highly increase their values. The application of structural health monitoring (SHM) methods on AM parts is proposed in this paper by implementing the internal design capabilities of the AM parts. First, the influence of the internal top surface layers on the surface wave propagation characteristics was studied. A round part with different top skin thicknesses in each quarter (10, 20, 30, and 40 layers) was designed and fabricated of polylactic acid (PLA). The height of each layer was 0.1 mm and different spectral characteristics were observed in each quarter. Then, the location of an external compression loading was estimated with the help of different skin thicknesses on a plate designed with five zones. Although estimation of the defect or loading on the structure has always been a challenge in SHM studies, the use of hidden geometries helps to effectively overcome this challenge. Surface response to excitation method was used in this study to estimate the loading location by using two piezoelectric elements. A simple algorithm was used to estimate the loading zones in all the test cases.

Miniaturized (127 to 154) GHz Dipole Arrays in 28 nm Bulk CMOS With Enhanced Efficiency

This article presents the design of integrated antennas in the D-band (110-170 GHz). First, an electromagnetic analysis is used to tune the propagation characteristics of surface waves supported on an artificial magnetic conductor (AMC). Next, a subarray of two miniaturized dipoles is designed where each dipole attains axial resonance and the separation between them is optimized for substrate wave cancellation. This subarray simultaneously performs spatial power combining and substrate wave cancellation, leading to significant increase of the effective isotropic radiated power (EIRP). Two miniaturized dipoles with axial length of 252 μm and spacing of 450 μm was fabricated in 28 nm bulk CMOS with low resistivity silicon (10 Q·cm). Each dipole is fed by a cascade of two triplers and a power amplifier. Measurements show a gain of 2.3 dBi, EIRP of 12.2 dBm at 139 GHz and a 3 dB bandwidth of 127-154 GHz (19% fractional) without using any additional substrates, lenses, or postprocessing steps. Scalability of this technique for forming larger arrays is also presented.

Impact of damage on the effective properties of network materials and on bulk and surface wave propagation characteristics

We analyze in this contribution the propagation of bulk and Rayleigh surface waves in periodic architectured materials undergoing internal damage. An elastic damageable continuum-based model is developed in the framework of the thermodynamics of irreversible processes, whereby the displacement experiences a jump across the faces of the propagating crack. The crack propagation involves an enhancement of the displacement field associated with embedded discontinuities, which remain localized within each (triangular type) finite element. The displacement discontinuity is regulated by the traction separation behavior described by an exponential cohesive model with damage hardening followed by softening. The effective mechanical properties of the overall network are evaluated versus the increasing damage. The phase velocities for the longitudinal and transverse modes are then computed continuously versus the amount of damage, considering successively the situations of symmetrically and unsymmetrically distributed damage occurrence and propagation. Simulation results show that although the crack pattern is different in these two situations, it has no impact on the evolution of the effective moduli versus global damage. The phase velocities computed based on the effective moduli decrease as damage propagates within the network; thus, it is an indicator of the amount of global damage.

Surface plasmon oscillations in a semi-bounded semiconductor plasma

We study the dispersion properties of surface plasmon (SP) oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange (CE) force associated with the spin polarization of electrons and holes as well as the effects of the Fermi degenerate pressure and the quantum Bohm potential. Starting from a quantum hydrodynamic model coupled to the Poisson equation, we derive the general dispersion relation for surface plasma waves. Previous results in this context are recovered. The dispersion properties of the surface waves are analyzed in some particular cases of interest and the relative influence of the quantum forces on these waves are also studied for a nano-sized GaAs semiconductor plasma. It is found that the CE effects significantly modify the behaviors of the SP waves. The present results are applicable to understand the propagation characteristics of surface waves in solid density plasmas.

Field measurements of interface waves and geoacoustic characterization of near surface sediment and soil

There is a need for rapid and nondestructive sensing of near-surface shear properties of the ground and seafloor. Our approach is to measure interface wave dispersion and invert these measurements to extract a shear wave speed profile. Field measurements of interface waves using geophones and accelerometers will be presented. A laser Doppler vibrometer (LDV) will also be incorporated in the suite of sensors for the measurement of wave properties. Data from these sensors will be compared to understand the coupling of the sensors into the soil or sediment and its effect on the measurements. Geoacoustic and geotechnical properties will be estimated using the interface wave data. The uncertainty and resolution of the estimates in different sediment/soil types will be explored. The Interface Wave Testing Facility at the University of Rhode Island will also be used to understand the surface wave propagation characteristics in different type of sediments/soils. [Work supported by Army Research Office and the Office of Naval Research.]

A Simulation Study of Surface Breaking Crack in Concrete Beam Based on Time-Reversed Theory of Surface Wave

Existing non-destructive test methods are usually ineffective in detection of surface breaking cracks with large depths in concrete structure. This paper introduces a method suitable for detection of deep cracks based on surface wave time reversal theory. A numerical simulation based on the finite element model is performed to investigate surface cracks detection. A damage index was defined based on the correlation coefficient between the actuated and the reconstructed wave signals. The results demonstrated that the presence of crack had a significant influence on the propagation characteristics of surface waves along concrete. Cracks in different sizes were introduced and correlated with the damage index. Enlarging the crack depth resulted in an increase in the distortion of reconstructed signals, and a higher damage index was obtained. The results illustrated the effectiveness of the surface wave time-reversal process in identifying cracks in concrete structures.

Long-period ground motions in a laterally inhomogeneous large sedimentary basin: observations and model simulations of long-period surface waves in the northern Kanto Basin, Japan

To conduct practical evaluations of the long-period ground motions (period of 4 to 8 s) in a laterally inhomogeneous large sedimentary basin, we constructed a three-dimensional (3D) sedimentary velocity structure model for the northern Kanto Basin in Japan using a simple velocity gradient function, where strong lateral variations of seismic velocities in the sediments were expected. The model construction employs waveform analysis and geophysical data from vertical seismic profiling and microtremor surveys in the target region. To validate the velocity structure model, we conducted large-scale 3D finite-difference method simulations of the long-period ground motions for two shallow moderate earthquakes: the northern Tochigi earthquake and the northern Ibaraki earthquake. The simulation results for both earthquakes accurately reproduced the observed long-period ground motions in terms of arrival times, amplitudes, and durations of surface waves. By detailed comparisons of the seismograms for observational and simulated data, we demonstrated that the lateral variation of the seismic velocities in the sediments determines the characteristics of the surface wave propagation in the northern Kanto Basin. Such analyses can provide a better understanding of the complex propagation characteristics of surface waves in laterally inhomogeneous, large sedimentary basins.

Numerical investigation on the head-on collision between unequal-sized droplets with multiple-relaxation-time lattice Boltzmann model

Droplet collision is a fundamental and important phenomenon in multiphase flow. Compared with equal-sized droplet collision, unequal-sized cases have been much less examined and understood. In the present study, the high density ratio lattice Boltzmann multiphase model proposed by Lee et al. (2010) and Lee (2009) is realized into the multiple-relaxation-time formulation in the axisymmetric cylindrical coordinate, which succeeds in achieving both high density ratio and low viscosity. Using this model, the head-on droplet collision between unequal-sized droplets is investigated from the aspects of the diameter ratio, Ohnesorge number (Oh), and the Weber number (We) by discussing their effects on the time-resolved evolutions of droplet shape, flow field, and the mixing process. It is found that the diameter ratio is crucial in determining the droplet dynamics and outcome, since at low diameter ratio the droplet deforms slightly and exhibits the characteristics of surface wave propagation. Whereas, as the diameter ratio increases the droplet deforms more largely and symmetrically, which is easier to result in reflexive separation, and gas bubble is likely to be entrapped in the droplet at medium diameter ratio. Besides, it is found that the initial smaller droplet tends to spread or penetrate more into the larger one with increasing diameter ratio, while the “mixing pattern” (whether axially nailed into, or penetrate/spread from the side) is not obviously affected by the diameter ratio. The Oh number is found to affect the mixing process more than the droplet dynamics and the outcome, since at low Oh number the smaller droplet penetrates axially into the larger one, at medium Oh number it tends to spread on the larger one’s surface, while at high Oh number it accumulates at its initial side. The effect of We number on mixing is found to be relevant with the Oh number and diameter ratio. As We number increases, at high Oh number the initial smaller droplet spreads more widely on the larger one’s surface; at low Oh number, the initial smaller droplet penetrates axially deeper into the larger one at low diameter ratio, while tends to spread on the larger one’s side surface at large diameter ratio.

Surface waves of the 2011 Tohoku earthquake: Observations of Taiwan's dense high‐rate GPS network

AbstractSurface waves generated by the 2011 Mw 9.0 Tohoku, Japan earthquake were recorded by both the high‐rate GPS and broadband seismic stations in Taiwan. In this study, we investigate the precision of high‐rate GPS displacements and estimate the feasibility of using GPS for seismology study in Taiwan. One hertz observations of 210 continuous GPS stations in Taiwan and neighboring islands were processed using a precise point positioning technique to estimate the absolute epoch‐by‐epoch positions generated by the Tohoku earthquake. Modified sidereal filtering was used to correct for near‐daily periodical variations of high‐rate position time series that may be influenced by multipath effects, and a band‐pass filter was used to remove noises from marginal frequencies. For all the 210 stations, the GPS precision after modified sidereal filtering improved from 8.2 to 7.4 mm in the horizontal and from 19.5 to 12.7 mm in the vertical components except for about 20% of the data with large position errors. After applying the band‐pass filter in the teleseismic frequency band (0.008–0.08 Hz), excluding 54 stations with noisy data, 156 continuous GPS stations were selected. Surface wave displacements derived from both high‐rate GPS and broadband seismometers are highly consistent, and the correlation coefficients are enhanced by a band‐pass filter (0.008–0.08 Hz) from 0.85 to 0.95 in the horizontal and from 0.58 to 0.85 in the vertical components. We consider continuous GPS can be used as an alternative approach to study characteristics of surface wave propagation in Taiwan.

Surface wave propagation characteristics in atmospheric pressure plasma column

In the typical experiments of surface wave sustained plasma columns at atmospheric pressure the ratio of collision to wave frequency (ν/ω) is much greater than unity. Therefore, one might expect that the usual analysis of the wave dispersion relation, performed under the assumption ν/ω = 0, cannot give adequate description of the wave propagation characteristics. In order to study these characteristics we have analyzed the wave dispersion relationship for arbitrary ν/ω. Our analysis includes phase and wave dispersion curves, attenuation coefficient, and wave phase and group velocities. The numerical results show that a turning back point appears in the phase diagram, after which a region of backward wave propagation exists. The experimentally observed plasma column is only in a region where wave propagation coefficient is higher than the attenuation coefficient. At the plasma column end the electron density is much higher than that corresponding to the turning back point and the resonance.

Propagation Characteristics for Periodic Waveguide Based on Generalized Conservation of Complex Power Technique

The propagation characteristics of surface waves with periodic waveguides is examined based on the characterization of a unit cell through the generalized conservation of complex power technique (GCCPT). The bounded approach, in which the periodic structure is enclosed by perfectly conducting walls, is applied to facilitate discussion. Comparison among different matching techniques, including the mode-matching technique (MMT), conservation of complex power technique (CCPT), improper MMT with power decrement or increment (PD/PI-MMT), is taken to derive some properties for the generalized scattering matrix (GSM) in conjunction with these techniques. It is shown that the improper PD/PI-MMT, in contrast to the equivalence between the MMT and CCPT in the context of a closed waveguide, is in contradiction to the principle of conservation of complex power, and cannot be employed to express GSM for discontinuity. Further analysis, however, suggests that PI-MMT and PD-MMT are in duality symmetry, and can, in combination, restore the continuity of complex power in a periodic environment, which gives rise to the GCCPT. The propagation constants are determined from the eigenvalues of a transmission matrix for a unit cell with the aid of a solution selection rule. A number of numerical results are shown to demonstrate the efficiency and accuracy of our approach

間欠型交流磁場印加に伴い溶融金属自由表面上に励起される表面波動の伝播特性

間欠型交流磁場印加に伴い溶融金属自由表面上に励起される表面波動の伝播特性

Characteristics of Surface Wave Propagation at Nanouneter Range of Wave Length.

It is very important to know the characteristics of wave propagating on the surface of anisotropic materials for estimating the property of materials. It is known that crystal structures near the surface are different from those in bulk. The author deduced the boundary condition taking into consideration of surface density and surface stresses of materials in a previous paper. In the present paper, the boundary condition is used for examining the velocity of the surface wave against wave number. The dispersion of the surface wave in an isotropic material is first investigated, and it is shown that the wave velocity decreases with decreasing the wavelength in the case where the surface density and the surface stresses are taken into account. The dispersion properties of surface wave in anisotropic materials, in particular, Ni (001) and W (110) are next investigated, and the dispersion relationship obtained by a continuum approach is compared to the experimental results of surface phonon. The theoretical results considering the surface density and the surface stresses are almost agreed with the experimental ones. In this analysis, the surface density plays an important role for the explanation of behavior of surface phonon against the wave number.

Propagation characteristics of surface waves sustaining atmospheric pressure discharges: the influence of the discharge processes

The propagation characteristics of microwave frequency surface waves along atmospheric pressure plasma columns sustained in capillary tubes by these same waves are studied analytically and numerically. In contrast to what has been done to date in such a pressure range, our analysis includes the modelling of the discharge processes in order to account for their interdependence with the wave's propagation. To describe these processes and to determine the plasma parameters, we turn to a two-temperature model for non-equilibrium plasmas. The analysis of the wave dispersion is performed using a cold plasma, linear dielectric description; it assumes the local uniformity approximation, which is scrutinized. Also, we assume that the phase and attenuation coefficients of the wave, under given discharge conditions, depend only on the amount of power dissipated in the plasma per unit length. The obtained results are compared with known experimental data.

Surface wave propagation in central Asia: Observations of scattering and multipathing with the Kyrgyzstan broadband array

We studied the propagation of Rayleigh waves at regional distances in central Asia using a combination of array processing techniques and surface wave analysis. We present results from the detailed analysis of three representative events recorded by a 10‐station, broadband network that has been running in the central Asian country of Kyrgyzstan since 1991: an Ms = 5.1 event near Ashkhabad, Turkmenistan; an Ms = 5.8 event in south central Tibet; and the October 7, 1994, nuclear explosion at Lop Nor. We find there is a remarkable difference in the propagation characteristics of surface waves along these three paths. The path from the event in Turkmenistan is simple and is well approximated by propagation through a laterally homogeneous medium. Array processing shows the entire Rayleigh wave train stacks coherently and arrives from an azimuth close to that predicted by a great circle path. Furthermore, estimates of dispersion curves and fundamental mode signals determined for individual stations show little variation across the array. The Tibet and Lop Nor paths are completely different. We find strong evidence for complicated multipathing and scattering effects along both of these paths. We observe a three‐stage pattern in the Tibet case: (1) the early, lowest‐frequency part of the Rayleigh wave packet arrives as a coherent signal from close to the great circle path azimuth; (2) this is overpowered in the period range around 20 s by a strong multipath signal that propagates across the array from a much more southerly azimuth; and (3) periods below 20 s rapidly become incoherent, and the signal does not have a well‐defined direction of propagation. The Lop Nor path shows similar complexity. On this path there is little dispersion for measurable periods greater than 10 s, so the low‐frequency energy arrives in an Airy phase. The Airy phase stacks somewhat coherently (it stacks, but significant power is lost in the best beam), and slowness analysis shows it arrives from an azimuth 14° north of the great circle path azimuth. Like the Tibet event, the direction of propagation of the shorter periods cannot be resolved. These results are consistent with crustal structure in central Asia. The multipathing and scattering from the Tibet and Lop Nor events are not surprising given these waves propagate across highly variable crust and high topography resulting from the collision of India with Eurasia. The relative simplicity of the Turkmenistan event path reinforces this as almost all of that path traverses the relatively undeformed Turan platform of Uzbekistan.

Characteristics of surface-wave propagation in dissipative cylindrical plasma columns

Electromagnetic surface waves dissipate energy as they propagate in plasma columns. The transfer of energy to the discharge generally occurs through collisional processes — hence the name ‘collisional’ surface waves. It affects the direction of propagation of the wave, and is responsible in particular for the turning back of the axial wavenumber on the phase diagram. The rate of collisions also influences the respective contribution of surface waves and radiation (unguided) waves to the total electromagnetic field. These considerations are of interest in improving the reliability and accuracy of the electron density diagnostic based on surface waves. This paper takes advantage of the many articles published in the domain of guided waves for antennas.