Acoustic Axis Research Articles

Transient time-delay focusing of shock waves in thin liquids

Abstract

Experimental Study of Diffraction of Elastic Waves on Crack Model

Small-opening slots have been used to simulate cracks in butt welds. The influence of the orientation of the slot ribs on their detectability with pulse echo and diffraction methods of ultrasonic testing has been studied. It is shown that the processes occurring during the scattering of elastic waves on cracks should be modeled by a three-dimensional problem. However, theoretical analytical and numerical studies in this area most often concern two-dimensional problems of diffraction of elastic waves, where the target edge under study is located on the acoustic axis of the ultrasound source and/or receiver and is oriented perpendicular to the incident beam. The article presents experimental results illustrating the influence of the orientation of the edge (rib) in three-dimensional problems on the received signals both when using diffraction schemes of the TOFD type, and in classical ultrasonic testing by the pulse echo method according to the “tandem” scheme and with the transducers turned according to the “duet” scheme.

TO A QUESTION ABOUT QUASIBAND OF ACOUSTIC AXIS OF THE ANGLE BEAM PROBE

On the basis of modelling an acoustic path of the angle beam probe with a reflector as a side drilled hole influence of two factors resulting to quasiband of acoustic axis of the angle beam probe is shown, first of which is connected to change of amplitude echo signal owing to attenuation of a shear wave in the environment due to absorption and dispersion, and the second factor – with change of amplitude owing to a divergence of wave fronts radiated and received elastic waves. Influence of the first factor is increased with growth of attenuation and depth of reflector, and the second – on increase of distance up to a reflector practically does not depend. Quantitative estimations have revealed a ratio of influence of both factors on size of a angle quasiband of acoustic axis on value of factor of attenuation of shear waves. Reduction of an angle quasidand with increase of radius piezoplate of the angle beam probe is shown at constant operation frequency, that is at narrowing the directivity characteristic of the probe.

Эскпериментальное исследование дифракции упругих волн на модели трещины

Small opening notches are used to simulate cracks in butt welds. The study of the influence of the notch edges orientation on their detectability when using pulse-echo and diffraction methods of ultrasonic testing. It is shown that the processes occurring during the elastic waves scattering on cracks must be modeled by a three-dimensional problem. However, theoretical analytical and numerical studies in this area most often concern two-dimensional problems of elastic waves diffraction, when the target studied edge is located on the acoustic axis of the ultrasound transmitter and / or receiver and is oriented perpendicular to the incident beam. The article presents experimental results illustrating the influence of the target point (edge) orientation in three-dimensional problems on the received signals both when using diffraction schemes of the TOFD type, and in the classical ultrasonic testing by the pulse-echo method according to the "tandem" scheme and with the turn of the transducers according to the "duet ".

Extreme acoustic anisotropy in crystals visualized by diffraction tensor

Anisotropic acoustic wave propagation in single crystals is a fundamental phenomenon enabling operation of various acoustic, acousto-electronic and acousto-optic devices. It provides a variety of device performances and application fields, but its role in pre-estimation of achievable device characteristics and location of crystal orientations with desired properties is often underestimated. A geometrical image of acoustic anisotropy can be an important tool in design of devices based on wave propagation in single crystals or combinations of anisotropic materials. We propose a fast and robust method for survey and visualization of acoustic anisotropy based on calculation of the eigenvalues of bulk acoustic wave (BAW) diffraction tensor (curvature of the slowness surface). The stereographic projection of these eigenvalues clearly reveals singular directions of BAW propagation (conical acoustic axes) in anisotropic media and areas with large and small BAW beam divergence. The method is illustrated by application to three crystals of different symmetry used in different types of acoustic devices: paratellurite, lithium niobate and potassium gadolinium tungstate. The specific features of acoustic anisotropy are discussed for each crystal in terms of their potential application in devices. In addition, we demonstrate that visualization of acoustic anisotropy of lithium niobate helps to find orientations supporting propagation of high-velocity surface acoustic waves.

Acoustic Camera-Based Pose Graph SLAM for Dense 3-D Mapping in Underwater Environments

In this article, a novel dense underwater 3-D mapping paradigm based on pose graph simultaneous localization and mapping (SLAM) using an acoustic camera mounted on a rotator is proposed. The demands of underwater tasks, such as unmanned construction using robots, are growing rapidly. In recent years, the acoustic camera, which is a state-of-the-art forward-looking imaging sonar, has been gradually applied in underwater exploration. However, distinctive imaging principles make it difficult to gain an intuitive perception of an underwater environment. In this study, an acoustic camera with a rotator was used for dense 3-D mapping of the underwater environment. The proposed method first applies a 3-D occupancy mapping framework based on the acoustic camera rotating around the acoustic axis using a rotator at a stationary position to generate 3-D local maps. Then, scan matching of adjacent local maps is implemented to calculate odometry without involving internal sensors, and an approximate dense global map is built in real time. Finally, based on a graph optimization scheme, offline refinement is performed to generate a final dense global map. Our experimental results demonstrate that our 3-D mapping framework for an acoustic camera can achieve dense 3-D mapping of underwater environments robustly and accurately.

Analysis of multiple shear wave modes in a nonlinear soft solid: Experiments and finite element simulations with a tilted acoustic radiation force

Tissue nonlinearity is conventionally measured in shear wave elastography by studying the change in wave speed caused by the tissue deformation, generally known as the acoustoelastic effect. However, these measurements have mainly focused on the excitation and detection of one specific shear mode, while it is theoretically known that the analysis of multiple wave modes offers more information about tissue material properties that can potentially be used to refine disease diagnosis. This work demonstrated proof of concept using experiments and finite element simulations in a uniaxially stretched phantom by tilting the acoustic radiation force excitation axis with respect to the material's symmetry axis. Using this unique set-up, we were able to visualize two propagating shear wave modes across the stretch direction for stretches larger than 140%. Complementary simulations were performed using material parameters determined from mechanical testing, which enabled us to convert the observed shear wave behavior into a correct representative constitutive law for the phantom material, i.e. the Isihara model. This demonstrates the potential of measuring shear wave propagation in combination with shear wave modeling in complex materials as a non-invasive alternative for mechanical testing.

Acoustic factors affecting interaural level differences for cochlear-implant users.

Bilateral cochlear-implant (BICI) listeners primarily use interaural level differences (ILDs) to localize sound in the horizontal plane. However, the ILD magnitude is altered at different frequencies and azimuths due to a combination of several acoustic phenomena such as the acoustical bright spot, acoustic axis, and microphone porting. This paper investigated the effects of BICI microphone placement on ILDs through an analysis of head-related transfer functions. At-the-canal BICI microphone placement provided both larger and more monotonic ILD-azimuth functions than behind-the-ear microphone placement. Results have implications for the fitting of clinical devices and their effect on sound localization in BICI users.

The Influence of Intratermocline Eddies on Sound Propagation in the Deep Part of the Sea of Japan

The results of stochastic modeling of the influence of positive and negative intratermocline eddies (lenses) on the spatiotemporal structure of acoustic fields in the deep part of the Sea of Japan are presented. The lens shape was modeled by an ellipse. The lens center and the emitter were located on the axis of the underwater sound channel. The vertical distribution of the acoustic field inside the lens was studied at various ranges in front of the center, in the center and behind the center of the lens, as well as at ranges of 40 and 100 km. A negative lens focuses the ray paths on the axis of underwater sound channel at all ranges. A positive lens has a defocusing effect, yet with an increase in range it decreases significantly. The impulse response of the propagation channel was studied on the underwater acoustic channel axis at the ranges of 40 and 100 km. The maxima of impulse response during the passage of the sound emitter through the negative lens shift in time towards increasing, and when passing through the positive lens – towards decreasing with respect to the impulse response of the propagation channel in the absence of lenses.

SOME FEATURES OF ULTRASONIC TESTING OF CAST IRON OBJECTS WITH FLAKE AND GLOBULAR GRAPHITE USING NORMAL LINEAR PROBES WITH PHASED ARRAYS

Computer modelling of the acoustic characteristics of signals of direct normal probe with phased array (PFR) in the cast iron with flake and globular graphite was performed. As a result the form of acoustic pulses of a longitudinal wave, depending on the passed by wave distance and the values of attenuation coefficient for different models of cast iron was calculated. The main modeled characteristics of the probe include the directivity characteristic and the change in the amplitude of the signal along the acoustic axis. It is shown that the difference in the PFR directivity characteristics for cast iron with flake graphite of different models and steel is due to two factors – significantly lower longitudinal wave velocities in cast iron compared to steel and a decrease in its operating frequency due to attenuation. In this case, for cast iron with globular graphite, a small change in the width of the diagrams is due only to the lower speed of longitudinal waves in cast iron compared to steel. For cast iron with flake graphite model 3, the phenomenon of nonlinear attenuation due to a decrease in the frequency of the maximum of the signal spectrum during the propagation of a longitudinal wave in cast iron with a corresponding decrease in the frequency – dependent attenuation coefficient is established. Evaluation of the nonlinearity of attenuation for cast iron with globular graphite showed that it is very small. The influence of calculation of initial signal delays on the velocity of longitudinal waves in steel on the directivity characteristics in cast iron, decreasing with increasing focus distance, is established. It is shown that for cast iron with flake graphite there are cases when the direction of transmitting of PFR in cast iron is practically absent.

Acoustic Vortex Beam Generation by a Piezoelectric Transducer Using Spiral Electrodes**Supported by the National Natural Science Foundation of China under Grant Nos 11772349, 11472299, 51704015, 11972354 and 11972365 and the China Agricultural University Education Foundation under Grant No 1101-240001.

We propose an innovative method to generate acoustic vortex waves based on a disc piezoelectric transducer that is coated with multi-arm coiled electrodes. Finite element simulation results for single-arm to four-arm coiled electrodes indicate that the method could modulate amplitude and phase spatial distribution of the acoustic waves near the acoustic axis by acoustic field synthesis principle, making the waves rotate spirally in space and form stable focused vortex beams. Compared with the traditional method that requires electronic control of an array consisting of a large number of transducers, this method provides a more effective and compact solution.

ABOUT OF THE METHOD OF DECREASE RAIL TRANSPORT IMPACT NOISE IN LOW FREQUENCY RANGE

The method of decrease impact noise between of wheel pairs rail transport and rail joints being main sources of noise is analyzed. The spectrum of such noise reaches a maximum in an octave strip of 31,5 Hz and sharply decreases in a strip of 1 kHz. The practical implementation dipole effect can be received by formation a pair of the knock impulse sources when the direction of acoustical axes is along the railway under small angle. The compensatory effect when one rail joint for example right moves according left joint in other rail on the distance d having half of wave length of the basic low-frequency range of shock impulses is reached. The system of standing waves in the interval d by an antiphase pair of sources with coherent components in the basic frequency 31,5 Hz and odd harmonics is formed. The new additional effect to noise reduction by replacement the rectangular rail joint edges on the oblique-angled rail joints having 45 degree edge angle is carried out.

QUANTIFICATION OF ACOUSTIC RADIATION FORCES ON SOLID OBJECTS IN FLUID.

Theoretical models allow design of acoustic traps to manipulate objects with radiation force. Here, a model of the acoustic radiation force by an arbitrary beam on a solid object was validated against measurement. The lateral force in water of different acoustic beams was measured and calculated for spheres of different diameter (2-6 wavelengths λ in water) and composition. This is the first effort to validate a general model, to quantify the lateral force on a range of objects, and to electronically steer large or dense objects with a single-sided transducer. Vortex beams and two other beam shapes having a ring-shaped pressure field in the focal plane were synthesized in water by a 1.5-MHz, 256-element focused array. Spherical targets (glass, brass, ceramic, 2-6 mm dia.) were placed on an acoustically transparent plastic plate that was normal to the acoustic beam axis and rigidly attached to the array. Each sphere was trapped in the beam as the array with the attached plate was rotated until the bead fell from the acoustic trap because of gravity. Calculated and measured maximum obtained angles agreed on average to within 22%. The maximum lateral force occurred when the target diameter equaled the beam width; however, objects up to 40% larger than the beam width were trapped. The lateral force was comparable to the gravitation force on spheres up to 90 mg (0.0009 N) at beam powers on the order of 10 W. As a step toward manipulating objects, the beams were used to trap and electronically steer the spheres along a two-dimensional path.

Properties of acoustic axes in triclinic media

We developed a method of obtaining relationships that describe the position of the acoustic axes in a triclinic medium and the dependencies between them. It is proved that these relations are linearly independent in real number system. However, any relationship algebraically depends on other two relationships. The relation between derived relationships and those obtained in earlier papers is also investigated. The formulae defining the change of these relationships when rotating around the axes of the coordinate system are derived. It is proved that the fulfillment of five relations is necessary and sufficient for the definition of all acoustic axes in a given coordinate system. It is shown that the acoustic axis in a given phase direction exists if and only if the specified two vectors of dimension five are collinear. For an orthorhombic medium, these relations are represented in an explicit form by homogeneous polynomials of the sixth degree in the components of the phase direction vector and the third degree in the stiffness coefficients. It is shown that in symmetry planes, only two of these relations are not identically equal to zero. The theory is illustrated in two numerical examples of anisotropic media. In the first example, for a triclinic medium, the positions of the sixteen acoustic axes are shown as the intersection points of the graphs of three relationships on the plane (phase polar and azimuth angles). In this case, six points corres-pond to the intersections of P and S1 phase velocities sheets, and ten points correspond to the intersections of S1 and S2 phase velocities sheets. The second example demonstrates the definition of all acoustic axes in an orthorhombic medium based on the derived relationships. To illustrate this example, we consider only one quadrant due to symmetry with respect to symmetry planes.

The kinematics of S waves in acoustic orthorhombic media

ABSTRACTOrthorhombic models are often used in the seismic industry nowadays to describe azimuthal and polar anisotropy and reasonably realistic in capturing the features of the earth interior. It is challenging to handle so many model parameters in the seismic data processing. In order to reduce the number of the parameters for P wave, the acoustic orthorhombic medium is proposed by setting all on‐axis S wave velocities to zero. However, due to the coupled behaviour for P and S waves in the orthorhombic model, the ‘S wave artefacts’ are still remained in the acoustic orthorhombic model, which kinematics needs to be defined and analysed. In this paper, we analyse the behaviour of S wave in acoustic orthorhombic media. By analysis of the slowness surface in acoustic orthorhombic media, we define the S waves (or S wave artefacts) that are more complicated in shape comparing to the one propagating in an acoustic transversely isotropic medium with a vertical symmetry axis. The kinematic properties of these waves are defined and analysed in both phase and group domain. The caustics, amplitude and the multi‐layered case for S wave in acoustic orthorhombic model are also discussed. It is shown that there are two waves propagating in this acoustic orthorhombic medium. One of these waves is similar to the one propagating in acoustic vertical symmetry axis media, whereas another one has a very complicated shape consisting of two crossing surfaces.

A Mirror Method for Measuring Directional Patterns in the Auxiliary (Azimuthal) Plane of Angle Transducers

A new mirror method is proposed for measuring directional patterns of angle piezoelectric transducers in an auxiliary (azimuthal) plane. Measurements of directional patterns in the auxiliary plane were carried out for transducers with angles of probe ranging from 34° to $$70^\circ $$ using the mirror method on a steel sample with plane-parallel surfaces. It has been established that for transducers with wedge angles close to the first critical one (probe angle $$34^\circ $$ ), the beam angle of the directional pattern in the auxiliary plane widens; this can be explained by a refracted longitudinal (head) wave participating in pattern formation. It is shown that directional patterns can be effectively measured in the auxiliary plane of piezoelectric transducers for azimuthal angles ranging within $$ \pm 15^\circ $$ from the acoustic axis.

Echolocation clicks of free-ranging Irrawaddy dolphins (Orcaella brevirostris) in Trat Bay, the eastern Gulf of Thailand.

Little is known about the vocalizations of Irrawaddy dolphins (Orcaella brevirostris) in the Gulf of Thailand. The present study first described the echolocation clicks of Irrawaddy dolphins in Trat Bay, in the eastern Gulf of Thailand, using a broadband hydrophone system. Over 2 h of acoustic recordings were collected during 14-day study periods in December 2017 and December 2018. Several criteria were used to judge if a click was on axis or as close to the acoustic axis as possible. To calculate the distance of dolphins, a low-budget localization method based on arrival time differences between the direct and indirect signals was used in the present study. The clicks had a mean peak-to-peak source level of 192 ± 3 dB re 1 μPa, an energy flux density source level of 131 ± 3 dB re 1 μPa2s, a mean centroid frequency of 98 ± 10 kHz, a mean duration of 16 ± 2 μs, and a -3 dB bandwidth of 79 ± 13 kHz. The click parameters of the Irrawaddy dolphins in Trat Bay were slightly different from the clicks recorded from the dolphins in Sundarbans, Bangladesh. The present study provided a basic description of the click characteristics of Irrawaddy dolphins in Trat Bay, which could contribute to the management and conservation strategies for local Irrawaddy dolphins, and a basic reference for the proper input parameters in passive acoustic monitoring and detection.

Direct Three-Dimensional Measurement of Refractive Index via Dual Photon-Phonon Scattering.

We developed a microscopy technique that can measure the local refractive index without sampling the optical phase delay of the electromagnetic radiation. To do this, we designed and experimentally demonstrated a setup with two colocalized Brillouin scattering interactions that couple to a common acoustic phonon axis; in this scenario, the ratio of Brillouin frequency shifts depends on the refractive index, but not on any other mechanical and/or optical properties of the sample. Integrating the spectral measurement within a confocal microscope, the refractive index is mapped at micron-scale three-dimensional resolution. As the refractive index is probed in epidetection and without assumptions on the geometrical dimensions of the sample, this method may prove useful to characterize biological cells and tissues.

Anisotropy of acoustic and thermal expansion properties of TlInSe2 crystals

ABSTRACTBased on experimental studies of acoustic wave velocities in TlInSe2 crystals, all components of their elastic stiffness and compliance tensors are determined. TlInSe2 has three acoustic axes parallel to the principal crystallographic directions. The lowest velocities of acoustic eigenwaves are used to estimate the acousto-optic figure of merit. We analyse deviations from purely longitudinal and transverse polarization states, as well as the obliquity of acoustic energy flow. Temperature dependences of strains along the three principal crystallographic directions and of acoustic wave velocities v11, v22 and v33 are measured. Anomalous behaviour of these parameters occur at T1245 K and T2145 K. It is shown that the symmetry of TlInSe2 becomes lower than tetragonal below the temperature point T1.

Acoustic beam pattern for a push-pull laser interferometric sound sensor

A push-pull laser interferometric sound sensor uses two parallel laser beams where both beams are exposed to the sound filled fluid. In arrays of conventional piezoelectric hydrophones, each array element produces a voltage and the beam pattern is obtained by deriving the response as a function of acoustic wave angle in terms of electrical power divided by the maximum response power along the acoustic axis. In a push-pull laser interferometric sound sensor the response function is an optical path difference or phase difference between the two laser beams as a function of acoustic wave angle. In an analogous way, we derive a response function in terms of the optical path difference between two optical line sensors as a function of acoustic wave angle and divide by the response along the acoustic axis. This normalized response function is squared to obtain the beam pattern for a push-pull laser interferometric sensor. We compare this beam pattern to that of a conventional line array.