Longitudinal Shear Wave Research Articles

Dual-Wave ZnO Film Ultrasonic Transducers for Temperature and Stress Measurements.

ZnO film ultrasonic transducers for temperature and stress measurements with dual-mode wave excitation (longitudinal and shear) were deposited using the reactive RF magnetron sputtering technique on Si and stainless steel substrates and construction steel bolts. It was found that the position in the substrate plane had a significant effect on the structure and ultrasonic performance of the transducers. The transducers deposited at the center of the deposition zone demonstrated a straight columnar structure with a c-axis parallel to the substrate normal and the generation of longitudinal waves. The transducers deposited at the edge of the deposition zone demonstrated inclined columnar structures and the generation of dominant shear or longitudinal shear waves. Transducers deposited on the bolts with dual-wave excitation were used to study the effects of high temperatures in the range from 25 to 525 °C and tensile stress in the range from 0 to 268 MPa on ultrasonic response. Dependencies between changes in the relative time of flight and temperature or axial stress were obtained. The dependencies can be described by second-order functions of temperature and stress. An analysis of the contributions of thermal expansion, strain, and the speed of sound to changes in the time of flight was performed. At high temperatures, a decrease in the signal amplitude was observed due to the decreasing resistivity of the transducer. The ZnO ultrasonic transducers can be used up to temperatures of ~500 °C.

Simultaneous measurement of thickness and ultrasonic wave velocity using a combination of laser-generated multiple wave modes in the thermoelastic regime

ABSTRACT This paper introduces a reliable laser ultrasonic technique without damage to the surface in the thermoelastic regime that provides a one-side access method for simultaneously determining the thickness and ultrasonic wave velocity by employing multiple wave modes. Initially, this study determines the optimal separated distance between two laser beams to achieve an effective signal-to-noise ratio of the employed wave modes. Subsequently, a pre-established ratio of 0.95 for the velocity of skimming longitudinal waves and longitudinal waves enables the simultaneous calculation using a combination of the skimming longitudinal wave, reflected shear wave, and mode-converted longitudinal wave in a single measurement. Experiments were carried out on various plane plates made of aluminium alloy 6061, ranging in thickness from 4 to 20 mm, demonstrating a high accuracy in thickness measurement, with a maximum absolute error of 0.05 mm. Compare the results of ultrasonic wave velocity measurements with theoretical calculations, the maximum absolute error is 32 m/s and 80 m/s for longitudinal wave and shear wave, respectively.

Acoustic radiation force-induced longitudinal shear wave for ultrasound-based viscoelastic evaluation

Acoustic radiation force (ARF) is widely used to induce shear waves for evaluating the mechanical properties of biological tissues. Two shear waves can be generated when exciting with ARF: a transverse shear wave, also simply called shear wave (SW), and a longitudinal shear wave (LSW). Shear waves (SWs) have been broadly used to assess the mechanical properties. Some articles have reported that the LSW can be used to evaluate mechanical properties locally. However, existing LSW studies are mainly focused on the group velocity evaluation using optical coherence tomography (OCT). Here, we report that a LSW generated with ARF can be used to probe viscoelastic properties, including shear modulus and viscosity, using ultrasound. We took advantage of the surface boundary effect to reflect the LSW, named RLSW, to address the energy deficiency of LSW induced by ARF. We systematically evaluated the experiments with tissue-mimicking viscoelastic phantoms and validated by numerical simulations. Phase velocity and dispersion comparison between the results induced by a RLSW and a SW exhibit good agreement in both the numerical simulations and experimental results. The Kelvin-Voigt (KV) model was used to determine the shear modulus and viscosity. RLSW shows great potential to evaluate localized viscoelastic properties, which could benefit various biomedical applications such as evaluating the viscoelasticity of heterogeneous materials or microscopic lesions of tissues.

Polarization state conversion achieved by chiral mechanical metamaterial

Recently, metamaterials have driven advancements in wave propagation and polarization control. Chiral elastic metamaterials, in particular, have attracted considerable attention due to their distinctive properties, such as acoustical activity and auxeticity. Such characteristics arise from the additional degrees of freedom for tuning the embedded micro- and macro-rotations. In this study, we demonstrate an unusual energy exchange between longitudinal and in-plane shear waves in a 3D chiral mechanical metamaterial. The structural design is capable of inducing up to a 90∘ rotation in the plane of polarization. Additionally, this capacity for conversion is achieved by employing both an arrangement of chiral cells and a single meta-atom. This peculiar behavior enables a seamless switch between the three polarization states existing within a solid material, namely, the longitudinal state, the shear horizontal state, and the shear vertical state. Furthermore, a 2D discrete mono-atomic mass-spring model featuring inclined connectors is used to characterize the distinctive energy exchange between modes. This characterization is based on the retrieval of the pertinent elastic coefficients. The engineered chiral metamaterial polarization converter stands as a promising device for momentum conservation conversions and applications in elasto-dynamic polarimetry.

Delta Radiomics Based on Longitudinal Dual-modal Ultrasound Can Early Predict Response to Neoadjuvant Chemotherapy in Breast Cancer Patients

To develop a monitoring model using radiomics analysis based on longitudinal B-mode ultrasound (BUS) and shear wave elastography (SWE) to early predict pathological response to neoadjuvant chemotherapy (NAC) in breast cancer patients. In this prospective study, 112 breast cancer patients who received NAC between September 2016 and March 2022 were included. The BUS and SWE data of breast cancer were obtained prior to treatment as well as after two and four cycles of NAC. Radiomics features were extracted followed by measuring the changes in radiomics features compared to baseline after the second and fourth cycles of NAC(△R[C2], △R [C4]), respectively. The delta radiomics signatures were established using a support vector machine classifier. The area under receiver operating characteristic curve (AUC) values of △RBUS (C2) and △RBUS (C4) for predicting the response to NAC were 0.83 and 0.84, while those of △RSWE (C2) and △RSWE (C4) were 0.88 and 0.90, respectively. △RSWE exhibited significantly superior performance to △RBUS for predicting NAC response (Delong test, p<0.01). No significant differences were observed in the performances between △R (C2) and △R (C4) based on BUS or SWE data. The longitudinal dual-modal ultrasound radiomics (LDUR) model had an excellent discrimination, good calibration and clinical usefulness, with the AUC, sensitivity and specificity of 0.97, 95.52% and 91.11%, respectively. The LDUR model achieved excellent performance in predicting the pathological response to chemotherapy during the early stages of NAC for breast cancer.

Visualization of Human Hand Tendon Mechanical Anisotropy in 3D Using High-Frequency Dual-Direction Shear Wave Imaging.

High-resolution ultrasound shear wave elastography has been used to determine the mechanical properties of hand tendons. However, because of fiber orientation, tendons have anisotropic properties; this results in differences of shear wave velocity (SWV) between ultrasound scanning cross sections. Rotating transducers can be used to achieve full-angle scanning. However, this technique is inconvenient to implement in clinical settings. Therefore, in this study, high-frequency ultrasound (HFUS) dual-direction shear wave imaging (DDSWI) based on two external vibrators was used to create both transverse and longitudinal shear waves in the human flexor carpi radialis tendon. SWV maps from two directions were obtained using 40-MHz ultrafast imaging at the same scanning cross section. The anisotropic map was calculated pixel by pixel, and 3D information was obtained using mechanical scanning. A standard phantom experiment was then conducted to verify the performance of the proposed HFUS DDSWI technique. Human studies were also conducted where volunteers assumed three hand postures: relaxed (Rel), full fist (FF), and tabletop (TT). The experimental results indicated that both the transverse and the longitudinal SWVs increased due to tendon flexion. The transverse SWV surpassed the longitudinal SWV in all cases. The average anisotropic ratios for the Rel, FF, and TT hand postures were 1.78, 2.01, and 2.21, respectively. Both the transverse and the longitudinal SWVs were higher at the central region of the tendon than at the surrounding region. In conclusion, the proposed HFUS DDSWI technique is a high-resolution imaging technique capable of characterizing the anisotropic properties of tendons in clinical applications.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Stress State Near Cracks Originating from the Edges of a Thin Rigid Inclusion Caused by the Action of Longitudinal Shear Waves

Stress State Near Cracks Originating from the Edges of a Thin Rigid Inclusion Caused by the Action of Longitudinal Shear Waves

Noncontact longitudinal shear wave imaging for the evaluation of heterogeneous porcine brain biomechanical properties using optical coherence elastography.

High-resolution quantification of heterogeneous brain biomechanical properties has long been an important topic. Longitudinal shear waves (LSWs) can be used to assess the longitudinal Young's modulus, but contact excitation methods have been used in most previous studies. We propose an air-coupled ultrasound transducer-based optical coherence elastography (AcUT-OCE) technique for noncontact excitation and detection of LSWs in samples and assessment of the nonuniformity of the brain's biomechanical properties. The air-coupled ultrasonic transducer (AcUT) for noncontact excitation of LSWs in the sample has a center frequency of 250 kHz. Phase-resolved Doppler optical coherence tomography (OCT) was used to image and reconstruct the propagation behavior of LSWs and surface ultrasound waves at high resolution. An agar phantom model was used to verify the feasibility of the experimental protocol, and experiments with ex vivo porcine brain samples were used to assess the nonuniformity of the brain biomechanical properties. LSWs with velocities of 0.83 ± 0.11 m/s were successfully excited in the agar phantom model. The perivascular elastography results in the prefrontal cortex (PFC) of the ex vivo porcine brains showed that the Young's modulus was significantly higher in the longitudinal and transverse directions on the left side of the cerebral vessels than on the right side and that the Young's modulus of the PFC decreased with increasing depth. The AcUT-OCE technique, as a new scheme for LSW applications in in vivo elastography, can be used for noncontact excitation of LSWs in brain tissue and high-resolution detection of heterogeneous brain biomechanical properties.

Noncontact and rapid measurement of elastic properties of metals with a dual-mode bulk-wave EMAT

ABSTRACT The elastic mechanical behaviour of materials is very important to the design and service safety evaluation of mechanical load components. In order to accurately measure the elastic mechanical behaviour of metal structures with a non-destructive testing way, a dual-mode bulk-wave electromagnetic acoustic transducer (EMAT) is developed for both ultrasonic longitudinal wave and shear wave measurement. The elastic modulus and Poisson’s ratio of metals are directly obtained with the velocities of the longitudinal and shear waves. In order to improve the efficiency of electromagnetic acoustic transducer, the electromagnetic acoustic parameters were characterised and optimised by numerical simulation. The results show that the developed dual-mode EMAT can successfully excite and receive longitudinal and shear waves, and the elastic modulus and Poisson’s ratio of different materials (copper, aluminium and steel) obtained through experiments using the developed dual-mode EMAT are very close to the reference values.

Longitudinal motion of focused shear wave beams in soft elastic media.

Shear waves are employed in medical ultrasound imaging because they reveal variations in viscoelastic properties of soft tissue. Frequencies below 1 kHz are required due to the substantially higher attenuation and lower propagation speeds than for compressional waves. Shear waves exhibiting particle motion in the direction of propagation, referred to as longitudinal shear waves, can be generated with longitudinal motion of a circular disk on the surface of a soft elastic medium. This approach permits imaging of the longitudinal shear wave with a conventional ultrasound transducer that is coaxial with the source of the shear wave. Presented here is a mathematical model describing the complete wave field generated by displacement at the surface of an isotropic elastic half-space. Numerical simulations are shown for longitudinal, transverse, torsional, and radial source polarizations, with emphasis on focused longitudinal shear waves. Predictions are consistent with measurements of light beams revealing that the longitudinal electric field component produces a smaller focal spot than the transverse field component [Dorn, Quabis, and Leuchs, Phys. Rev. Lett. 91, 233901 (2003)]. Simulations are compared with preliminary measurements of a focused longitudinal shear wave beam generated in a soft tissue phantom by longitudinal motion of a spherically concave piston.

Finite element analysis of laser ultrasonic in functionally graded material

Functionally graded material (FGM) has great advantages compared with homogeneous material. However, it is prone to occur in delamination failure because of stress concentration. Laser ultrasonic (LU) has many advantages in the detection of complex structural material. Therefore, it is appropriate for the detection of the functionally graded material. In this paper, the finite element method is used to study the laser ultrasonic in TC4/Inconel718 functionally graded material, focusing on the influence of material interfaces and the material component of transition layers on the ultrasound. The results show that material interfaces can increase the amplitude of the Rayleigh wave as well as attenuate and scatter the longitudinal wave and shear wave. The material component of transition layers influences the increased amplitude of the Rayleigh wave indirectly. The velocity of ultrasound in the functionally graded material is reduced with the increase of the propagation depth. This study provides an appropriate method for the detection of the functionally graded material and lays a foundation for the application of laser ultrasonic in it.

Fatigue state characterisation of steel pipes using ultrasonic shear waves.

The phenomenon of the reduction in the propagation speed of an ultrasonic wave when it travels through a fatigue zone has been well studied in the literature. Additionally, it has been established that shear waves are more severely affected by the presence of such a zone, compared with longitudinal waves. Our study utilises these phenomena to develop a method able to characterise the fatigue state of steel pipes. Initially, the existing theory regarding the increased sensitivity of shear waves to the presence of fatigue is validated through measuring and comparing the change in propagation speed of both longitudinal and bulk shear waves on flat geometries, at different fatigue states. The comparison is achieved with the aid of ultrasonic speed C-scans of both longitudinal and shear waves, with the latter now being obtainable through our implementation of advances in Electromagnetic Acoustic Transducers (EMAT) technology. EMATs have not been traditionally used for producing C-scans, and their ability do to so with adequate repeatability is demonstrated here; we show that shear wave scanning with EMATs now provides a possibility for inspection of fatigue damage on the inner surface of pressure-containing components in the nuclear power industry. We find that the change in ultrasonic wave speed is amplified when shear waves are used, with the magnitude of this amplification agreeing well with the theory. Following the verification of the theory, the use of EMATs allowed us to tailor the shear wave scanning method to pipe geometries, where C-scans with conventional piezoelectric transducers would not have been possible, with the results successfully revealing the presence of fatigue zones.

Quantitative assessment of muscle properties in polymyositis and dermatomyositis using high-frequency ultrasound and shear wave elastography

Polymyositis (PM) and dermatomyositis (DM) are two common types of idiopathic inflammatory myopathy and can lead to a poor prognosis and quality of life. We designed this cross-sectional study to investigate the abilities of high-frequency ultrasound (HFUS) and shear wave elastography (SWE) to assess muscle properties in patients with PM and DM and to distinguish healthy muscles from diseased muscles with PM and DM. A total of 60 patients (26 PM cases and 34 DM cases) and 65 matched healthy volunteers were continuously included in the case and control groups, respectively. For the bilateral deltoid, biceps brachii, rectus femoris, and vastus lateralis, the muscle thickness, echo intensity, and longitudinal shear wave velocity (SWV) of all participants were measured using HFUS and SWE. The intra- and interobserver reliability of SWV measurements of patients with PM and DM and the receiver operating characteristic curve for HFUS and SWE for PM and DM were analyzed. Patients with PM and DM had significantly decreased muscle thickness and increased muscle echo intensity compared to healthy controls (P<0.001). The patients' and healthy participants' deltoid, biceps brachii, rectus femoris, and vastus lateralis thickness was 19.75 and 23.00 mm, 20.45 and 22.80 mm, 18.40 and 20.20 mm, and 20.00 and 22.80 mm, respectively. Except for the biceps brachii, the mean SWV in the longitudinal orientation in patients with PM and DM significantly decreased (P<0.01). The mean SWV of the patients' and healthy participants' deltoid, rectus femoris, and vastus lateralis was 2.47 and 2.57 m/s, 1.73 and 1.87 m/s, and 1.57 and 1.77 m/s, respectively. Excellent intra- and interobserver reliability of SWV measurements on the deltoid and rectus femoris of PM and DM patients were found (intraclass correlation coefficient >0.95; P<0.001). The diagnostic performance of echo intensity in lower-extremity proximal muscles for PM and DM was excellent [area under the curve (AUC) >0.9]. The thickness of most muscles displayed moderate diagnostic performance (the AUC ranged from 0.700 to 0.775). The SWV of the vastus lateralis showed a stable performance (AUC =0.741). The combined diagnostic performance of echo intensity and thickness and the combined diagnostic performance of the 3 indicators were relatively high (the AUC ranged from 0.871 to 0.936 and from 0.898 to 0.938, respectively). Muscle thickness and echo intensity showed statistical differences in different disease stages of PM and DM (P'<0.01). HFUS and SWE may serve as imaging biomarkers for the diagnosis of PM and DM by detecting abnormal muscle thinning, enhanced muscle echo intensity, and reduced muscle SWV.

Investigation of the relationship between tensile viscoelasticity and unloaded ultrasound shear wave measurements in ex vivo tendon

Mechanical properties of biological tissues are of key importance for proper function and in situ methods for mechanical characterization are sought after in the context of both medical diagnosis as well as understanding of pathophysiological processes. Shear wave elastography (SWE) and accompanying physical modelling methods provide valid estimates of stiffness in quasi-linear viscoelastic, isotropic tissue but suffer from limitations in assessing non-linear viscoelastic or anisotropic material, such as tendon. Indeed, mathematical modelling predicts the longitudinal shear wave velocity to be unaffected by the tensile but rather the shear viscoelasticity. Here, we employ a heuristic experimental testing approach to the problem to assess the most important potential confounders, namely tendon mass density and diameter, and to investigate associations between tendon tensile viscoelasticity with shear wave descriptors. Small oscillatory testing of animal flexor tendons at two baseline stress levels over a large frequency range comprehensively characterized tensile viscoelastic behavior. A broad set of shear wave descriptors was retrieved on the unloaded tendon based on high frame-rate plane wave ultrasound after applying an acoustic deformation impulse. Tensile modulus and strain energy dissipation increased logarithmically and linearly, respectively, with the frequency of the applied strain. Shear wave descriptors were mostly unaffected by tendon diameter but were highly sensitive to tendon mass density. Shear wave group and phase velocity showed no association with tensile elasticity or strain rate-stiffening but did show an association with tensile strain energy dissipation.The longitudinal shear wave velocity may not characterize tensile elasticity but rather tensile viscous properties of transversely isotropic collagenous tissues.

Elastic moduli parameterization and inversion considering nanopores effects in shale

Nanopores are widely developed in organic kerogen in shale. Due to the large surface-bulk ratio, nanopores cause significant surface effects that affect the overall elastic properties of shale. It is essential to consider the effects of nanopores when applying the prestack seismic inversion technique for shale reservoir prediction. Based on classical elastic theory, the technique of amplitude variation with offset (AVO) can usually extract velocity of the longitudinal wave and shear wave, elastic modulus, and density in shale reservoir from prestack seismic amplitudes but often ignores the surface effects of nanopores. For this reason, we have derived a new AVO parameterization combining the nanoporoelasticity theory and AVO technique. The newly derived parameterization contains four parameters (shear modulus of matrix, nanopores-related parameter, shear modulus of saturated rock, and density) which can be used to estimate the nanopore properties of shale. The model test and real seismic data examples verify the feasibility and suitability of the proposed method by applying the Bayesian inversion technique with smooth background constraint.

Surface excitation of focused shear wave beams in soft elastic media: Theory

Shear wave propagation is employed in medical ultrasound imaging, because it reveals variation in the viscoelastic properties of tissue. Frequencies below 1 kHz are required for imaging with shear waves in soft tissue due to their high attenuation and low propagation speeds, compared to compressional waves with frequencies above 1 MHz used for ultrasound imaging. Shear waves exhibiting particle motion in the direction of propagation, referred to as longitudinally polarized shear waves, can be generated by applying longitudinal motion of a circular disk to the surface of a soft elastic medium. This approach is used in practice because it permits imaging of the longitudinal shear wave with a conventional ultrasound transducer that is coaxial with the source of the shear wave. Presented here are the theoretical framework and numerical simulations that illustrate effects of focusing on longitudinally polarized shear waves. Longitudinal, transverse, radial, and torsional source polarizations are considered. The present investigation was motivated initially by an experimental study in optics due to Dorn et al. [Phys. Rev. Lett. 91, 233901 (2003)]. Our predictions for shear wave beams support their measurements of light beams revealing that the longitudinal electric field component produces a smaller focal spot than the transverse field component.

Visualization of Human Skeletal Muscle Mechanical Anisotropy by Using Dual-Direction Shear Wave Imaging.

Ultrasound (US) shear wave elasticity imaging (SWEI) is a mature technique for diagnosing the elasticity of isotropic tissues. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be diagnosed correctly using SWEI because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, SWEI has been studied for measuring the anisotropic properties of muscles by rotating the transducer; however, this is difficult for clinical practice. In this study, a novel dual-direction shear wave imaging (DDSWI) technique was proposed for visualizing the mechanical anisotropy of muscles without rotation. Longitudinal and transverse shear waves were created by a specially designed external vibrator and supersonic pushing beam, respectively; the SWVs were then tracked using ultrafast US imaging. Subsequently, the SWV maps of two directions were obtained at the same scanning cross section, and the mechanical anisotropy was represented as the ratio between them at each pixel. The performance of DDSWI was verified using a standard phantom, and human experiments were performed on the gastrocnemius and biceps brachii. Experimental results of phantom revealed DDSWI exhibited a high precision of <0.81% and a low bias of <3.88% in SWV measurements. The distribution of anisotropic properties in muscle was visualized with the anisotropic ratios of 1.54 and 2.27 for the gastrocnemius and biceps brachii, respectively. The results highlight the potential of this novel anisotropic imaging in clinical applications because the conditions of musculoskeletal fiber orientation can be easily and accurately evaluated in real time by DDSWI.

Transmission detection of internal defects in billets using shear ultrasonic waves

We used ultrasonic shear waves for nondestructive defect detection in a billet using transmitted waves. We utilized the deviation the time-of-flight (TOF) obtained by cross-correlation of transmitted waves of a defect-free reference plane and that of a measurement plane containing a defect. We compared the performance of longitudinal waves and shear waves at different wavelengths in detecting the diameter of a circular defect in two-dimensional (2D) simulation and the TOF for a cylindrical defect while changing the vibration direction of shear waves in three-dimensional (3D) simulation. Shear waves detected defects better than longitudinal waves in the 2D simulation, especially at wavelengths of 1.4–2.4 mm. In the 3D simulation, the maximum TOF was larger when the vibration direction was perpendicular to the defect’s major axis than when it was parallel in the measurement using shear waves. This suggests a defect’s shape can be estimated by measurement using shear waves.

Investigation of the Effect of Temperature on Ultrasonic, Mechanical and Thermal Properties in Single Silver Nanowire

The present paper reports the elastic, mechanical and thermophysical properties of silver nanowire (Ag NW) using ultrasonic techniques at temperature dependent. Higher order elastic constants are calculated using Coulomb and Born-Mayer potential up to second nearest neighbour. To compute mechanical parameters such as young modulus, bulk modulus, shear modulus tetragonal modulus, Poisson's ratio, fracture to toughness ratio and Zener anisotropy factor for finding imminent performance of the single silver nanowire at temperature dependent using second order elastic constants. The Ag NW is found to be brittle in nature at room temperature. Finally, we have evaluated the ultrasonic velocities, ultrasonic attenuation due to phonon–phonon interaction and thermoelastic relaxation for longitudinal wave and shear waves along &lt;100&gt;, &lt;110&gt; and &lt;111&gt; crystallographic directions in the temperature range 100-300K of silver nanowire using the higher order elastic constants. The attained results are discussed in correlation with available outcomes on these properties for the silver nanowire.