High Acoustic Impedance Research Articles

Phase transformation kinetics of zirconium under ramp wave loading with different windows

The effect of window acoustic impedance on the wave profile of phase transition of zirconium under ramp wave compression is investigated in experiment and simulation. In the experiments, a ramp wave driven by magnetic pressure is applied to the zirconium samples backed windows with different acoustic impedances such as LiF, sapphire and free surface based on the compact pulsed power generator CQ-4. The experimental wave profiles measured by an advanced laser interference velocimeter show that the characteristic particle velocity of the onset phase transition from to is about 331.0 m/s in the conditions of LiF widow and free surface with low acoustic impedance, and it is approximately 301.9 m/s for the sapphire window with higher acoustic impedance. The corresponding onset pressure of phase transition varies from about 9.14 GPa to 8.27 GPa. The result shows that this onset pressure of phase transition, which is affected by diverse factors, is not the inherent value of phase transition belonging to the material properties. In order to describe these dynamic responses in experiment well, the numerical simulation of phase transition dynamics of zirconium is conducted in one-dimensional hydrodynamic code, in which included are the muti-phase equation of state based on Helmholtz free energy, the equation of non-equilibrium phase transition dynamics, and Steinberg constitutive relationship. The simulated results show that they can reflect the physical processes of elasto-plastic transition and - phase transition as well, which are excellently consistent with the experimental data. The relaxation times of - phase transition in three different acoustic impedance experiments are nearly the same (30 ns), and their finishing times of phase transition are all about 100 ns. The calculated quasi-isentrope of zirconium below 20 GPa in the pressure-volume and temperature-pressure thermodynamic planes shows that the isentrope and shock adiabat exhibit tiny difference before phase transition, and then separate gradually with the increase of pressure. The isentrope lies below the shock adiabat after the onset of phase transition. At about 20 GPa, the temperature of zirconium under ramp wave loading is bout 100 K lower than that under shock loading. Meanwhile, the abrupt change of volume at phase transition causes the Lagrange sound speed to reduce about 7% and then comes back to the bulk sound speed again after the phase transition has been finished.

The importance of sill thickness and timing of sill emplacement on hydrocarbon maturation

Magmatic sills in sedimentary basins can be relatively easy to interpret on seismic data because they stand out due to their high acoustic impedance in relation to the sediments. However, determining sill thickness is challenging unless the sills are drilled. This study explores the influence of magmatic sill thickness and timing of emplacement on temperature and hydrocarbon maturation in sedimentary basins. A 230 km long 2D transect through the Vøring Basin in the Norwegian Sea is modeled and sill thickness and timing of emplacement are the only parameters varied. The transect holds ∼40 sills that intruded at ∼55 Ma with a temperature of 1000 °C in a shale-dominated sequence. Several sill thickness scenarios were tested, but results for 0 m (no sills), 50 m and 100 m are presented here. Furthermore, the 50 m and 100 m thick sills were tested to intrude as upper and lower clusters separated by time intervals of 10 and 100 kyr. To study the effect of sills below seismic resolution, 1D modeling of well 7316/5-1 in the Barents Sea was performed. This well contains 9 sills distributed in an upper and a lower group. Vitrinite reflectance data from the well allow studying the effect of thin sills on temperature and maturation. The results show a clear connection between sill thickness and the temperature and maturation history of the basin. The largest impact of sill intrusions is at 3–5 km depth. For sills intruding as clusters, there are regionally marginal differences related to timing of emplacement but local differences especially in the close vicinity of the sills occur. This work indicates that the interpretation of sill thickness has a substantial influence on the prediction of the maturation and petroleum potential of sedimentary basins holding magmatic intrusions. Sills below seismic resolution contribute to increased maturation in its surroundings. Differences in the timing of sill emplacement within 10–100 kyr show local effects that may influence the petroleum potential of source rocks between two sill complexes.

The role of a composite polycarbonate-aerogel face shield in protecting the human brain from blast-induced injury: A fluid–structure interaction (FSI) study

Background Blast-induced traumatic brain injury is the most prevalent injury sustained by combat soldiers at the frontline. The current study aims to investigate the effectiveness of composite polycarbonate-aerogel face shields with different configurations in mitigating blast-induced brain injuries. Method A series of dynamic fluid–structure interaction simulations of a helmeted head subjected to a frontal free field blast was performed, to evaluate the effectiveness of the current conventional polycarbonate face shield and three other composite face shields with different configurations when exposed to a frontal free-field blast. Results The simulation results demonstrated that the sandwiched structured face shields of polycarbonate and aerogel provided superior blast attenuation than a single-layered polycarbonate face shield. The alternate multi-layered transparent materials of high and low densities provided the best attenuation of blast pressure transmission to the head, with the polycarbonate exterior shell casing contributing to the structural integrity of the face shield, while the lower dense aerogel filler providing high acoustic impedance to blast wave transmission. Conclusion This study provides further insights on future development and design of personal protective equipment in mitigating blast-induced injuries to the head.

Porous lead zirconate titanate ceramics with optimized acoustic properties for high-frequency ultrasonic transducer applications

Acoustic properties of porous PZT ceramics intended to be used as backing in high-frequency transducer applications are investigated using a novel method where an electroded piezoelectric thick film is deposited on the backing under test. Two backings with pore sizes 1.5 μm and 10 μm were obtained by sintering a mixture of ceramic powder and an organic template, their porosity was evaluated by scanning electron microscopy at 15%, leading to a density around 6.5 g/cm3. The electroacoustic impulse responses of these devices were measured considering the backing as a propagation medium, the initial thickness of which was chosen small enough to allow back-wall echoes to be detected and large enough to be able to separate the signals in time domain. Then the thickness of the backing was reduced (from around 2 mm to less than 1 mm) and the measurements were repeated. Acoustic properties were then deduced: attenuation coefficients reaching 4 dB/mm/MHz and group velocities around 3400 m/s were obtained, leading to an acoustic impedance around 22 MRa. Such combination of high attenuation and moderate acoustical impedance make these materials an interesting solution for high-resolution ultrasonic imaging transducers.

Varying ultrasound power level to distinguish surgical instruments and tissue.

We investigate a new framework of surgical instrument detection based on power-varying ultrasound images with simple and efficient pixel-wise intensity processing. Without using complicated feature extraction methods, we identified the instrument with an estimated optimal power level and by comparing pixel values of varying transducer power level images. The proposed framework exploits the physics of ultrasound imaging system by varying the transducer power level to effectively distinguish metallic surgical instruments from tissue. This power-varying image-guidance is motivated from our observations that ultrasound imaging at different power levels exhibit different contrast enhancement capabilities between tissue and instruments in ultrasound-guided robotic beating-heart surgery. Using lower transducer power levels (ranging from 40 to 75% of the rated lowest ultrasound power levels of the two tested ultrasound scanners) can effectively suppress the strong imaging artifacts from metallic instruments and thus, can be utilized together with the images from normal transducer power levels to enhance the separability between instrument and tissue, improving intraoperative instrument tracking accuracy from the acquired noisy ultrasound volumetric images. We performed experiments in phantoms and ex vivo hearts in water tank environments. The proposed multi-level power-varying ultrasound imaging approach can identify robotic instruments of high acoustic impedance from low-signal-to-noise-ratio ultrasound images by power adjustments.

Simulating the Linearly Elastic Solid–Solid Interaction with a Cut Cell Method

In this work, a cut cell-based sharp interface method is developed to deal with the interaction between linearly elastic solids in Eulerian framework. The material interface is represented by cut faces, and evolved by level set equation. Finite volume scheme is applied and strong coupling is achieved by using the Riemann solver for linearly elastic solid–solid interaction on the material interface. Original Ghost Solid Method (OGSM) and Modified Ghost Solid Method (MGSM) are realized in the Eulerian framework for comparison. Simulation results show that OGSM can lead to severe nonphysical oscillations when the density ratio is high, which is same as the results in KK. The location of wave front calculated by Ghost Solid Methods (GSMs) deviates from the exact location, because the evaluation of the ghost points deviates from the real interface location. The developed cut cell-based method gives accurate wave front location, and is stable for high density and acoustic impedance ratio and high-order reconstruction.

Predictions of defect detection performance of air-coupled ultrasonic rail inspection system

A rail inspection system based on ultrasonic guided waves and non-contact (air-coupled) ultrasound transduction is under development at the University of California at San Diego. The system targets defects in the rail head that are major causes of train accidents. Because of the high acoustic impedance mismatch between air and steel, the non-contact system poses severe challenges and questions on the defect detection performance. This article presents an extensive numerical study, conducted with a local interaction simulation approach, to model the ultrasound propagation and interaction with defects in the proposed system. This model was used to predict the expected detection performance of the system in the presence of various defects of different sizes and positions, and at varying levels of signal-to-noise ratios. When possible, operating variables for the model were chosen consistently with the field test of an experimental prototype that was conducted in 2014. The defect detection performance was evaluated through the computation of receiver operating characteristic curves in terms of probability of detection versus probability of false alarms. The study indicates that despite the challenges of non-contact probing of the rail, quite satisfactory inspection performance can be expected for a variety of defect types, sizes, and positions. Beyond the specific cases examined in this article, this numerical framework can also be used in the future to examine a larger variety of field test conditions.

Seismic inversion as a predictive tool for porosity and facies delineation in Paleocene fluvial/lacustrine reservoirs, Melut Basin, Sudan

The Melut Basin is a rift basin in the interior Sudan linked to the Mesozoic-Cenozoic Central and Western African Rift System. The Paleocene Yabus Formation is the main reservoir deposited in heterogeneous fluvial/lacustrine environment. Delineation of channel sandstone from shale is a challenge in reservoir exploration and development. We demonstrate a detailed 3D quantitative seismic interpretation approach that integrates petrophysical properties derived from well logs analysis. A porosity transform of acoustic impedance inversion provided a link between elastic and rock properties. Thus, we used seismic porosity to discriminate between different facies with appropriate validation by well logs. At the basin scale, the results revealed lateral and vertical facies heterogeneity in the Melut Basin. Good reservoir quality is observed in the Paleocene Yabus Formation. The sand facies indicated high porosity (20%) corresponding to low acoustic impedance (20000–24000 g ft/(cm3.s)). However, lower quality reservoir is observed in the Cretaceous Melut Formation. The porosity of sand/shale facies is low (5%), corresponding to high acoustic impedance (29000–34000 g ft/(cm3.s)). This suggests that the Yabus Sandstone is potentially forming a better reservoir quality than Melut Formation. At the reservoir scale, we evaluated the facies quality of Yabus Formation subsequences using petrophysical analysis. The subsequences YB1 to YB3, YB4 to YB7 and YB8 to YB10 showed relatively similar linear regressions, respectively. The subsequence of YB4 to YB7 is considered the best reservoir with higher porosity (25%). However, subsequence YB1 to YB3 showed lower reservoir quality with higher shale volume (30%). This attributed to floodplain shale deposits in this subsequence. Similarly, the high porosity (20%) recognized in deeper subsequences YB6 to YB9 is due to clean sand facies. We learnt a lesson that appropriate seismic preconditioning, exhaustive petrophysical analysis and well log validation are important keys for improved reservoir quality prediction results in fluvial/lacustrine basins.

Effect of RC load on the performance of a three-stage looped thermoacoustic engine

Thermoacoustic heat engine is a type of machine converting thermal energy into acoustic energy with the attracting characteristics of high reliability and environmental friendliness. This work proposed a three-stage looped thermoacoustic engine, where a compliance tube is utilized as the phase adjuster, to realize the high acoustic impedance and the near traveling-wave acoustic field in the regenerator, which is significant for effective thermoacoustic conversion. In order to investigate its performance with low-grade thermal energy, the output acoustic power of the engine is measured with the variable load method. It can be found that as the resistance decreases, the efficiency of the engine may rise, but the required heating temperature also rises. Thus, there exists a trade-off between the efficiency and the heating temperature, and the relative Carnot efficiency is adopted as a main index to evaluate the performance of the system. The maximum relative Carnot efficiency of 12.6% (the corresponding efficiency was 3.2%) was achieved in our experiments, when the heating temperatures of the three stages were 120 °C.

Effect of phase adjustment on the acoustic field of a cascade thermoacoustic engine

This study set out to explore the influence of phase adjustment on the acoustic field of a cascade thermoacoustic engine. The system consists of one standing wave unit and one traveling wave unit arranged in series. The straight-line configuration allows suppressing a time-averaged mass flow or Gedeon streaming, which causes some unwanted convective heat transport and reduces the efficiency of the system. Theoretically, the regenerator of the traveling wave unit must be operated within the traveling wave phasing and high impedance region in order to achieve an efficient performance. The various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally to adjust the position of the sweet spot as well as to achieve the high acoustic impedance in the regenerator. The effective tuning methods with less modification here are accomplished by changing the volume of the down-cavity and reducing the flow area of the down-resonator by inserting the pencil. However, the pencil insertion scheme causes an extra loss due to viscous dissipation that should be taken into account. The change of the down-resonator length has a strong effect on the acoustic field in the system. After the phase-adjustment schemes are completely implemented, the performance of the proposed system is significantly improved, in which the regenerator of the traveling wave unit operates within the traveling wave phase region with high acoustic impedance. This prototype operated with air at atmospheric pressure can supply acoustic power up to 33 W to the down-resonator, which is about 9.5% of Carnot efficiency.

Fully-disposable multilayered phononic crystal liquid sensor with symmetry reduction and a resonant cavity

Phononic crystals are artificial structures with unique capabilities to control the transmission of acoustic waves. These novel periodic composite structures bring new possibilities for developing a fundamentally new sensor principle that combines features of both ultrasonic and resonant sensors. This paper reports the design, fabrication and evaluation of a phononic crystal sensor for biomedical applications, especially for its implementation in point of care testing technologies. The key feature of the sensor system is a fully-disposable multi-layered phononic crystal liquid sensor element with symmetry reduction and a resonant cavity. The phononic crystal structure consists of eleven layers with high acoustic impedance mismatch. A defect mode was utilized in order to generate a well-defined transmission peak inside the bandgap that can be used as a measure. The design of the structures has been optimized with simulations using a transmission line model. Experimental realizations were performed to evaluate the frequency response of the designed sensor using different liquid analytes. The frequency of the characteristic transmission peaks showed to be dependent on the properties of the analytes used in the experiments. Multi-layered phononic crystal sensors can be used in applications, like point of care testing, where the on-line measurement of small liquid samples is required.

Simulation and experimental study of the sensor emitting frequency for ultrasonic tomography system in a conducting pipe

Ultrasonic tomography techniques provide flow visualization capability, non-invasively and non-intrusively, to enhance the understanding of complex flow processes. There is limited ultrasonic research in tomography imaging systems in the tomogram analysis of fluid flow in a conducting pipe because of a high acoustic impedance mismatch, which means that very little ultrasonic energy can be transmitted through the interface. The majority of industrial pipelines are constructed from metallic composites. Therefore, the development and improvement of ultrasonic measurement methods to accommodate a stainless steel pipe are proposed in this paper. Experimental and simulation distribution studies of the ultrasonic emitting frequency in acrylic versus stainless steel pipes were studied, measured and analyzed. During the simulation, ultrasonic transducers were placed on the surface of the investigated pipe to inspect the ultrasonic sensing field. The distribution of the sound wave acoustic pressure was simulated based on the physical dimensions and parameters of the actual experimental hardware set-up. We developed ultrasonic acoustic models using the finite element method with COMSOL software, and experiments were carried out to validate the simulation results. Finally, by performing the static phantoms tests, a feasibility study of ultrasonic tomography system was presented to investigate the void fraction of liquid column inside a stainless steel pipe.

Analysis of Hydrostatic Pressure Zones in Fabi Field, Onshore Niger Delta, Nigeria

The Analysis of hydrostatic pressure of Fabi Field onshore Niger delta was carried out to understand the subsurface depth pressure variations in the field. The well logs were analyzed to identify hydrostatic pressure zones through points of deviation from the compaction trends of the sediments and attribute crossplots while seismic inversion was carried out on the seismic data to obtain the lateral hydrostatic pressure variations in Fabi Field. The well logs exhibited normal compaction trends from depth level of 7200 ft to 8625 ft. At depth level of 8625 ft to 9000 ft, the velocity, density and resistivity logs deviated from the normal compaction trends. This point of deviations from the compaction trends of the sediments were identified as overpressure zones. Through crossplots of velocity and density logs, two overpressure generating mechanism of the Fabi Field such as under compaction and unloading were revealed. The under compaction was characterized by a linear drop in velocity and increase in density with depth while Unloading is characterized by abrupt decrease in velocity and at constant change in density. The results of acoustic impedance inversion revealed the lateral hydrostatic pressure variations of the Fabi Field. The onsets of over pressure zones are found around 1600 ms to about 1630 ms while very high overpressure gradients occur between 1950 ms to 2150 ms. These zones are characterized by very high acoustic impedance. The area extents of the positive anomalies (increase in acoustic impedance) are mostly consistent with the pressure while negative anomalies (low acoustic impedance) are interpreted as reservoir or sand zones.

Lung ultrasound: a promising tool to monitor ventilator-associated pneumonia in critically ill patients.

Ventilator-associated pneumonia (VAP) is the most frequent intensive care unit (ICU)-acquired infection that is independently associated with mortality. Accurate diagnosis and timely treatment have been shown to improve the prognosis of VAP. Chest X-ray or computed tomography imaging are used for conventional assessment of VAP, but these methods are impractical for real-time measurement in critical patients. Therefore, lung ultrasound (LUS) has been increasingly used for the assessment of VAP in the ICU. Traditionally, LUS has seemed unsuitable for the detection of lung parenchyma owing to the high acoustic impedance of air; however, the fact that the reflection and reverberation in the detection region of the ultrasound reflect the underlying pathology of lung diseases has led to the increased use of ultrasound imaging as a standard of care supported by evidence-based and expert consensus in the ICU. Considering that any type of pneumonia causes air volume changes in the lungs, accumulating evidence has shown that LUS effectively measures the presence of VAP as well as dynamic changes in VAP. This review offers evidence for ultrasound as a noninvasive, easily repeatable, and bedside means to assess VAP; in addition, it establishes a protocol for qualitative and quantitative monitoring of VAP.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-016-1487-y) contains supplementary material, which is available to authorized users.

Sensitivity study of multilayer thin-film bulk acoustic resonator for mass sensor application

The sensitivity of multilayer thin-film bulk acoustic resonators (MTFBARs) used as mass sensors is investigated. MTFBAR sensors with the structure of a mass-sensitive layer/electrode layer/piezo layer/electrode layer were used. Two methods, one using electric impedance and the other displacement, were adopted for the determination of sensitivity. Simulation results show that the two methods agree well, and the characteristic acoustic impedance and thickness of the non-piezo layers strongly affect mass sensitivity. It was found that high acoustic impedance in the non-piezo layer is not helpful for sensitivity improvement. Sensitivity is improved by choosing an appropriate thickness for the low acoustic impedance non-piezo layer, and the maximum sensitivity can be obtained by choosing suitable thickness combinations for the layers. Moreover, it was found that MTFBAR quality factor and sensitivity are simultaneously improved by adopting a high-quality-factor non-piezo layer with low acoustic impedance for an air working environment, whereas a balance between quality factor and sensitivity is found through optimization of the non-piezo layers for a water working environment. These results can be used for the design and application of MTFBAR mass sensors.

Effects of compensating the temperature coefficient of frequency with the acoustic reflector layers on the overall performance of solidly mounted resonators

Thin film acoustic wave resonator based devices require compensation of temperature coefficient of frequency (TCF) in many applications. This work presents the design and fabrication of temperature compensated solidly mounted resonators (SMRs). The characteristics of each material of the layered structure have an effect on the device TCF but depending on the relative position with respect to the piezoelectric material in the stack. The influence of material properties of the different layers composing the device on the TCF is discussed in detail. TCF behavior simulation is done with Mason’s model and, to take into account the deterioration of overall performance due to the finite lateral size and shape of the resonator, we have used 2D and 3D finite element modelling of the resonators. The overall behavior of the device for external loads is predicted. SMRs are designed according to simulations and fabricated with different configurations to obtain TCF as near to zero as possible with an optimized response. Resonators are made by depositing Mo/AlN/Mo piezoelectric stacks on acoustic reflectors. As reflector materials, conductive W and insulating WOx films have been used as high acoustic impedance materials. SiO2 films are used as low acoustic impedance material.

The performance improvement of a cascade thermoacoustic engine by adjusting the acoustic impedance in the regenerator

A novel cascade configuration consisting of one standing wave unit and one travelling wave unit arranged in series is studied in this paper. Theoretically, a straight-line cascade engine provides an efficient energy conversion, reduces the difficulties of fabrication and allows no Gedeon streaming. In order to achieve such a powerful cascade thermoacoustic engine, the regenerator of the travelling wave unit must be operated in high impedance and travelling wave phasing region. Various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally in order to adjust the position of the sweet spot as well as to promote the acoustic impedance in the regenerator. It is found that the effective tuning methods with less modification here are accomplished by changing the volume of down-cavity and reducing the flow area of down-resonator by inserting the pencil. The exploration also shows that the acoustic field in the system is quite sensitive to the effect of down-resonator length. The performance of the proposed system is clearly improved after the phase-adjustment schemes are completely implemented, in which the regenerator works within the sweep spot zone with high acoustic impedance. Copyright © 2016 John Wiley & Sons, Ltd.

Cavity Resonance Sensor With Disposable Analyte Container for Point of Care Testing

The use of phononic crystals and resonant structures as sensing platforms paves the way to the development of new biomedical technologies. An acoustic sensor with a resonant cavity and a disposable element was investigated in this paper. The sensor consists of seven layers with high acoustic impedance mismatch. The disposable element used was a glass spectrophotometry cuvette and, during the experimentation, it was filled with different liquid analytes showing characteristic transmission features that could be used as measures to differentiate and identify them. Experimental transmission curves were obtained using an electronic characterization system that uses a double sideband modulation technique to acquire valuable information about the structure being analyzed. Simulations using the 1-D transmission line method were performed to support the experimental realizations. The frequency of maximum transmission has been found to be strongly dependent on the speed of sound of the analyte under test.

Micromachining and validation of the scanning acoustic microscope spatial resolution and sensitivity calibration block for 20-230 MHz frequency range.

Scanning acoustic microscopy (SAM) is used as a routine non-destructive test tool for different diagnostic examinations: detection of defects such as microcracks, delamination, disbonding, inclusions, subsurface features in materials such as pores and cracks. SAM can be operated in a wide frequency range from Megahertz to Gigahertz. SAM measurement spatial resolution is diffraction limited by the wavelength of the acoustic wave in particular medium and also depends on individual transducers geometry. Actual SAM spatial resolution can be determined by measuring calibrated lithographically formed microstructures in high acoustic impedance materials. Numerical acoustic signal simulation method, based on the diffraction approach, was employed for the selection of the calibration block pattern geometry and linear dimensions of the elements. Universal calibration block for SAM operating in a 20-230 MHz frequency range was micromachined in high acoustic impedance ceramic substrates. Differently spaced (from 18 to 185 µm) lines of the same width and different widths (from 17 to 113 µm) but similar spacing lines were imposed in alumina ceramics employing one step lithography process, i.e. femtosecond laser ablation. Proposed SAM calibration pattern linear dimensions were characterized employing optical and scanning electron microscopy. Finally the samples were measured with SAM employing different frequency transducers and results were compared with the numerical simulations. It was obtained that resolution of SAM operating with 230 MHz transducer is not worse than 40 µm.

Hierarchical Assembly of Tungsten Spheres and Epoxy Composites in Three-Dimensional Graphene Foam and Its Enhanced Acoustic Performance as a Backing Material.

Backing materials play important role in enhancing the acoustic performance of an ultrasonic transducer. Most backing materials prepared by conventional methods failed to show both high acoustic impedance and attenuation, which however determine the bandwidth and axial resolution of acoustic transducer, respectively. In the present work, taking advantage of the structural feature of 3D graphene foam as a confined space for dense packing of tungsten spheres with the assistance of centrifugal force, the desired structural requirement for high impedance is obtained. Meanwhile, superior thermal conductivity of graphene contributes to the acoustic attenuation via the conversion of acoustic waves to thermal energy. The tight contact between tungstate spheres, epoxy matrix, or graphene makes the acoustic wave depleted easily for the absence of air barrier. The as-prepared 3DG/W80wt%/epoxy film in 1 mm, prepared using ∼41 μm W spheres in diameter, not only displays acoustic impedance of 13.05 ± 0.11 MRayl but also illustrates acoustic attenuation of 110.15 ± 1.23 dB/cm MHz. Additionally, the composite film exhibits a high acoustic absorption coefficient, which is 94.4% at 1 MHz and 100% at 3 MHz, respectively. Present composite film outperforms most of the reported backing materials consisting of metal fillers/polymer blending in terms of the acoustic impedance and attenuation.