Pointing Bias in “Spatial Matched Filter” Beamforming at a Tri-Axial Velocity-Sensor due to Non-Perpendicular Axes

This paper investigates how non-perpendicularity in a tri-axial velocity sensor would affect the tri-axial velocity-sensor#39s azimuth-elevation beam-pattern in terms of the beam#39s pointing direction and directivity. The vertical axis was adopted as the reference axis for the analysis and a rotation matrix developed to represent the non-perpendicularity in Euclidean space. The beampattern of this deformed tri-axial velocity sensor is then analytically studied. It was found that the non-perpendicularity does not affect the overall shape of the beampattern, but only introduces a pointing offset. Also, the non-perpendicularity imperfectionreduces the directivity of the imperfect triaxial velocity sensor relative to a perfect case. This finding developed in closed the pointing bias for the described deformity hence serves for non-iterative post data acquisition correction

Anisotropic nonlinear elasticity in a spherical bead pack: influence of the fabric anisotropy

Stress-strain measurements and ultrasound propagation experiments in glass bead packs have been simultaneously conducted to characterize the stress-induced anisotropy under uniaxial loading. These measurements, realized respectively with finite and incremental deformations of the granular assembly, are analyzed within the framework of the effective medium theory based on the Hertz-Mindlin contact theory. Our work shows that both compressional and shear wave velocities and consequently the incremental elastic moduli agree fairly well with the effective medium model by Johnson et al. [J. Appl. Mech. 65, 380 (1998)], but the anisotropic stress ratio resulting from finite deformation does not at all. As indicated by numerical simulations, the discrepancy may arise from the fact that the model doesn't properly allow the grains to relax from the affine motion approximation. Here we find that the interaction nature at the grain contact could also play a crucial role for the relevant prediction by the model; indeed, such discrepancy can be significantly reduced if the frictional resistance between grains is removed. Another main experimental finding is the influence of the inherent anisotropy of granular packs, realized by different protocols of the sample preparation. Our results reveal that compressional waves are more sensitive to the stress-induced anisotropy, whereas the shear waves are more sensitive to the fabric anisotropy, not being accounted in analytical effective medium models.Comment: 9 pages, 8 figure

Azimuth-elevation direction finding using a microphone and three orthogonal velocity sensors as a non-collocated subarray

2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Reverberant Elastography for the Elastic Characterization of Anisotropic Tissues

We derive closed-form solutions for reverberant elastography in anisotropic elastic media by adapting the framework used in electromagnetic theory to treat transverse isotropic materials. Different sample-setup geometries are analyzed, highlighting their relevance for both optical coherence elastography (OCE) and ultrasound elastography (USE). Numerical simulations using finite elements are used to validate the proposed solutions in practical cases. OCE experiments are conducted in ex vivo chicken muscle samples for the characterization of in-plane and out-of-plane shear modulus assuming a transverse isotropic elastic model. Additionally, we obtained a generalized geometry-independent solution for the isotropic media case, thus unifying previous results for reverberant elastography.Comment: 12 pages, 14 figure

Experimental And Numerical Study Of Sonic Wave Propagation In Freezing Sand And Silt

Thesis (Ph.D.) University of Alaska Fairbanks, 2009A numerical model for delineating the temperature-velocity relationship of freezing porous media and soil is developed in Matlab based on Leclaire's Biot-type three-phase theory. Leclaire's theory gives lower sonic velocities than the experimental results because it does not take into consideration the effect of the solid-ice frame when water is freezing. To take the solid-ice effective frame into account, the average bulk and shear moduli estimation are modified with a proposed procedure. The modification gives higher P-wave and S-wave velocities that fit experimental data well. A comprehensive suite of physical and acoustic laboratory experiments are conducted on artificial sands, sand-clay mixtures and Fairbanks silts to investigate the temperature-velocity relationship during the freezing process and the effects of grain size and fine clay content. A Multi-channel ultrasonic scanning system (MUSS) is designed, installed and programmed for the experimental computerized ultrasonic tomography (CUST) study. The inward and outward freezing process and freezing front development in Fairbanks silt samples are observed using computerized ultrasonic tomography (CUST) in the laboratory. The experiments generate sonic wave velocity and temperature distribution during the freezing process. The freezing front is clearly identified in the CUST as a function of time and temperature. Comprehensive numerical finite element method (FEM) simulations, which account for the conduction in porous media, the latent heat effect and the nonlinear thermal properties of soil, are performed on the inward and outward freezing process of Fairbanks silt based on the experimental conditions. In conjunction with the temperature-velocity model developed in the study, sonic wave velocity tomograms are generated. The results are comparable with those obtained by CUST. The study indicates that CUST is an effective method for studying freezing processes and has potential for indirect measurement of unfrozen water content variations in the soil without interfering with the freezing process

Mining Safety and Sustainability I

Safety and sustainability are becoming ever bigger challenges for the mining industry with the increasing depth of mining. It is of great significance to reduce the disaster risk of mining accidents, enhance the safety of mining operations, and improve the efficiency and sustainability of development of mineral resource. This book provides a platform to present new research and recent advances in the safety and sustainability of mining. More specifically, Mining Safety and Sustainability presents recent theoretical and experimental studies with a focus on safety mining, green mining, intelligent mining and mines, sustainable development, risk management of mines, ecological restoration of mines, mining methods and technologies, and damage monitoring and prediction. It will be further helpful to provide theoretical support and technical support for guiding the normative, green, safe, and sustainable development of the mining industry

Effect of Stress Magnitude and Stress Rate on Elastic Properties of the Reservoir Rocks

We studied the effect of stress magnitude and stress rate on elastic properties of the reservoir rocks. We designed and developed experiments to study: (i) the dynamic and static elastic moduli of reservoir rocks, (ii) quantifying the effects of wave’s amplitude on the longitudinal and transverse velocities in porous media, and (iii) anisotropy of sandstone subjected to stress in dry and saturated statuses

Magnetoelectric Sensor Systems and Applications

In the field of magnetic sensing, a wide variety of different magnetometer and gradiometer sensor types, as well as the corresponding read-out concepts, are available. Well-established sensor concepts such as Hall sensors and magnetoresistive sensors based on giant magnetoresistances (and many more) have been researched for decades. The development of these types of sensors has reached maturity in many aspects (e.g., performance metrics, reliability, and physical understanding), and these types of sensors are established in a large variety of industrial applications. Magnetic sensors based on the magnetoelectric effect are a relatively new type of magnetic sensor. The potential of magnetoelectric sensors has not yet been fully investigated. Especially in biomedical applications, magnetoelectric sensors show several advantages compared to other concepts for their ability, for example, to operate in magnetically unshielded environments and the absence of required cooling or heating systems. In recent years, research has focused on understanding the different aspects influencing the performance of magnetoelectric sensors. At Kiel University, Germany, the Collaborative Research Center 1261 “Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics”, funded by the German Research Foundation, has dedicated its work to establishing a fundamental understanding of magnetoelectric sensors and their performance parameters, pushing the performance of magnetoelectric sensors to the limits and establishing full magnetoelectric sensor systems in biological and clinical practice