Acoustic Wave Research Articles

Simple and sensitive method for in vitro monitoring of red blood cell viscoelasticity by Quartz Crystal Microbalance with dissipation monitoring (QCM-D)

Viscoelasticity (VE) is the intrinsic mechano-dynamic property enabling red blood cells (RBCs) to undergo prompt and repeated deformations while maintaining structural integrity. Assessing RBC VE and how different stressors can affect it is of great interest. Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) is a technology exploiting high-frequency acoustic waves to probe soft matter rheological properties. In the present study, a QCM-D method is reported for in vitro monitoring of cell VE in viable RBCs. The method is based on casting a sensor-adherent cell monolayer and modeling it as an effective viscoelastic medium, and allows to extrapolate proxy values of both the elastic and the viscous cell shear moduli. Real-time VE changes induced by the known cell VE stressors temperature, medium tonicity, glutaraldehyde, methyl-β-cyclodextrin and cytochalasin D have been reliably identified. The method is relatively simple and inexpensive, non-invasive, and able to seize subtle changes of cell biomechanics. Hence, it could be usefully exploited for in vitro assessment of RBC rheological properties and their alterations induced by external chemico-physical stimuli.

Crowdsourcing human observations expands and enhances volcano monitoring records

Volcano monitoring is constrained by the distribution of sensors that record activity. Here, we explore the role of crowdsourcing to broaden acoustic monitoring records by surveying people across Aotearoa New Zealand about the sounds they heard following the 2022 climactic eruption of Hunga volcano in Tonga. We compare the 1930 survey responses to geophysical records of the pressure waves and find that they align well, both recording ~5-7 audible signals of varying amplitude with a peak of 60-80 decibels, arriving in two 30-minute phases ~3 hours post-eruption, travelling North-to-South. The crowdsourced observations fill instrumental gaps regarding the wave’s audible frequencies and contribute insights into interactions between the far-field acoustic wave and the social and built environment. Descriptions of short-lived impacts reveal that pressure waves are capable of substantial disturbances thousands of kilometers from the vent. We demonstrate that crowdsourcing can support traditional monitoring as a reliable low-cost method to capture perishable data.

Chemical and Acoustical Mixed-Mapping of Geological Materials from Laser-Induced Plasmas: A Comprehensive Approach to Differentiate Mineral Phases.

The acoustic wave produced alongside laser-induced plasmas can be used in conjunction with the recorded atomic spectra of plasma emission to expand the physicochemical information acquired from a single inspection event. Among the most interesting uses of acoustic information is the differentiation of mineral phases with similar optical responses coexisting in geological targets. In addition, laser-induced plasma acoustics (LIPAc) can provide data related to the inspected material's hardness, density, and compactness. In this paper, we present a dual acoustic-optic laser-based strategy for the generation of high-resolution surface images of mineral samples. By combining simultaneous multimodal LIBS (laser-induced breakdown spectroscopy) and LIPAc spectral data from laser-induced plasmas, we explore the mineralogical composition of rocks embedded in resin matrixes to distinguish their chemical composition as well as their crystal phases based on physical changes caused by the different spatial arrangements of the constituent atoms. The multispectral polyhedron created by merging singular optical maps, one per detected elements, and the coincidental acoustic map enhance the distinction between regions present within the matrix of a host rock as compared to the differentiation yielded by each technique when used separately. The chemical information guides the composition of the mineral phases in the host rock. Then, the physical information obtained from acoustics may reinforce the identification of the detected mineral phase, draw the geological history of the inspected section, and showcase possible transformations, mainly of polymorphic nature. To test the combination proposed herein, we also inspected a septarian nodule featuring an ensemble of mineral phases with different origins. Mixed optical and acoustic responses from laser-produced plasmas of this complex sample allowed us to obtain more specific information. This approach constitutes a reliable and high-throughput tool for studying the surface of geological samples, which can substantially supplement well-established techniques for mineralogical analysis such as Raman spectroscopy and X-ray diffraction.

Surface acoustic wave platform integrated with ultraviolet activated rGO-SnS2 nanocomposites to achieve ppb-level dimethyl methylphosphonate detection at room-temperature

Dimethyl methylphosphonate (DMMP) is commonly used as an alternative for demonstrating to detect sarin, which is one of the most toxic but odorless chemical nerve agents. Among various types of DMMP sensors, those utilizing surface acoustic wave (SAW) technology provide notable advantages such as wireless/passive monitoring, digital output, and a compact, portable design. However, key challenges for SAW-based DMMP sensors operated at room temperature lies in simultaneous enhancement of sensitivities and reduction of detection limits. In this study, we developed a binary material strategy by combining reduced graphene oxide (rGO) and tin disulfide (SnS2) with (100)-facets orientation as sensing layers of SAW device for DMMP detection utilized at room temperature. Ultraviolet (UV) light was applied to activate the sensitive film and reduce the sensor's response time. The developed SAW DMMP sensor demonstrated a superior sensitivity (−1298.82 Hz/ppm), a low detection limit of 50 ppb, and a hysteresis below 1.5%, along with fast response/recovery time (39.2 s/28.4 s), excellent selectivity, long-term stability and repeatability. The formation of shrub-like rGO-SnS2 heterojunctions with abundant surface defects and large specific surface areas, high-energy (100) crystalline surfaces of SnS2, and photogenerated carriers generated by UV irradiation were pinpointed as the crucial sensing mechanisms. These factors collectively enhanced adsorption and reaction dynamics of DMMP molecules.

Development of a low frequency acoustic energy harvesting system by using piezoelectric transducers mounted on a metallic plate placed inside the centre of a hollow cylinder

Abstract In this work, we are demonstrating an innovative acoustic energy harvesting system that utilizes a hollow polyvinyl dichloride cylinder with a metallic circular plate placed at the centre inside with five piezoelectric transducers mounted on it. A speaker, used as a source of acoustic waves, is fixed at the top of the cylinder by using a clamp. The cylinder, upon exposure to incident acoustic waves, induces resonance within it, generating an amplified stationary wave. The generated vibration drives the metallic plate mounted with piezoelectric transducers, which serves as a diaphragm. As a result, a pressure difference is developed across it and due to piezoelectric effect on the transducers, electricity is produced. Experimental results show that the system output voltage and power depends on various factors, including the elastic properties of the metallic plate, resonance frequency, and the distance of separation between the acoustic source and the plate. At an incident sound pressure level of 75 dB, the experimental results show that, at an acoustic resonance frequency of 310 Hz, the system yielded a maximum peak to peak voltage of 1000 mV and output power of 0.612 µW. Incorporation of a voltage doubler circuit with the harvester increases its power to 57.6 µW. The simplicity in design and cost-effectiveness of the proposed acoustic energy harvesting system renders it to be a promising avenue for energy harvesting implementations.

Local maximum synchrosqueezing adaptive transformation for cross-instantaneous frequencies analysis

Abstract To overcome the shortcomings of existing time-frequency (TF) analysis (TFA) methods in analyzing signals containing cross-instantaneous frequencies (IFs), this paper proposes an adaptive TFA technique combined with image processing methods based on local maximum synchrosqueezing transform. The core idea of the proposed algorithm is to localize the filtering of signals containing several different IF components using kernel functions containing several different directions, respectively, to achieve energy separation at the crossing frequencies. In turn, the local maximum synchrosqueezing transform is used to rearrange the TF energy to the true IF ridges of the signal to improve the TF energy concentration. Simulation data demonstrates that the proposed algorithm has higher energy aggregation and better noise immunity, especially for signals with cross-IFs. Applying the proposed method to animal acoustic and radar wave signals of pedestrians can accurately describe the differences in the frequency change patterns and the temporal distribution of energy in the signals, thereby providing a judgment basis for effectively identifying and classifying the signals.

Time-dependent acoustic waves generated by multiple resonant bubbles: application to acoustic cavitation

Time-dependent acoustic waves generated by multiple resonant bubbles: application to acoustic cavitation

Scattering of Acoustic Waves by an Inhomogeneous Elastic Cylindrical Shell of Finite Length in a Half-Space

An analytical solution to the problem of diffraction of a plane acoustic wave on a radially inhomogeneous thick-walled elastic cylindrical shell of finite length is obtained. The cylindrical shell is located in an acoustic half-space filled with an ideal liquid. The boundary of the half-space is an acoustically rigid or acoustically soft surface. The results of calculations of the acoustic field in the far zone are presented.

Non-contact rotation of a small object using a combination of ultrasound standing and traveling waves

Noncontact transportation and separation techniques using airborne ultrasound are attractive for use in industrial fields in which micrometer- to millimeter-sized objects can be levitated, rotated, and transported in the air using acoustic standing-wave and traveling-wave fields. This paper discusses a method to rotate a small object in the air without physical contact using ultrasound. The experimental system comprises a vibrating disk with four bolt-clamped Langevin-type ultrasound transducers and two semicircular reflectors. The flexural vibration of the disk generates an acoustic standing wave between them, and a small object can be levitated at the nodal position. An acoustic traveling wave was generated in the horizontal direction in an asymmetric acoustic field by inclining one of the two reflectors, which induced rotation of the object in the clockwise or counterclockwise direction. The acoustic intensity in the circumferential direction acting on the object was then calculated, and the directions of rotation predicted by the calculations corresponded with the experimental results. Higher input currents produced higher rotation speeds; the rotation speed reached a maximum value of 6.8 ± 0.9 rps at an input current of 1.1 App.

Graphene Decorated Shear Horizontal Surface Acoustic Wave Resonator as Humidity Sensor

Graphene Decorated Shear Horizontal Surface Acoustic Wave Resonator as Humidity Sensor

Burner and Flame Transfer Matrices of Jet-Stabilized Flames: Influence of Jet Velocity and Fuel Properties

Abstract To achieve the decarbonization of electrical power generation, gas turbines need to be upgraded to combust high-hydrogen content fuels reliably. One of the main challenges in this upgrade is the burner design. A promising burner concept for a high-hydrogen fuel mixture are jet burners, which are highly flashback resistant thanks to their high bulk velocity. Due to its nonacoustically compact extension and the presence of hydrogen in the fuel mixture, new challenges arise in assessing the (thermo)acoustic response of this burner design. A burner transfer matrix (BTM) and the flame transfer function (FTF) or transfer matrix (FTM) are typically measured with the multimicrophone method (MMM) to assess the performance of new burner types in relation to thermoacoustic stability. With the switch toward hydrogen, the fuel/air mixture is significantly altered in its properties regarding the speed of sound and density, which are of fundamental importance for acoustic waves propagation and their reconstruction via the MMM, as highlighted in recent work. In this work, we extend this discussion by studying the influence of the gas composition within the burner when measuring BTMs, and its indirect effect on the assessment of FTFs. Experimentally, we achieve this by adapting the preheating temperature during the measurement of the BTM with a nonreactive mixture in order to match the speed of sound of the hydrogen–air mixture required to flow in the burner under reactive conditions. Additionally, we present an analytical model for the jet burner transfer matrix, which is validated against the experimental data. Since the BTM is fundamental for the assessment of the FTM and FTF, the propagation of the error of changing fuel mixtures in the burner is evaluated. The influence of the variation in reactant composition of the BTM on the FTM assessment is noticeable, particularly in the gain of the FTFs. Furthermore, the influence of the total mass flow and, thus, the bulk flow velocity on the FTF is analyzed.

Addressing cycle‐skipping in full‐waveform inversion using acoustic wave energy

AbstractLimitations in acquisition technologies lead to insufficient low‐frequency signals in field seismic data. Local optimization methods are the common approaches for full‐waveform inversion. Inaccurate initial velocity models and lack of low‐frequency signals in seismic data typically cause the local‐gradient‐based full‐waveform inversion to converge to a local minimum due to cycle‐skipping. The existing energy‐based objective functions can generate artificial low‐frequency signals successfully by squaring the pressure but overlook the law of energy conservation, which may mislead model updates. To overcome this issue, we combine acoustic wave potential energy and kinetic energy to develop a new objective function that fits the acoustic wave energy. The new acoustic‐wave‐energy‐based full‐waveform inversion considers the law of energy conservation. The new system creates low‐frequency signals to avoid cycle‐skipping and produce an accurate smooth background velocity model, which provides a sufficient starting model for conventional full‐waveform inversion. Numerical examples demonstrate that the combination of acoustic‐wave‐energy‐based full‐waveform inversion and conventional full‐waveform inversion can deliver more faithful and accurate final results than conventional full‐waveform inversion alone.

Hierarchical Nanostructures as Acoustically Manipulatable Multifunctional Agents in Dynamic Fluid Flow.

Acoustic waves provide a biocompatible and deep-tissue-penetrating tool suitable for contactless manipulation in in vivo environments. Despite the prevalence of dynamic fluids within the body, previous studies have primarily focused on static fluids, and manipulatable agents in dynamic fluids are limited to gaseous core-shell particles. However, these gas-filled particles face challenges in fast-flow manipulation, complex setups, design versatility, and practical medical imaging, underscoring the need for effective alternatives. In this study, flower-like hierarchical nanostructures (HNS) into microparticles (MPs) are incorporated, and demonstrated that various materials fabricated as HNS-MPs exhibit effective and reproducible acoustic trapping within high-velocity fluid flows. Through simulations, it is validated that the HNS-MPs are drawn to the focal point by acoustic streaming and form a trap through secondary acoustic streaming at the tips of the nanosheets comprising the HNS-MPs. Furthermore, the wide range of materials and modification options for HNS, combined with their high surface area and biocompatibility, enable them to serve as acoustically manipulatable multimodal imaging contrast agents and microrobots. They can perform intravascular multi-trap maneuvering with real-time imaging, purification of wastewater flow, and highly-loaded drug delivery. Given the diverse HNS materials developed to date, this study extends their applications to acoustofluidic and biomedical fields.

A spurious-free SAW filter employing a novel transducer structure on bulk LiNbO3 substrates

In order to cope with the ubiquitous wireless connections and the rapid transmission of data in communication systems, surface acoustic wave filters are required to have high performance. With a large electromechanical coupling coefficient (K2), conventional bulk 64°YX-LiNbO3 substrates are attractive for low-cost mass production of surface acoustic wave (SAW) resonators. However, the influence of the transverse modes restricts their practical application. In this work, a novel and simple tilted transducer is fabricated, and successfully achieved spurious-free passband SAW filters based on 64°YX-LN piezoelectric substrates. In this work, the transverse modes suppression method is theoretically studied and designed, and the effectiveness of the energy concentrated structure is verified. The optimal tilt IDT angle for eliminating the influence of transverse modes in Al/64 °YX-LN structure is about 6°. Subsequently, based on the above research, three types of tilted resonators were designed and fabricated, which not only verified the reliability of the aforementioned results but also enhanced the performance of the devices, compensating for the deficiency caused by the reduction of the Q factor due to the tilted structure. Finally, based on the double busbar tilted structure, a SAW filter was designed, which has a large 3 dB fractional bandwidth (FBW) and a spurious-free passband. The SAW filter designed in this work has low cost and excellent performance, and can be mass produced. In the field of low-cost RF devices, this work contributes to maintaining the competitive advantage of SAW technology.

Honeycomb-Shaped Phononic Crystals on 42°Y-X LiTaO3/SiO2/Poly-Si/Si Substrate for Improved Performance and Miniaturization

A SAW device with a multi-layered piezoelectric substrate has excellent performance due to its high Q value. A multi-layer piezoelectric substrate combined with phononic crystal structures capable of acoustic wave reflection with a very small array can achieve miniaturization and high performance. In this paper, a honeycomb-shaped phononic crystal structure based on 42°Y-X LT/SiO2/poly-Si/Si-layered substrate is proposed. The analysis of the bandgap distribution under various filling fractions was carried out using dispersion and transmission characteristics. In order to study the application of PnCs in SAW devices, one-port resonators with different reflectors were compared and analyzed. Based on the frequency response curves and Bode-Q value curves, it was found that when the HC-PnC structure is used as a reflector, it can not only improve the transmission loss of the resonator but also reduce the size of the device.

Surface acoustic wave amplification by drifting electrons in semiconducting epitaxial graphene on silicon carbide

Abstract A theory is presented for the amplification of a surface acoustic wave (SAW) due to its interaction with conduction electrons in gate-controlled epitaxial graphene (epigraphene) on a SiC substrate. It is assumed that the SAW is launched onto the substrate in the direction of an external dc electric field applied to the graphene sample and causing the conduction electrons to drift at a speed greater than the speed of the SAW. The wavelength of the SAW is assumed to be shorter than the mean free path of the electrons, so that the quantum regime of interaction of those electrons with the SAW is realized. The Green’s function method is used to calculate the SAW gain as a function of the electron concentration in epigraphene and the external dc electric field strength. It is shown that the substrate-induced band gap in the electronic spectrum of epigraphene leads to a significant (at least an order of magnitude) increase in the SAW gain as compared to the case of gapless graphene. In addition, the opening of the band gap results in a non-monotonic dependence of the SAW gain on the electron concentration, controlled by the gate voltage applied to the graphene sample. This dependence is characterized by the presence of a distinct maximum at a certain value of electron concentration (of about 2 × 10 12 cm−2 for typical values of the other parameters involved), which distinguishes it from the monotonic concentration dependence of the SAW gain in gapless graphene.

The acoustic Galton board

Phononic crystals are a class of materials with periodic structures that influence the propagation characteristics of acoustic waves through periodically arranged structural units. Here, we have developed the acoustic Galton board (AGB), a groundbreaking apparatus that serves as a cost-effective and user-friendly tool for demonstrating phononic crystal properties such as band gaps, Bragg scattering, and local resonance. The device comprises an elastic wave signal generator, an enhanced Galton board featuring a sophisticated pillar-nail array, and a signal receiver. The experimental results we have obtained demonstrate the significant impact of the AGB on elastic wave dispersion, effectively creating bandgaps that impede wave transmission within specific frequency ranges while allowing unhindered propagation in others. Furthermore, the AGB can simulate phononic crystals using both the Bragg scattering mechanism, achieved through the design of periodic rigid pillar-nail arrays, and the locally resonant mechanism, facilitated by the design of pillar-nail arrays with composite material structures. Additionally, the AGB can extend its applications to serve as a simulation tool for elastic metamaterials.

Ultra-broadband underwater meta-absorber with gradient impedance-matched composite material

Abstract We have developed an underwater acoustic meta-absorber that exhibits ultra-broadband absorption, with most of absorption coefficients exceeding 0.9 across the frequency range of 1 kHz−20 kHz. This performance is achieved through the localized trapping of acoustic waves and efficient energy dissipation, facilitated by local resonances within meticulously designed, impedance-matched composite materials. The designed gradient structure of the absorber allows for a reduced width of 84 mm (0.05λ at 1 kHz) and a customizable length, determined by the number of unit cells, each with a length of 15 mm (0.01λ at 1 kHz). This different design approach yields an ultra-broadband meta-absorber of compact dimensions, offering a promising alternative for the development of underwater absorption metamaterials and their practical applications.

Versatile Standing Wave Generation Between Arbitrarily Oriented Surfaces Using Acoustic Metasurface Deflectors and Retroreflectors

Acoustic wave devices using standing wave configurations have gained interest in various fields like healthcare diagnostics and manufacturing. Their functionalities span from cell sorting to microscale fiber assembly through periodic acoustic pressure fields. Conventional methods usually require parallel acoustic emitters and reflective surfaces, producing constrained standing wave patterns. In this paper, an effective approach for creating versatile acoustic standing wave fields using an acoustic metasurface deflector and retroreflector is introduced. The deflector manipulates the direction of incoming acoustic waves coupled with the retroreflector to reflect these waves back to the source. The proposed design allows the creation of standing waves that are not constrained by the relative angles of the two surfaces involved and allows for customizable wave patterns beyond the standard limits with enhanced adaptability. The system's effectiveness is evaluated through computational simulations using finite element analysis and experimental validation based on a 3D‐printed prototype. Results suggest that versatile standing waves between arbitrarily oriented surfaces can be produced through the careful design of the metasurface deflector and retroreflector. This approach can improve the performance of standing wave applications in particle manipulation, thus broadening the range of practical implementations for ultrasound and acoustofluidic technologies.

Acoustic Wave Velocities in Bridge Steels and the Effects on Ultrasonic Testing

Ultrasonic testing is utilized to ensure weld quality during the fabrication of steel bridges by identifying discontinuities that are classified as either acceptable or rejectable. The classification of a discontinuity can be affected by differences in the acoustic properties of the material under test and the reference standard used for calibration. Differences in wave velocity affect the refracted angle and amplitude of refracted shear waves. As a result, indications can be missed or incorrectly classified, or incorrectly located in the material. The objective of this research study was to characterize the acoustic wave velocities in a sample of contemporary steels to better understand the range over which velocities may vary for common steels. To address this objective, a series of velocity measurements have been conducted for shear waves propagating through different directions in steel plates of different strengths and reported manufacturing processes. The study also examines the loss of signal amplitude that results from changes in the refracted angle of shear waves used for the inspection of welds. Beam splitting that may occur in anisotropic materials and the potential impact on signal amplitudes is also presented. It was shown in the research that relatively small differences in velocity between the material under test and the reference standard cause a loss of sensitivity of the test. Data presented in the paper documents wave velocity and anisotropic ratios for a population of contemporary bridge steels used for the fabrication of steel bridges and an assessment of how velocity differences affect the amplitude of reflected shear waves.