Acoustic Impedance Ratio Research Articles

Plasma-enhanced chemical vapor deposition a-SiOCN:H low-Z thin films for bulk acoustic wave resonators

The 5th generation (5G) wireless telecommunication standards with newly defined frequency bands up to 6 GHz are currently established around the world. While outperforming surface acoustic wave (SAW) filters above 1 GHz, bulk acoustic wave (BAW) resonators in multiplexers for radio-frequency front-end (RFFE) modules continuously face higher performance requirements. In contrast to free-standing bulk acoustic resonators (FBARs), solidly mounted resonator (SMR) technology uses an acoustic Bragg mirror, which has already been successfully applied for several GHz applications. In this work, we investigate the potential of amorphous hydrogenated silicon-oxycarbonitride (a-SiOCN:H) thin films synthesized with low-temperature plasma-enhanced chemical vapor deposition (PECVD) as a low acoustic impedance (low-Z) material. Compared to the state-of-the-art where in Bragg mirrors up to now SiO2 is used as standard, the acoustic impedance ratio against the high-Z material tungsten (W) is enhanced for a better device performance. To limit the expected increase in viscous loss when the acoustic impedance is reduced, to a minimum, predominantly the mass density was reduced while keeping the mechanical elasticity high. By doing so, acoustic impedance values as low as 7.1 MRayl were achieved, thereby increasing the impedance ratio of high-Z to low-Z materials from 8:1 up to 14:1.

Refraction of a triple-shock configuration at planar fast–slow gas interfaces

This paper characterizes the refraction of a triple-shock configuration at planar fast–slow gas interfaces. The primary objective is to reveal the wave configurations and elucidate the mechanisms governing circulation deposition and velocity perturbation on the interface caused by triple-shock refraction. The incident triple-shock configuration is generated by diffracting a planar shock around a rigid cylinder, and four interfaces with various $Z_{{r}}$ (i.e. acoustic impedance ratio across the interface) are considered. An analytical model describing the triple-shock refraction is developed, which accurately predicts both the wave configurations as well as circulation deposition and velocity perturbation. Depending on $Z_{{r}}$ , three distinct patterns of transmitted waves can be anticipated: a triple-shock configuration; a four-shock configuration; a four-wave configuration. The underlying mechanism for the formation of these wave configurations is elucidated through shock polar analysis. A novel physical insight into the contribution of triple-shock refraction to the interface perturbation growth is provided. The results indicate that the reflected shock in an incident triple-shock configuration makes significant negative contribution to both circulation deposition and velocity perturbation. This investigation elucidates the underlying mechanism responsible for the relatively insignificant contribution of baroclinic circulation to the Richtmyer–Meshkov-like instability induced by a non-uniform shock, and provides an explanation for the decrease in growth rate of interface perturbation amplitude with increasing Atwood number.

Design and construction of the Texas Christian University impedance tube

The two-microphone impedance tube test method is a well-established and widely used technique for determining the acoustic absorption coefficient and impedance ratio of materials. This method uses two closely spaced microphones to simultaneously measure the incident and reflected sound waves. A two-microphone impedance tube measurement system made of 6061-T6 Aluminum with a diameter of 3 inches, a 0.5 inch wall thickness, and microphones spaced 2.7 inches apart has been constructed for undergraduate research at Texas Christian University (TCU). These geometrical values suggest a usable frequency range of 50 Hz to 2637.77 Hz as referenced in ASTM Standard E1050-19. Validation of the system was achieved by taking measurements on Owen Corning Type 705 pressed fiberglass board with a 1-inch thickness and comparing them to absorption data provided by the manufacturer. Additional validation measurements were taken without a test sample in place. All validation tests suggest that the TCU impedance tube is an accurate measurement system.

Evaluation backscattering coefficients of heterogeneous media containing multispecies scatterers and lipids

Many attempts have been reported to evaluate tissue characterization from echo signals using the backscatter coefficient (BSC) as an indicator. In the evaluation of the BSC of the biological tissues, it is known that the effects of attenuation properties such as scattering attenuation and absorption attenuation, as well as interference between different scatterers, are significant. In this study, the effects of attenuations and interference were verified by evaluating a phantom with high absorption attenuation and a phantom with a mixture of two types of scatterers. Both the reflector method and the reference phantom method were applied to BSC evaluation for these phantoms, and the accuracy of the evaluation was verified. The results suggest that the effect of the acoustic impedance ratio between the scatterer and the surrounding medium tends to be reflected in the accuracy of the evaluation in media with large absorption attenuation. On the other hand, the difference between the mathematical theory and the actual evaluation results was observed due to interference effects. In terms of the accuracy of the evaluation method, the reflector method is effective in the vicinity of the focus, while the reference phantom method is effective in terms of application.

Analysis of the band structure of transient in-plane elastic waves based on the localized radial basis function collocation method

In this paper, the localized radial basis function collocation method is applied to investigate the in-plane elastic wave propagation of 2D phononic crystals. The direct method with local support domain in one line is used to enhance the stability of the localized radial basis function collocation method when dealing with the derivative calculations in the boundary and interface conditions. The Houbolt method is employed to discretize the time, and then the Fast Fourier Transform is adopted to obtain the band structure according to the wave vectors in the first Brillouin Zone. Different acoustic impedance ratios, filling rates, and lattice forms are studied. The numerical results can be used to validate the band structures obtained directly from the frequency domain.

Propagation and attenuation of stress waves in heterogeneous elastic rods

In this paper, the propagation and attenuation of stress waves induced by an integrable external load in an elastic rod with multiple inclusions are investigated. The traveling wave method is suggested for obtaining the reflection coefficient, transmission coefficient, and attenuation coefficient of the wave propagating from one media to another. Furthermore, the effects of wavelength and the size of inclusion on elastic wave propagation are calculated by the finite element method. The results show that the theoretical solution is fitted well with the finite element numerical results. The attenuation coefficient is influenced by material parameters, wavelength, and the number of inclusions. The smaller wavelength or more inclusions will incur the more obvious attenuation phenomenon. Moreover, the reflection coefficient and transmission coefficient are affected by the acoustic impedance ratio of the matrix and the inclusion. The results of this paper can be served as the theoretical basis for the study of wave propagation in heterogeneous materials.

Seismic identification of tight-oil reservoirs by using 3D rock-physics templates

Tight-oil reservoirs are classified as unconventional hydrocarbon resources, having a complex system of pores and cracks and low porosity/permeability. A good pore-crack connectivity is required for hydrocarbon production, but clay minerals filling the pores and throats may hinder the fluid migration. Thus, the combined effects of the pore-crack network and the presence of clay are the main factors controlling the reservoir properties and its storage capacity. In this study, a suite of cores was collected from a reservoir located in the north of the Songliao Basin (China), and establish their microstructure by scanning electron microscopy. Then, ultrasonic experiments were performed under in-situ conditions to analyze the influence of clay minerals and porosity on the elastic waves. The triple-porosity, differential-effective-medium and self-consistent theories were used to calculate the stiffness moduli by considering the effects of pores, cracks and clay minerals, and to analyze the influence of these reservoir properties on the P-wave attributes. According to attenuation, acoustic impedance and phase-velocity ratio, a multi-scale 3D rock-physics template was established. By using the ultrasonic, sonic-log and seismic data, the templates were calibrated and then the reservoir characteristics were estimated. Two 2D seismic lines were considered and the corresponding predicted reservoir properties were compared to the well-log data and the actual production reports, showing that the porosity and clay content predictions are consistent with these data, and that the oil production areas are all located within the high-cracked porous zones. The 3D rock-physics templates can effectively estimate the distribution of high-quality tight-oil reservoirs.

Broadband low-frequency sound insulation performance of quasi-zero stiffness local resonant acoustic metamaterial plate

For realizing the effective broadband insulation of sound at low frequencies, a novel local resonant acoustic metamaterial plate having quasi-zero stiffness is proposed. Based on the classical mass-spring local resonance model, a metastructure is constructed by introducing additional inclined springs with negative stiffness. First, the normalized equivalent stiffness of the quasi-zero stiffness structure is derived from the perspective of dynamics. Then, by employing the method of equivalent medium, a sound insulation model of the metastructure is established theoretically. For validation, numerical simulations as well as experimental measurements are carried out. It is demonstrated that in the positive (equivalent) stiffness regime, increasing either the stiffness ratio or pre-compression can significantly reduce the local resonance frequency of the metastructure, which exhibits the great insulation performance around the local resonance frequency. For a typical example, the proposed metastructure can achieve a transmission loss of 30 dB around 10 Hz. In contrast, within the negative stiffness regime, the metastructure does not exhibit local resonance, thus avoiding sound insulation valley caused by the “coincidence effect”. Compared with traditional materials or similar metamaterials, the proposed metastructure has significant advantages in sound insulation (e.g. more than 30 dB drop over a wide frequency band of 53－1500 Hz). By analyzing the equivalent mass density, reflection coefficient, and acoustic impedance ratio of the metastructure, the physical mechanism behind its superior insulation performance is further explored. The equivalent mass density changes from positive to negative and tends to infinity at the insulation peak. The insulation peak is attributed to a nearly perfect total reflection of sound wave caused by impedance mismatch, while the insulation valley is caused by low-frequency “coincidence effect” originating from the local resonance band gap. The using of the quasi-zero stiffness local resonance to achieve low-frequency broadband sound insulation overcomes the disadvantages of traditional metamaterials such as reduced stiffness or additional mass, thus becoming vastly attractive for constructing low-frequency broad band sound insulation structures.

Shock-induced bubble collapse near solid materials: effect of acoustic impedance

Abstract

Water‐flooding and consolidation of reservoir chalk – effect on porosity and Biot's coefficient

ABSTRACTImproved oil recovery from chalk reservoirs by water‐flooding may cause mechanical weakening and change in elasticity. Confined compressive strength testing of chalk from a North Sea reservoir was done in water‐saturated and oil‐saturated conditions. During testing, elastic wave velocities were sampled by ultrasonic transducers, so that subsequently Biot's coefficient could be modelled. The porosity declined via an ‘elastic phase’, a ‘transitional phase’, an ‘elastoplastic phase’ and a ‘strain hardening phase’, but Biot's coefficient indicates that these terms may be partly misleading. In the ‘elastic phase’, porosity and Biot's coefficient decrease, indicating elastoplastic deformation. In the ‘transitional phase’, Biot's coefficient increases as a reflection of breaking contact cement (pore collapse), whereas Biot's coefficient remains stable in the ‘elastoplastic phase’, indicating elastic deformation on the virgin curve. Plastic deformation takes place during phases of creep, where both porosity and Biot's coefficient decrease. Similarly, in the ‘strain hardening phase’, both porosity and Biot's coefficient decrease as a reflection of elastoplastic deformation. For chalk with 45%–47% porosity, the ‘transitional phase’ begins at 8 MPa axial stress when water‐saturated and at 12 MPa when oil‐saturated. For chalk with 41%–43% porosity, the corresponding stresses are 16 and 20 MPa. For chalk with 32%–36% porosity, the corresponding stresses are 23 and 31 MPa. Chalk samples with irreducible water saturation and movable oil were water‐flooded. They yield at stresses close to corresponding oil‐saturated samples, but after flooding show compaction trends not significantly different from the water‐saturated samples. Water‐flooding promotes pore collapse as reflected in an increasing Biot's coefficient. The consequent softening effect on acoustic impedance is small as compared with the effect of increasing fluid density. With respect to 4D seismic, water‐flooding causes distinctly higher acoustic impedance and Poisson's ratio irrespective of compaction.

MEASUREMENT THICKNESS OF PROTECTIVE-DECORATIVE COATINGS ON CONCRETE BASES

The factors affecting to the ultrasonic testing of the coating thickness on concrete are considered. The structure and design of the transducer used to solve this problem. Features of the organization of the measurement process are described. Options for creating reference samples for tuning and testing ultrasonic thickness gauges used to solve this problem. The results of measuring the thickness of the polyurethane coating on concrete obtained on the Bulat 3 device using a specialized transducer are presented. The characteristics of concrete, which necessitate the use of special protective and decorative materials (surface abrasion, insufficient density, low hydrophobicity, etc.), and the characteristics of organic polymer coatings (adhesion, elasticity, wear resistance, chemical resistance, and hardness), which depend significantly on dry film thickness (protective layer). It is indicated that in order for the coating to ensure the fulfillment of the declared parameters taking into account economic feasibility, it is necessary to fulfill the requirements for a given minimum coating thickness, and that the use of the ultrasonic testing method seems to be the optimal method for measuring the coating thickness. Factors affecting the measurement process (the ratio of acoustic impedances, reflection coefficient and its variation range for various types of concrete and the most common coatings) are also considered. It is indicated that, based on a number of experiments with different types of transducers (dual element, single element and single element with the delay line), the maximum sensitivity and measurement range are ensured by using a direct single element transducer with a delay line. The data on the choice of the operating frequency of the transducer is given, depending on the range of measured coating thicknesses. The design and construction of the transducer, the features of the construction of its elements and their influence on the transducer characteristics, the principle of measuring the coating thickness and its implementation on the Bulat 3 ultrasonic thickness gauge are described. The char-acteristics of the device that allowed it to be used for such measurements are indicated. Information is provided on various options for the implementation of reference samples of the coating, on the methodology for their testing and the measurement results.

Electromechanical impact analysis of 2–2 cement-based piezoelectric sensor considering resistor

The model of the 2–2 type cement-based piezoelectric sensor, which is connected with a resistor while under the impact mechanical load, is established in this article. The dynamic theoretical expressions are acquired by utilizing the separation variable method and the matrix coefficient method and then used to analyze and discuss the electrical properties and the influence of the resistance value, which is verified correctly by numerical analysis. Also, the effect of resistor value and different material parameters on dynamic properties of such sensor is further investigated. And a reverse voltage is proposed to balance the displacement of the free-end and the stress of the fixed-end to enhance the safety. At last, the acoustic impedance ratio associated with the compatibility of the composite is discussed. The conclusions discussed in this work could provide some theoretical references for optimizing the design of the 2–2 cement-based piezoelectric sensor connected to electrical components in practical application.

A Petrov-Galerkin finite element interface method for interface problems with Bloch-periodic boundary conditions and its application in phononic crystals

In this paper, we propose a Petrov-Galerkin finite element interface method (PGFEIM) to solve the elliptic and elastic interface problems with Bloch-periodic boundary conditions. The main idea of this method is to choose the standard finite element basis independent of the interface to be the test function basis, and choose a piecewise linear function satisfying the jump conditions across the interface to be the solution basis. The grid we use is a non-body-fitted grid. The PGFEIM is capable of dealing with sharp-edged interface problems with matrix coefficients and nonhomogeneous jump conditions. Further, we extend this method to compute the band structure of anti-plane transverse waves and in-plane elastic waves in phononic crystals. Different acoustic impedance ratios, arbitrary complex scatterer geometries and various material properties are considered and discussed. Numerical experiments demonstrate that the PGFEIM is nearly second order accurate in the L∞ norm for interface problems, and it is accurate and efficient for computing the band structure of phononic crystals.

Diagenesis-driven pore fluid discrimination

In order to determine a direct hydrocarbon indicator in an oil field formed by low- to medium-porosity fast sandstone, we examine wireline data from four wells. Fluid substitution indicates that the sensitivity of the acoustic impedance and Poisson's ratio to oil-to-brine changes is very small. It appears, however, that due to diagenetic processes, the porosity in the brine-filled strata is noticeably smaller than that in the oil-saturated intervals. This porosity difference makes the impedance in the presence of oil noticeably smaller than that where brine is present. The respective impedance cutoff can serve as a discriminator for fluid detection in the seismically derived acoustic impedance volumes. The lesson learned is that merely relying on a rock-physics tool, such as fluid substitution, may not necessarily provide a fluid-detection recipe. Instead, we need to examine a plethora of natural events that may affect rock properties and then translate these effects into seismically detectable variables.

Acoustic extraordinary transmission manipulation based on proximity effects of heterojunctions

Heterojunctions between two crystalline semiconductor layers or regions can always lead to engineering the electronic energy bands in various devices, including transistors, solar cells, lasers, and organic electronic devices. The performance of these heterojunction devices depends crucially on the band alignments and their bending at the interfaces, which have been investigated for years according to Anderson’s rule, Schottky-Mott rule, Lindhard theory, quantum capacitance, and so on. Here, we demonstrate that by engineering two different acoustic waveguides with forbidden bands, one can achieve an acoustic heterojunction with an extraordinary transmission peak arising in the middle of the former gaps. We experimentally reveal that such a transmission is spatially dependent and disappears for a special junction structure. The junction proximity effect has been realized by manipulating the acoustic impedance ratios, which have been proven to be related to the geometrical (Zak) phases of the bulk bands. Acoustic heterojunctions bring the concepts of quantum physics into the classical waves and the macroscopic scale, opening up the investigations of phononic, photonic, and microwave innovation devices.

Experimental Study of Acoustic Performance of Porous Metals at High Temperatures

Based on an improved two-microphone transfer function method, a testing system for the exploration of acoustic performance of porous materials under high temperature conditions was developed with porous foam copper as one of research objects. The acoustic performances of some porous metallic materials were studied in the temperature range of 300°C to 700°C under the premise of ensuring the temperature stability that makes the measurement uncertainty be ± 6°C at high temperatures. The sound absorption coefficient and the acoustic impedance ratio of porous coppers at different ambient temperatures were acquired accordingly. And then the influence of the variation of temperature fields on the acoustic properties of porous metals was analyzed. The experimental results are in good agreement with the theoretical analysis, which proves the rationality of design of the device and provides important references and specific guidance for future study of the acoustic properties of porous metal materials.

Anchor Loss Calculation for Ring Shape Anchored Contour Mode Disk Resonators

Miniaturization is the most sophisticated method for achieving UHF and SHF resonance frequencies in RF MEMS resonators. However, by reducing the dimensions of the resonators, the size of their supports become more comparable with the size of the resonator and anchor loss becomes the dominant loss mechanism, thereby suppressing the quality factor. This study considers, Ring Shape Anchored Contour Mode Disk Resonator and calculates anchor loss effects using both energy loss and acoustic impedance ratio methods. Results of analytical calculations are verified using finite element harmonic analysis. Simulation results show that RSACMDRs have an acceptable quality factor in comparison with the other state-of-the-art resonators.

Determination and influence evaluation of the acoustic impedance ratio for thermal co-evaporation

Metal-halide perovskites are promising materials for applications like lasers and solar cells. In this work, we show the importance of an accurate determination of the source material parameters (acoustic impedance ratio and density) for thermal co-evaporation of soft materials like perovskites. We use here methylammonium iodide and lead(II)iodide for the exemplary deposition of methylammoniumlead(II)triiodide. We measure the thickness of the deposited layers by scanning electron microscopy cross sections and monitor the frequency change of the quartz crystal microbalances. We use a model with a one-dimensional acoustical composite resonator for the correct determination of the acoustic impedance ratio, resulting in values of 0.025 ± 0.002 for methylammonium iodide and of 0.11 ± 0.01 for lead(II)iodide. We use the resulting material parameters to deposit a layer of crystalline methylammonium lead triiodide with an accurately controlled stoichiometry of MAPbIx with x = 3.2 ± 0.2. We show the impact assuming false acoustic impedance ratios by simulating the actual evaporation rates of the source materials. We show that the ratio of the evaporation rates changes significantly during the deposition process. This results in a strong stoichiometry gradient in the perovskite layer and a mismatch in the average stoichiometry for a typical absorber thickness of 600 nm.

A BEM for band structure and elastic wave transmission analysis of 2D phononic crystals with different interface conditions

In this paper, a boundary element method (BEM) is developed and applied to compute the band structures and the elastic wave transmission of 2D phononic crystals which have different interface conditions between the scatterers and the matrix. The 2D phononic crystals consist of circular or square solid cylinders periodically embedded in a solid matrix forming a square lattice. For a periodic unit-cell, the boundary integral equations for both the scatterer and the matrix are formulated. After discretizing the boundary integral equations and for an infinite periodic structure, a linear eigenvalue equation related to the Bloch wave vector is obtained by substituting the periodic boundary conditions and the interface conditions. While for the corresponding semi-infinite periodic structure, a linear equation set is obtained from which the elastic wave transmission can be obtained. To verify the present BEM, some representative numerical examples are presented for the phononic crystals with different acoustic impedance ratios. The numerical results indicate that the present BEM can efficiently provide accurate results for phononic crystals with arbitrary shapes and different interface conditions, and the interface conditions have important effects on the band structures and the elastic wave transmission.

Application of simultaneous prestack inversion in reservoir facies identification

Poststack inversion is purely acoustic because there is no mode conversion at normal incidence. Therefore, P-wave impedance is the only information that can be estimated from poststack inversion of P-wave data. In full prestack inversion, both the low- and high-frequency components of the P-wave acoustic impedance can be extracted from the seismic data. In addition to the P-wave acoustic impedance, S-wave information or Poisson's ratio can also be estimated from prestack data. This provides fluid information for the reservoirs; thus, prestack inversion has an advantage over poststack inversion. We determined k, KC, m, and mC which are, respectively, the slope of the natural logarithm of shear impedance against the natural logarithm of acoustic impedance, the intercept of the natural logarithm of shear impedance against the natural logarithm of acoustic impedance, the slope of the natural logarithm of density against the natural logarithm of acoustic impedance, and the intercept of the natural logarithm of shear impedance against the natural logarithm of acoustic impedance. We also needed a set of angle-dependent wavelets, which are derived from angle stacks. Hence, we built three angle stacks; the near-angle stack (0–11 degrees), middle-angle stack (11–20 degrees), and far-angle stack (20–29 degrees). Using these angle stacks, we built three statistical angle-dependent wavelets. Finally, with log information we built an initial model for acoustic impedance, and tried to solve the inversion matrix using the conjugate gradient method. By solving this, we could simultaneously derive the acoustic impedance, shear impedance, and density sections from prestack data. Simultaneous inversion used the assumption of a constant shear wave to compressional wave velocity ratio, and the generalized Garnder equation, which are only valid in clastic rocks. The simultaneous prestack inversion method was used for the identification of reservoir facies in one of the hydrocarbon fields in Iran. With this method, four facies were identified; these were confirmed by reservoir geological information and well data.