Thermal cavitation mechanism for generation of underwater sound

The implosion of a vapour bubble generated by spark discharges in seawater can generate high power pulses in the frequency band up to a few hundred kHz, useful to obtain high-resolution imaging of the sea subboftom. In this paper, a physical model is illustrated to explain the origin of the process generating the bubble in a conducting liquid, together with a brief review of the hypofhized ideas on the growth and implosion mechanism of the bubble. A description is given of the implementation of a numerical scheme for the solution of a set of equations describing the temperature and electric field distributions in the liquid in the prebreakdown stage. According to this model, electrical breakdown and subsequent thermal cavitation in seawater is governed by Joule heating with a temperature dependent electrical conductivity. Measurements of the discharge of the paraboloidal sparker-based source confirm the validity of the energy model, showing a good agreement of the predicted time required for liquid vaporization with the observed breakdown time

Evaluation of a time reversal technique for low frequency acoustic measurements in a reverberant tank

The objective of this work is to validate the efficiency of a recently proposed technique for acoustic measurements of transducer response. This technique allows measurements to be done in a reverberant tank at considerably lower frequencies than the limit imposed by free-field conditions. The method is based on time reversal, a concept originally developed for sound propagation in marine environment, that performs signal deconvolution. with a very little amount of data processing. It was seen that the method can be used to focus at a fixed point a transmit pulse several ms long, allowing calibrations down to the low kHz range in a 3-4 m tank. Early investigations already showed that the focusing of the acoustic field depends on the frequency. In this work, further measurements were done at the new tank facility of the Underwater Acoustics Laboratory at the Istituto di Acustica "O. M. Corbino" to evaluate the accuracy of the results

Underwater acoustic transducer calibration in the frame of European mast project MAS2 - CT94 - 0095

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Microbial biofilm modulation by ultrasound: current concepts and controversies

Biofilm elimination is often necessary during antimicrobial therapy or industrial medical manufacturing decontamination. In this context, ultrasound treatment has been frequently described in the literature for its antibiofilm effectiveness, but at the same time, various authors have described ultrasound as a formidable enhancer of bacterial viability. This discrepancy has found no solution in the current literature for around nine years; some works have shown that every time bacteria are exposed to an ultrasonic field, both destruction and stimulation phenomena co-exist. This co-existence proves to have different final effects based on various factors such as: ultrasound frequency and intensity, the bacterial species involved, the material used for ultrasound diffusion, the presence of cavitation effects and the forms of bacterial planktonic or biofilm. The aim of this work is to analyze current concepts regarding ultrasound effect on prokaryotic cells, and in particular ultrasound activity on bacterial biofilm

The Ultrasound effects on non tumoral cell line at 1 MHz therapeutic frequency

The aim of this research is to investigate some bioeffects due to Therapeutic Ultrasound (1 MHz and 50<I PA<60 W/cm 2) which could allow to enhance drugs or genes delivery in non tumoral cells. Ultrasound (US) has been demonstrated to alter the cell membrane permeability due to a biophysical mechanism, Sonoporation, and exploited as a promising non-invasive gene transfer method. We have used the NIH-3T3 cell line as a model system and exposed it to US medical equipment for 15, 30, 45, 60 minutes at distances of 10 and 15 cm from the source transducer, corresponding to the far field region where z>z last=a 2/4gammma;=4.0±0.4 cm. We have worked with the maximum power in pulsed system with 75% duty cycle. Characterization of the unfocused, planar and with a circular geometry 1 MHz source transducer, was performed and the acoustics pressure was measured by a calibrated 0.5 mm needle hydrophone; moreover, the pressure field generated by the source transducer was simulated. The US effects on cells were assessed by Fourier transform infrared (FTIR) Imaging with focal plane array (FPA) detector. By the IR analysis, the US exposure on non tumoral cells has induced a change of the intensity for CH 2 asymmetric stretching (2924 cm -1) band in the lipid region (3000-2800 cm -1) that it could detect an energy-dependent process. It has already shown that cells invest energy to catalyze lipid movement in order to maintain a specific transmembrane phospholipid distribution. Although asymmetry is the rule for control cells, the loss of asymmetry could be associated with the permeability change of plasma membrane inducing temporary pores. © Published under licence by IOP Publishing Ltd