Search Results (16)

The crust and upper mantle structure of Mars is determined in the depth range of 0 to 100 km, by means of dispersion analysis and its inversion, which is performed for the surface waves present in the traces of the seismic event: S1094b. From these traces, Love and Rayleigh waves are measured in the period range of 4 to 40 s. This dispersion was calculated with a combination of digital filtering techniques, and later was inverted to obtain both models: isotropic (from 0 to 100 km depth) and anisotropic (from 0 to 15 km depth), which were calculated considering the hypothesis of the surface wave propagation in slightly anisotropic media. The seismic anisotropy determined from 0 to 5 km depth (7% of S-velocity variation and ξ ~ 1.1) could be associated with the presence of sediments or lava-flow layering, and wide damage zones surrounding the long-term fault networks. For greater depths, the observed anisotropy (17% of S-velocity variation and ξ ~ 1.4) could be due to the possible presence of volcanic materials and/or the layering of lava flows. Another cause for this anisotropy could be the presence of layered intrusions due to a single or multiple impacts, which could cause internal layering within the crust. Finally, the Moho depth is determined at 50 km as a gradual transition from crust to mantle S-velocities, through an intermediate value (3.90 km/s) determined from 50 to 60 km-depth. Full article

A study of the azimuthal variation in the surface wave fundamental-mode phase velocity is performed for the Philippine Sea Plate (PSP). This azimuthal variation has been anisotropically inverted for the PSP to determine the isotropic and anisotropic structure of this plate from 0 to 260 km. This azimuthal variation is due to anisotropy in the upper mantle. The crust is found in an isotropic structure, but the lithosphere and asthenosphere exhibit anisotropic structures. For the lithosphere, the main cause of anisotropy is the alignment of anisotropic crystals approximately parallel to the direction of seafloor spreading, and the fast axis of the seismic velocity is in the direction of ~163° of azimuth. For the asthenosphere, the seismic anisotropy can be derived from the lattice-preferred orientation (LPO) in response to the shear strains induced by mantle flow, and the fast axis of the seismic velocity is also the direction of ~163° of azimuth. This result suggests that a mantle flow pattern may occur in the asthenosphere and seems to be approximately parallel to the direction of seafloor spreading observed for the lithosphere. Finally, the changes in the parameter ξ with depth are studied to estimate the depth of the lithosphere–asthenosphere boundary (LAB), observing a clear change in this parameter at 80 km depth. Full article

Seismic metamaterials have gained significant attention for their ability to reduce seismic wave energy. However, numerical simulations have dominated the majority of research on seismic metamaterials, with relatively few field experiments validating their effectiveness. Additionally, the focus has primarily been on attenuating Rayleigh waves, with less attention given to Love waves. In this study, we first designed a seismic metamaterial featuring a periodic and symmetric array of square holes using numerical simulations as our research platform. We then explored its attenuation effects on Rayleigh waves, particularly Love waves, through field experiments. The results revealed not only differences in energy attenuation between these wave types but, more importantly, uncovered a phenomenon that we termed Bandgap-Induced Attenuation Mode Inversion within the ultra-broadband gap that was generated by the seismic metamaterials, where Love waves exhibited greater attenuation than Rayleigh waves below 50 Hz, while Rayleigh waves exhibited greater attenuation above 50 Hz. These findings highlight the necessity of considering both wave types when designing cost-effective seismic metamaterials, providing valuable insights for the development and application of metamaterials that can effectively mitigate the energy of different seismic wave modes. Full article

This paper studies elastic stress wave propagation generated by an impact in a system consisting of a moving striker rod and an initially stationary semi-infinite rod. This research emphasizes the role of different general impedances in affecting the response during the wave propagation process. The Rayleigh–Love rod theory is used in this research to consider lateral inertia and Poisson’s effects on longitudinal waves in rods, as these factors lead to greater stress results compared to the traditional wave equation. To solve the complex wave equations in a Rayleigh–Love rod with different general impedances, the numerical inversion of Laplace transformation is applied and verified using the results of previous research. This study demonstrates that variations in general impedances cause different wave reflection and transmission behaviors at the interface. As the wave interacts with this discontinuity of impedance, it may be amplified or attenuated, and changes in impedance can significantly affect wave propagation behaviors. Full article

This paper presents an in-depth study of the stress wave behavior propagating in a Rayleigh–Love rod with sudden cross-sectional area variations. The analytical solutions of stress waves are derived for the reflection and transmission propagation behavior at the interface of the cross-sectional area change in the rod, considering inertia and Poisson’s effects on the rod material. Examples solved using the finite element method are provided to verify the correctness of the analytical results. Based on the forward analysis of Rayleigh–Love wave propagation in a rod impacted by a striker rod, an impact-echo-type nondestructive testing (NDT) method is proposed to conduct defect assessment in rod-type structural components with sudden cross-sectional area changes within a cover medium. This proposed NDT method can identify the location, extension, and cross-sectional area drop ratios of an irregular zone in the rod to be inspected. Full article

This pioneer study determined the azimuthal variation in surface-wave fundamental-mode phase velocity for the Arabian plate, concluding that this variation is not due to seismic anisotropy but to lateral heterogeneity, which is compatible with anisotropic earth models of azimuthal isotropy. The study area was divided in six regions with similar surface-wave phase velocities. We determined their corresponding SH and SV-velocity models versus depth (from 0 to 260 km) by means of the anisotropic inversion of surface-wave phase velocities under the hypothesis of surface-wave propagation in slightly anisotropic media. We observed seismic anisotropy from 10 to 100 km depth. From these models, the parameter ξ was calculated for each region, and the most conspicuous features of the study area were described in terms of this parameter, such as the existence of the plume material propagation in the Arabian shield from the Afar plume, or the existence of a lithospheric keel, which was observed in previous studies beneath the Arabian platform, the Mesopotamian Plain and the Zagros belt. Full article

The longitudinal dynamic response of a large-diameter-bored pile is investigated considering the bottom sediment and the radial unloading of the surrounding soil. First, the sediment between the pile tip and the bedrock is treated as a fictitious soil pile with a cross-sectional area similarto that of the pile tip. The large-diameter-bored pile (including the fictitious soil pile) is considered as a Rayleigh–Love rod and is divided into finite segments. Under theseconditions, the three-dimensional (3D) effect of the wave propagation along the pile is indirectly simulated by considering the transverse inertia of the pile to avoid complicated calculations. Meanwhile, the surrounding soil is divided into finite annular zones in the radial direction, with the soil properties varying radially as well to simulate the radial unloading of the surrounding soil during construction. The governing equation for each soil zone is built and solved, from zone to zone, to obtain the shear stress acting on the pile. Then, the governing equation for the fictitious soil pile (i.e., the sediment) is solved to derive the dynamic action at the pile tip. In a similar manner to that ofthe fictitious soil pile and together with the recursion method, the governing equation for the pile is solved to obtain the pile’s complex impedance and velocity response. The proposed solution is verified and then introduced to portray the coupling effect of the sediment, pile parameters and radial unloading of the surrounding soil on the longitudinal dynamic response of the large-diameter-bored pile. Full article

The propagation of blast-induced vibration velocity in the rock mass varies depending on many parameters. Due to a large number of effective parameters and the variability in the rock mass environment, it is not possible to create a vibration velocity propagation model using all of these parameters. On the other hand, it is important to determine the blast vibration velocity level in urban infrastructure works and mining operations near settlements. Recent studies on the subject have been interested in the determination of blast-induced vibration velocity by the back analysis estimations of advanced statistical approaches and artificial intelligence approaches. However, sudden changes in rock mass properties such as fault zones cause significant errors in the advanced statistical approaches functions used at the level of blast-induced vibration velocity. In this study, the variation of the blast-induced vibration velocities under the influence of the fault zone has been discussed. There is a fault zone along the northwest line of the Quarry boundary. The influence of the fault zone on the blast-induced vibration propagation was determined by comparing the vibration velocities behind the fault zone with the vibration velocities in the non-fault zone. Accordingly, it has been concluded that the fault zone has the potential to create significant differences due to the reflection/refraction of surface waves (Rayleigh and Love waves) in vibration velocity values in areas close to the fault zone have the potential. Full article

Surface acoustic waves (SAWs) are the guided waves that propagate along the top surface of a material with wave vectors orthogonal to the normal direction to the surface. Based on these waves, SAW sensors are conceptualized by employing piezoelectric crystals where the guided elastodynamic waves are generated through an electromechanical coupling. Electromechanical coupling in both active and passive modes is achieved by integrating interdigitated electrode transducers (IDT) with the piezoelectric crystals. Innovative meta-designs of the periodic IDTs define the functionality and application of SAW sensors. This review article presents the physics of guided surface acoustic waves and the piezoelectric materials used for designing SAW sensors. Then, how the piezoelectric materials and cuts could alter the functionality of the sensors is explained. The article summarizes a few key configurations of the electrodes and respective guidelines for generating different guided wave patterns such that new applications can be foreseen. Finally, the article explores the applications of SAW sensors and their progress in the fields of biomedical, microfluidics, chemical, and mechano-biological applications along with their crucial roles and potential plans for improvements in the long-term future in the field of science and technology. Full article

Surface acoustic wave (SAW) sensors for the detection of magnetic fields are currently being studied scientifically in many ways, especially since both their sensitivity as well as their detectivity could be significantly improved by the utilization of shear horizontal surface acoustic waves, i.e., Love waves, instead of Rayleigh waves. By now, low-frequency limits of detection (LOD) below 100 pT/$\sqrt{\mathrm{Hz}}$ can be achieved. However, the LOD can only be further improved by gaining a deep understanding of the existing sensor-intrinsic noise sources and their impact on the sensor’s overall performance. This paper reports on a comprehensive study of the inherent noise of SAW delay line magnetic field sensors. In addition to the noise, however, the sensitivity is of importance, since both quantities are equally important for the LOD. Following the necessary explanations of the electrical and magnetic sensor properties, a further focus is on the losses within the sensor, since these are closely linked to the noise. The considered parameters are in particular the ambient magnetic bias field and the input power of the sensor. Depending on the sensor’s operating point, various noise mechanisms contribute to $f^0$ white phase noise, $f^{-1}$ flicker phase noise, and $f^{-2}$ random walk of phase. Flicker phase noise due to magnetic hysteresis losses, i.e. random fluctuations of the magnetization, is usually dominant under typical operating conditions. Noise characteristics are related to the overall magnetic and magnetic domain behavior. Both calculations and measurements show that the LOD cannot be further improved by increasing the sensitivity. Instead, the losses occurring in the magnetic material need to be decreased. Full article

Particulate matter (PM) is reported to be dangerous and can cause respiratory and health issues. Regulations, based on PM concentration, have been implemented to limit human exposition to air pollution. An innovative system with surface acoustic wave (SAW) sensors combined with a 3 Lpm cascade impactor was developed by our team for real time mass concentration measurements. In this study, we compare the PM sensitivity of two types of SAW sensors. The first one consists of delay lines based on Rayleigh waves propagating on a Lithium Niobate Y-X 128° substrate. The second one is a based-on Love waves on AT-Quartz. Aerosols were generated from NaCl for PM2.5 and from Silicon carbide for PM10. The sensors’ responses was compared to a reference sensor based on optical measurements. The sensitivity of the Rayleigh wave-based sensor is clearly lower than the Love wave sensor for both PMs. Although less sensitive, Rayleigh wave sensors remain very promising for the development of self-cleaning sensors using RF power due to their high electromechanical factor. To check the performance of our system in real conditions, we tested the sensitivity to PM from cigarette smoke using Rayleigh SAW. The PM2.5 stage showed a phase shift while the PM10 did not respond. This result agrees with previous studies which reported that the size of particles from cigarette smoke varies between 0.1 to 1.5 µm. A good correlation between the reference sensor’s response and the phase variation of SAW sensors was obtained. Full article

Various surface-wave exploration methods have become increasingly important tools in investigating the properties of subsurface structures. Inversion of the experimental dispersion curves is generally an indispensable component of these methods. Accurate and reliable calculation of partial derivatives of surface-wave dispersion curves with respect to parameters of subsurface layers is critical to the success of these approaches if the linearized inversion strategies are adopted. Here we present an open-source MATLAB package, named SWPD (Surface Wave Partial Derivative), for modeling surface-wave (both Rayleigh- and Love-wave) dispersion curves (both phase and group velocity) and particularly for computing their partial derivatives with high precision. The package is able to compute partial derivatives of phase velocity and of Love-wave group velocity analytically based on the combined use of the reduced delta matrix theory and the implicit function theorem. For partial derivatives of Rayleigh-wave group velocity, a hemi-analytical method is presented, which analytically calculates all the first-order partial differentiations and approximates the mixed second-order partial differentiation term with a central difference scheme. We provide examples to demonstrate the effectiveness of this package, and demo scripts are also provided for users to reproduce all results of this paper and thus to become familiar with the package as quickly as possible. Full article

Earthquakes are one of the major natural calamities as well as a prime subject of interest for seismologists, state agencies, and ground motion instrumentation scientists. The real-time data analysis of multi-sensor instrumentation is a valuable knowledge repository for real-time early warning and trustworthy seismic events detection. In this work, an early warning in the first 1 micro-second and seismic wave detection in the first 1.7 milliseconds after event initialization is proposed using a seismic wave event detection algorithm (SWEDA). The SWEDA with nine low-computation-cost operations is being proposed for smart geospatial bi-axial inclinometer nodes (SGBINs) also utilized in structural health monitoring systems. SWEDA detects four types of seismic waves, i.e., primary (P) or compression, secondary (S) or shear, Love (L), and Rayleigh (R) waves using time and frequency domain parameters mapped on a 2D mapping interpretation scheme. The SWEDA proved automated heterogeneous surface adaptability, multi-clustered sensing, ubiquitous monitoring with dynamic Savitzky–Golay filtering and detection using nine optimized sequential and structured event characterization techniques. Furthermore, situation-conscious (context-aware) and automated computation of short-time average over long-time average (STA/LTA) triggering parameters by peak-detection and run-time scaling arrays with manual computation support were achieved. Full article

Conventionally discussed dynamic mechanisms of elastic strain energy redistribution in near-contact surface regions include P and S elastic wave pulses radiating from the contact surface. At the same time, the elastic strain energy can be transferred by localized vortex-like elastic waves (Rayleigh, Love, Stoneley wave, and so on). In the paper, we numerically studied the main features of the formation and propagation of localized vortex-like waves in the surface layers under the contact zone. The study was done using the numerical method of movable cellular automata. We showed that the initial phase of dynamic contact interaction with a nonzero tangential component of contact velocity is accompanied by the formation of a so-called elastic vortex. The elastic vortex is a fully dynamic object, which is characterized by shear stress concentration and propagates at the shear wave speed. We first revealed the ability of the elastic vortex to propagate toward the bulk of the material and transfer elastic strain energy deep into the surface layer in a localized manner. We analyzed the dependence of the direction of vortex propagation on the tangential contact velocity, contact pressure and Young’s modulus of the material. The results of the study are important for better understanding the dynamic mechanisms contributing to inelastic strain accumulation or gradual degradation of surface layers. Full article

The propagation of surface acoustic Love modes along ZnO/glass-based structures was modeled and analysed with the goal of designing a sensor able to detect changes in the environmental parameters, such as liquid viscosity changes and minute amounts of mass supported in the viscous liquid medium. Love mode propagation was modeled by numerically solving the system of coupled electro-mechanical field equations and Navier–Stokes equations. The phase and group velocities and the attenuation of the acoustic wave propagating along the 30° tilted c-axis ZnO/glass structure contacting a viscous non-conductive liquid were calculated for different ZnO guiding layer thicknesses, added mass thicknesses, and liquid viscosity and density. The three sensor responses, i.e., the wave phase and group velocity, and attenuation changes are calculated for different environmental parameters and related to the sensor velocity and attenuation sensitivities. The resulted sensitivities to liquid viscosity and added mass were optimized by adjusting the ZnO guiding layer thickness corresponding to a sensitivity peak. The present analysis is valuable for the manufacture and application of the ZnO-glass structure Love wave sensors for the detection of liquid properties, such as viscosity, density and mass anchored to the sensor surface. Full article