Difference In Acoustic Impedance Research Articles

Extraction and characteristic analysis of the nonlinear acoustic impedance of circular orifice in the presence of bias flow

The acoustic behavior of the circular orifice is influenced by the bias flow and high amplitude sound excitation. The present study proposes an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation to extract the nonlinear acoustic impedance of circular orifice. Impact coefficients of the bias flow on the acoustic impedance of circular orifice are defined as the ratio of the acoustic impedance difference between the cases in the presence and absence of bias flow under high amplitude sound excitation to that under low amplitude sound excitation. The effects of bias flow Mach number, orifice diameter, plate thickness, and porosity on the impact coefficients under different amplitude sound excitations are studied, and the impact coefficients could collapse all the predictions by using the non-dimensional sound particle velocity. The fitting formulas of nonlinear acoustic impedance of circular orifice are presented by using nonlinear regression analysis.

Full-duplex two-way no-relay cross-media communication method based on acoustic wave conversion

Abstract Due to the difference in acoustic impedance between water and air, the water interface becomes a natural barrier. Underwater sound waves will bounce when they propagate to the water surface. Electromagnetic waves and light waves in the air will rapidly attenuate after passing through the water surface and going underwater, making it difficult to complete air-water cross-media information transmission. In this article, we first analyze the theoretical characteristics and vibration model of the water surface after medium collision, and develop a new full-duplex communication method across the air-ocean medium, which does not rely on relay equipment and only uses three transmission media in the air. Propagate signals in the sea channel physical field to achieve two-way communication, using the mutual conversion between laser, acoustic, and radio frequency signals to fill the gap in cross-media communication technology that can simultaneously achieve two-way, full-duplex and non-relay. It has been verified through experimental installations carried out in laboratory water tanks and large comprehensive anechoic pools that it is able to achieve full-duplex communication links across the air-sea surface, indicating that the combination of laser acousticization and radio frequency-acoustic wave conversion can be used across medium full-duplex wireless communication provides a feasible method for communication that breaks through the water interface.

Physics-Embedded Neural Networks for Enhanced Ultrasonic Brain Tomography

Abstract Ultrasound imaging, valued for its non-invasiveness and cost-effectiveness, faces challenges in brain imaging due to acoustic impedance differences. This study introduces PEN-UBT, a deep learning-based method, combining Convolutional Neural Network for Forward Propagation (CN-FP) and Subnetwork for Inversion (SNI). CN-FP simplifies wavefield calculations, while SNI facilitates mapping from wavefield to model. PEN-UBT achieves high-fidelity imaging of the skull and soft tissues, excelling in scenarios with varying thrombus velocities. It demonstrates exceptional tissue resolution in brain slices, reducing imaging time to 1.13 seconds. PEN-UBT’s success extends its applicability beyond brain imaging, contributing to the broader field of medical imaging technologies.

Analysis of a standing wave thermoacoustic engine with multiple unit stages

The thermoacoustic engine is an eco-friendly technology capable of harnessing solar and waste energy for electricity generation, in conjunction with a linear alternator, and can function as a heat pump. This engine type holds significant appeal due to its simplistic design, devoid of any mechanical moving components, comprising only a stack sandwiched between heat exchangers within a resonator. When the temperature gradient across the stack reaches the critical threshold (onset temperature), the working gas undergoes spontaneous oscillation. Typically, a high onset temperature is necessary to induce gas oscillation in a thermoacoustic engine due to viscous losses within the system. A method to lower the onset temperature by increasing the number of unit stages consisting of stacks and heat exchangers so that the engine can utilize low-grade thermal sources has been developed to overcome this challenge. However, this method has only been applied to traveling-wave thermoacoustic engines. Its application in standing-wave engines, which offer a more compact and straightforward structure, remains unexplored. This research aims to examine how the number of unit stages in a standing-wave thermoacoustic engine influences the onset temperature and acoustic field. The onset temperature is estimated using a fundamental hydrodynamics equation and the investigation of the acoustic field throughout the engine using DeltaEC software. Results showed that the strategic positioning of multiple unit stages is essential to achieve a low onset temperature. The minimum onset temperature, approximately 92°C, is obtained when three- or four-unit stages are installed. Additionally, increasing the number of unit stages does not affect the acoustic impedance and phase difference between pressure and velocity in the stack, while simultaneously enhancing both acoustic power output and thermal efficiency.

Deep Learning With Physics-Embedded Neural Network for Full Waveform Ultrasonic Brain Imaging.

The convenience, safety, and affordability of ultrasound imaging make it a vital non-invasive diagnostic technique for examining soft tissues. However, significant differences in acoustic impedance between the skull and soft tissues hinder the successful application of traditional ultrasound for brain imaging. In this study, we propose a physics-embedded neural network with deep learning based full waveform inversion (PEN-FWI), which can achieve reliable quantitative imaging of brain tissues. The network consists of two fundamental components: forward convolutional neural network (FCNN) and inversion sub-neural network (ISNN). The FCNN explores the nonlinear mapping relationship between the brain model and the wavefield, replacing the tedious wavefield calculation process based on the finite difference method. The ISNN implements the mapping from the wavefield to the model. PEN-FWI includes three iterative steps, each embedding the F CNN into the ISNN, ultimately achieving tomography from wavefield to brain models. Simulation and laboratory tests indicate that PEN-FWI can produce high-quality imaging of the skull and soft tissues, even starting from a homogeneous water model. PEN-FWI can achieve excellent imaging of clot models with constant uniform distribution of velocity, randomly Gaussian distribution of velocity, and irregularly shaped randomly distributed velocity. Robust differentiation can also be achieved for brain slices of various tissues and skulls, resulting in high-quality imaging. The imaging time for a horizontal cross-sectional imag e of the brain is only 1.13 seconds. This algorithm can effectively promote ultrasound-based brain tomography and provide feasible solutions in other fields.

Geophysical Research on an Open Pit Mine for Geotechnical Planning and Future Land Reclamation: A Case Study from NW Macedonia, Greece

In open pit mining areas, knowledge of geotechnical conditions (e.g., overburden thickness, background slope, and fault locations) ensures geotechnical safety during exploitation as well as reclamation planning. The Greek Public Power Corporation initiated a research program after stability issues emerged on the southern side of the Mavropigi open pit mine in NW Macedonia. Geotechnical wells revealed steeply dipping bedrock and thin tectonic contact, indicating the need for the detailed imaging of the subsurface for future stability measures. For this purpose, a geophysical investigation aimed to extract information mostly for the dip of the interface between schist bedrock and overlaying Neogene sediments and/or limestones. Based on the high contrast of electrical properties between schists and limestones, as well as the differences in acoustic impedance and formation thickness, the seismic reflection and electrical resistivity tomography (ERT) methods were selected. The suitability of the seismic reflection for its application in this area was checked by generating synthetic seismic data, which resulted from the simulation of seismic wave propagation for geological models of the area. The acquisition parameters were determined after the noise test. Field seismic data processing produced a depth-migrated section, which revealed the existence of a fault. The use of dipole–dipole and gradient arrays, in 2D and 3D electrical resistivity measurements, ensured both the lateral and vertical mapping of schist bedrock and detected limestone bodies within the overburden. Also, the tectonic contact zone between limestone and schist formations was properly imaged. The comparison between geoelectrical and seismic sections indicated that the seismic reflection method provided a more accurate estimate of fault inclination. Finally, the geophysical survey enriched the geotechnical models necessary for sustainable mining (e.g., rational exploitation, the optimization of productivity, and zero accidents) including the planning of future reclamation.

A small-scale swimmer actuated by acoustic radiation force

A small-scale swimmer based on a piezoelectric actuator is proposed in this work, which could serve as the thruster for a minitype underwater robot. The out-of-plane stretching vibration mode in the thickness direction of the piezoelectric actuator is selected as the operating mode. Acoustic radiation propultion is generated due to the difference in acoustic impedance between solid and liquid media, then the opposite acoustic driving force makes the swimmer move forward. The vibration modes of piezoelectric actuator in dry and wet modals are compared through the finite element simulation, and verified by mechanical vibration characteristic test. Then a prototype with the size of Φ 37 mm × 45 mm is fabricated. The underwater performance shows that its linear speed achieves 33.93 mm s−1 under the voltage of 160 Vp–p with the frequency of 900 Hz and has a capacity of carrying 20 g loads, which confirms the feasibility of the proposed underwater driving method.

Accurate Detection of Concrete Pavement Thickness Based on Ultrasonic Array

Thickness detection of concrete pavement is a critical step in construction completion acceptance and serves as an important metric for subsequent pavement performance evaluations. The crux of thickness evaluation lies in determining the interface reflection echo propagation sound time. Based on the acoustic impedance difference between the surface layer and contact layer, pavement can be classified into two types: large-difference and small-difference. By examining the singularity of the detection signal, we employed the improved correlation coefficient method and the wavelet transform maximum value method to identify the interface reflection echo sound time. This study refines the traditional correlation coefficient method by using the surface direct wave as the reference signal, simplifying the signal analysis process. In actual detection, for the type of concrete pavement with large differences in acoustic impedance, the average relative error between the improved correlation coefficient method and the core drilling method can be reduced to 1.7%; for the type with small differences, the average relative error of the detection results obtained using the wavelet transform modulus maximum method can be reduced to 1.9%, showcasing high accuracy.

Development and experimental verification of an active noise cancellation (ANC) method for non-invasive sensing

Ultrasonic wave propagation may be used in non-invasive sensing to identify the properties of a fluid in a container. An ultrasonic excitation can be coupled into the liquid or the gas through the walls of the container and detected by a receiver on the other side. However, in addition to this fluid path, another signal will also propagate through the structure and is referred as noise in this study. For most materials, this structural noise will be of higher amplitude compared to the fluid signal due to the large acoustic impedance difference between the solid container and the fluid. In this paper, an active noise cancellation (ANC) method is developed and demonstrated on an experimental setup. It was shown that this method cancels more than 90% of the noise signal in a given time window of interest. A sequential version of this cancellation method is also proposed, and it was shown that its performance improves as the number of canceling excitations is increased. The performance was found to be independent of the location of canceling transducers and position of the silence window but dependent on the width of the silence window. As an example, the ANC method was applied to noise cancellation of a signal travelling through water in a stainless-steel container. The signal-to-noise ratio (SNR) of the water signal in the window of interest was increased by 148% from 13.98 dB to 34.68 dB by using the proposed ANC method.

Theoretical and numerical modeling of Rayleigh wave scattering by an elastic inclusion

This work presents theoretical and numerical models for the backscattering of two-dimensional Rayleigh waves by an elastic inclusion, with the host material being isotropic and the inclusion having an arbitrary shape and crystallographic symmetry. The theoretical model is developed based on the reciprocity theorem using the far-field Green's function and the Born approximation, assuming a small acoustic impedance difference between the host and inclusion materials. The numerical finite element (FE) model is established to deliver a relatively accurate simulation of the scattering problem and to evaluate the approximations of the theoretical model. Quantitative agreement is observed between the theoretical model and the FE results for arbitrarily shaped surface/subsurface inclusions with isotropic/anisotropic properties. The agreement is excellent when the wavelength of the Rayleigh wave is larger than, or comparable to, the size of the inclusion, but it deteriorates as the wavelength gets smaller. Also, the agreement decreases with the anisotropy index for inclusions of anisotropic symmetry. The results lay the foundation for using Rayleigh waves for quantitative characterization of surface/subsurface inclusions, while also demonstrating its limitations.

Debonding Detection in Aluminum/Rigid Polyurethane Foam Composite Plates Using A0 Mode LAMB Wave EMATs

Aluminum/rigid polyurethane foam composite plates (ARCPs) are widely used for thermal insulation. The interface debonding generated during manufacturing degrades the thermal insulation performance of an ARCP. In this study, the debonding of an ARCP, a composite plate with a porous and damped layer of rigid polyurethane foam (RPUF), was detected using A0 mode Lamb wave electromagnetic acoustic transducers (EMATs). The low energy transmission coefficient at the interface caused by the large acoustic impedance difference between aluminum and RPUF made the detection difficult. Based on these structural characteristics, an A0 mode Lamb wave with large out-of-plane displacement was used to detect the debonding. EMATs are preferred for generating A0 mode Lamb waves due to their advantages of being noncontact, not requiring a coupling agent, and providing convenient detection. A finite element simulation model considering the damping of the RPUF layer, the damping of the PU film at the interface, and the bonding stiffness of the interface was established. The simulation results indicated that the Lamb wave energy in the aluminum plate transmits into the RPUF layer in small amounts. However, the transmitted energy rapidly attenuated and was not reflected into the aluminum plate, as the RPUF layer was thick and highly damped. Therefore, energy attenuation was evident and could be used to characterize the debonding. An approximately linear relationship between the amplitude of the received signals and the debonding length was obtained. Experiments were performed on an ARCP using EMATs, and the experimental results were in good agreement with the simulation results.

Demonstration of Fat Properties in Diagnostic Ultrasound Images through the Development of a Modular Phantom

The proportion of fat content in the body is important in the classification and grading of disease. In a clinical situation, the image characteristics of adipose tissue are used as information in diagnosing disease. Therefore, the imaging characteristics of adipose tissue on ultrasound images should be understood in a comprehensive manner. In this study, we describe the imaging characteristics of adipose tissue using ultrasound phantoms representing three different fat fractions. The three fat fractions were 0%, 40%, and 80%, and the phantoms consisted of agarose gel containing either distilled water or one of two emulsions. To characterize the fat content, the gel phantoms were scanned using an Accuvix V10 ultrasound system. Both the brightness of the ultrasound image and the attenuation of the ultrasound echo increased with increasing fat content. Deep structures could not be observed clearly in areas with high fat content. Both pure water and fat appeared to be echo-free. Pure water displayed acoustic enhancement, while fat displayed acoustic shadowing. However, the emulsion appeared to be hyperechoic because of the difference in acoustic impedance between water and fat. The results show that well-characterized fat fraction images can potentially be used to understand the characteristics of adipose tissue human body on ultrasound.

Experimental vs. Numerical Computation of Acoustic Analyses on the Thickness Influence of the Multilayer Panel

Sound-absorbing panels made with a perforated front and a sound-absorbing material on the back have been used in many forms of construction for a long time. It is a reasonably efficient system, obtaining high values of sound absorption at a specific resonant frequency, depending on the design of the structure of the sound-absorbing multilayer panel. The present work considers an acoustic panel in two constructive types, consisting of four layers: a front panel made of perforated sheet, polyethylene foam foil, basalt wool board with two different thicknesses, and a back panel of the non-perforated sheet. Due to the different thicknesses of the basalt wool board, for the multilayer structure of the acoustic panel, differences in acoustic impedance and acoustic absorption can be highlighted, experimentally determined with an impedance tube, using the transfer function method (TFM) based on EN ISO 10534-2 in the frequency range 100–3200 Hz. In the meantime, a method was developed to predict the sound absorption coefficient, namely the prediction of sound absorption coefficient using the transfer matrix method (PSAC-TMM). This computational model of the multilayer acoustic panel is introduced considering the internal geometry of the multilayer panel, as well as the computation of the acoustic impedance of each layer, all gathered through the transfer matrix method (TMM). Comparative analyses between experimental data and predictive results using PSAC-TMM were performed, validating the PSAC-TMM as a predictive method to estimate the sound absorption coefficient for acoustic multilayer panels.

Effect of thickness on the performance parameters of modified 1–3 piezoelectric composites

In this study, a modified 1–3 piezoelectric composite was designed to investigate the relationship between its thickness and properties of piezoelectric composites. First, the modified 1–3 piezoelectric composite was simulated using COMSOL to obtain the resonant and anti-resonant frequencies of each piezoelectric composite thickness, and the electromechanical coupling coefficient, acoustic impedance, acoustic velocity, and frequency difference of the corresponding thickness were calculated. Second, the modified 1–3 piezoelectric composite was simplified using series-parallel theory and uniform field theory, and the relevant piezoelectric performance parameters of the piezoelectric composites of different thicknesses were calculated. The above results were verified experimentally, and the experimental results were in good agreement with the simulation results. Although the theoretical calculation results deviated slightly from the experimental results, the overall trend was consistent with the experimental results. Finally, the performance parameters of the modified 1–3 piezoelectric composite and traditional 1–3 piezoelectric composite with a thickness of 7.5 mm were compared. It was found that the acoustic impedance of this modified 1–3 piezoelectric composite was smaller than that of the traditional 1–3 piezoelectric composite, and the electromechanical coupling coefficient was larger than that of the traditional 1–3 piezoelectric composite. Therefore, this modified 1–3 piezoelectric composite has great potential for the preparation of high-performance piezoelectric ultrasonic transducers.

Acousto-Photolithography for Programmable Shape Deformation of Composite Hydrogel Sheets.

Stimuli-responsive hydrogels with programmable shapes produced by defined patterns of particles are of great interest for the fabrication of small-scale soft actuators and robots. Patterning the particles in the hydrogels during fabrication generally requires external magnetic or electric fields, thus limiting the material choice for the particles. Acoustically driven particle manipulation, however, solely depends on the acoustic impedance difference between the particles and the surrounding fluid, making it a more versatile method to spatially control particles. Here, an approach is reported by combining direct acoustic force to align photothermal particles and photolithography to spatially immobilize these alignments within a temperature-responsive poly(N-isopropylacrylamide) hydrogel to trigger shape deformation under temperature change and light exposure. The spatial distribution of particles can be tuned by the power and frequency of the acoustic waves. Specifically, changing the spacing between the particle patterns and position alters the bending curvature and direction of this composite hydrogel sheet, respectively. Moreover, the orientation (i.e., relative angle) of the particle alignments with respect to the long axis of laser-cut hydrogel strips governs the bending behaviors and the subsequent shape deformation by external stimuli. This acousto-photolithography provides a means of spatiotemporal programming of the internal heterogeneity of composite polymeric systems.

Effect of interface structure on thermal conductivity and stability of diamond/aluminum composites

Diamond/aluminum composites were fabricated by gas pressure infiltration with pure aluminum and pristine diamond, nanoscale W or WC coated diamond as raw materials. The influence of interfacial phase type and size on the thermal conductivity of the composites was investigated. The evolution of microstructure and properties of composites under temperature shock environment was also analyzed. The introduction of W and WC coatings inhibits the formation of interfacial phase Al4C3, while the generation of amorphous carbon in WC-coated diamond/aluminum composite causes a weak interface bonding and huge acoustic impedance difference with diamond, leading to a decrease in thermal conductivity. The W-coated diamond/aluminum composite shows the optimal thermal properties after 1000 cycles of temperature shock treatment. The introduction of W coating can improve performance stability while maintaining high thermal conductivity, making them promising thermal management composites.

A simple classroom exercise for teaching principles of ultrasound diagnostic using two springs

We present a novel method for demonstrating the physical principles of ultrasound imaging at a level suitable for educational programmes up to the university level, using a simple mechanical model that is very inexpensive and accessible to a broad variety of educational institutions. The method revolves around the use of one or two steel springs that can be extended on a flat surface. The spring represents a tissue and the longitudinal wave traveling along the spring represents the propagation of an ultrasound wave in tissue. This method allows students to gain direct experience with wave propagation, reflection and transmission in tissue as well as insight into the physical processes underlying ultrasound imaging. These include equally the ultrasound diagnostic device measurement of the depth of various tissue boundaries, modelled as a simple measurement of the time elapsed between the emission of a wave and the detection of a wave reflected from an object intersecting the spring. An ultrasound device probes the boundary between a formation (an organ or a lesion) and surrounding tissue by registering the amplitude of reflection on the formation, which is proportional to a difference in acoustic impedance between the formation and the tissue. The amplitude of the reflected wave in our apparatus is also proportional to acoustic impedance between the spring and an object like a plastic ruler intersecting the spring, whose stiffness and consequently acoustic impedance can be adjusted by its offset. It is also easy to clearly see the reflected wave on the boundary of two coupled springs (two tissues) with different acoustic impedances. We represent a series of representative measurements using our mechanical model demonstrating its good precision.

Experimental study on pressure evolution of detonation waves penetrating into water

Propagation of detonation waves crossing the gas–liquid interface is a basic phenomenon worth studying for underwater detonation engines. In this work, the pressure evolution of detonation waves penetrating into water is theoretically and experimentally investigated. The one-dimensional shock wave theory is adopted to solve the pressure–velocity relations of the reflected and transmitted shock wave in different mediums. Experiments under different filling pressure are performed based on a two-phase shock tube system. Theoretical results show that the range of pressure rise ratios between the detonation and transmitted wave is 2.40–2.50. Its trend is determined by the total atoms number of fuel under low filling pressure, but dominated by the ratio of C/H atoms under high filling pressure. Experimental results demonstrate that pressure rise ratios are in good agreement with the theoretical values. There are similar attenuation laws (decay to 50% in 0.3 ms) for subsequent pressure development after those two waves. Under the interface effect, the transmitted wave is stretched and the pressure zone becomes wider. The difference of acoustic impedance between two phases leads to wave property changes at the interface and exit. These changes result in the reciprocating cavitation zones and reformed shock waves in the water, greatly influencing the water pressure.

Fabrication and Modeling of Matching System for Air-Coupled Transducer.

The tremendous acoustic impedance difference between the piezoelectric composite and air prevents the ultrasonic transition, resulting in low amplitude for the received signal for the composite defect detection using an air-coupled transducer. The matching system, which includes the matching layers and bonding layers attached to the piezoelectric composite, can reduce the acoustic impedance difference and benefit the acoustic transition. In this paper, the fabrication method and modeling for the matching layers are proposed to optimize the transducer performance. The effects of bonding layer material on the transducer performance are also discussed. Experiments were conducted for modeling validation. The proposed model can predict the matching layer acoustic properties with an error of less than 11%. The bonding layer using the same material as the first matching layer can help to increase the sensitivity by about 33% compared to the traditional epoxy bonding. The optimized air-coupled ultrasonic transducer, based on the results of this study, has a 1283 mV amplitude in the air, which is 56% higher than commercially available transducers, and can identify the defects in two typical non-metallic composite materials easily.

Self-Enhanced Acoustic Impedance Difference Strategy for Detecting the Acidic Tumor Microenvironment.

B-mode ultrasound imaging is a significant anatomic technique in clinic, which can display the anatomic variation in tissues. However, it is difficult to evaluate the functional state of organs and display the physiological information in organisms such as the tumor acidic microenvironment (TME). Herein, inspired by the phenomenon of sonographic acoustic shadow during detecting calculus in clinic, a strategy of self-enhanced acoustic impedance difference is proposed to monitor the acidic TME. BiF3@PDA@PEG (BPP) nanoparticles can self-aggregate in a specific response to the acidic TME to form huge "stones" BiF3@PDA, resulting in an increase of local tumor density, and further causing a significant acoustic impedance difference. In in vitro experiments, the enhanced ultrasound signals change from 15.2 to 196.4 dB, which can discriminate different pH values from 7.0 to 5.0, and the sensitivity can reach to 0.2 value. In in vivo experiments, the enhanced ultrasound signal is 107.7 dB after BPP self-aggregated, displaying the weak acidic TME that has a close relationship with the size and species of the tumor. More importantly, the accuracy is away from the interference of pressure because huge "stones" BiF3@PDA change little. However, SonoVue microbubbles will diffuse and rupture under pressure, which results in false positive signals. To sum up, this strategy will be helpful to the further development of ultrasound molecular imaging.