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Low-intensity ultrasound stimulation is a technique used in therapeutic ultrasound for bone regeneration. However, the underlying mechanisms are still poorly understood. In vitro studies on cell cultures are implemented to understand the processes involved. To analyze the effects of ultrasonic waves on cells, the control of the delivered acoustic intensity is essential. However, depending on the insonification protocol chosen, multiple reflections and standing waves that form inside the culture medium strongly hinder the estimates. In this work, we propose the development and the experimental validation of an anti-reflection cover. We demonstrate that this custom-designed device is effective in avoiding multiple reflections and makes it possible to artificially replace the layer of culture medium with a large amount of water. Finally, an analytical study of the acoustic intensity delivered to the cells is proposed.

Made available in DSpace on 2018-11-26T17:41:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-01. Added 1 bitstream(s) on 2021-07-15T15:01:41Z : No. of bitstreams: 1 S0104-66322017000200385.pdf: 1967784 bytes, checksum: e6fe4fe77bb10d78edf91db1a7d8d920 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The benefits of high-intensity ultrasound in diverse processes have stimulated many studies based on biomass pretreatment. In order to improve processes involving ultrasound, a calorimetric method has been widely used to measure the real power absorbed by the material as well as the cavitation effects. Peanut shells, a byproduct of peanut processing, were immersed in acidified aqueous solutions and submitted to an ultrasonic field. Acoustic power absorbed, acoustic intensity and power yield were obtained through specific heat determination and experimental data were modeled in different conditions. Specific heat values ranged from 3537.0 to 4190.6 J.kg(-1).K-1, with lower values encountered for more concentrated biomass suspensions. The acoustic power transmitted and acoustic intensity varied linearly with the applied power and quadratically with solids concentration, reaching maximum values at higher applied nominal power and for less concentrated suspensions. A power yield of 82.7% was reached for dilute suspensions at 320 W, while 6.4% efficiency was observed for a concentrated suspension at low input energy (80 W). State Univ Sao Paulo UNESP, Food Engn & Technol Dept, Inst Biosci Humanities & Exact Sci IBILCE, Campus Sao Jose Do Rio Preto, BR-15054000 Sao Paulo, Brazil State Univ Sao Paulo UNESP, Food Engn & Technol Dept, Inst Biosci Humanities & Exact Sci IBILCE, Campus Sao Jose Do Rio Preto, BR-15054000 Sao Paulo, Brazil FAPESP: 2013/09344-4 FAPESP: 2013/17497-5

In this work a method for the virtual sensing of the acoustic intensity is derived for exterior vibro-acoustic radiation of a complex deepdrawn structure. The proposed method estimates the acoustic intensity and acoustic pressure resulting from structural excitation in the full acoustic domain, by utilizing a model-based state estimator in the form of a Kalman filter. The used model is a high fidelity, fully coupled vibro-acoustic finite element model with infinite elements to model the acoustic radiation to infinity. The model is reduced to about 0.1% of the original size by a Krylov based model order reduction technique that preserves the stability of the full model. This allows for the usage of the model in a Kalman filter. The effectiveness of the Kalman filter is demonstrated with several numerical experiments, in which both the measured pressure and the measured sound intensity are compared with the estimations from the filter at several locations. Furthermore, the robustness of the filter to changing acoustic environments is assessed. ispartof: MECHANICAL SYSTEMS AND SIGNAL PROCESSING vol:134 status: Published online

The optimization techniques are explored in the direction of arrival (DOA) estimation based on single acoustic pressure gradient vector sensor (APGVS). By analyzing the working principle and measurement errors of the APGVS, acoustic intensity approaches (AI) and the minimum variance distortionless response beamforming approach based on single APGVS (VMVDR) are deduced. The radius to wavelength ratio of the APGVS must be not bigger than 0.1 in the actual application, otherwise its DOA estimation performance will degrade significantly. To improve the robustness and estimation performance of the DOA estimation approaches based on single APGVS, two modified processing approaches based on single APGVS are presented. Simulation and lake trial results indicate that the performance of the modified approaches based on single APGVS are better than AI and VMVDR approaches based on single APGVS when the radius to wavelength ratio is not bigger than 0.1, and the two modified DOA estimation methods have excellent estimation performance when the radius to wavelength ratio is bigger than 0.1.

The article of record as published may be found at https://doi.org/10.1121/1.4789358 Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5–7 energy to nonadjacent modes 8–20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2–4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments. The ASIAEX and NLIWI experiments were supported jointly by the National Science Council of Taiwan and the U.S. Office of Naval Research.

Three popular numerical techniques are employed to examine the acoustic pressure and intensity features present in several environments of interest. Free field propagation and analytically tractable planar interfacial two-fluid transmission and reflection are used to benchmark the commercial software package COMSOL. Canonical Pekeris-type waveguides are used as initial points of comparison to illustrate COMSOL's ability to capture all pertinent physics. Additional environments with non-trivial bathymetry and varying sound speed profiles are then used to examine the rich feature set anticipated in experimental data. Predictions of recently estimated and experimentally verified physical phenomena serve as further proof of the accuracy of implementation of the Finite Element Method. Guidelines and recommendations are provided for future studies using COMSOL along with circumstances under which traditional treatment of the air-water interface is appropriate and when an explicit full-physics model is required. http://archive.org/details/lowfrequencycous1094549353 Civilian, Department of the Navy Approved for public release; distribution is unlimited.

Progress in developing a new measurement method for ultrasound output power is described. It is a thermal-based technique with the acoustic power generated by a transducer being absorbed within a specially developed polyurethane rubber material, whose high absorption coefficient ensures energy deposition within a few mm of the ultrasonic wave entering the material. The rate of change of temperature at the absorber surface is monitored using the pyroelectric voltage generated from electrodes disposed either side of a 60 mm diameter, 0.061 mm thick membrane of the piezoelectric polymer polyvinylidene fluoride (pvdf) bonded to the absorber. The change in the pyroelectric output voltage generated by the sensor when the transducer is switched ON and OFF is proportional to the delivered ultrasound power. The sensitivity of the device is defined as the magnitude of these switch voltages to a unit input stimulus of power (watt). Three important aspects of the performance of the pyroelectric sensor have been studied. Firstly, measurements have revealed that the temperature dependent sensitivity increases over the range from approximately 20°C to 30°C at a rate of +1.6% °C(-1). Studies point to the key role that the properties of both the absorbing backing layer and pvdf membrane play in controlling the sensor response. Secondly, the high sensitivity of the technique has been demonstrated using an NPL Pulsed Checksource, a 3.5 MHz focused transducer delivering a nominal acoustic power level of 4 mW. Finally, proof-of-concept of a new type of acoustic sensor responding to time-averaged intensity has been demonstrated, through fabrication of an absorber-backed hydrophone of nominal active element diameter 0.4 mm. A preliminary study using such a device to resolve the spatial distribution of acoustic intensity within plane-piston and focused 3.5 MHz acoustic fields has been completed. Derived beam profiles are compared to conventional techniques that depend on deriving intensity from acoustic pressure measurements made using the sensor as a calibrated hydrophone.

A methodology for assessing the quality and analysing the sound field of a numerical solution for an aeroacoustic problem is presented using an in-duct propagation problem as example. Namely an analysis of the acoustic energy conservation provides insight about the solution quality; sources of numerical error as well as physical source of sound are located by an analysis of the acoustic intensity; a mode analysis provides information about the sound field in the duct and a visualisation of the average pathway of sound by the acoustic intensity helps the interpretation of the modal amplitude data. The problem chosen for the presentation deals with the propagation of a single acoustic mode upstream through the tapering inlet duct of a centrifugal compressor. The propagation of tone noise is a typical problem for computational aeroacoustics. The numerical approach employs high-order finite-difference discretisation schemes with structured body-fitted meshes. An overset grid approach allows to overcome the geometrical complexity of the problem. The conservation of the acoustic energy is found to be violated by less than 3% in case of a potential base flow. In this case major sources of error are found in the interpolation between overset and background mesh. In case of a non-potential flow with boundary layers at the wall, the conservation of acoustic energy cannot be claimed. Consequently, it shows an increase of the acoustic energy, for which the accelerated flow in the nozzle is identified as source. It is shown that the filtering scheme affect the solution more than the spatial discretisation, if the grid resolution is relatively high. A strong scattering of energy into higher radial modes is detected. The fifth and sixth radial mode are found to be preferred in the current example. They are excited in the nozzle with a similar level. For these high radial modes, the transport of acoustic energy takes place further away from the duct wall. This explains the relatively large drop of about 20 dB for the average sound pressure level at the wall over the inlet nozzle.

The article of record as published may be found at https://doi.org/10.1121/1.3158818 In this paper Creamer's [(1996). J. Acoust. Soc. Am. 99, 2825–2838] transport equation for the mode amplitude coherence matrix resulting from coupled mode propagation through random fields of internal waves is examined in more detail. It is shown that the mode energy equations are approximately independent of the cross mode coherences, and that cross mode coherences and mode energy can evolve over very similar range scales. The decay of cross mode coherence depends on the relative mode phase randomization caused by coupling and adiabatic effects, each of which can be quantified by the theory. This behavior has a dramatic effect on the acoustic field second moments like mean intensity. Comparing estimates of the coherence matrix and mean intensity from Monte Carlo simulation, and the transport equations, good agreement is demonstrated for a 100-Hz deep-water example. This work was supported by the Office of Naval Research and the Naval Undersea Warfare Center’s (NUWC) Under- Sea Warfare (USW) chair at the Naval Postgraduate School.

The article of record as published may be found at https://doi.org/10.1109/JOE.2004.836997 We present analyses of fluctuations seen in acoustic signals transmitted by two 400-Hz sources moored as part of the ASIAEX 2001 South China Sea (SCS) experiment. One source was near the bottom in 350-m deep water 31.3 km offshore from the receiving array, and the other was near the bottom in 135-m deep water 20.6 km alongshore from the array. Time series of signal intensity measured at individual phones of a 16-element vertical line array are analyzed, as well as time series of intensity averaged over the array. Signals were recorded from 2 May to 17 May 2001. Fluctuations were observed at periods ranging from subtidal (days) to the shortest periods resolved with our signaling (10 s). Short-period fluctuations of depth- and time-averaged intensity have scintillation indexes (computed within 3-h long windows) which peak at values near 0.5 during an interval of numerous high-amplitude internal gravity waves, and which are lower during intervals with fewer internal waves. The decorrelation times of the averaged intensity (energy level) are also closely related to internal wave properties. Scintillation indexes computed for unaveraged pulses arriving at individual phones often exceed unity. This work was supported by the U.S. Office of Naval Research.

Acoustic intensity is a vectorial measure of acoustic energy flow through a given region of interest. Three-dimensional measurement of acoustic intensity requires special microphone array configurations. This paper provides a theoretical analysis of open spherical microphone arrays for the 3-D measurement of acoustic intensity. The calculations of the pressure and the particle velocity components of the sound field inside a closed volume are expressed using the Kirchhoff-Helmholtz integral equation. The conditions which simplify the calculation are identified. This calculation is then constrained to a finite set of microphones positioned at prescribed points on an open sphere. Several open spherical array topologies are proposed. Their magnitude and directional errors and measurement bandwidths are investigated via numerical simulations. A comparison with conventional open-sphere 3-D intensity probes is presented.

Date of Conference: 21-23 July 2008 Conference name: 2008 5th IEEE Sensor Array and Multichannel Signal Processing Workshop In this paper, performance of the recently proposed Cross Ambiguity Function - Direction Finding (CAF-DF) technique is compared with the Space Alternating Generalized Expectation Maximization (SAGE) technique. The CAF-DF, iteratively estimates direction of arrival (DOA), time-delay, Doppler shift and amplitude corresponding to each impinging signal onto an antenna array by utilizing the cross ambiguity function. On synthetic signals, based on Monte Carlo trials, performances of the algoritms are tested in terms of root Mean Squared Error (rMSE) at different Signal-to-Noise Ratios (SNR). Cramer-Rao lower bound is included for statistical comparisons. Simulation results indicate the superior performance of the CAF-DF technique over SAGE technique for low and medium SNR values. © 2008 IEEE.

Behavioral and ecological studies would benefit from the ability to automatically identify species from acoustic recordings. The work presented in this article explores the ability of hidden Markov models to distinguish songs from five species of antbirds that share the same territory in a rainforest environment in Mexico. When only clean recordings were used, species recognition was nearly perfect, 99.5%. With noisy recordings, performance was lower but generally exceeding 90%. Besides the quality of the recordings, performance has been found to be heavily influenced by a multitude of factors, such as the size of the training set, the feature extraction method used, and number of states in the Markov model. In general, training with noisier data also improved recognition in test recordings, because of an increased ability to generalize. Considerations for improving performance, including beamforming with sensor arrays and design of preprocessing methods particularly suited for bird songs, are discussed. Combining sensor network technology with effective event detection and species identification algorithms will enable observation of species interactions at a spatial and temporal resolution that is simply impossible with current tools. Analysis of animal behavior through real-time tracking of individuals and recording of large amounts of data with embedded devices in remote locations is thus a realistic goal. © 2008 Acoustical Society of America. 123 2424 2431 Cited By :87

Recent advances in video compression such as the current state-of-the-art H.264/AVC standard in conjunction with increasingly available bitrate through new technologies like 3G, and WiMax have brought mobile health (m-Health) healthcare systems and services closer to reality. Despite this momentum towards m-Health systems and especially e-Emergency systems, wireless channels remain error prone, while the absence of objective quality metrics limits the ability of providing medical video of adequate diagnostic quality at a required bitrate. In this paper we investigate different encoding schemes and loss rates in medical ultrasound video transmission and come to conclusions involving efficiency, the trade-off between bitrate and quality, while we highlight the relationship linking video quality and the error ratio of corrupted P and B frames. More specifically, we investigate IPPP, IBPBP and IBBPBBP coding structures under packet loss rates of 2%, 5%, 8% and 10% and derive that the latter attains higher SNR ratings in all tested cases. A preliminary clinical evaluation shows that for SNR ratings higher than 30 db, video diagnostic quality may be adequate, while above 30.5 db the diagnostic information available in the reconstructed ultrasound video is close to that of the original. © 2008 IEEE. 5326 5329 Conference code: 75336 Cited By :6

We consider the use of orthogonal frequency division multiplexing (OFDM) for covert acoustic telemetry. To reduce the complexity of the receiver we use a multiband approach, modulating each band by OFDM. The system has been tested at sea in a highly time-varying environment. A total bandwidth of 3.6 kHz was divided in 16 subbands. Data rates of 4.2 and 78 bit/s were adopted over ranges up to 52 km. At 78 bit/s, communication is successful at SNRs down to −8 dB, whereas the lower rate allows data transfer at SNRs down to at least −16 dB.

Intensity techniques are now widely used for two purposes: sound power determination and source identification. The work described in this presentation illustrates an application of the latter type. As part of a noise control program for a small domestic appliance, a narrow‐band intensity measurement system was developed based on a face‐to‐face microphone probe, a two‐channel FFT analyzer, and a personal computer. The probe was used to measure the nearfield normal intensity on planes parallel to the device's major surfaces. Graphical display of these data allowed the radiated sound field to be visualized at any desired frequency. Further, it was possible to distinguish between various types of component sources by examining the field in detail. For example, airborne sound that is generated within the device and radiates to the exterior through apertures or “leaks” was plainly visible. Radiation from the exterior surface of the device resulting from direct vibrational excitation of the surface and from structure‐borne vibration could also be identified. Knowledge of this type was used to advantage to guide the noise control treatment program. Nearfield surveys conducted after these modifications yielded a particularly vivid indication of the effects and benefits of the individual modifications.

The aim of the present study is to compare two different acoustic analogies applied to time-resolved particle image velocimetry (PIV) data for the prediction of the acoustic far-field generated by the flow over a rectangular cavity. We consider the model problem of sound radiating from an open, two-dimensional, shallow cavity with an aspect ratio of 2 at a Reynolds number of 3.0 × 104 (based on the cavity length). The study is carried out by simultaneous high-speed two-dimensional PIV and sound measurements. The instantaneous flow field is obtained from the PIV measurements. The emitted sound is then calculated using Curle’s analogy and Vortex Sound Theory. To our knowledge, Vortex Sound Theory is used here for the first time in combination with time-resolved PIV data. The acoustic analogies are derived through rather different pathways, and the mathematical schemes used to solve the equations are sensitive in a different way to factors such as data resolution, noise level, and complexity of the geometry. Both methods indicate that the trailing edge of the cavity is the main sound source. The predictions of the acoustic field obtained by applying the two methods are analyzed and compared with the measured sound. For the presented case, the results show that both analogies estimate the overall sound pressure level quite well and that they give very similar results, both in total intensity and in the spectral distribution of the emitted sound.