Ultrasonic Pulse Transmission Method Research Articles

Impact of drying-wetting cycles on the small strain behaviour of compacted clay

Small strain shear modulus (Gmax) is an important parameter for assessing the performance of compacted soils that underlie typical transport infrastructure assets such as railway tracks. This is particularly important when considering changes in climate patterns, which are expected to yield larger seasonal soil-atmosphere moisture fluctuations. This in turn results in the progressive variation of the small strain properties of compacted soils during their service life (i.e. drying and wetting). In this study, the small strain shear behaviour was evaluated for an intermediate plasticity clay (i.e. kaolin) in a series of drying and wetting cycles. Four different dying and wetting boundaries were considered to explore a wide range of moisture amplitudes during 10 drying-wetting cycles. Drying and wetting was controlled using gravimetric water content in order to mimic realistic field conditions typically observed at substructure level. An ultrasonic pulse transmission method was used to capture the change in small strain stiffness and volume at discrete points during the drying-wetting cycles. The results reveal clear distinctions in behaviour for all four boundaries considered, with wetting boundaries having the greatest influence on behaviour. In this instance, specimens brought to full saturation during wetting exhibited an increase in the small strain shear modulus during progressive drying-wetting cycles. However, a reduction was observed when the wetting boundary was restricted to the compacted state. Measured volume changes were also in agreement with these findings, however there was some evidence of volume increase when drying to residual conditions. The results suggest that this is associated with the formation of the partial pendular state where a loss of capillary contacts between particles occurs. Furthermore, when all data for 10 drying-wetting cycles is plotted in the e-Gmax space, a linear relationship is observed for different constant water content levels. Remarkably, this trend is shown to be independent of the boundary conditions considered in this study or number of drying-wetting cycles.

Influence of Nb2O5 Additive on Elastic and Dielectric Properties of NiCuZn Ferrites

The influence of Nb2O5 additive on elastic and dielectric properties of NiZnCu ferrite is reported. The longitudinal and shear wave velocities were measured by ultrasonic pulse transmission method. The elastic constants increased as the Nb2O5 contents increased. The dielectric parameters such as dielectric constant (ɛ′) and dielectric loss tangents as a function of frequency and Nb2O5 additive composition for all samples at room temperature. The variations in the dielectric constant (ɛ′) and dielectric loss tangents values were explained using Maxwell–Wagner interfacial polarization according to Koops phenomenological theory. AC conductivity was increased with an increase in the frequency. A reduction in AC conductivity with Nb2O5 additive is reported.

Finite-Element Analysis of Noise Preceding the Arrival of S-Wave in Ultrasonic Measurements of Rock Velocities.

For oil and gas seismic exploration, rock velocities are essential parameters to tease out reservoir properties from seismic data. The ultrasonic pulse transmission (UPT) method has been a gold standard to estimate reservoir rock velocities in the laboratory. Regarding the UPT method, accurate determination of the travel time of waves plays a significant role in robustly measuring rock velocities. One of the most conventional ways to obtain the travel time is through the arrival picking. However, unclear noise virtually exists preceding the arrival of S-wave interfering with this arrival picking, which, sometimes, can cause enormous errors to measured S-wave velocity. Herein, we develop a 2-D, three-component (2D-3C) finite-element modeling (FEM) algorithm aiming to interpret the noise by combining with UPT measurements. The proposed 2D-3C FEM not only can efficiently compute ultrasonic wavefield radiated by circular P- or S-wave transducers but also able to obtain synthetic waveforms in the testing of S-wave velocity where polarization directions of S-wave transducers are arranged as nonparallel. To analyze the simulated ultrasonic waveforms, we introduce frequently-used concepts of edge and direct plane waves to build elastodynamic models of the ultrasonic wavefield. Then, we compare numerical results with experimental measurements. Our 2D-3C FEM results show good agreement with experimental waveforms both in P- and S-wave velocity testings. Whereafter, we pinpoint constitutions of the noise preceding the arrival of S-wave. Comparison of numerical and experimental waveforms suggests that the edge P-wave with its reflected and converted modes partially contributes to this noise, while the rest part of the noise may stem from the effects of the compressional dipole, the couplant smeared between a transducer and a sample, and inherently parasitic longitudinal vibrations of S-wave transducers. The interpretations on this noise have the potential to benefit future design of more effective S-wave transducers.

Elastic, impedance spectroscopic and dielectric properties of TiO2 doped nanocrystalline NiCuZn spinel ferrites

ABSTRACTNanocrystalline Ni0.4Cu0.3Zn0.3Fe2O4 ferrites doped with TiO2 (0–10 wt %) were prepared by the sol-gel method. Elastic properties of synthesized samples were studied with the help of ultrasonic pulse transmission method. The elastic constants initially increase with an increase in TiO2 up to 1 wt % and then decline. LCR-Q meter was used to study the dielectric properties within 50 Hz to 5 MHz range of the frequency. The dielectric constant (ϵ′) and dielectric loss tangents were decreased continuously with increased frequency for all the selected samples at room temperature revealing normal dielectric behavior of ferrites. Also, the AC conductivity was increased with an increase in the frequency for all the selected samples. Cole-Cole plots were obtained for all investigated samples and showed single semicircle which indicates that the electrical conduction process appears only due to grain boundaries.

Effects of Zn2+-Zr4+ ions on the structural, mechanical, electrical, and optical properties of cobalt ferrites synthesized via the sol–gel route

In the present study, we examined the effects of doping with Zn–Zr on the structural, optical, electrical, and mechanical properties of cobalt ferrite. Nanocrystalline cobalt ferrites comprising CoZnxZrxFe2-2xO4 (x = 0.0 to 0.4, Δx = 0.1) were prepared via the sol–gel route. X-ray diffraction analysis indicated the formation of a spinel phase in the ferrites. An additional ZrO2 phase was observed for x = 0.3. Characteristic absorption bands at frequencies of 580–610 cm−1 and 375–400 cm−1 related to spinel structures were observed in the Fourier transform infrared FTIR spectra obtained for the ferrites. The elastic constants decreased as the Zn–Zr contents increased. The longitudinal and shear velocities of ultrasound through the ferrite materials were measured using the ultrasonic pulse transmission method. The variations in the ultrasound velocities could be attributed to the changes in density. The dielectric parameters ɛ′ (dielectric constant) and tanδ (dielectric loss tangent) were analyzed as functions of the frequency and Zn–Zr composition. Both ɛ′ and tanδ decreased as the frequency and Zn–Zr contents increase. The variations in the values of parameters ɛ′ and tanδ were explained using Maxwell–Wagner interfacial polarization according to Koops phenomenological theory. The values of the activation energy and Curie temperature were calculated based on plots of the thermal variation in the direct current resistivity. The activation energy values indicated that electron hopping was the mechanism responsible for conduction in the ferrites.

Determining the influence of pressure and temperature on the elastic constants of anisotropic rock samples using ultrasonic wave techniques

Measuring rock elastic constants and anisotropy parameters and understanding their changes in response to changes in pressure and temperature is crucial for modeling and interpreting seismic measurements. The rapid advance in seismic exploration and characterization of conventional and unconventional reservoirs requires a thorough understanding of variations in seismic velocities in response to variations of the rock elastic constants and anisotropy parameters. In attempt to develop this understanding, we measured variations in the elastic constants of three rock samples in the lab as a function of temperature (up to 600 ∘C) and pressure (up to 150 MPa) to simulate the in-situ conditions using a triaxial ultrasonic pulse transmission method. The rock samples used in this study came from a metamorphic rock core sample collected from a geothermal reservoir at the Larderello Geothermal Field in Italy. The rock samples have different chemical and structural composition and inherently contain both vertical transverse isotropy (VTI) and orthorhombic isotropy. We used two different methods to calculate the elastic stiffness constants and corresponding anisotropic parameters including VTI and orthorhombic isotropy. Our results showed that increasing the pressure leads to an increase in the orthorhombic constants while increasing the temperature leads to a decrease in these constants. The lagging decrease of the elastic constants with respect to the decrease in the pressure is explained by the hysteresis phenomenon. These observations and results will promote a better understanding and interpretation of reservoirs within the seismic domain.

Experimental identification of the transition from elasticity to inelasticity from ultrasonic attenuation analyses

The transition from recoverable elastic to permanent inelastic deformation is marked by the onset of fracturing in the brittle field. Detection of this transition in materials is crucial to predict imminent failure/fracturing. We have used an ultrasonic pulse transmission method to record the change in waveform across this transition during fracturing experiments. The transition from elastic to inelastic deformation coincides with a minimum in ultrasonic attenuation (i.e., maximum wave amplitude). Prior to this attenuation minimum, the existing microfractures close. After this minimum, new microfractures form and attenuation increases until peak stress conditions, at which point, larger fractures form leading to complete sample failure. In our experiments, velocity changes are not sensitive enough to be indicative for the transition from elastic to inelastic deformation. Analysis of attenuation, not velocity, may thus detect imminent failure in materials. Our results may help detect fracturing in borehole casings or the near-wellbore area, or they may help predict imminent release of energy by seismic rupture.

Ultrasonic velocity measurements on thin rock samples: Experiment and numerical modeling

The ultrasonic pulse transmission (UPT) method has been the gold standard for laboratory measurements of rock elastic properties for decades, and it is used by oil and gas industry and service companies routinely. In spite of the wide acceptance and use of the UPT method, experimentalists are still looking for ways to further extend the limits of its applicability and to improve its state-of-the-art practices. One of the problems that limits wider application of the method is the length of the standard samples used (approximately 40–100 mm). This is a crucial limitation either in the case of a damaged core when preparation of a standard size sample is impossible or in the case when an ultrasonic experiment is combined with saturation or desiccation processes that might be extremely time-consuming on the long samples. On the other hand, thinner samples are not typically used due to the implication of inhomogeneity of stress fields inside and whereas few results of the measurements on thin disc samples have been reported in the literature, detailed justifications of the procedures have not been done yet. To fill this gap, we compare ultrasonic velocities measured at confining stresses up to 50 MPa done on standard and thin samples with lengths of 60 and 15 mm, respectively. First, we evaluate a new developed experimental setup for ultrasonic measurements on thin discs and develop a detailed experimental procedure. Then, we use finite-element modeling to numerically simulate stress fields in both types of samples. Finally, we compare the ultrasonic velocities measured on the thin discs and on standard samples and determine how to obtain reliable elastic properties on thin samples.

Spectroscopic, elastic and dielectric properties of Ho3+ substituted Co-Zn ferrites synthesized by sol-gel method

Ho3+ substituted cobalt-zinc ferrite with a chemical formula Co0.7Zn0.3HoxFe2−xO4 (0≤x≤0.1) were synthesized by sol-gel method. Synthesized samples were characterized by using X-ray diffraction, field emission scanning electron microscopy, Raman, Infrared and UV–visible spectroscopy. X-ray diffraction patterns show the formation of cubic spinel structure of all the synthesized samples. The gradual changes in the Raman spectra of Co-Zn ferrite were observed at higher level of Ho3+ substitution. The Raman band shows that there is a strong electron-phonon coupling in the investigated ferrite system and is the highest for the T32g mode as compared to A1g and T22g modes. Fourier transform infrared spectroscopy shows that the vibration bands corresponding to Fe–O is slightly varied with the substitution of Ho3+ substitution. UV–visible spectra was studied by using the optical absorbance measurements in the wavelength ranges from 500 to 800nm. The estimated energy band gap is found to increase from 1.72 to 1.84eV with the increase in Ho3+ substitution. The elastic properties such as longitudinal velocity, shearing velocity, elastic constant, Poisson's ratio and Debye temperature were measured at room temperature by using the ultrasonic pulse transmission method. It is found that the elastic constant and Debye temperature decreased with the increase in Ho3+ substitution. A linear relationship between Debye temperature, elastic constant and average sound velocity with the Ho3+ substitution is observed and discussed in this manuscript. Dielectric properties have been investigated as function of frequency. The dispersion of the dielectric properties was discussed in the light of Koop's theory in accordance with the Maxwell-Wagner polarization.

Ultrasonic method for measuring the gas holdup of gas-liquid bubbly flow in a small-diameter pipe

Based on ultrasonic sound pressure attenuation, the ultrasonic pulse transmission method is proposed for measuring gas holdup in gas-liquid two-phase bubbly flows. Two ultrasonic transducers are positioned on opposite sides of a vertical upward pipe with an inner diameter of 20 mm. To obtain the relationship between ultrasonic attenuation and gas holdup, the mean value of the first pulse sequence of ultrasonic signals is first extracted as the measured signal. We used the quick closing valve method to obtain the gas holdup as the set value. Second, the relationship between the gas holdup and measured ultrasonic signals was established. The experiment result shows that the ultrasonic attenuation rate is significantly different at low and high gas holdups, as indicated by the bubble size images with a high-speed camera. We also investigated the ultrasonic field distribution using numerical simulation. The bubble size has an important effect on the ultrasonic attenuation coefficient, which provides a further physical explanation and reference for the experimental phenomena.

Experiment study of pore structure effects on velocities in synthetic carbonate rocks

Carbonate rocks have a complex pore structure, show strong heterogeneity, and have a wide range of velocities that lead to more complicated velocity-porosity relationships compared with sandstones. We designed and prepared 72 carbonate synthetic cores with known pore structures according to the control variate principle. We measured the P- and S-wave velocities of these cores by an ultrasonic pulse transmission method, analyzed the effects of the pore aspect ratio (AR) and pore size [Formula: see text] on velocities, and compared the experimental results with predictions of effective medium theories (EMTs). The matrix of our synthetic cores was consolidated mixture of carbonate cuttings and epoxy. We randomly imbedded predesigned penny-shaped silicone disks or expandable polystyrene balls into the matrix during the core preparation process to simulate secondary pores. The experimental results indicated that Han’s empirical linear velocity-porosity relation was a good prediction for cores with only interparticle pores. Secondary pores played an important role in the velocity variation of carbonates. Cores with a larger AR had faster velocities. Different ARs could lead to velocity variations as high as [Formula: see text] at a given porosity. When the wavelengths [Formula: see text] were larger than the pore size, cores with larger secondary pores found higher velocities under the same pore shape, pore fluid, and porosity condition. Different pore sizes could contribute to nearly 15% velocity variation at a given porosity. The comparison between our measurements and EMT predictions indicated that for carbonate rocks with a complicated pore structure, the self-consistent model gave more reliable predictions when the secondary pore size was relatively small ([Formula: see text]) and Kuster and Toksoz formulations as well as the differential effective medium model gave more satisfactory results when the secondary pore size was relatively large ([Formula: see text], or even smaller).

Elastic Anisotropy of a Metamorphic Rock Sample of the Canadian Shield in Northeastern Alberta

The presence of fractures and textures cause metamorphic rock masses to be seismically anisotropic. Neglect of this anisotropy in the processing of field seismic data causes problems in the final reflection images both in terms of their quality and in the true positioning of subsurface features. To quantify the degree of seismic anisotropy in the subsurface, one method is to estimate the anisotropic parameters from the elastic stiffnesses of a rock sample. Using the ultrasonic pulse transmission method, measurements of the compressional and shear wave phase velocities as a function of confining pressure are used to calculate the elastic stiffnesses of a metamorphic granite core sample from the Precambrian basement in northeastern Alberta. Velocities are measured parallel, normal and oblique to an identified foliation plane of the sample assumed to be a transversely isotropic medium. The compressional wave velocities are measured to be in the range of 5,352–6,019 m/s along the foliation plane and 4,752–5,396 m/s normal to the foliation plane over the range of confining pressures from 0 to 60 MPa. Besides providing valuable in situ velocity information for the velocity models, the results also confirm the anisotropic behavior of the metamorphic rock with the estimated compressional and shear wave anisotropy valued at 12 and 8 %, respectively. Such degree of seismic anisotropy should be taken into consideration at the seismic scale when working with three-dimensional geophysical models of the Precambrian basement to minimize any out-of-plane anomalies in the final seismic sections.

High-frequency seismic response during permeability reduction due to biopolymer clogging in unconsolidated porous media

The accumulation of biopolymers in porous media, produced by stimulating either indigenous bacteria or artificially introduced microbes, readily blocks pore throats and can effectively reduce bulk permeability. Such a microbial clogging treatment can be used for selective plugging of permeable zones in reservoirs and is considered a potentially promising approach to enhance sweep efficiency for microbial enhanced oil recovery (MEOR). Monitoring in situ microbial growth, biopolymer formation, and permeability reduction in the reservoir is critical for successful application of this MEOR approach. We examined the feasibility of using seismic signatures (P-wave velocity and attenuation) for monitoring the in situ accumulation of insoluble biopolymers in unconsolidated sediments. Column experiments, which involved stimulating the sucrose metabolism of Leuconostoc mesenteroides and production of the biopolymer dextran, were performed while monitoring changes in permeability and seismic response using the ultrasonic pulse transmission method. We observed that L. mesenteroides produced a viscous biopolymer in sucrose-rich media. Accumulated dextran, occupying 4%–6% pore volume after [Formula: see text] days of growth, reduced permeability more than one order of magnitude. A negligible change in P-wave velocity was observed, indicating no or minimal change in compressive stiffness of the unconsolidated sediment during biopolymer formation. The amplitude of the P-wave signals decreased [Formula: see text] after [Formula: see text] days of biopolymer production; spectral ratio analysis in the 0.4–0.8-MHz band showed an approximate 30%–50% increase in P-wave attenuation ([Formula: see text]) due to biopolymer production. A flow-induced loss mechanism related to the combined grain/biopolymer structure appeared to be the most plausible mechanism for causing the observed increase in P-wave attenuation in the ultrasonic frequency range. Because permeability reduction is also closely linked to biopolymer volume, P-wave attenuation in the ultrasonic frequency range appears to be an effective indicator for monitoring in situ biopolymer accumulation and permeability reduction and could provide a useful proxy for regions with altered transport properties.

Elastic behaviour of Cr3+ substituted Co–Zn ferrites

The elastic behaviour of Cr3+ substituted Co–Zn ferrites system; Co0.7Zn0.3CrxFe2−xO4 where x=0.0 to 0.5 in step of 0.1 were prepared by ceramic method. Ultrasonic Pulse transmission method at room temperature was employed to determine the elastic properties of the presently investigated samples. Values of longitudinal and shear wave velocities were increased with an increases in Cr composition x. Using these value of velocities; Young's modulus, rigidity modulus, bulk modulus, longitudinal modulus and Poisson's ratio were calculated. The values of moduli were increased with an increases in Cr composition x. Debye temperature of all sample were calculate using the Anderson equation and it shows increasing trend with an increases in Cr composition x. The behaviour elastic moduli of Co0.7Zn0.3CrxFe2−xO4 are interpreted in terms of bonding force between atoms.

Anisotropic elastic moduli of carbonates and evaporites from the Weyburn‐Midale reservoir and seal rocks

ABSTRACTAssuming Vertical Transverse Isotropy (VTI) symmetry the elastic anisotropy as a function of confining pressure of four carbonates and one evaporite from the Williston sedimentary basin in Saskatchewan, Canada is investigated using the ultrasonic pulse transmission method. Ultrasonic P‐ and S‐ wave velocities are obtained from cylindrical plugs cut from a main sample along horizontal, vertical and 45° orientations with respect to the sample's presumed vertical axis of symmetry. The elastic constants were then calculated from the measured velocities and densities. Anisotropy was quantified by estimating Thomsen parameters (Thomsen 1986) from elastic constants. The results show that the samples are at the best weakly anisotropic. The presence of microcracks and pores as well as the heterogeneity of the samples play an important role in defining the P‐ and S‐ wave velocities. The weak anisotropy found in these samples suggests that ‘intrinsic’ properties of these rocks negligibly contribute to the anisotropy observed at the seismic scale.

Ultrasonic pulse transmission method and ultrasonic diagnostic apparatus

For the purpose of preventing noticeable interleave blocks on a display screen, when a number of packets P is defined, P (≧2) ultrasonic pulse transmissions are conducted in one direction to acquire one acoustic line signal. At that time, if a number of interleaves I is defined, the ultrasonic pulse transmissions in the one direction are each interleaved with ultrasonic pulse transmissions for acquiring (I−1) acoustic line signals that belong to (I−1) frames different from the frame to which the former acoustic line signal belongs.

A physical model study of effect of fracture aperture on seismic wave

Based on Hudson’s theoretical hypothesis of equivalent fracture model, inserting aligned round chips in solid model can simulate fractured media. The effect of fractures on the propagation of P and S waves can be observed by changing the fracture thickness. The base model is made of epoxy resin, and the material of fractures is a kind of low-velocity mixture containing silicon rubber. With constant diameter and number of fractures in each model, one group of models can be formed through changing the thickness of fracture. These models have the same fracture density. By using the ultrasonic pulse transmission method, the experiment records time and waveform of P and S waves in the direction parallel and perpendicular to the fracture orientation. The result shows that, with the same fracture density, changing fracture aperture will affect both velocity and amplitude of P and S waves, and the effect on P-wave amplitude is much greater than that on the velocity. Moreover, the variation in velocity of S wave is more obvious in the slow shear wave (S2), while the variation in amplitude is more obvious in the fast shear wave (S1). These properties of wave propagation are useful for seismic data processing and interpretation.

Medical ultrasonic imaging pulse transmission method

A medical ultrasound imaging pulse transmission method transmits at least three pulses, including at least two pulses of different amplitude and at least two pulses of differing phase. The larger-amplitude pulse is transmitted with a larger aperture and the smaller-amplitude pulses are transmitted with respective smaller subapertures. The subapertures are arranged such that the sum of the subapertures used for the smaller-amplitude pulses is equal to the aperture used for the larger-amplitude pulse. In this way, pulses of differing amplitudes are obtained without varying the power level of individual transducer elements, and precise control over pulse amplitude is provided.

Experimental Investigation of Dynamic Response of Compacted Clayey Soils

Abstract A study was conducted to determine the dynamic properties of compacted clayey soils subjected to low amplitude vibration. A fast and simple ultrasonic pulse transmission method was used. Tests were conducted on three clayey soils with low to high plasticity compacted using standard and modified Proctor effort over a range of water contents. The samples were allowed to dry after compaction and P-wave velocity, S-wave velocity, Poisson's ratio, and shear modulus were determined. The effects of soil type, compaction conditions, and degree of saturation on the dynamic response of the soils were investigated. The elastic wave velocities and the dynamic shear modulus increased as the soil plasticity decreased. The velocities and the modulus increased and the Poisson's ratio decreased as the degree of saturation decreased due to drying. Generally, the velocities and moduli increased significantly at the early stages of drying with the changes becoming more gradual as drying progressed. Variations were high for soils compacted with low energy and high water content. The shear moduli of the soils were also estimated using a common empirical equation. Suction values obtained for the test soils in a different study were used as effective stresses in the estimation. The estimated shear moduli agreed well with the measured values.

Linear and Nonlinear Ultrasonic Properties of Granular Soils

ABSTRACTThe ultrasonic pulse transmission method (100-500 kHz) was adapted to measure compressional (P) and shear (S) wave velocities for synthetic soils fabricated from quartz-clay and quartz-peat mixtures. Velocities were determined as samples were loaded by small (up to 0.1 MPa) uniaxial stress to determine how stress at grain contacts affects wave amplitudes, velocities, and frequency content. Samples were fabricated from quartz sand mixed with either a swelling clay or peat (natural cellulose). P velocities in these dry synthetic soil samples were low, ranging from about 230 to 430 m/s for pure sand, about 91 to 420 m/s for sand-peat mixtures, and about 230 to 470 m/s for dry sand-clay mixtures. S velocities were about half of the P velocity in most cases, about 130 to 250 m/s for pure sand, about 75-220 m/s for sand-peat mixtures, and about 88-220 m/s for dry sand-clay mixtures. These experiments demonstrate that P and S velocities are sensitive to the amount and type of admixed second phase at low concentrations. We found that dramatic increases in all velocities occur with small uniaxial loads, indicating strong nonlinearity of the acoustic properties. Composition and grain packing contribute to the mechanical response at grain contacts and the nonlinear response at low stresses.