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Forward modelling of sedimentary systems is a method that simulates sedimentation processes over geological time to generate a set of facies distributed in a depositional space. The objective of using forward modelling in this work was to build a 3D facies model from which a synthetic seismic simulation was generated, and then to analyse the relation of seismic-stratigraphic interpretations with the knowledge of the a priori generated sedimentological model. This modelling methodology was applied in a pre-salt field in the Santos Basin, Brazilian offshore, focused on the Barra Velha Formation. The modelling parameters used were: (i) the initial surface of bathymetric depth; (ii) the lake-level variation; (iii) the subsidence map; and (iv) the deposition rates of the facies. Average-constant of acoustic impedance values were assigned to each facies and a synthetic seismic was obtained. With the facies and synthetic models available, it was possible to analyse: (i) the distribution of thicknesses and proportion of facies by region; (ii) the vertical stacking pattern and lateral facies variation; (iii) the Wheeler distance × time diagram; and (iv) the seismic reflector patterns through the seismic facies classification. Through these analyses it was possible to better understand the possibilities and limitations of seismic stratigraphy as an interpretation auxiliary tool in pre-salt carbonate environments. [ABSTRACT FROM AUTHOR]

In this research, a design method for triply periodic minimal surface (TPMS) structures with a high specific strength for broadband sound absorption is proposed. The graded TPMS structures are controlled by linear, quadratic, and sine functions. Homogeneous TPMSs and graded TPMSs were manufactured by laser powder bed fusion (LPBF) with AlSi7Mg powder, and acoustic impedance tube, compression, and digital image correlation (DIC) tests were applied to obtain the sound absorption and compression properties. The sound absorption coefficient of a homogeneous gyroid increases as the height and offset thickness of the surface increase, and it increases as element size decreases. The sound absorption peak shifts to low frequencies as the height of the structure increases. The average sound absorption coefficient at 1/3 octave from 500 to 6300 Hz of the graded TPMS with a porosity from 60.51 to 77.59% (surface of incident sound wave to rigid backing) is superior to that of the graded TPMS with a porosity from 77.59 to 60.51%, but the latter has a broadband sound absorption coefficient. The compression and DIC results of graded TPMS also show excellent mechanical properties and energy absorption characteristics. [ABSTRACT FROM AUTHOR]

An air-coupled transducer was developed in this study, utilizing hollow glass microsphere-organosilicon composites as an acoustically matching layer, which demonstrated outstanding acoustic performance. Firstly, a comparison and analysis of the properties and advantages of different substrates was carried out to determine the potential application value of organosilicon substrates. Immediately after, the effect of hollow glass microspheres with different particle sizes and mass fractions on the acoustic properties of the matching layer was analyzed. It also evaluated the mechanical properties of the matching layer before and after optimization. The findings indicate that the optimized composite material attained a characteristic acoustic impedance of 1.04 MRayl and an acoustic attenuation of 0.43 dB/mm, displaying exceptional acoustic performance. After encapsulating the ultrasonic transducer using a 3D-printed shell, we analyzed and compared its emission and reception characteristics to the commercial transducer and found that its emission acoustic pressure amplitude and reception voltage amplitude were 34% and 26% higher, respectively. Finally, the transducer was installed onto a homemade ultrasonic flow meter for practical application verification, resulting in an accuracy rate of 97.4%. [ABSTRACT FROM AUTHOR]

The acoustic metamaterial in the form of a petal-shaped channel embedded Helmholtz resonator (P-CEHR) is proposed for perfect sound absorption. According to theoretical predictions, numerical simulations, and experiments, the P-CEHR achieves perfect low-frequency (e.g., 200 Hz) sound absorption across a deep subwavelength thickness (e.g., 1/34 of the corresponding acoustic wavelength). Compared with the circular-shaped channel embedded Helmholtz resonator, the sound absorption peak and bandwidth of P-CEHR are significantly improved (e.g., increased by 20.9% and 60.0%, respectively) under fixed overall dimensions. Physically, the introduction of the petal shape changes the fluid dynamic characteristics of the channel, resulting in the periodic distribution of particle velocity along the circumferential direction and the expansion of the area of the viscous boundary layer. By adjusting the morphology of the embedded channel, the tortuosity ratio and the relative static flow resistance of the channel can be regulated appropriately, so that the resonator can meet the acoustic impedance matching condition and achieve excellent sound absorption performance. This work provides a method for improving the performance of acoustic absorption metamaterials with built-in air channels and has guiding significance for the control of low-frequency noise. [ABSTRACT FROM AUTHOR]

The 1-3 piezoelectric composite is the key component of the acoustic transducer, which is widely used in detection, due to the high energy conversion efficiency, cheap raw material, and low aging. To reveal the influence of epoxy mixture, used to connect the piezoelectric column, on the composite performance, a 1-3 piezoelectric composite model was built. The effects of mixture properties on the impedance curves, vibration mode, and deformation displacement of the composite were determined. Six 1-3 piezoelectric composites with different filling mixture properties, by changing the glass microspheres’ mass ratio in the epoxy, were prepared and measured to validate the model. The results showed that with the increase in the proportion of the glass microsphere in the epoxy mixture, the vibration coupling of the piezoelectric composites was gradually eliminated. The acoustic impedance was reduced by 12%. The electromechanical coupling coefficient and effective electromechanical coupling coefficient were increased by 5.4% and 8.3%, respectively. The density and Young’s modulus decrease in filling mixture can significantly improve piezoelectric composite performance.

A lack of labeled examples is a problem in different domains, such as text and image processing, medicine, and static reservoir characterization, because supervised learning relies on vast volumes of these data to perform successfully, but this is quite expensive. However, large amounts of unlabeled data exist in these domains. The deep semi-supervised learning (DSSL) approach leverages unlabeled data to improve supervised learning performance using deep neural networks. This approach has succeeded in image recognition, text classification, and speech recognition. Nevertheless, there have been few works on pre-stack seismic reservoir characterization, in which knowledge of rock and fluid properties is fundamental for oil exploration. This paper proposes a methodology to estimate acoustic impedance using pre-stack seismic data and DSSL with a recurrent neural network. The few labeled datasets for training were pre-processed from raw seismic and acoustic impedance data from five borehole logs. The results showed that the acoustic impedance estimation at the well location and outside it was better predicted by the DSSL compared to the supervised version of the same neural network. Therefore, employing a large amount of unlabeled data can be helpful in the development of seismic data interpretation systems.

Non-Hermitian scattering systems respecting parity-time symmetry exhibit unidirectional invisibility or reflectionlessness at an exceptional point of the scattering matrix. In this study, we investigate the scattering properties of a one-dimensional acoustic parity-time-symmetric multilayered medium. Parity-time symmetry is defined by a spatial small-amplitude square-wave modulation of the medium parameters in the complex plane. Such a multilayered medium has been demonstrated to reach an exceptional point and support unidirectional invisibility for balanced real and imaginary part modulations of the refractive index. Through the analysis of interference within the medium, we show that the complex modulation of acoustic impedance instead of the refractive index governs the exceptional point of the scattering matrix and determines the occurrence of the unidirectional invisibility. This unidirectional invisibility is further investigated for more general cases of complex parameter distribution including unequal modulation amplitudes and rectangular wave modulation. Our study provides an intuitive physical picture of the occurrence of unidirectional invisibility induced by an exceptional point in acoustic wave systems. Moreover, this study could facilitate the design and practical realization of acoustic parity-time-symmetric structures. [ABSTRACT FROM AUTHOR]

In this paper, a study to determine the acoustic properties of Chihuahua, Manchego, and panela cheeses is carried out by applying acoustic spectroscopy in the ultrasound spectrum. The products were purchased at a local store in the capital city of Chihuahua. The echoscope block of the GAMPT® acoustic tomograph with acoustic sensor at 2 MHz was used to measure the acoustic phase velocity (m/s), which depended on the thickness, with a quasiregular ambient temperature of 16 °C. The acoustic tomograph used transmission with normal incidence. Measurements were performed in triplicate. The volumetric density and acoustic impedance of the cheeses, as well as the rheological properties, were determined through an indirect method. The results show that the acoustic phase velocities of the Chihuahua, Manchego and panela cheeses were APVChi ≈ 1221.47 m/s, APVman ≈ 1436.05 m/s, and APVpan ≈ 1142.28 m/s, respectively. The volumetric densities of the Chihuahua, Manchego, and panela cheeses were ρChi ≈ 1.16 gr/cm3, ρman ≈ 1.11 gr/cm3, and ρpan ≈ 1.70 gr/cm3 to 12.1 °C, respectively. [ABSTRACT FROM AUTHOR]

Compared to magnetic resonance imaging (MRI) and X-ray computed tomography (CT), ultrasound imaging is safer, faster, and more widely applicable. However, the use of conventional ultrasound in transcranial brain imaging for adults is predominantly hindered by the high acoustic impedance contrast between the skull and soft tissue. This study introduces a 3D AI algorithm, Brain Imaging Full Convolution Network (BIFCN), combining waveform modeling and deep learning for precise brain ultrasound reconstruction. We constructed a network comprising one input layer, four convolution layers, and one pooling layer to train our algorithm. In the simulation experiment, the Pearson correlation coefficient between the reconstructed and true images was exceptionally high. In the laboratory, the results showed a slightly lower but still impressive coincidence degree for 3D reconstruction, with pure water serving as the initial model and no prior information required. The 3D network can be trained in 8 h, and 10 samples can be reconstructed in just 12.67 s. The proposed 3D BIFCN algorithm provides a highly accurate and efficient solution for mapping wavefield frequency domain data to 3D brain models, enabling fast and precise brain tissue imaging. Moreover, the frequency shift phenomenon of blood may become a hallmark of BIFCN learning, offering valuable quantitative information for whole-brain blood imaging. [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-layer micro-perforated panel structure based on a curled space for broadband sound absorption at low frequencies, which increases the number of perforated panel layers in a limited space using a curled space. The absorption coefficients of the structure under plane wave conditions were calculated using the transfer matrix method and the finite element method. It is demonstrated that the multilayer micro-perforated panel structure can ensure high absorption (consistently over 90%) in the frequency range of 400~5000 Hz. The sound absorption mechanism of the multi-layer micro-perforated panel structure is investigated by using the acoustic impedance along with the reflection coefficient of the complex frequency surface. In addition, we also discuss the effects of the micro-perforated panel parameters on the structural sound absorption coefficient. The results show that the proposed multi-layer micro-perforated panel structure provides an excellent solution for sound absorption in a limited space. [ABSTRACT FROM AUTHOR]

Shale gas has become of interest of geoscientists globally because of its potentials to expand our energy supply. This research used well logs data and total organic carbon (TOC) data from Perth and Canning Basins, Australia. The objective of this research is to investigate source rock potential of the study area by examining the relationship between TOC content and seismic acoustic impedance (AI) derived from well log data, using regression analysis. The outcomes of this research show that for claystone/siltstone, the relationship between AI and TOC is nonlinear, while for shale the correlation is linear. However, there is no fixed equation that can be used as a standard for this linear/nonlinear relationship. Results show that for a certain type of lithology, the relationship between TOC and AI is different for different formations. This is interpreted to be caused by different depositional environment, diagenesis, mineralogical composition and different depth of burial. Findings of this study are expected to provide some new insights into the relationship between AI and TOC for various types of lithology and contribute to shale gas exploration studies. [ABSTRACT FROM AUTHOR]

Acquiring seismic data with multichannel, multiple‐streamer and even multi‐componentsystems at sea provides excellent images of the Earth. However, the cost and complexity of operations prevent their use in busy areas such as ports or in sensitive environments such as lagoons. In the latter cases, mono‐channel Chirp or Boomer systems are the most viable instruments for marine surveys. The lack of multiple offsets prevents the use of standard tools for amplitude‐versus‐offset and velocity analysis, which are necessary for the lithological characterization of rocks, especially for the shallow sediments in offshore engineering. In this paper, we present a few recent techniques that exploit the traveltime and amplitude of multiple reflections to compensate for the offset limitation, including a new algorithm for the joint tomographic inversion of direct arrivals, primaries and multiples. We have developed a cost‐effective workflow for mono‐channel surveys based on a data‐driven, physically consistent philosophy that attempts to approximately extract lithological parameters, such as P velocity, anelastic absorption, acoustic impedance and even density. We applied the proposed workflow to a real field experiment and obtained a semi‐quantitative estimate for shallow sediments that can be used by offshore engineers. [ABSTRACT FROM AUTHOR]

The objective of this paper is to experimentally identify the primary sources of pressure when a laser-induced cavitation bubble is collapsing to a wall with specific emphases on the material acoustic impedance and thickness. Both high-speed videos and local wall pressure measurements were performed for various standoff ratios γ, bubble diameters, and wall materials. In the case of a rigid wall, in addition to the known high pressure for γ < 0.6 where the bubble attaches and collapses on the wall (ring collapse), at γ ≈ 1.12 where the jet is dominant, and low pressure obtained at γ ≈ 0.913 , where neither effect is significant, we further captured similar pressure profiles during the collapse after the first rebound at γ ≈ 1.16 for the ring collapse, γ ≈ 1.79 for the jet, and γ ≈ 1.41 for the minimal, respectively. This indicates a strong jet is typically followed by a strong ring collapse. Generally, the pressure from the second collapse increases faster with the bubble size than that of the first collapse. For walls featuring smaller acoustic impedance or thickness, which cannot be approximated as rigid bodies or accessed by pressure sensor, our unique bubble edge analyzing tool shows that the ring collapse and jet effects are moved to smaller values of γ. The maximum pressure exerted on the wall in these cases is smaller than that on the rigid wall. Finally, we summarized the asymptotic evolution curves of each edge which bound the bubble dynamics at different standoff ratios. [ABSTRACT FROM AUTHOR]

With the advent of the intelligence era, flexible piezoelectric tactile sensors are the key components for sensing information and sending signals. The performance parameters of piezoelectric sensors are closely related to the selection of piezoelectric materials. Compared with conventional piezoelectric materials, polyvinylidene fluoride (PVDF) has significant advantages in flexibility, stretchability, chemical stability, electromechanical conversion, ease of use, and acoustic propagation impedance. As a result, PVDF has become a popular topic of research. This paper introduces the working principle of piezoelectric materials and flexible piezoelectric sensors based on PVDF materials and details the research progress of different materials based on PVDF for the preparation of flexible piezoelectric tactile sensors, such as: PVDF and its copolymers for the preparation of flexible piezoelectric sensors and PVDF doped with other functional materials for the preparation of flexible piezoelectric sensors. In this paper, the advantages and disadvantages of different materials and the development prospects of PVDF flexible piezoelectric sensors are summarized to provide some insights for high‐performance flexible PVDF piezoelectric sensors. [ABSTRACT FROM AUTHOR]

The rock mechanical properties influence the selection of drilling parameters, optimized drilling trajectory, and appropriate hydraulic fracturing intervals. Estimating the 3-D spatial distribution of these geomechanical properties at the reservoir scale is a challenging task, especially in the case of limited data only at the well locations. Advanced geostatistical techniques can be utilized to represent a reservoir's inherent spatial variation more realistically. In this study, we investigate the spatial variability of rock mechanical properties, including Young's modulus, shear modulus, bulk modulus, and Poisson's ratio, as major constituents of the reservoir geomechanical model. The data are extracted from a hydrocarbon field located southwest of Iran and consist of forty wells. We first build a 1-D model of rock elastic moduli at each well by integrating petrophysical and core-based laboratory measurements and then develop a corresponding 3-D model using geostatistical simulation techniques. Thereafter, 3-D seismic data are employed to optimize the geomechanical model. Results show that the integration of well logs with seismic data increases the accuracy of field-wise 3-D elastic moduli models. Furthermore, we used various co-simulation techniques to demonstrate the improving effect of complementary data in constructing a more realistic reservoir geomechanical model. [ABSTRACT FROM AUTHOR]

The advance in digital diagnostic technologies has significantly facilitated the detection of dental caries. Despite the increase in clinically available digital diagnostic aids for dental caries, there is yet to be a comprehensive summary of all available technology. This review aims to provide an overview of digital diagnostic aids for the clinical detection of dental caries, particularly those at an initial stage. Currently available digital diagnostic aids for caries detection can be classified into four categories according to the initial source of energy, including radiation-based aids, light-based aids, ultrasound-based aids, and electric-based aids. Radiation-based aids use ionizing radiation, normally X-ray, to produce images of dental structures. Radiation-based aids encompass digital bitewing radiography and cone beam computed tomography. Light-based aids employ light or laser to induce signals for the detection of the changes in the carious dental hard tissue. Common light-based aids include digital transillumination and light/laser-induced fluorescence. Ultrasound-based aids detect the signal of ultrasound waves to assess the acoustic impedance of the carious teeth. The ultrasound caries detector is an available ultrasound-based aid. Electric-based aids assess the changes in the electric current conductance or impedance of the teeth with caries. Available electric-based aids include electrical conductance measurement and alternating current impedance spectroscopy. Except for these clinically available digital diagnostic aids, many digital diagnostic aids for caries detection are still under development with promising results in laboratory settings. [ABSTRACT FROM AUTHOR]

Embedded sensors operating within a reinforced concrete structure enable the timely detection of structural degradation causes, such as chloride ions present in the pore solution. The best communication protocol to use for inter‐device communication within the concrete structure would ideally be wireless such as an ultrasonic system. Concrete is a composite material which imposes constraints on ultrasonic transmission, especially when operating at frequencies above 100kHz where incident radiation is scattered by the aggregate. Furthermore, for an effective coupling mechanism, a liquid with high acoustic impedance is required to reduce energy reflection at the interface. This paper outlines the design, construction, and characterisation of a range of Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) which are specifically designed to operate in liquids, at frequencies near or below 100kHz. The PMUT devices described in this paper have diaphragm diameters ranging between 550μm and 2,000μms which sizes are needed for PMUTs to resonate at the required low frequency. This paper outlines the device geometry calculations and the design and fabrication of the prototype devices. The resonant frequencies were determined using a laser vibrometer. [ABSTRACT FROM AUTHOR]

This paper examines effective and environmentally friendly materials intended for noise insulation and soundproofing applications, starting with materials that have gained significant attention within last years. Foam-formed materials based on cellulose fibers have emerged as a promising solution. The aim of this study was to obtain a set of foam-formed, porous, lightweight materials based on cellulose fibers from a resinous slurry pulp source, and to investigate the impact of surfactant percentage of the foam mixtures on their noise insulation characterisitcs. The basic foam-forming technique was used for sample assembly, with three percentages of sodium dodecyl sulphate (as anionic surfactant) related to fiber weight, and a standardised sound transmission loss tube procedure was used to evaluate noise insulation performance. Results were obtained as observations of internal structural configurations and material characteristics, and as measurements of sound absorption/reflection, sound transmission loss, and surface acoustic impedance. Based on the findings within this study, the conclusions highlight the strong potential of these cellulosic foams to replace widely used synthetic materials, at least into the area of practical noise insulation applications. [ABSTRACT FROM AUTHOR]

Due to the influence of mass law, traditional lightweight sandwich structures have struggled to surpass solid structures in sound insulation performance. To this end, we propose an acoustic metamaterial structure with a sandwich configuration based on the re-entrant negative Poisson's ratio (NPR) structure and systematically investigate its sound transmission loss (STL) performance under incident plane wave conditions. We used the acoustic impedance tube method to experimentally study the sound insulation performance of the re-entrant NPR sandwich structure under free boundary conditions, and then established an acoustic analysis simulation model based on COMSOL Multiphysics software, which verified that the results obtained by the experiment and the numerical simulation were in good agreement. The results show that the sandwich structure exhibits excellent sound transmission loss performance in the studied frequency range (250–4000 Hz), and the overall sound insulation performance exceeds the curve of the mass theorem, basically achieving more than 20 dB when the sandwich thickness is 2 cm. Finally, we conduct parametric studies to establish a correlation between the geometric design of NPR sandwich structures and their sound transmission loss performance. The research shows that the changes of the length of the ribs, the distance from the ribs to the center of the unit, and the length of the upper wall and the lower wall have a significant impact on the sound insulation performance of the re-entrant NPR sandwich structure, while the change of the wall thickness basically will not affect the sound insulation performance of the sandwich structure. This research can provide practical ideas for the engineering application of noise suppression designs of lightweight structures. [ABSTRACT FROM AUTHOR]

To further improve the operational performance of a phononic crystal air-coupled ultrasonic transducer while reducing the number of simulations, an intelligent optimization design strategy is proposed by combining finite element simulation analysis and artificial intelligence (AI) methods. In the proposed strategy, the structural design parameters of 1–3 piezoelectric composites and acoustic impedance gradient matching layer are sampled using the optimal Latin hypercube sampling (OLHS) method. Moreover, the COMSOL software is utilized to calculate the performance parameters of the transducer. Based on the simulation data, a radial basis function neural network (RBFNN) model is trained to establish the relationship between the design parameters and the performance parameters. The accuracy of the approximation model is verified through linear regression plots and statistical methods. Finally, the NSGA-II algorithm is used to determine the design parameters of the transducer. After optimization, the band gap widths of the piezoelectric composites and acoustic impedance gradient matching layer are increased by 16 kHz and 13.5 kHz, respectively. Additionally, the −6 dB bandwidth of the transducer is expanded by 11.5%. The simulation results and experimental results are consistent with the design objectives, which confirms the effectiveness of the design strategy. This work provides a feasible strategy for the design of high-performance air-coupled ultrasonic transducers, which is of great significance for the development of non-destructive testing technology. [ABSTRACT FROM AUTHOR]

Understanding the response mechanism of multiparameter rock fractures can improve the accuracy of crack diagnosis. In this study, three types of rock samples with notches were subjected to three-point bending tests. The fracture morphology was observed using scanning electron microscopy, and real-time resistivity and acoustic emission (AE) data were used to describe the crack propagation. The spatial distribution of the electric potential was simulated based on practical crack morphologies and can explain the correlation between rock fracture and rock resistivity or AE. The results reveal that the initiation and propagation of cracks reconstructs the electrical potential distribution characteristics of the rock samples and changed their overall resistivity. The crack growth rate was proportional to the rate of increase in the resistivity rate, and the resistivity increased with nonuniform crack growth. Crack geometry complexity affected circuit connectivity, and a higher resistivity change rate was typically caused by cracks with more uniform propagation. The resistivity variation had the same trend as the fracture toughness, whereas the AE energy exhibited a similar trend to the fracture energy evolution. The cumulative AE count of the granite fracture was the largest, and the peak AE count of coal was larger than that of sandstone. In the main frequency band of 100 ± 25 kHz, a relatively large AE event occurred during crack initiation, and the AE amplitude of granite was the largest. The primary fracture propagation increased the peak AE count, amplitude, energy, and fracture energy release efficiency. During rock fracture, the opening of a microscopic bedding plane and a matrix fracture results in time-varying resistivity and AE characteristics. The complementary electrical and acoustic parameters help describe the details of crack propagation behaviour. Highlights: Cracks restructure the electrical potential distributions in rock samples and change the resistivity. The acoustic emission (AE) energy exhibits a similar trend to the fracture energy evolution. The relationship between the resistivity and AE is mutually verified and complementary. [ABSTRACT FROM AUTHOR]

The unreliable prediction of the low-frequency components from inverted acoustic impedance causes uncertainty in quantitative seismic interpretation. To address this issue, we first calculate various seismic and geological attributes that contain low-frequency information, such as relative geological age, interval velocity, and integrated instantaneous amplitude. Then, we develop a method to predict the low-frequency content of seismic data using these attributes, their high-frequency components, and recurrent neural networks. Next, we test how to predict the low-frequency components using stacking velocity obtained from velocity analysis. Using all the attributes and seismic data, we propose a supervised deep learning method to predict the low-frequency components of the inverted acoustic impedance. The results obtained in both synthetic and real data cases show that the proposed method can improve the prediction accuracy of the low-frequency components of the inverted acoustic impedance, with the best improvement in a real data example of 57.7% compared with the impedance predicted using well-log interpolation. [ABSTRACT FROM AUTHOR]

The sound absorption coefficient (SAC) of a composite multi-cell sound absorber in the low- and mid-frequency range is investigated by using experiment and numerical method. The composite sound absorber includes a MPP (micro-perforated panel) layer, a porous material layer, and an air cavity layer. The sandwich acoustic structure consists of an air cavity layer in between two MPP layers, which is backed by another air cavity layer. Maa's model was used to describe the MPP layer, and the porous material layer was established by using Delany and Bazley's model. The transfer matrix method (TMM) was used to calculate the surface impedance of each acoustic unit-cell of the composite multi-cell sound absorber, and the SAC of the composite multi-cell sound absorber was predicted by using the equivalent circuit method. Finite element (FE) models of the composite multi-cell sound absorbers are presented, and their sound absorption coefficient was measured by using an impedance tube method. The measurement data demonstrate the validity of the prediction results and are used to analyse various acoustic characteristics that depend on the structural parameters of each acoustic unit-cell. Furthermore, an optimal combination of the structural parameters of the composite multi-cell sound absorber can be realized by using the genetic algorithm (GA). The effect of the number of the acoustic unit-cells with different perforation ratios of the MPP layer and the depth of the air cavity layer is presented. They are the main design parameters that can control the SAC in different frequency ranges. The results also show that the SAC of the composite multi-cell sound absorber can be adjusted by increasing the number of the acoustic unit-cells and using the optimized design of the air cavity layer. [ABSTRACT FROM AUTHOR]

Mineral exploration is facing greater challenges nowadays because of the increasing demand for raw materials and the lesser chance of finding large deposits at shallow depths. To be efficient and address new exploration challenges, high‐resolution and sensitive methods that are cost‐effective and environmentally friendly are required. In this work, we present the results of a sparse 3D seismic survey that was conducted in the Zinkgruvan mining area, in the Bergslagen mineral district of central Sweden. The survey covers an area of 10.5 km2 for deep targeting of massive sulphides in a polyphasic tectonic setting. A total of 1311 receivers and 950 shot points in a fixed 3D geometry setup were employed for the survey. Nine 2D profiles and a smaller 3D mesh were used. Shots were generated at every 10 m, and receivers were placed at every 10–20 m, along the 2D profiles, and 40–80 m in the mesh area. An analysis of the seismic fold coverage at depth was used to determine the potential resolving power of this sparse 3D setup. The data processing had to account for cultural noise from the operating mine and strong source‐generated surface waves, which were attenuated during both pre‐ and post‐stack processing steps. The processing workflow employed a combination of 2D and 3D refraction static corrections, and post‐stack FK filters along inlines and crosslines. The resulting 3D seismic volume is correlated with downhole data (density and P‐wave, acoustic impedance, reflection coefficient), synthetic seismograms, surface geology and a 3D model of mineral‐bearing horizons in order to suggest new exploration targets at depth. The overall geological architecture at Zinkgruvan is interpreted as two EW overturn folds, an antiform and a synform, affected by later NS‐trending folding. Two strong sets of shallow reflections, associated with the Zn–Pb mineralization, are located at the hinge of an EW‐trending antiform, while a strong set of reflections, associated with the main mineralization, is located at the overturned apex of the EW synform. The NS Knalla fault that crosses the study area terminates the continuation of the mineral‐bearing deposits at depth towards the west, a conclusion solely based on the reflectivity character of the seismic volume. This study illustrates that sparse 3D data acquisition, while it has its own challenges, can be a suitable replacement for 2D profiles while line cutting, and environmental footprints can totally be avoided. [ABSTRACT FROM AUTHOR]

Effect of the acoustic metasurface on a broadband wave packet in a Mach 6 boundary layer is studied. Direct numerical simulations (DNSs) with time-domain impedance boundary condition (TDIBC) and metasurface with microstructures are performed. It is shown that DNS with TDIBC resolves the amplitude and phase information of the wave packet satisfactorily. The minor prediction discrepancy arises from the modeling error in the acoustic impedance. The interesting finding of this paper is that the metasurface behaves as an equivalent unsteady blowing-suction model to perturb the wall-normal velocity and then passively the pressure field. Although both pressure and wall-normal velocity appear in the characteristic-wave variable, the pressure can be decoupled to be updated by the Neumann condition, as usually employed in Navier–Stokes solvers. The dominant frequency scale that enables reproducing the stabilization effect of the metasurface is found to be slightly smaller than the energetic frequency maximum of the wave packet. This observation indicates that the high-frequency unsteadiness nature of the blowing-suction behavior is indispensable, which is induced by the interaction of the metasurface and the wave packet. For the stabilization mechanism, energy analysis reveals that a dilatation-related work near the wall is significantly suppressed by the metasurface, which agrees with the wall-normal location where the wave-packet fluctuation gets attenuated. [ABSTRACT FROM AUTHOR]

For investigating the nonlinear acoustic behavior of circular orifices under high amplitude sound excitation, an approach based on the three-dimensional time-domain computational fluid dynamics simulation is proposed to extract the nonlinear acoustic impedance of circular orifices. By solving laminar flow equations, the propagation of the acoustic signal in the vicinity of orifice is simulated, and the effect of the interaction among adjacent orifices is considered by using the lateral periodic boundary condition. The effects of diameter, thickness, and porosity on acoustic impedance under different amplitude sound excitations are studied. By using nonlinear regression analysis of the dimensionless parameters composed of particle velocity amplitude, frequency, and geometric parameters, fitting formulas of nonlinear acoustic impedance of circular orifices are presented. As an application of engineering computation, transmission loss of perforated silencers under low and high amplitude sound excitations is predicted by using the present acoustic impedance fitting formulas and via the finite element computation. By comparing the predicted and measured results, the accuracy and practicability of fitting formulas of nonlinear acoustic impedance of circular orifices are validated. [ABSTRACT FROM AUTHOR]

In order to weaken the Gibbs oscillation in the passband of periodic fluid-solid superlattice structure, a gradient fluid-solid superlattice structure (GFSL) with symmetrical linear distribution of solid layer filling fraction is designed by introducing structural gradient. Based on the transfer matrix method, the acoustic transmission characteristics of GFSL structure are calculated. On this basis, the effects of different gradient parameters on the sound transmission characteristics of GFSL structure are discussed to adjust the passband performance. The sound transmission characteristics of GFSL structure are verified from the perspectives of frequency domain and time domain by finite element method. The results show that the GFSL structure effectively eliminates the Gibbs oscillation and forms a flat broadband passband. The proposed GFSL structure has potential application value in underwater high-intensity ultrasonic energy concentration, acoustic impedance matching and filtering. [ABSTRACT FROM AUTHOR]

This paper derives and validates an analytical model for acoustic boundary conditions on a can-annular gas turbine combustion system composed of discrete cans connected to an open annulus upstream of a turbine. The analytical model takes one empirical parameter: a connection impedance between adjacent cans. This impedance is extracted from time-marching computations of two-can sectors of representative combustors. The computations show that reactance follows the Rayleigh conductivity, while resistance takes a value of order 0.1 as a weak function of geometry. With a calibrated value of acoustic resistance, the analytical model reproduces can-to-can transfer functions predicted by full-annulus computations to within 0.03 magnitude at compact frequencies. Varying the combustor–turbine gap length, both model and computations exhibit a minimum in reflected energy, which drops by 63% compared to the datum gap. A parametric study yields a design guideline for gap length at the minimum reflected energy, allowing the designer to maximise transmission from the combustion system and reduce damping requirements. [ABSTRACT FROM AUTHOR]

The lithological characterization of the seafloor is key information for offshore engineering, especially when it comes to pier and platform design. Undetected shallow gas pockets may cause the collapse of heavy platforms for hydrocarbon production. Unconsolidated sediments are not ideal for the basement of wind farms for electric power production. Drilling and coring can be used for local sampling, but continuous profiles or even areal coverage are far more preferable. High-resolution seismic profiles are successfully used when ports are not too busy, but otherwise, single-channel systems must be used. We show in this paper that even these simpler systems can be used to estimate parameters such as the acoustic impedance of shallow sediments directly beneath the seafloor. We exploit the amplitude decay of the multiple reflections between the seafloor and the surface, which does not depend on the source energy. If the offset between source and receiver is not too small, we can estimate the shallow P velocity and, via acoustic impedance, also the rock density. [ABSTRACT FROM AUTHOR]

With the growing global environmental awareness, the development of renewable and green materials has gained increased worldwide interest to substitute conventional materials and are favorable for sustainable economic development. This paper proposed a novel eco-friendly sound absorbing structure (NSAS) liner for noise reduction in elevator shafts. The base layer integrated with the shaft walls is a damping gypsum mortarboard, and a rock wool board and a perforated cement mortarboard are used to compose the NSAS. Based on the acoustic impedance theory of porous materials and perforated panels, the sound absorption theory of the NSAS was proposed; the parameter effects of the rock wool board (flow resistivity, porosity, structure factor) and perforated panel (perforated rates, thickness, density, perforated diameter) on NSAS absorption were discussed theoretically for absorption improvement, and experiments were also conducted. Numerical results showed that the perforation rate, the thickness of the perforated plate, and the porosity, flow resistance, and volume density of the rock wool board played a key issue in the absorption performances of the NSAS. Experiments verified the accuracy of the proposed theoretical model. Wideband sound absorption performance of the NSAS at frequencies between 500-1600 Hz was achieved in both numerical analysis and experiments, and the sound absorption coefficient was improved to 0.72 around 1000 Hz after parameter adjustments. The NSAS proposed in this paper can also be made of other renewable materials with preferable structure strength and still has the potential to broaden the absorption bandwidth. It can provide a reference for controlling the elevator shaft noise. [ABSTRACT FROM AUTHOR]

Conventional wireless communication faces limitations in underwater environments due to the high electromagnetic wave attenuation. Ultrasound provides an alternative, enabling communication for underwater drones and intrabody communication for implantable devices. However, the limited bandwidth of resonance-based piezoelectric transducers remains a challenge. In addition, the significant acoustic impedance mismatch between water and air hinders cross-boundary communication and necessitates direct contact between the medium and the transducers. To overcome these challenges, we propose to use a sub-terahertz photoacoustic effect for the generation of broadband ultrasound in a non-contact manner. The photoacoustic effect generates acoustic signals in a medium through thermal expansion caused by optical irradiation. We demonstrate that the use of periodically modulated continuous-wave sub-terahertz waves around 0.1 THz enables broadband signal generation efficiently owing to their high attenuation in water. We characterize the frequency response of the generated acoustic signals and demonstrate a proof of concept for underwater communication. [ABSTRACT FROM AUTHOR]

The effects of diatom mud coating on characteristic impedance is studied by using the double-thickness method. The parallel relationships among the concave arc column filled with diatom mud, honeycomb cells, the overall core layer, and micro-perforation are considered in using the acousto-electric analogy method. In the case of a series relationship of plates, the sound absorption coefficient of the honeycomb structure of the micro-perforated plate is calculated. The effects of diatom mud coating and dislocation arrangement on the sound absorption coefficient of sandwich panels are numerically simulated by COMSOL. To further verify the reliability of the sound absorption theoretical model, test specimens are made and the effects of dislocation arrangement and diatom mud coating on sound absorption performance are tested by using impedance tube equipment. The effect of dislocation arrangement and diatom mud coating on the sound absorption performance of low-frequency noise of sandwich panels is analysed from the parameters of sound absorption coefficient, resonance frequency, acoustic impedance, and fitting results. [ABSTRACT FROM AUTHOR]

Acoustic energy dissipates in multi-phase or multi-boundary materials. Hybrid composites are described as multi-phase with many interfaces between their materials. The current research proposes the study of the acoustic behavior of polymeric hybrid composites by estimating the time, velocity, and hybrid composite acoustic impedance. Two groups of hybrid composites were prepared, including unsaturated polyester with PMMA, except one with HDPE and the other with PS. Each group had 28%, 35%, and 40% weight fractions. An ultrasonic test measured the time to determine the velocity and then the acoustic impedance later. The results showed that increasing the weight fraction will increase the density with respect to the density of the reinforcing material. Different ultrasonic times were obtained with increasing weight fractions. As the weight fraction of PS increased, the time increased; unlike the velocity, it decreased but increased with density. In contrast, this behavior was changed if the hybrid had PE. The highest acoustic impedance was at 28% UP/PMMA + PS. In conclusion, UP/PMMA + PS can dissipate ultrasonic waves more than UP/PMMA + PE. [ABSTRACT FROM AUTHOR]

Theoretical and experimental features of using an acoustic interferometer for determining the velocity and attenuation of an acoustic wave in liquids with different acoustic impedances are studied. It is shown for the first time that the indicated impedance determines the ratio of the resonance values of the maximum and minimum transmission coefficient S12 for the same transmitter–receiver pair on the dependence of the transmission coefficient on the distance between the transducers. A methodology has been developed for determining the wave attenuation of a liquid free from the influence of "apparent" attenuation associated with the loss of part of the acoustic power to the transducers. [ABSTRACT FROM AUTHOR]

The quality of geothermal carbonate reservoirs is controlled by, for instance, depositional environment, lithology, diagenesis, karstification, fracture networks, and tectonic deformation. Carbonatic rock formations are thus often extremely heterogeneous, and reservoir parameters and their spatial distribution difficult to predict. Using a 3D seismic dataset combined with well data from Munich, Germany, we demonstrate how a comprehensive seismic attribute analysis can significantly improve the understanding of a complex carbonate reservoir. We deliver an improved reservoir model concept and identify possible exploitation targets within the Upper Jurassic carbonates. We use seismic attributes and different carbonate lithologies from well logs to identify parameter correlations. From this, we obtain a supervised neural-network-based 3D lithology model of the geothermal reservoir. Furthermore, we compare fracture orientations measured in seismic (ant-tracking analysis) and well scale (image log analysis) to address scalability. Our results show that, for example, acoustic impedance is suitable to identify reefs and karst-related dolines, and sweetness proves useful to analyse the internal reef architecture, whereas frequency- and phase-related attributes allow the detection of karst. In addition, reef edges, dolines, and fractures, associated with high permeabilities, are characterized by strong phase changes. Fractures are also identified using variance and ant tracking. Morphological characteristics, like dolines, are captured using the shape index. Regarding the diagenetic evolution of the reservoir and the corresponding lithology distribution, we show that the Upper Jurassic carbonate reservoir experienced a complex evolution, consisting of at least three dolomitization phases, two karstification phases, and a phase of tectonic deformation. We observe spatial trends in the degree of dolomitization and show that it is mainly facies-controlled and that karstification is facies- and fault-controlled. Karstification improves porosity and permeability, whereas dolomitization can either increase or decrease porosity. Therefore, reservoir zones should be exploited that experienced only weak diagenetic alteration, i.e. the dolomitic limestone in the upper part of the Upper Jurassic carbonates. Regarding the fracture scalability across seismic and well scales, we note that a general scalability is, due to a combination of methodological limitations and geological reasons, not possible. Nevertheless, both methods provide an improved understanding of the fracture system and possible fluid pathways. By integrating all the results, we are able to improve and adapt recent reservoir concepts, to outline the different phases of the reservoir's structural and diagenetic evolution, and to identify high-quality reservoir zones in the Munich area. These are located southeast at the Ottobrunn Fault and north of the Munich Fault close to the Nymphenburg Fault. [ABSTRACT FROM AUTHOR]

The ultrasonic velocity of molecules in medium supplies valid information about the binding forces between molecules. Surfactants are chemicals that self-assemble molecular clusters in a solution (oil or water phase) known as micelles. SLS has been suggested as a potentially effective topical microbicide for intravaginal usage to suppress and potentially prevent infection by various enveloped and non-enveloped viruses. The acoustical parameters such as ultrasonic velocity, density, and viscosity of a solution containing an anionic surfactant (SLS) and alcohols (Anise and Cinnamyl alcohol) are determined at various temperatures (303,313 and 323 K). Similarly, the acoustical parameters such as adiabatic compressibility (b), intermolecular free length (Lf), internal pressure (p) Rao's constant (Ra), absorption coefficient (a/f2), free volume (Vf), cohesive energy (CE), relaxation time (t), acoustic impedance (Za), and solvation number (Sn) were calculated from the observed values. At the end, it is concluded that SLS+water-Anise alcohol has been used as a best additive. This composite has a lower foaming tendency due to lower surface tension, leading to a newer product. [ABSTRACT FROM AUTHOR]

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Confining sound is of significant importance for the manipulation and routing of acoustic waves. We propose a Helmholtz resonator (HR) based subwavelength sound channel formed at the interface of two metamaterials for this purpose. The confinement is quantified through (i) a substantial reduction of the pressure and (ii) an increase in a specific acoustic impedance (defined by the ratio of the local pressure to the sound velocity)—to a very large value outside the channel. The sound confinement is robust to frequency as well as spatial disorder at the interface, as long as the interface related edge mode is situated within the bandgap. A closed acoustic circuit was formed by introducing controlled disorder in the HR units at the corners, indicating the possibility of confining sound to a point. [ABSTRACT FROM AUTHOR]

In this study, we studied how to connect a thermoacoustic engine (TAE) and an impulse turbine to construct a thermoacoustic generator for converting thermal energy into electric power. The thermoacoustic generator was separated into two sub-systems: (1) system A, which consisted of a looped-tube TAE and a branch tube, and (2) system B, which consisted of an impulse turbine loop and a branch tube. The sub-systems were evaluated individually using an acoustic driver to determine the driving conditions such as branch length, driving frequency, and temperature for the connected system. In system A, which included the TAE, the change in specific acoustic impedance was small with respect to the velocity amplitude. However, in system B, which included the impulse turbine, the change in specific acoustic impedance with respect to the velocity amplitude was nonlinear. The sub-systems were connected by branch pipes, whose lengths were determined from the individual sub-system evaluation results, and the device was confirmed to self-oscillate at the driving temperature. When the device was operated at the driving conditions, the frequency, velocity amplitude, and specific acoustic impedance with self-oscillation were the same as those of the individual sub-systems. This also confirms the validity of evaluating the TAE and impulse turbine separately. [ABSTRACT FROM AUTHOR]

Daerah penelitian ini terletak di Cekungan Bonaparte, Australia. Dalam memodelkan bawah permukaan dengan metode seismik inversi impedansi akustik, peneliti kebanyakan hanya menggunakan seismik inversi berbasis model based. Pada penelitian ini, penulis telah melakukan pemodelan impedansi akustik (IA) bawah permukaan dengan menggunakan metode seismik post-stack berbasis rekursif, model based, dan sparse spike. Penelitian ini bertujuan untuk mengetahui model impedansi akustik serta persebaran porositas dari hubungan log porositas dan impedansi akustik (IA) hasil inversi pada zona target daerah penelitian. Penelitian ini dilakukan menggunakan data seismik 3D post stack dan 4 data sumur yaitu MKS-1, MKS-2, MKS-3 dan MKS-4. Berdasarkan hasil pengolahan diperoleh bahwa persebaran impedansi akustik pada area target dengan seismik inversi berbasis rekursif, model based, dan sparse spike memiliki rentang IA sekitar 10000 ((ft/s)*(g/cc)) – 50000 ((ft/s)*(g/cc)) yang merupakan kisaran impedansi akustik untuk litologi sand berfluida – clean sand, serta memiliki persebaran porositas prediksi dari hasil seismik inversi memiliki rentang sekitar 0,037 – 0,176. Berdasarkan analisis kuantitatif terlihat bahwa seismik inversi sparse spike paling cocok dalam memodelkan parameter impedansi akustik dan porositas prediksi daerah penelitian dengan standar deviasi error sebesar 1867,167 untuk impedansi akustik prediksi dan 0,010 untuk porositas prediksi.