Changes In Acoustic Velocity Research Articles

NGHIÊN CỨU XÂY DỰNG MÔ HÌNH TÍN HIỆU THU CHO SONAR MẶT MỞ TỔNG HỢP NHIỀU MÁY THU VỚI DỮ LIỆU VỀ VẬN TỐC TRUYỀN ÂM Ở BIỂN VIỆT NAM

In this article,the received signal models are constructed for multi-receiver synthetic aperture sonar (SAS) using CW pulses and LFM pulses when considering the change of acoustic velocity in seawater and the Doppler effect. With a more complete description of the physical processes than the traditional models and the mathematical representation of signals, the proposed model can provide data sets for the research and thedevelopment of SAS imaging algorithms to save time and cost in actual data collection. The simulation results illustrate the characteristics of the signals generated from the proposed model with real data of acoustic velocity in Vietnam’s sea.

Generation of Synthetic Compressional Wave Velocity Based on Deep Learning: A Case Study of Ulleung Basin Gas Hydrate in the Republic of Korea

This study proposes a deep-learning-based model to generate synthetic compressional wave velocity (Vp) from well-logging data with application to the Ulleung Basin Gas Hydrate (UBGH) in the East Sea, Republic of Korea. Because a bottom-simulating reflector (BSR) is a key indicator to define the presence of gas hydrate, this study generates the Vp for identifying the BSR by detecting the morphology of the hydrate in terms of the change in acoustic velocity. Conventional easy-to-acquire logging parameters, such as gamma-ray, neutron porosity, bulk density, and photoelectric absorption, were selected as model inputs based on a sensitivity analysis. Long short-term memory (LSTM) and an artificial neural network (ANN) were used to design an efficient learning-based predictive model with sensitivity analysis for hyperparameters. The LSTM model outperforms the ANN model by preserving the geological sequence of the well-logging data. Ten-fold cross-validation was conducted to verify the consistency of the LSTM model and yielded satisfactory results, with an average coefficient of determination greater than 0.8. These numerical results imply that generating synthetic well-logging via deep learning can accurately estimate missing well-logging data, contributing to the reservoir characterization of gas-hydrate-bearing sediments.

Image Human Thorax Using Ultrasound Traveltime Tomography with Supervised Descent Method

The change of acoustic velocity in the human thorax reflects the functional status of the respiratory system. Imaging the thorax’s acoustic velocity distribution can be used to monitor the respiratory system. In this paper, the feasibility of imaging the human thorax using ultrasound traveltime tomography with a supervised descent method (SDM) is studied. The forward modeling is computed using the shortest path ray tracing (SPR) method. The training model is composed of homogeneous acoustic velocity background and a high-velocity rectangular block moving in the domain of interest (DoI). The average descent direction is learned from the training set. Numerical experiments are conducted to verify the method’s feasibility. Normal thorax model experiment proves that SDM traveltime tomography can efficiently reconstruct thorax acoustic velocity distribution. Numerical experiments based on synthetic thorax model of pleural effusion and pneumothorax show that SDM traveltime tomography has good generalization ability and can detect the change of acoustic velocity in human thorax. This method might be helpful for the diagnosis and evaluation of respiratory diseases.

Rime ice growth characterized by surface acoustic wave

We propose a new theoretical method and experimental investigation to characterize the growth process of rime ice through surface acoustic waves (SAWs). The Biot theory of dual-phase porous media was employed to construct a theoretical model to describe the acoustic wave propagation in porous rime ice; the transient changes in acoustic propagation attenuation and velocity were simulated; and the icing sensing mechanism of the acoustic wave propagation attenuation (∼18 dB) and the transient change in velocity (0.8 m/s) during the icing process was obtained. A 177.5 MHz waveguide type SAW micro–nano-device with an SU8/ST-90°X quartz multilayer composite film structure and a microfluidic cavity on the top of the acoustic device were designed and fabricated, and the transient attenuation in the growth of rime ice was evaluated experimentally. The experimental results indicated that the appearance of rime ice can be monitored accurately by utilizing the transient changes in acoustic wave velocity and attenuation. Therefore, the acoustic method can aid in the early warning of the development status of rime ice.

Low thermal conductivity of complex thermoelectric barium silicide film epitaxially grown on Si

We achieved substantially low thermal conductivity by introducing some crystal disorder into complex material BaSi2 films on Si substrates for realization of a high-performance thermoelectric material. The BaSi2 films/Si exhibited a low thermal conductivity of 0.96 W m−1 K−1 without nanostructuring, which is less than about two-thirds value of bulk BaSi2 and is the lowest among ecofriendly silicide materials. This substantially low thermal conductivity was brought by both the use of complex material with intrinsically low phonon group velocity and the introduction of point defects as the crystal disorder. The first-principles calculations revealed that the point defect modulates the phonon dispersion relation lowering longitudinal acoustic phonon group velocity. However, the transverse acoustic phonon group velocity was increased at the same time, resulting in a negligible change in average acoustic phonon group velocity. This indicated that the crystal disorder effect related to point defects in this system is enhancement of phonon scattering, not lowering phonon group velocity. The BaSi2 films/Si with point defects exhibited a higher thermoelectric power factor (2.9 μW cm−1 K−2) than bulk BaSi2. These results highlight that complex material BaSi2 film/Si with point defects, having substantially low thermal conductivity, is a candidate as a thermoelectric power generator material in the sensor network.

Study on plastic-brittleness mechanical properties and failure law of deep brittle shale under complex mechanical environment of wellbore

China has abundant deep shale gas resources, but the complex problem of wellbore collapse in horizontal well drilling is prominent. Aiming at the problem of wellbore collapse in deep brittle shale, deep shale’s mechanical loading simulation experiment scheme under a complex wellbore alternating mechanical environment was carried out. Triaxial mechanical tests of shale under different confining pressures are carried out in this paper. The stress-strain and acoustic characteristics of shale under different confining pressures during loading are analyzed, and rock’s stress-strain and dynamic acoustic response mechanisms are discussed. The mechanical constitutive relationship, plastic brittle mechanical properties, and anisotropic characteristics of deep brittle shale under a complex mechanical environment of the wellbore are studied. The collapse failure law of deep brittle shale wellbore is also analyzed. The results show that the deep brittle shale has high mechanical strength, is highly brittle, and developed bedding fractures. Under the condition of low confining pressure, the stress-strain curve of shale before fracture is mainly elastic deformation, and the plastic mechanical damage is not obvious. With the increase of confining pressure, shale’s compressive strength and elastic modulus increase, and its plastic damage gradually become apparent. In the process of triaxial loading, the change of acoustic wave velocity increases first and then decreases. With the increase of confining pressure, the peak stress point becomes smaller and smaller, revealing the plastic failure characteristics of rock under high confining pressure. The brittle features of shale under low confining pressure are obvious. The fracture morphology of rock after stress is mainly the splitting tensile fracture, and the number and size of cracks are significant. Under high confining pressure, shale exhibits plastic failure, and plastic damage characteristics are evident in the process of rock sample failure. Rock sample failure is mainly manifested as single shear failure or conjugate shear failure with tensile fracture. The experimental results show that the failure mode of brittle shale under a complex wellbore mechanical environment is mainly tensile splitting and shear coupling failure. The research results of this paper have particular guiding significance for the study of wellbore stability during drilling in the deep brittle shale formation.

Relative variations of nonlinear elastic moduli in polystyrene-based nanocomposites

In this paper we apply the methodology based on the analysis of changes in acoustic wave velocities under static stress for measurements of the third-order elastic moduli in three polystyrene-based nanocomposites with different fillers: SiO2 particles, halloysite natural tubules, and carbon black particles. The samples were fabricated by the same technology and our data provide information on relative changes of nonlinear properties of the composites caused by addition of the fillers. The data obtained for composites are compared with that for commercial grade polystyrene. The substantial variations of the nonlinear elastic moduli for composites with different types of fillers are demonstrated and analyzed. The results are in a qualitative agreement with theoretical predictions.

Ultrasonic based methods to characterize stability of water-in-crude oil emulsions

The potential of ultrasonic techniques to characterize water-in-oil emulsions is investigated for possible industrial applications. The emulsions for testing were prepared in mineral and crude oil samples of different types to study effects of selected variables and these were characterized for their stability and variations in droplet size distribution. Emulsions droplet structure was observed with optical microscopy and stability was examined by separation of water phase with time and changes were tracked by an ultrasonic probe. The ultrasonic parameters recorded were changes in acoustic velocity, signal attenuation and frequency spectrum of the propagating wave. The applicability of the technique to characterize emulsions of crude oils with different asphaltene content has been clearly demonstrated based on extensive testing and data analysis. The technique has been applied for the first time to determine acceptable levels of asphaltene content in crude oil to avoid formation of very stable emulsions. Attenuation measurements provided better illustration of water separation process from different emulsions compared to measurements of volume of water separated. Observed attenuation effects in ultrasonic wave have been linked to emulsion system rheology.

Influence of external swelling stress on the frequency characteristics of a volatile organic compound (VOC) sensor based on a polymer-coated film bulk acoustic resonator (FBAR)

Film bulk acoustic resonators (FBARs) are widely applied as gravimetric sensors for gas and biochemical analysis. For these devices, the sensing layer is usually coated on to the FBAR for qualitative analysis based on the frequency response according to the Sauerbrey relationship. Various polymers have been used as the sensing films for volatile organic compound (VOC) monitoring. The most significant works are focused upon developing sensing materials and optimizing the piezoelectric film to improve the performance of the sensors. However, the influence of the swelling stress upon the sensing film during vapor absorption on resonant frequency of the FBAR is often ignored. In this work, the influence of the swelling stress upon the frequency characteristics of the sensors based on polymer-coated FBARs have been investigated in detail. The elastic coefficient and acoustic wave velocity changes of the piezoelectric (AlN) layer in the FBAR in the presence of stress loads were calculated by the first-principle methods. In combination with the Mason model of the sensors, the resonant frequency shifts of the FBAR under swelling stress were obtained. The results show that the frequency shifts of the FBAR are enhanced with increased swelling stress that induce negative impacts upon the FBAR sensor-based operation. In order to improve the vapor sensing performance, the optimal thickness of the sensing film must be evaluated.

Dynamic compressibility and third-order optical nonlinearities in carbon/metal-based nanofluids.

The influence of the superposition of two high-irradiance optical beams on the mechanical properties exhibited by carbon nanotubes decorated with platinum nanoparticles was analyzed. The change in density, compressibility modulus and acoustic velocity in the samples suspended in acetone and ethanol was estimated by measuring the nonlinear refractive index tested by a two-wave mixing experiment. The nanotubes were prepared by a spray pyrolysis processing route and the metal decoration was carried by chemical vapor deposition. High-Resolution Transmission Electron Microscopy studies confirmed the multiwall nature of the carbon nanotubes; while energy-dispersive X-ray spectroscopy reveals the separated presence of platinum nanoparticles incorporated to the hybrid nanostructures. An Nd-YAG laser system emitting at 532 nm wavelength with 4 ns pulse duration was used for conducting the third-order nonlinear optical evaluations by a standard optical Kerr gate technique. Comparative experiments showed that the composition of the liquid solution plays an important role in the manipulation of the density exhibited by the nanofluids. Remarkably, the incorporation of Pt in the tubes originates stronger changes of the mechanical characteristics induced by optical nonlinearities in the nanofluids irradiated by nanosecond pulses. Within this work, it is highlighted that potential applications for developing multivalent logic operations by fuzzy mechano-optic effects exhibited by nanofluids can be contemplated.

Effect of Bifidobacterium-induced changes in tumor tissue acoustic properties on efficacy of high-intensity focused ultrasound ablation

To investigate the effects of Bifidobacterium on the acoustic characteristics of tumor tissue and how such acoustic changes affect the efficacy of high-intensity focused ultrasound (HIFU) ablation in nude mice. Forty mice bearing human breast cancer cell (MDA-MB-231) xenograft were randomized into experimental group (n=20) and control group (n=20) for intravenous injection of Bifidobacterium suspension (200 μL, 4 × 108 cfu/mL) and PBS (200 μL) for 3 consecutive days, respectively. Before and at 3 and 7 days after the first injection, shear wave elastography was used to evaluate the hardness of the tumor tissue. On day 7 after the first injection, 10 mice from each group were sacrificed and the sound velocity and sound attenuation of the tumor tissues were measured. The changes in the collagen fibers in the tumors were evaluated using Masson staining, and neovascularization in the tumor was assessed with immunohistochemistry for platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31). The remaining 10 tumor-bearing mice in each group were subjected to HIFU ablation, and the ablation efficiency was evaluated by assessing the changes in irradiation gray values, coagulative necrosis volume, energy efficiency factor (EEF) and irradiation area and by pathological examination with HE staining. In the experimental group, the collagen fibers in the tumor tissues were strong and densely aligned, and the tumors contained fewer new blood vessels showing strip-or spot-like morphologies. In the control group, the collagen fibers in the tumors were thin and loosely arranged, and the tumors showed abundant elongated or round new blood vessels. Bifidobacterium colonized in the tumor 7 days after the injection, and the tumor hardness was significantly greater in the experimental group than in the control group (P=0.01); the acoustic velocity (P=0.001) and the acoustic attenuation (P=0.000) of the tumor tissues were also greater in the experimental group. HIFU irradiation resulted in significantly greater changes in the gray scale of tumor (P=0.0006) and larger coagulative necrosis volume (P=0.0045) in the experimental group than in the control group, and the EEF was significantly smaller in the experimental group (P=0.0134). Bifidobacterium can cause changes in collagen fiber content, acoustic velocity and attenuation in the tumor tissue and reduce the EEF of HIFU irradiation, thereby improving the efficacy of HIFU irradiation.

Tracking fluids in multiple scattering and highly porous materials: Toward applications in non-destructive testing and seismic monitoring

Seismic and ultrasonic waves are sometimes used to track fluid injections, propagation, infiltrations in complex material, including geological and civil engineered ones. In most cases, one use the acoustic velocity changes as a proxy for water content evolution. Here we propose to test an alternative seismic or acoustic observable: the waveform decorrelation.We use a sample of compacted millimetric sand as a model medium of highly porous multiple scattering materials. We fill iteratively the sample with water, and track changes in ultrasonic waveforms acquired for each water level. We take advantage of the high sensitivity of diffuse coda waves (late arrivals) to track small water elevation in the material. We demonstrate that in the mesoscopic regime where the wavelength, the grain size and the porosity are in the same order of magnitude, Coda Wave Decorrelation (waveform change) is more sensitive to fluid injection than Coda Wave Interferometry (apparent velocity change). This observation is crucial to interpret fluid infiltration in concrete with ultrasonic record changes, as well as fluid injection in volcanoes or snow melt infiltration in rocky glaciers. In these applications, Coda Wave Decorrelation might be an extremely interesting tool for damage assessment and alert systems.

Relationships between mechanical and transport properties in Marcellus shale

We explore relationships among bulk modulus, crack density, and permeability through repetitive loading of Marcellus shale. Cumulative cyclic stressing (22–26 MPa with confinement of 24 MPa) is applied at a frequency of 0.05 Hz over 100,000 cycles. Changes in acoustic velocities are used to follow changes in dynamic bulk modulus, Poisson ratio, and crack density and to correlate these with bedding-parallel measurements of methane permeability. The shale is represented as an orthotropic elastic medium containing a dominant, noninteracting fracture set separated by thin laminae. An effective continuum model links permeability evolution to the evolution of the bulk modulus and crack density. Bulk modulus is linearly related to crack density by a scaling parameter representing rock fabric and fracture geometry. The Poisson ratio and bulk modulus of the intact, uncracked shale are approximated from our data. We propose a method for tracking permeability evolution of finely laminated shales using acoustic waves.

Geophysical Monitoring of Gaseous and Supercritical CO2 Fracture Flow Through a Brine-Saturated Shale Caprock

Pre-existing and induced fractures and faults can play a role as bypass conduits and fast leaking channels in CO2 storage sites. They should therefore be well characterized during site selection, and monitored thoroughly during operation to track the movement and fate of the CO2 plume. Despite to date extensive research on the geophysical properties of brine- and CO2-saturated porous reservoir rocks, changes in acoustic velocity and electrical resistivity during a sole fracture fluid displacement are, however, rather little investigated. Hence, we herein present a laboratory study of core-scale geophysical monitoring during drainage-imbibition cycles of the brine-CO2 system through a shale caprock core sample with a vertical fracture. The experiments were conducted using both gaseous and scCO2 with 4 and 9 MPa pore pressures, respectively, at 12 MPa confining pressure. The tests were performed at 40°C during the loading and unloading stages in order to look into the hysteresis effect. We used a fractured core sample from the Upper Jurassic organic-rich shales of the Draupne Formation, which is the primary caprock for the Smeaheia CO2 storage site – a full-scale CCS project in Norway. The primary objective of the experiment was to compare the geophysical measurements using gaseous and scCO2 drainage-imbibition cycles during the tests in a core-scale experiment. Moreover, we were interested to see how sensitive acoustic velocity and electrical resistance techniques are to the fracture fluid displacement using different CO2 phase states. The outcomes of our high-pressure high-temperature experiment of simultaneous measurements of fracture flow and geophysical properties indicate that potential leakage of injected CO2 through the fractured-shale caprock can be detected in the core-scale laboratory experiments. The performed drainage-imbibition cycles using gaseous and scCO2 resulted in different behaviors in P-wave velocity (Vp) and electrical resistance in axial and radial directions for these two phase states. The measured Vp during the displacement of fracture fluid, CO2-brine subsequent cycles, showed a limited sensitivity in terms of magnitude and relative change. The electrical resistance, on the other hand, shows higher sensitivity and larger variation during fluid displacement along the fracture. It was also observed that the crossplot of Vp versus electrical resistance could detect and even differentiate the different phases during the loading and unloading stages.

The effect of pore structure complexity and saturation history on the variations of acoustic velocity as function of brine and oil saturation in carbonates

Time lapse seismic is a major technique that has been successfully implemented to monitor reservoir dynamics (such as changes in fluid saturation) in sandstones but its applicability in carbonate rocks is not well understood yet. This study aims to improve our understanding of the time lapse seismic signature in carbonates oil reservoirs by investigating how acoustic velocity changes as a result of variations in the brine and oil saturation. To this scope, we utilize a core flooding system to perform brine-oil displacement experiment in three reservoir carbonate samples, while monitoring the acoustic velocity as function of brine saturation (Sw) changes. The fluid displacement experiment included injection of oil into the fully brine saturated samples until reaching irreducible brine saturation, followed by injection of brine until reaching the residual oil saturation. We also characterize the pore structure complexity of the samples using nuclear magnetic resonance (NMR) and micro-CT scans to investigate its effect on the velocity-saturation relationship. We finally compare the measured acoustic velocity as function of saturation with the predictions of Gassmann theory while considering both uniform and patchy fluid distribution styles.Our results show that both P- and S-wave velocity (Vp and Vs respectively) decrease as oil displaces brine and then they both increase as brine displaces oil. Nevertheless, the velocity-saturation relationship exhibits a hysteresis: velocities measured at a given saturation during brine injection tend to be higher than those measured during oil injection. Our analysis shows that the Vp-Sw trend during oil injection into brine saturated samples follows the lower bound predicted by Gassmann theory (i.e., uniform fluid distribution), while the brine flooding data follows the upper bound of Gassmann theory (i.e., patchy fluid distribution). The transition from the uniform to patchy fluids distribution seems to occur around the irreducible brine saturation. Since oil production or enhanced oil recovery can be represented by the process of brine displacing oil, our results suggest that patchy fluid distribution should be considered in Gassmann theory when performing feasibility studies to predict changes in Vp as function of saturation changes. This study also highlights the importance of pore structure in controlling the changes of saturation and the corresponding changes in acoustic velocity. Larger changes and hysteresis in the measured velocity as function of saturation seem to correlate with lower pore stiffness (i.e., more micro cracks and less content of intraparticle rounded pores).

Monitoring Local Changes in Granite Rock Under Biaxial Test: A Spatiotemporal Imaging Application With Diffuse Waves

AbstractDiffuse acoustic or seismic waves are highly sensitive to detect changes of mechanical properties in heterogeneous geological materials. In particular, thanks to acoustoelasticity, we can quantify stress changes by tracking acoustic or seismic relative velocity changes in the material at test. In this paper, we report on a small‐scale laboratory application of an innovative time‐lapse tomography technique named Locadiff to image spatiotemporal mechanical changes on a granite sample under biaxial loading, using diffuse waves at ultrasonic frequencies (300 kHz to 900 kHz). We demonstrate the ability of the method to image reversible stress evolution and deformation process, together with the development of reversible and irreversible localized microdamage in the specimen at an early stage. Using full‐field infrared thermography, we visualize stress‐induced temperature changes and validate stress images obtained from diffuse ultrasound. We demonstrate that the inversion with a good resolution can be achieved with only a limited number of receivers distributed around a single source, all located at the free surface of the specimen. This small‐scale experiment is a proof of concept for frictional earthquake‐like failure (e.g., stick‐slip) research at laboratory scale as well as large‐scale seismic applications, potentially including active fault monitoring.

Microscale characterization of rupture nucleation unravels precursors to faulting in rocks

Precursory signals, manifestations of microscale damage that precedes dynamic faulting, are key to earthquake forecasting and risk mitigation. Detections of precursors have primarily relied on measurements performed using sensors installed at some distance away from the rupture area in both field and laboratory experiments. Direct observations of continuous microscale damage accumulated during fault nucleation and propagation are scarce. Using an X-ray transparent triaxial deformation apparatus, we show the first quantitative high resolution three-dimensional (3D) information about damage evolution of rocks undergoing brittle failure. The dynamic microtomography images documented a spectrum of damage characteristics and different fault growth patterns. The interplay between various deformation mechanisms can result in either a positive, negative, or constant net volume change. Consequently, changes in rock density and acoustic wave velocities before faulting are expected to vary in different tectonics settings, hence making failure forecasting intrinsically dependent on rock type at depth.

Assessment of change in acoustic wave velocity of compacted expansive soil through experiments

In the present study, the non-metal acoustic waves monitor, TH204 has been used to determine P-wave velocity of compacted expansive soil under the condition of drying-wetting cycles with constant amplitude, to explore the change in P-wave velocity of compacted expansive soil with the cyclic number, cyclic amplitude and control moisture content. The results show that the P-wave velocity of the compacted expansive soil follows a non-linear decrease with increasing the cyclic number and tends to be stable. Also, under the conditions of equivalent control moisture rate and cyclic number, the cyclic amplitude has a great effect on the P-wave velocity of expansive soil. Thus, with increase in the cyclic amplitude, the P-wave velocity is decreased. Secondly, under the same cyclic number, the P-wave velocity changes with the control moisture rate monotonously. Further, the study shows that the peak values of P-wave velocity appear near the optimum moisture rate, and the peak value position remains unaltered with change in cyclic amplitude

Microstructural controls on the pressure-dependent permeability of Whitby mudstone

Abstract A combination of permeability and ultrasonic velocity measurements allied with image analysis is used to distinguish the primary microstructural controls on effective-pressure-dependent permeability. Permeabilities of cylindrical samples of Whitby mudstone were measured using the oscillating pore-pressure method at confining pressures ranging between 30 and 95 MPa, and at pore pressures ranging between 1 and 80 MPa. The permeability–effective pressure relationship is empirically described using a modified effective pressure law in terms of confining pressure, pore pressure and a Klinkenberg effect. Measured permeability ranges between 3×10 −21 and 2×10 −19 m 2 (3 and 200 nd), and decreases by approximately one order of magnitude across the applied effective pressure range. Permeability is shown to be less sensitive to changes in pore pressure than changes in confining pressure, yielding permeability effective pressure coefficients (χ) between 0.42 and 0.97. Based on a pore-conductivity model, which considers the measured changes in acoustic wave velocity and pore volume with pressure, the observed loss of permeability with increasing effective pressure is attributed dominantly to the progressive closure of bedding-parallel, crack-like pores associated with grain boundaries. Despite only constituting a fraction of the total porosity, these pores form an interconnected network that significantly enhances permeability at low effective pressures. Supplementary material: A CSV file containing all experimental conditions and a tabulation of results is available at https://doi.org/10.6084/m9.figshare.c.3785741

An Adaptive Array Excitation Scheme for the Unidirectional Enhancement of Guided Waves.

Control over the direction of wave propagation allows an engineer to spatially locate defects. When imaging with longitudinal waves, time delays can be applied to each element of a phased array transducer to steer a beam. Because of the highly dispersive nature of guided waves (GWs), this beamsteering approach is suboptimal. More appropriate time delays can be chosen to direct a GW if the dispersion relation of the material is known. Existing techniques, however, need a priori knowledge of material thickness and acoustic velocity, which change as a function of temperature and strain. The scheme presented here does not require prior knowledge of the dispersion relation or properties of the specimen to direct a GW. Initially, a GW is generated using a single element of an array transducer. The acquired waveforms from the remaining elements are then processed and retransmitted, constructively interfering with the wave as it travels across the spatial influence of the transducer. The scheme intrinsically compensates for the dispersion of the waves, and thus can adapt to changes in material thickness and acoustic velocity. The proposed technique is demonstrated in simulation and experimentally. Dispersion curves from either side of the array are acquired to demonstrate the scheme's ability to direct a GW in an aluminum plate. The results show that unidirectional enhancement is possible without a priori knowledge of the specimen using an arbitrary pitch array transducer. The experimental results show a 34-dB enhancement in one direction compared with the other.