Transverse and Longitudinal Thermomagnetic Waves in Conducting Media

In anisotropic conducting media, the excited thermomagnetic waves at different orientations of the magnetic field and temperature gradient significantly depend on the direction of the anisotropic medium. Theoretical calculations of the electrical conductivity tensor ik  depending on the frequency of the thermomagnetic wave are of scientific interest. In this theoretical work, the frequencies of the thermomagnetic wave at k T   || and at k T ⊥   were found, and it was proven that at longitudinal (k T   || ) and at transverse (k T ⊥   ) the direction of the frequency and growth rate of these waves depends differently on the external magnetic field. The work theoretically studies the conditions for the excitation of thermomagnetic waves. It is indicated that the directions of external fields play a significant role in the appearance of growing waves in the sample. It is shown that, depending on the value of the electrical conductivity tensor ik  , thermomagnetic waves are excited in the longitudinal (i.e. k T   || ) and transverse (i.e.k T ⊥   ) directions. The frequencies of these thermomagnetic waves in both the longitudinal and transverse directions have been calculated. The growth rates of these waves are determined by the values of the inverse electrical conductivity tensor ik  . It has been proven that the excited wave is mainly of a thermomagnetic nature. In theory, the dispersion equation obtained is of algebraically high powers relative to the oscillation frequency. The dispersion equation in both cases (longitudinalk T   || and transverse k T ⊥   ) contains terms in which there are thermomagnetic frequencies in a low degree of frequency. It has been proven that if the value of the electrical conductivity tensor ik  is the same, then the propagation frequencies of thermomagnetic waves are different. The theory is constructed without an external magnetic field 0 0 =Н . In the presence of an external magnetic field, the conditions for the excitation of thermomagnetic waves, and of course the conditions for their growth, will change significantly.

The accurate measurement of the prestress for bolt has been intensively investigated in recent years. Many research studies have been conducted to improve the accuracy of prestress measurement using ultrasound techniques; in particular, the real-time prestress of bolt can be obtained without the requirements to calibrate the original load when ultrasonic longitudinal and transverse waves are applied simultaneously. However, there are few studies that have focused on ultrasonic transducers that can generate longitudinal and transverse waves simultaneously. Furthermore, research on coatings deposited directly on the top of the bolts for the excitation of longitudinal and transverse waves has not been reported. ZnO coating is widely used for the ultrasonic transducer due to its excellent piezoelectric property and stable structure in high temperatures. Therefore, it is an outstanding candidate for the excitation of both longitudinal and transverse waves and has a good application prospect in the field of bolt prestress measurement by ultrasonic sound wave with high accuracy. In this paper, ZnO piezoelectric coatings were deposited on (100)-oriented Si substrates by radio frequency sputtering techniques. The morphology, structure, and echo signal characteristics of the coatings were characterized by SEM, AFM, XRD, and ultrasonic measurement instruments. The experimental results showed that Ar/O2 ratio and deposition position exhibited significant effects on the excitation waveform of the ZnO piezoelectric coating. When the Ar/O2 ratio reduced to 1:3, the coating could excite both transverse and longitudinal waves. However, when the deposition position gradually moved away from the sputtering center, the transverse wave gradually enhanced. The coating could excite a pure transverse wave when the sample was at the edge of the effective sputtering area, which showed that the type of the excitation wave and the relative intensity of each wave could be well controlled by the Ar/O2 ratio and deposition position. These research results have a good application prospect in bolt stress measurement.

Multicomponent seabed seismic data acquisition, processing and interpretation of pressure and shear data are bringing new insight into seismic exploration and reservoir characterization. The reason we want to record "dual-wave" data is at least twofold. First, to improve seismic lithology and fluid prediction, as shear waves carry additional information about lithology, pore fluids, and fractures in the subsurface. Second, to improve seismic imaging, as joint processing and analysis of both pressure and shear data reduces the ambiguity of structural and stratigraphic interpretation. Independently of the use of multicomponent sensors, seabed seismic data recordingoffers the generic advantage of flexibility of the acquisition geometry. As virtually any pattern of shots and receivers is possible, data acquisition can be optimized to provide the most revealing subsurface image. In this paper, we present results from analysis of multicomponent seabed seismic data from the Tommeliten Alpha Field and the Statfjord Field, offshore Norway. Introduction Multicomponent marine technology holds a promising potential for risk reduction in seismic exploration. While oil and gas from large and geologically simple fields have constituted a substantial part of the world's hydrocarbon production up to now, new resources are to a greater extent found in small traps in geologically complex areas or in subtle traps that are difficult to identify. Petroleum reserves thus become progressively more difficult to discover and develop and the financial risks increase while the economic margins tend to decrease. The demand is therefore high for new technology that can reduce risk through more accurate prospect definition. The use of converted shear (PS) waves in addition to conventional pressure or compressional (P) waves offers a possibility to better address the risk elements in petroleum exploration work. In the 1970-80's, attempts were made to extract shear wave information from marine seismic data acquired in surveys with conventional sources and pressure-sensitive hydrophones located in the water column. The methods rely on double mode conversions at or just below the water bottom, giving PSSP reflections. For a given angle of incidence, mode conversion from compressional P-wave to S-wave is quite efficient in "hard" water-bottom environments. The water bottom shear velocity is the most critical parameter affecting the generation of observable PSSP reflections. Their amplitudes can be comparable to normal P-wave reflections when the S-wave velocity is greater than one-third of the water-bottom P-wave velocity1,2. In most areas, however, as the sea floor shear velocity is much lower, this is not a viable technique to record high quality shear wave data in the marine environment. Other solutions thus were investigated. Unless shear waves were generated by source devices on the sea floor, the methods necessarily had to rely on mode conversion by reflection from P-wave to S-wave at reflectors in the subsurface. In the early 80's, a few oil companies started to investigate how shear waves could be recorded on the seabed. Forinstance, Conoco Inc. considered the use of a marine shear wave vibrator source for shear wave excitation, while Shell Offshore Inc. investigated the potential of recording shear waves by using a "marine shear wave cable". However, to our knowledge, no results from these analyses were published in the open literature. In the late 80's, Statoil developed a concept for acquiring fourcomponent (4C) seismic data directly on the sea floor. Known as SUMIC (SUbsea seisMIC) the technique would enable the recording of both shear and compressional waves by planting into the seabed se

Wave propagation in porous materials is of relevance in many fields of acoustics such as geophysics, noise cancellation, and biomedical imaging. In contrast to classical elastic materials, poroelastic materials support three types of elastic waves and exhibit a distinctive dispersion in the presence of viscous fluids. In addition to the compression and shear wave, a secondary compression wave, often named Biot slow wave, exists. Both, the slow compression wave and the shear wave are highly attenuated. This poses crucial difficulties for experimental detection. We overcome this challenge by using high frame rate ultrasound imaging for wave tracking inside saturated, highly porous melamine foams. To our knowledge, we show the first experimental speed and attenuation measurements inside a soft porous materials. In particular, experimental detection of the slow compression wave is scarce, and no direct imaging inside a porous material has been reported. Both wavespeeds are governed by the weak frame of the foam and exhibit a strong dispersion due to the fluid viscosity. Our experiments have direct implications for medical imaging: Melamine foams exhibit a similar microstructure as lung tissue. Furthermore, other organs such as the liver can be modeled as a soft porous material.Wave propagation in porous materials is of relevance in many fields of acoustics such as geophysics, noise cancellation, and biomedical imaging. In contrast to classical elastic materials, poroelastic materials support three types of elastic waves and exhibit a distinctive dispersion in the presence of viscous fluids. In addition to the compression and shear wave, a secondary compression wave, often named Biot slow wave, exists. Both, the slow compression wave and the shear wave are highly attenuated. This poses crucial difficulties for experimental detection. We overcome this challenge by using high frame rate ultrasound imaging for wave tracking inside saturated, highly porous melamine foams. To our knowledge, we show the first experimental speed and attenuation measurements inside a soft porous materials. In particular, experimental detection of the slow compression wave is scarce, and no direct imaging inside a porous material has been reported. Both wavespeeds are governed by the weak frame of the fo...

Wave arrival detection in acoustic well logs via the wigner distribution and generalized Allan Variance

Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) is a noninvasive thermal technique that enables rapid heating of a specific area in the human body. Its clinical relevance has been proven for the treatments of soft tissue tumors, like uterine fibroids, and for the treatments of solid tumors in bone. In MR-HIFU treatment, MR-thermometry is used to monitor the temperature evolution in soft tissue. However, this technique is currently unavailable for bone tissue. Computer models can play a key role in the accurate prediction and monitoring of temperature. Here, we present a computer ray tracing model that calculates the heat production density in the focal region. This model accounts for both the propagation of shear waves and the interference between longitudinal and shear waves. The model was first compared with a finite element approach which solves the Helmholtz equation in soft tissue and the frequency-domain wave equation in bone. To obtain the temperature evolution in the focal region, the heat equation was solved using the heat production density generated by the raytracer as a heat source. Then, we investigated the role of the interaction between shear and longitudinal waves in terms of dissipated power and temperature output. The results of our model were in agreement with the results obtained by solving the Helmholtz equation and the frequency-domain wave equation, both in soft tissue and bone. Our results suggest that it is imperative to include both shear waves and their interference with longitudinal waves in the model when simulating high intensity focused ultrasound propagation in solids. In fact, when modeling HIFU treatments, omitting the interference between shear and longitudinal waves leads to an over-estimation of the temperature increase in the tissues.

The properties and resonant absorption mechanism of the Alfvén compressional waves are discussed for a cold plasma. The parametric analysis of the dispersion equation shows that unlike the incompressible case the excitation of the compressional surface waves near the resonant surface depends on the specific values of the plasma parameters across this surface. The oscillation frequency and the resonant absorption coefficient of these waves also show a different behavior from those of Alfvén waves. The phase velocity ω/k∥ depends on the perpendicular wave number k⊥, and the absorption coefficient is proportional to (Ka)2/3, where K = (k∥² + k⊥)1/2 and 2a is the scale length of the density variation.

Ultrasonic waves from radial mode excitation of a piezoelectric disc on the surface of an elastic solid

Artificial intelligence approach in mixed convection heat transfer under transverse mechanical vibrations in a rectangular cavity

We present the variations of electrical parameters of dielectric barrier discharge (DBD) when the DBD generator is used for the material modification, whereas the relevant physical mechanism is also elaborated. An equivalent circuit model is applied for a DBD generator working in a filament discharging mode, considering the addition of epoxy resin (EP) as the plasma modified material. The electrical parameters are calculated through the circuit model. The surface conductivity, surface potential decay, trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated. It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage. The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process. Moreover, the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment. The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface. The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.

The thermal excitation, regulation, and detection of charge carriers in solid-state electronics have attracted great attention toward high-performance sensing applications but still face major challenges. Manipulating thermal excitation and transport of charge carriers in nanoheterostructures, we report a giant temperature sensing effect in semiconductor nanofilms via optoelectronic coupling, termed optothermotronics. A gradient of charge carriers in the nanofilms under nonuniform light illumination is coupled with an electric tuning current to enhance the performance of the thermal sensing effect. As a proof of concept, we used silicon carbide (SiC) nanofilms that form nanoheterostructures on silicon (Si). The sensing performance based on the thermal excitation of charge carriers in SiC is enhanced by at least 100 times through photon excitation, with a giant temperature coefficient of resistance (TCR) of up to -50%/K. Our findings could be used to substantially enhance the thermal sensing performance of solid-state electronics beyond the present sensing technologies.

While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. An exact analytic solution of linearized hydrodynamics equations is obtained that describes the shear waves in inhomogeneous, inviscid, compressible fluids with piece-wise continuous parameters in a uniform gravity field. The solution is valid under surprisingly general assumptions about the environment and reduces to some classical wave types in appropriate limiting cases. Free shear waves in bounded and unbounded domains as well as excitation of the shear waves by a point source are considered. Edge waves propagating along vertical and inclined rigid boundaries are found in rotating and non-rotating fluids. A possible role of the shear acoustic-gravity waves in a coupled ocean-atmosphere system is discussed.

While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. An exact analytic solution of linearized hydrodynamics equations is obtained that describes the shear waves in inhomogeneous, inviscid, compressible fluids with piece-wise continuous parameters in a uniform gravity field. The solution is valid under surprisingly general assumptions about the environment and reduces to some classical wave types in appropriate limiting cases. Free shear waves in bounded and unbounded domains as well as excitation of the shear waves by a point source are considered. Edge waves propagating along vertical and inclined rigid boundaries are found in rotating and non-rotating fluids. A possible role of the shear acoustic-gravity waves in a coupled ocean-atmosphere system is discussed.

Weyl’s Gauge Principle of 1929 has been used to show that a five‐dimensional gauge field wherein the fifth dimension is conserved in the same mathematical sense as the conservation of mass embeds a four‐dimensional hyper surface into the five dimensional manifold. The equations specifying the geometry of the embedded hyper surface are similar in form to Einstein’s field equations of his General Theory of Relativity. These field equations become Einstein’s field equations when one takes the fifth dimension to be mass density. This means the predictions of Einstein’s General Theory may be achieved in two different ways. One by using Einstein’s method and the other by using a five dimensional manifold of space, time and mass density while restricting mass to be conserved. The five dimensional gauge fields associated with these phenomena are converted into a four dimensional curved hyper surface by the conservation of mass. The mathematical equivalence of the two methods provides the justification to seek what predictions might be made considering the five dimensional gauge field wherein the electromagnetic fields are inductively coupled to the gauge gravitational field. This presentation will present the logic showing how Einstein’s General Theory of Relativity may be derived from the five dimensional manifold using the conservation of mass. Comparison of predictions of perihelion advance by using the view from the embedded four‐dimensional hyper surface and from the five dimensional manifold shows the equivalence of the two methods of viewing physical phenomena. The inductive coupling between the electromagnetic and gravitational fields may be given experimental support by showing that predictions of the Earth’s magnetic moment due to its spinning gravitational mass is within 7% of the experimentally measured value. Such an inductively coupling between the gravitational gauge field and the electromagnetic gauge field provides an opportunity to seek predictions of the resulting five dimensional wave equations. Whereas in Maxwellian electromagnetism there are two, coupled, vector wave equations in the five dimensional gauge field there are three, coupled, vector wave equations that are also coupled to a scalar wave equation. The presentation will discuss the resulting transverse and longitudinal solutions to this system of wave equations. It will show that the inductive coupling with the gravitational field provides a very weak gravitational component to the transverse waves. It will also show that the longitudinal wave solutions may be independent of the transverse solutions and that the longitudinal solutions consist of only electric and gravitational vector components with an accompanying scalar wave. Longitudinal electrogravitic waves do not interact with the propagation medium as do transverse waves and make good candidates for space communication. Not only will longitudinal waves pass through intervening material, but they may be made very directive and, thereby, avoid a 1/r2 loss. The presentation will also present an antenna design for converting transverse electromagnetic waves into longitudinal electrogravitic waves for using current transmitting laser communication equipment and the reciprocal antenna design for converting longitudinal waves back into transverse waves to use current receivers.

The response of an exponentially diverging magnetic flux tube embedded in an isothermal solar atmosphere to the propagation of transverse tube waves and random transverse pulses generated in the solar convection zone is studied analyt- ically. General solutions are presented and applied to solar flux tubes located in the interior region and at the boundary of supergranulation cells. It is shown that the period of the free oscillations driven by transverse waves and pulses ranges from 7 to 10 min for the considered values of the tube magnetic field, and that these oscillations decay in time as t −3/2 . Since the observational signatures of these transverse oscillations are hard to detect, we also consider the generation of longitudinal tube waves by nonlinear mode coupling and the excitation of free atmospheric oscillations by longitudinal waves. Our results show that the basic properties of oscillations driven by transverse and longitudinal tube waves are different. While transverse waves excite oscillations with 7−10 min periods, oscillations by longitudinal waves have periods near 3 min. This is consistent with the observed 3-min oscillations inside the supergranule cells but inconsistent with the 7-min oscillations observed in the chro- mospheric network. We suggest that an explanation of the observed 7-min oscillations might be found by taking into account a more realistic structure of flux tubes located in the magnetic network.