Characteristics Of Acoustic Field Research Articles

Influence of high-intensity ultrasound application on the kinetics of sugar release from acid suspensions of artichoke (Cynara scolymus) biomass

The study of sugar release kinetics is an essential step prior to developing new technologies for applying in the bioethanol industry. To this end, the kinetics of reducing and total sugar release (extraction/hydrolysis) from artichoke waste were obtained in different conditions to evaluate the solubility of free sugars from raw matter and the hydrolysis of larger chain molecules separately. Thus, experiments of extraction with water (WE), hydrolysis (HY) in acid solutions and a conventional industrial hydrolysis (IHY), which combines dissolution and hydrolysis effects, were carried out. All of the treatments were studied with ultrasound application (US) or with conventional agitation (AG). Compared to AG experiments, US application accelerated the sugar dissolution reducing 50% the time to reach the equilibrium. The decrease in the biomass concentration in the suspensions increased the US effects in HY experiments. In IHY experiments, US was also able to enhance the final yield of sugars achieving relative reducing sugar and total sugar amounts 213% and 175%, significantly higher than AG experiments. The rheological changes in the suspensions during treatments can explain the different magnitude of ultrasound effects. The acoustic field characterization and the measurement of viscosity in the acid suspensions agreed with these results.

Distortion of the ambient low-frequency acoustic field by moorings

Moored receivers are often employed to collect long time series of underwater acoustic data to monitor the ocean. Moorings typically contain a float and other elements, acoustic parameters of which are rather distinct from those of seawater. In the frequency range of primary interest in seismo-acoustics and noise interferometry, the size of a mooring and dimensions of its float may be of the order of the acoustic wavelength or smaller. Then, acoustic measurements are performed in the near field of a strong scatterer. Assuming a spherical shape of the float, this paper aims to quantify the difference between the ambient and measured characteristics of low-frequency acoustic fields. Diffraction is shown to significantly affect low-frequency acoustic fields in a vicinity of a compact object even when the object is small compared to the wavelength. Scattering-induced low-frequency perturbations in oscillatory velocity are generally much larger than pressure perturbations in the vicinity of sub-wavelength objects. These perturbations prevent mounted vector sensors from measuring correctly the direction of the free-field oscillatory velocity. The feasibility of a posteriori compensation of the distortions in scalar and vector sensor measurements will be discussed. [Work supported by ONR.]Moored receivers are often employed to collect long time series of underwater acoustic data to monitor the ocean. Moorings typically contain a float and other elements, acoustic parameters of which are rather distinct from those of seawater. In the frequency range of primary interest in seismo-acoustics and noise interferometry, the size of a mooring and dimensions of its float may be of the order of the acoustic wavelength or smaller. Then, acoustic measurements are performed in the near field of a strong scatterer. Assuming a spherical shape of the float, this paper aims to quantify the difference between the ambient and measured characteristics of low-frequency acoustic fields. Diffraction is shown to significantly affect low-frequency acoustic fields in a vicinity of a compact object even when the object is small compared to the wavelength. Scattering-induced low-frequency perturbations in oscillatory velocity are generally much larger than pressure perturbations in the vicinity of sub-wavelength obje...

Acoustic focusing effect based on artificial periodic structure

To achieve high-efficiency acoustic focusing, an artificial periodic acoustic structure composed of two-dimensional three-component cell arrays was used to manipulate the transmission wave fronts of acoustic waves, and the acoustic field characteristics were numerically simulated by COMSOL finite element software. The results showed that whether the spherical acoustic wave generated by the point excitation source or the planar acoustic wave generated by the linear excitation source was used as the incident wave, an emission focus point can be generated at the top of the acoustic model. The intensity of the acoustic pressure at the focus point depended on the frequency of the incident acoustic waves. Under the same vibration period, the acoustic pressure will increase first and then decrease. It will reach a maximum value at the resonance frequency. In addition, when the model was cut into a right-angled trapezoidal structure with the axis of symmetry as a cross-section, the acoustic wave can produce a variable-direction focusing effect, and the “acoustic levitation” effect can also be realized. This series of anomalous acoustic phenomena can provide a new direction for acoustic directional transmission, acoustic wave detection, and acoustic stealth.

Numerical and experimental study of a looped travelling‐wave thermoacoustic electric generator for low‐grade heat recovery

Thermoacoustic technology has drawn increasing attention due to its advantages such as reliability and environmental benignity. Aiming at low-grade heat recovery, we developed a travelling-wave thermoacoustic electric generator consisting of a looped travelling-wave thermoacoustic engine and a linear alternator. In order to explore the operating characteristics of the electric generator, we numerically analyzed the acoustic field characteristics with a modified model. The analysis shows that high acoustic impedance appears in all three stages, and the travelling-wave component dominates the acoustic field of the loop, which is significant for both thermoacoustic conversion and acoustic power propagation. Furthermore, we also investigated the effects of external electric compliance, resistance, and hot end temperature on the output electric power, thermal-electric efficiency, and other related parameters. In the experiments, a thermal-electric efficiency of 3.7% with an output electric power of 24 W has been achieved, when the hot end temperature is 120°C. The relative Carnot efficiency can exceed 14% when the hot end temperature is between 120°C and 190°C. The promising results demonstrate the significant potential of thermoacoustic electric generation in low-grade heat recovery.

Ambient infrasound noise in urban environments

Associated with the emerging use of infrasound at tactical ranges (less than 50 km in complicated terrain), there is an increased need to deploy infrasound arrays in urban environments near sources of interest in order to record small signals. Initial urban deployment research demonstrated successful monitoring of a single source within 1 km utilizing rooftop infrasound arrays. In order to understand the applicability of this technique for a broader range of sources, the impact of the urban array design on noise reduction and detection of signals of interest must be assessed. These source signals, recorded within an urban scenario, are embedded in a complicated ambient noise environment with multiple coherent clutter sources and an overall decrease in the signal-to-noise ratio. Understanding these ambient acoustic field characteristics requires deconvolving observed coherent signals from time-varying atmospheric effects for different levels of urbanization. This paper presents an initial approach to instrumenting the urban environment with consideration of wind filter effects and data analysis to estimate total ambient acoustic field for a subset of urban zones. This work then provides a definition of urbanization that can be related to the infrasound wavefield. Permission to publish was granted by the Director, Geotechnical and Structures Laboratory.

Effect of trapped ion on the shock properties in opposite charged dusty plasma

The dust acoustic frequency properties and dissipative electrostatic field characteristics in opposite charged viscous dusty fluid plasma having trapped ion have been disused for quasineutrality case. The modified dissipative Burgers equation was analytically derived. The contributions of positive dust parameter, trapped ion, ion temperatures and charge to mass ratio between polarity grains on shock potential and its related electrostatic field have been investigated.

Acoustic Field Characterization of Medical Array Transducers Based on Unfocused Transmits and Single-Plane Hydrophone Measurements.

Medical ultrasonic arrays are typically characterized in controlled water baths using measurements by a hydrophone, which can be translated with a positioning stage. Characterization of 3D acoustic fields conventionally requires measurements at each spatial location, which is tedious and time-consuming, and may be prohibitive given limitations of experimental setup (e.g., the bath and stage) and measurement equipment (i.e., the hydrophone). Moreover, with the development of new ultrasound sequences and modalities, multiple measurements are often required to characterize each imaging mode to ensure performance and clinical safety. Acoustic holography allows efficient characterization of source transducer fields based on single plane measurements. In this work, we explore the applicability of a re-radiation method based on the Rayleigh–Sommerfeld integral to medical imaging array characterization. We show that source fields can be reconstructed at single crystal level at wavelength resolution, based on far-field measurements. This is herein presented for three practical application scenarios: for identifying faulty transducer elements; for characterizing acoustic safety parameters in focused ultrasound sequences from 2D planar measurements; and for estimating arbitrary focused fields based on calibration from an unfocused sound field and software beamforming. The results experimentally show that the acquired pressure fields closely match those estimated using our technique.

Theoretical aspects of monitoring synergistic processes in the rock massif

In this article, the grounds for considering of rocks massif as a nonlinear medium with dissipative properties have been shown that as a result of the combined influence of normal and tangential stresses around the workings, synergistic effects are observed with the formation of similar structures, which leads to the appearance of a quasi-stationary damped stress wave, and this , in turn, makes it possible to predict the nature of changes in the stress-strain state of the rock massif in space-time continuum. Taking into account the influence of the mining operations speed, a theoretical justification for diagnostics the physicomechanical properties and the stress state of sedimentary rocks has been developed by using the dynamic and kinematic characteristics of acoustic and electric fields. The theoretically established relationship of the stress state of massif of quartz-containing rocks with its elastic and electrical parameters follows taking into account the damped wave nature of the processes around the mine workings. Obtained results indicates the principal possibility of quantitative assessment of stress components acting in the rock massif using determined physical parameters of the massif.

Acoustic Focusing Imaging Characteristics Based on Double Negative Locally Resonant Phononic Crystal

To achieve high-efficiency and high-resolution acoustic focusing, we used artificial periodic acoustic structures composed of cell arrays to manipulate the acoustic transmission wave front, and used finite element software to simulate the acoustic field characteristics. We found that when focuses generated by arc-shaped acoustic excitation sources are incident on one side of the model, the energy will be localized within the structure to reduce its transmission loss, and then the high-resolution emission focus will be generated on the other side of the model. The magnitude of the acoustic pressure at the focus point will change with the frequency of the incident acoustic wave and will reach an extreme value at the resonant frequency. In addition, we explored the acoustic transmission characteristics of structures at different widths and found that it is only necessary to increase the width of the model by an integer multiple of half a wavelength to achieve low loss focusing effects at various distances. The acoustic phenomena studied in this paper may provide new methods for the application of photoacoustic signal detection, ultrasound medical imaging and ultrasonic nondestructive testing.

Experimental Determination of Acoustic Field Characteristics in a Natural Shallow Water Basin in Different Seasons of the Year

The results from processing data obtained in a series of field experiments on sound propagation in a natural shallow water basin are presented. The focus is on identifying the mode structure. Vertical profiles of the acoustic pressure and spectrograms of the basin’s response function are analyzed.

Acoustic field characteristics of a free-piston Stirling cryocooler with large cooling capacity at liquid nitrogen temperature

A free-piston Stirling cryocooler (FPSC) with a large cooling capacity (i.e., from several hundred Watt to thousand Watt) at liquid nitrogen temperature is promising in boil-off gas recondensation and high temperature superconducting (HTS) applications. Based on thermoacoustics, this work focuses on revealing the intrinsic relationship between the internal acoustic field and cooling performance of a FPSC. The main phase shifting parameters including the moving mass of the displacer, regenerator porosity and operating frequency are systematically studied through simulation and experiment. The results indicate that the increase of displacer moving mass has limited effect on the acoustic impedance match between the cooler and the linear compressor, while the exergy loss in the regenerator will decrease dramatically due to the variation of volume flow rate therein. In contrast, the acoustic impedance match is sensitive to the regenerator porosity, and a higher regenerator porosity leads to a considerable thermal ineffectiveness loss in the regenerator and thus degrades the cooler efficiency. In addition, the acoustic field of the FPSC is strongly influenced by the operating frequency. For a fixed cooling power, a higher operating frequency causes a larger volume flow rate in the regenerator, hence the friction loss and the required acoustic power increase accordingly. Upon the analysis, experimental validation was carried out and the initial results demonstrate a reasonable agreement.

The influence on acoustic frequency characteristics of conductivity gradual-varying tissue in magnetoacoustic tomography (MAT)

BackgroundAs a functional imaging technology, magneto acoustic tomography (MAT) has broad application prospect in early tumor diagnosis and image monitoring during treatment. MethodThe influence on the acoustic field characteristics of the gradual change in conductivity was studied in magneto-acoustic tomography with current injection (MAT-CI) in this article. ResultTheoretical analysis showed that the value of electro-acoustic conversion ratio (E-ACR) was different in different source frequencies under the same conductivity gradual-varying boundary. ConclusionThe frequency characteristics of the acoustic pressure tend to shift towards the low frequency region. This conclusion provides a theoretical foundation for the MA signal detection and processing system optimization in the area of conductivity gradual-varying.

Directional acoustic transmission based on metamaterials

To explore the simple low-loss operation of directional acoustic transmission technology, the propagation of acoustic waves in resonant phononic crystals was studied, and a transmission model based on acoustic metamaterials was constructed. Using the local resonance characteristics between acoustic waves and original cells, the multi-directional transmission of acoustic waves was modeled in the COMSOL software. It was found that acoustic waves generated by a point source are refocused into another point source after passing through the transmission model, and that the transmission loss is small. Under the control of this model, the effect of point-source propagation in various directions was achieved. The acoustic field characteristics of the model samples were also tested to verify the feasibility of the model structure, providing a new direction for applications such as underwater acoustic communication and detection.

A convenient, reliable, and fast acoustic pressure field measurement method for magnetic resonance-guided high-intensity focused ultrasound systems with phased array transducers

BackgroundWith the expanding applications of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU), there is an urgent need for a convenient, reliable, and fast acoustic pressure field measurement method to aid treatment protocol design, ensure consistent and safe operation of the transducer, and facilitate regulatory approval of new techniques. Herein, we report a method for acoustic pressure field characterization of MR-HIFU systems with multi-element phased array transducers. This method integrates fiber-optic hydrophone measurements and electronic steering of the ultrasound beam with MRI-assisted HIFU focus alignment to the fiber tip.MethodsA clinical MR-HIFU system (Sonalleve V2, Profound Medical Inc., Mississauga, Canada) was used to assess the proposed method. A fiber-optic hydrophone was submerged in a degassed water bath, and the fiber tip location was traced using MRI. Subsequently, the nominal transducer focal point indicated on the MR-HIFU therapy planning software was positioned at the fiber tip, and the HIFU focus was electronically steered around the fiber tip within a 3D volume for 3D pressure field mapping, eliminating the need for an additional, expensive, and MRI-compatible 3D positioning stage. The peak positive and negative pressures were measured at the focus and validated using a standard hydrophone measurement setup outside the MRI magnet room.ResultsWe found that the initial MRI-assisted HIFU focus alignment had an average offset of 2.23 ± 1.33 mm from the fiber tip as identified by the 3D pressure field mapping. MRI guidance and electronic beam steering allowed 3D focus localization within ~ 1 h, i.e., faster than the typical time required using the standard laboratory setup (~ 3–4 h). Acoustic pressures measured using the proposed method were not significantly different from those obtained with the standard laboratory hydrophone measurements.ConclusionsIn conclusion, our method offers a convenient, reliable, and fast acoustic pressure field characterization tool for MR-HIFU systems with phased array transducers.

Influence of sound directions on acoustic field characteristics within a rectangle-shaped sonoreactor: Numerical simulation and experimental study

Acoustic field intensity and distribution are the most important factors for the efficiency of ultrasonic processing. Recent simulation studies suggested that sound direction could influence both acoustic field intensity and distribution, but this influence has scarcely been investigated experimentally so far. In this work, we systematically studied the influence of sound directions on the acoustic field with up to five directions via both simulation and experiment. Fluid-structure interaction (FSI) harmonic response simulation and aluminum foil erosion experiment were employed to study the acoustic field under different directional combinations of ultrasonic sources. Results of simulation coincided well with that of experiment, which indicated that acoustic intensity, uniformity and cavitation characteristics were significantly affected by sound directions. Based on the results, several influence rules of sound directions were proposed. Optimal acoustic field with sound intensity of 30 times higher than that of single-wall excitation and severe cavitation volume of 95% was obtained. This work provides useful guidelines for acoustic field design of high-intensity ultrasonic apparatus.

A multi-stage traveling-wave thermoacoustically-driven refrigeration system operating at liquefied natural gas temperature

This study proposes a multi-stage travelling-wave thermoacoustically refrigeration system (TAD-RS) operating at liquefied natural gas temperature, which consists of two thermoacoustic engines (TAE) and one thermoacoustic refrigerator (TAR) in a closed-loop configuration. Three thermoacoustic units connect each other through a resonance tube of small cross-sectional area, achieving “self-matching” for efficient thermoacoustic conversion. Based on the linear thermoacoustic theory, a model of the proposed system has been built by using DeltaEC program to show the acoustic field characteristics and performance. It is shown that with pressurized 5 MPa helium as working gas, the TAEs are able to build a stable and strong acoustic field with a frequency of about 85 Hz. When hot end temperature reaches 923 K, this system can provide about 1410 W cooling power at 110 K with an overall exergy efficiency of 15.5%. This study indicates a great application prospect of TAD-RS in the field of natural gas liquefaction with a large cooling capacity and simple structure.

Metamaterial-based passive phased arrays: Resolution, losses, and characterization

Metamaterial and metasurface-based passive phased arrays provide novel means for the manipulation of acoustic fields. As passive elements, metasurfaces can provide local phase delays which enable the steering of sound fields and facilitate extraordinary wave phenomena. Some aspects that affect the performance of these passive elements include the spatial resolution/aliasing effect, the component resonances that shape the transmission spectra, and the thermoviscous losses that limit the transmission efficiency [X. Jiang, L. Yong, and L. Zhang, J. Acoust. Soc. Am. 141(4), EL363–368, April 2017]. Efficient acoustic field characterization is essential for investigating these issues with the ultimate aim of optimizing the geometrical parameters of the structure. This talk will address some details of the physics of metamaterial-based passive arrays and the broadband approach for assessing their transmission properties, with the aim of improving the design cycle and exploring novel uses.

Influence of volute basic circle diameter on the pressure fluctuations and flow noise of a low specific speed sewage pump

To reveal the effect of the volute basic circle diameter D3 on the performance of low specific sewage pumps, three different volutes equipped with the same impeller were designed for a low specific speed sewage pump. The global characteristics were obtained from the experiments, which presented that the volute basic circle diameter affects pump performance obviously. Computational fluid dynamics (CFD) was adopted to analyze the flow in the pump, as well as the velocity and pressure fields. Acoustic software LMS Virtual.Lab was adopted to analyze the acoustic field characteristics of the different models. The particle image velocimetry (PIV) technology was adopted to verify the results obtained by CFD and the qualitative agreement of the velocity obtained by CFD numerical calculation and PIV measurement is very good. It shows that the volute basic circle diameter has a small influence on the velocity distribution in the impeller. However, it changes the flow in the volute significantly. As D3 increases, the 2D streamline smoothens and the velocity distribution becomes uniform, whereas the pressure fluctuations and radial force of the impeller weaken. Furthermore, when the volute basic circle diameter increases to a certain extent, the pressure fluctuations almost have no change. The flow induced noise in volute A# is the largest, whereas it is the smallest in volute B#. There is an optimal volute basic circle diameter for a pump with ultra-thick blade not only to achieve the highest efficiency, but also to achieve excellent operating stability.

Acoustic field characterization of a clinical magnetic resonance-guided high-intensity focused ultrasound system inside the magnet bore.

With the expanding clinical application of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU), acoustic field characterization of MR-HIFU systems is needed for facilitating regulatory approval and ensuring consistent and safe power output of HIFU transducers. However, the established acoustic field measurement techniques typically use equipment that cannot be used in a magnetic resonance imaging (MRI) suite, thus posing a challenge to the development and execution of HIFU acoustic field characterization techniques. In this study, we developed and characterized a technique for HIFU acoustic field calibration within the MRI magnet bore, and validated the technique with standard hydrophone measurements outside of the MRI suite. A clinical Philips MR-HIFU system (Sonalleve V2, Philips, Vantaa, Finland) was used to assess the proposed technique. A fiber-optic hydrophone with a long fiber was inserted through a 24-gauge angiocatheter and fixed inside a water tank that was placed on the HIFU patient table above the acoustic window. The long fiber allowed the hydrophone control unit to be placed outside of the magnet room. The location of the fiber tip was traced on MR images, and the HIFU focal point was positioned at the fiber tip using the MR-HIFU therapy planning software. To perform acoustic field mapping inside the magnet, the HIFU focus was positioned relative to the fiber tip using an MRI-compatible 5-axis robotic transducer positioning system embedded in the HIFU patient table. To perform validation measurements of the acoustic fields, the HIFU table was moved out of the MRI suite, and a standard laboratory hydrophone measurement setup was used to perform acoustic field measurements outside the magnetic field. The pressure field scans along and across the acoustic beam path obtained inside the MRI bore were in good agreement with those obtained outside of the MRI suite. At the HIFU focus with varying nominal acoustic powers of 10-500W, the peak positive pressure and peak negative pressure measured inside the magnet bore were 3.87-68.67MPa and 3.56-12.06MPa, respectively, while outside the MRI suite the corresponding pressures were 3.27-67.32MPa and 3.06-12.39MPa, respectively. There was no statistically significant difference (P>0.05) between measurements inside the magnet bore and outside the MRI suite for the p+ and p- at any acoustic power level. The spatial-peak pulse-average intensities (ISPPA ) for these powers were 312-17816W/cm2 and 220-15698W/cm2 for measurements inside and outside the magnet room, respectively. In addition, when the scanning step size of the HIFU focus was increased from 100μmto 500μm, the execution time for scanning a 4×4mm2 area decreased from 210min to 10min, the peak positive pressure decreased by 14%, the peak negative pressure decreased by 5%, and the lateral full width at half maximum dimension of pressure profiles increased from 1.15mm to 1.55mm. The proposed hydrophone measurement technique offers a convenient and reliable method for characterizing the acoustic fields of clinical MR-HIFU systems inside the magnet bore. The technique was validated for use by measurements outside the MRI suite using a standard hydrophone calibration technique. This technique can be a useful tool in MR-HIFU quality assurance and acoustic field assessment.

Experimental characterization of velocity and acoustic fields of single-stream subsonic jets

The characterization of velocity and acoustic fields from a single-stream free jet operating at subsonic regimes is essential for aeronautical applications. For instance, the investigation of exhaust gases from single or coaxial nozzles or from bleed valve in turbojets and turbofan engines is crucial for understanding the mechanisms of noise generation and propagation and eventually for finding ways to reduce aircraft noise. This article evaluates the velocity and acoustic fields of an isothermal single jet discharging from a circular 38.1mm conical nozzle at three different Mach and Reynolds numbers of 0.25 (Re=2.5×105), 0.50 (Re=4.9×105) and 0.75 (Re=6.8×105), respectively. Pitot-tube and hot-wire probes were used to identify the mean velocity profiles in longitudinal and transversal directions in the wake of the jet. The hot-wire anemometry system was also used to evaluate the turbulence intensity distribution over eleven axial lines, from the centerline to the edge of the nozzle. The accuracy of hot-wire anemometers for turbulent intensities lower than 15% at low and high subsonic Mach numbers was evaluated by comparing the experimental measurements with available data from the literature. An acoustic investigation was carried out by analyzing the sound pressure level obtained at six positions in the far field, with viewing angles ranging from 40° to 110°. The results were integrated to a database with sound pressure level as a function of Strouhal number, aiming to provide a benchmark for further RANS-based methods applied to aeroacoustic simulations of single jets.