Cavitation Noise Spectra Research Articles

Наблюдение кавитационного шума без субгармоники

The evolution of the cavitation noise (CN) spectra in the field of a focusing emitter with an increase in the intensity of ultrasound (US) was studied. Spectra without subharmonics f0/2 were recorded for the first time, where f0 is the frequency of the ultrasound generating cavitation,. Such a spectrum is observed in partially degassed water at a high duty cycle of ultrasonic pulses. The threshold for the appearance of sonoluminescence (SL) coincides with the threshold for the appearance of the frequency f0/2 in the CR spectrum. In a pulsed field at an ultrasonic intensity much higher than the cavitation threshold, the SL intensity increases with an increase in the duty cycle of the pulses, while the intensity of the f0/2 line in the CS spectrum decreases.

Study of cavitation noise without subharmonics

The evolution of the cavitation noise (CN) spectra in the field of a focusing emitter with an increase in the intensity of ultrasound (US) was studied. Spectra without subharmonics f0/2 were recorded for the first time, where f0 is the frequency of the ultrasound generating cavitation,. Such a spectrum is observed in partially degassed water at a high duty cycle of ultrasonic pulses. The threshold for the appearance of sonoluminescence (SL) coincides with the threshold for the appearance of the frequency f0/2 in the CR spectrum. In a pulsed field at an ultrasonic intensity much higher than the cavitation threshold, the SL intensity increases with an increase in the duty cycle of the pulses, while the intensity of the f0/2 line in the CS spectrum decreases. Keywords: sonoluminescence, subharmonics.

Sonoluminescence emission spectra of a 3.6 MHz HIFU in sweeping mode

Use of sweeping mode with a 3.6 MHz High Intensity Focused Ultrasound (HIFU) allows cavitation activity to be controlled. This is especially true in the pre-focal zone where the high concentration of bubbles acts as an acoustic reflector and quenches cavitation above this area. Previous studies attributed the enhancement of cavitation activity under negative sweep to the activation of more bubble nuclei, requiring deeper investigations. After mapping this activity with SCL measurements, cavitation noise spectra were recorded. The behavior of the acoustic broadband noise follows the sonochemical one i.e., showing the same attenuation (positive scan) or intensification (negative scan) of cavitational activity. In 1 M NaCl 3.7 mM 2-propanol solution saturated by a mixture of Ar-15.5%O2-2.2%N2, intensities of SL spectra are high enough to allow detection of several molecular emissions (OH, NH, C2, Na) under negative frequency sweeps. This is the first report of molecular emissions at such high frequency. Their intensities are low, and they are very broad, following the trend obtained at fixed frequency up to 1 MHz. Under optimized conditions, CN emission chosen as a spectroscopic probe is strong enough to be simulated, which is reported for the first time at such high frequency. The resulting characteristics of the plasma do not show any spectral difference, so bubble nature is the same in the pre-and post-focal zone under different sweeping parameters. Consequently, SL and SCL intensification was not related to a change in plasma nature inside the bubbles but to the number of cavitation bubbles.

Flow-mode water treatment under simultaneous hydrodynamic cavitation and plasma

Over the last two decades, the scientific community and industry have made huge efforts to develop environmental protection technologies. In particular, the scarcity of drinking water has prompted the investigation of several physico-chemical treatments, and synergistic effects have been observed in hyphenated techniques. Herein, we report the first example of water treatment under simultaneous hydrodynamic cavitation and plasma discharge with the intense generation of radicals, UV light, shock waves and charged particles. This highly reactive environment is well suited to the bulk treatment of polluted water (i.e. E. coli disinfection and organic pollutant degradation). We have developed a new prototype and have efficiently applied this hybrid technology to water disinfection and the complete degradation of methanol in water with the aim of demonstrating its scalability. We have analyzed the mechanisms of water disinfection under the abovementioned conditions and verified them by measuring cavitation noise spectra and plasma emission spectra. We have also used the degradation of textile dyes and methanol solutions as an indicator for the formation of radicals.

Characterising the cavitation activity generated by an ultrasonic horn at varying tip-vibration amplitudes

Dual-perspective high-speed imaging and acoustic detection is used to characterise cavitation activity at the tip of a commercial 20 kHz (f0) ultrasonic horn, over 2 s sonications across the range of input powers available (20 – 100%). Imaging at 1 × 105 frames per second (fps) captures cavitation-bubble cluster oscillation at the horn-tip for the duration of the sonication. Shadowgraphic imaging at 2 Mfps, from an orthogonal perspective, probes cluster collapse and shock wave generation at higher temporal resolution, facilitating direct correlation of features within the acoustic emission data generated by the bubble activity. f0/m subharmonic collapses of the primary cavitation cluster directly beneath the tip, with m increasing through integer values at increasing input powers, are studied. Shock waves generated by periodic primary cluster collapses dominate the non-linear emissions of the cavitation noise spectra. Transitional input powers for which the value of m is indistinct, are identified. Overall shock wave content within the emission signals collected during sonications at transitional input powers are reduced, relative to input powers with distinct m. The findings are relevant for the optimisation of applications such as sonochemistry, known to be mediated by bubble collapse phenomena.

Combined method for acoustic cavitation research

At present, the field of applications of powerful ultrasound is expanding intensively, and the improvement of equipment and technological processes continues. With that, the key factor in the effect of ultrasonic vibrations on processes in liquids and liquid-like media is cavitation, i.e. the phenomenon of formation, pulsation and collapse of gas microbubbles under the influence of variable pressure. The widespread introduction of promising ultrasound technologies is largely constrained by the fact that the patterns of cavitation generation are not well understood, and the data known in the literature are contradictory and are characterized by low reproducibility. This paper describes an innovative method for studying ultrasonic cavitation. In order to increase the reproducibility of the results and the reliability of the conclusions about the correlation of various cavitation effects, it is proposed to register simultaneously the parameters characterizing these effects. An installation designed to implement this method has been developed and tested. The installation provides the ability to register the full output signal of the hydrophone, the intensity of the glow generated in the cavitation region - sound luminescence, the cavitation noise spectrum and its individual components. Technical characteristics of the installation allow you to adjust the rate of development of the cavitation region by varying the duration and period of the ultrasound pulses. It is possible to conduct experiments both in low-frequency (LF) and high-frequency (HF) fields as well as in interacting HF and LF ultrasonic fields. During the testing of the installation, the results were obtained that are of considerable interest from the point of view of refining the ideas about the mechanism for generating cavitation effects. It was found that preliminary treatment of the liquid in an ultrasonic field with the aim of its degassing for 15–20 min provides a significant increase in the reproducibility of measurements, especially for liquids with a high gas content. Based on a comparison of the time dependences of the signals of the cavitation sensor and the photomultiplier output, the characteristic stages of the development of the cavitation region are distinguished, which differ in the dynamics of the development of the cavitation region and in the composition of the cavitation noise spectra recorded.

Monitoring of Cavitation Parameters in Ultrasound Surgery

The results of numerical modeling and experimental studies of cavitation bubble pulsations are presented. A new method for providing feedback in ultrasonic devices is proposed. The method is based on subharmonic analysis of cavitation noise spectra and spectra of optical radiation scattered by the cavitation region in the process of laser beam probing.

Model scale cavitation noise spectra prediction: Combining physical knowledge with data science

Ships underwater radiated noise is a subject of great and increasing interest in naval architecture because of its impacts on the environment and on the on-board comfort. Among the different noise sources, the propeller is usually the dominant one, especially when it cavitates. For this reason a lot of efforts have been spent in studying the cavitation noise spectra in order to be able to predict its main characteristics at design stage. Nowadays, in order to reach this goal, the state-of-the-art solution is to perform model scale experiments. Unfortunately, this requires time-consuming tests in a cavitation tunnel with a model of the propeller and results are affected by scale effects that must be correctly interpreted. For these reasons, in this paper authors propose a hybrid approach which may be adopted to predict the main characteristics of the cavitation noise spectra without requiring an actual experiment. Moreover, the same approach may be used also in order to overcome typical model scale problems. For this purpose a hybrid modelling approach able to exploit both the physical knowledge of the problem and the real data obtained from many cavitation tunnel experiments performed on different propellers in different working conditions have been developed. Results on real data in both interpolation and extrapolation tasks will support the validity and the effectiveness of the proposal.

Examination of aqueous solution with a concentration of PAA WF1 high-molecular weight polyacrylamide polymer using a cavitation noise spectrum

This paper presents spectral characteristics obtained for various intensities of ultrasounds for water and aqueous solution with a concentration of PAA WF1 (CH2CHCONH2CH2)n n = 30,000 − 50,000 (molecular weight 4.4 · 106 g/mol) with the concentrations of 0.25% and 0.1%. The experiment aimed at examining the dependence of the intensity of cavitation and the area of the biggest changes in the characteristics of cavitation noise spectrum on the intensity of ultrasounds was carried out as the first. Then, there were performed tests that consisted in sonication of the solution at a constant intensity of ultrasounds. The aim was to investigate the changes occurring in the cavitation clouds as well as the changes in the characteristics of the cavitation noise spectrum along with a change in the properties of the solution subjected to continuous action of ultrasonic waves. Finally, there were presented the spectral characteristics at different intensities of ultrasounds in order to determine the impact of the continuous sonication on the test solution.

Sonoluminescence and acoustic emission spectra at different stages of cavitation zone development

The way in which a cavitation zone develops in a focused pulsed ultrasound field is studied in this work. Sonoluminescence (SL), total hydrophone output and cavitation noise spectra have been recorded across a gradual, smooth increase in applied voltage. It is shown that the cavitation zone passes through a number of stages of evolution, according to increasing ultrasound intensity, decreasing pulse period and increasing ultrasound pulse duration. Sonoluminescence is absent in the first phase and the hydrophone output spectra consists of a main line with two or three harmonics whose intensity is much lower than that of the main (fundamental) line. The second stage sees the onset of SL whose intensity increases smoothly and is accompanied by the appearance of higher harmonics and subharmonics in the cavitation noise spectra. In some cases, the wide-band (WBN) component can be seen in noise spectra during the final part of the second stage. In the third stage, SL intensity increases significantly and often quite sharply, while WBN intensity increases in the same manner. This is accompanied by a synchronous increase in the absorption of ultrasound by the cavitation zone, which is manifested in a sharp decrease in the hydrophone output. In the fourth stage, both SL and WBN intensities tend to decrease despite the increased voltage applied to the transducer. Furthermore, the fundamental line tends to decrease in strength as well, despite the increasing ultrasound intensity. The obtained results clearly identify the different stages of cavitation zone development using cavitation noise spectra analyses. We then hypothesize that three of the above stages may be responsible for three known types of ultrasound action on biological cells: damping viability, reversible cell damage (sonoporation) and irreversible damage/cytotoxicity.

Cavitation noise from elastic response of metals in ultrasonic cavitation erosion

Noise from the cavitation around propellers is the main noise source of marine vehicles. In our experiment, we found that the material of the propeller also affected the cavitation noise, especially on their frequencies. Three most commonly used metal propeller materials, including brass (B), aluminum bronze (AlB), and stainless steel (SS), were placed in an ultrasonic cavitation system. They presented different spectral peaks in the measured cavitation noise spectrum, and the one with higher elastic modulus has a higher noise frequency. According to the numerical validation, this phenomenon is attributed to the elastic response of different metals under the impaction of the collapsing bubbles, and the elastic modulus of the metals is the dominant mechanical factor that affects the frequency.

The evolution of a cavitation zone in a focused ultrasonic field

We have experimentally studied the generation of sonoluminescence (SL) and cavitation noise in the field of a focusing ultrasonic radiator during a gradual smooth increase in the applied voltage. In addition to the SL signal, we have recorded the output signal of a hydrophone situated behind the focal region of the radiator and measured the cavitation-noise spectrum. Four stages in the development of a cavitation zone have been distinguished as manifested by the specific character of dependences of the measured parameters on the voltage applied to the radiator. Spectral signs of the cavitation-noise characteristic of each stage of development of the cavitation zone.

Influence of surface tension on cavitation noise spectra and particle removal efficiency in high frequency ultrasound fields

Physical cleaning methods are applied in the semiconductor industry and have become increasingly challenging due to the continued scaling of semiconductors device elements. Cavitation and acoustic phenomena are known to play a fundamental role in megasonic cleaning. Hence, a better understanding of cavitation phenomena in multi-bubble systems is crucial. Here, a study on the effects of lower bulk surface tension and different O2 concentrations on the bubble activity in the megahertz range is presented. A lower bulk surface tension (45 mN/m) with respect to ultra pure water (72 mN/m) is obtained by adding a non-ionic surface-active agent (Triton X-100). After a thorough surfactant characterization, a Triton X-100-containing cleaning solution is investigated under pulsed and continuous acoustic fields, for different acoustic amplitudes and gas concentrations. It is demonstrated that cavitation activity, measured by means of ultraharmonic cavitation noise, is enhanced in presence of a lower surface tension, under continuous acoustic fields. In addition, cavitation measurements performed under pulsed fields reveal the existence of optimal pulse-off times, for which a maximum of activity is observed. These optimal pulse-off time values are linked to the bubble dissolution theoretical times and experimentally verified. To end, cavitation noise measurements are correlated to cleaning performance in megasonic fields by means of particle removal and damage tests on patterned wafers. A clear increase in particle removal efficiency of 78 nm SiO2 particles is obtained when Triton X-100 is employed, at the optimized process conditions. In addition, the number of defects due to cavitation bubbles is significantly reduced for lower surface tension, at particle removal efficiencies <60%. The results here reported constitute a different approach towards more efficient megasonic cleaning processes.

Towards an understanding and control of cavitation activity in 1 MHz ultrasound fields

Various industrial processes such as sonochemical processing and ultrasonic cleaning strongly rely on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in a vessel is strongly depending on the ultrasonic process conditions. It is therefore crucial to quantify cavitation activity as a function of the process parameters. At 1MHz, the active cavitation bubbles are so small that it is becoming difficult to observe them in a direct way. Hence, another metrology based on secondary effects of acoustic cavitation is more suitable to study cavitation activity. In this paper we present a detailed analysis of acoustic cavitation phenomena at 1MHz ultrasound by means of time-resolved measurements of sonoluminescence, cavitation noise, and synchronized high-speed stroboscopic Schlieren imaging. It is shown that a correlation exists between sonoluminescence, and the ultraharmonic and broadband signals extracted from the cavitation noise spectra. The signals can be utilized to characterize different regimes of cavitation activity at different acoustic power densities. When cavitation activity sets on, the aforementioned signals correlate to fluctuations in the Schlieren contrast as well as the number of nucleated bubbles extracted from the Schlieren Images. This additionally proves that signals extracted from cavitation noise spectra truly represent a measure for cavitation activity. The cyclic behavior of cavitation activity is investigated and related to the evolution of the bubble populations in the ultrasonic tank. It is shown that cavitation activity is strongly linked to the occurrence of fast-moving bubbles. The origin of this “bubble streamers” is investigated and their role in the initialization and propagation of cavitation activity throughout the sonicated liquid is discussed. Finally, it is shown that bubble activity can be stabilized and enhanced by the use of pulsed ultrasound by conserving and recycling active bubbles between subsequent pulsing cycles.

The characteristic of cavitation noise and the intensity measurement of hydrodynamic cavitation

In the present work,the cavitation bubble cloud and cavitation noise in the contraction-divergence channel have been investigated.With increasing the liquid speed,the bubbles state changes from discrete cavitation cloud to continuous cavitation cloud and the cavitation noise spectrum with broad peak changed to continuous spectrum.The central frequency and value of the peak in the noise spectrum changed with the liquid speed increasing.The integral of the cavitation noise spectrum in [0-50 kHz] shows that the integral valve increased sharply with the liquid speed increasing,and it can indicate the cavitation intensity.There are two kinds of cavitation situation,just like the acoustic cavitation which includes transient cavitation and stable cavitation.

ICONE19-43535 COMPARISON OF THE WATER AND SODIUM CAVITATION PHENOMENA IN VENTURI

The present paper described the comparison of onset cavitation coefficient and noise spectrum between water and sodium. The water experiment was conducted at 56°, 74° and 90℃. These temperatures corresponded to the same kinematic viscosity of sodium cavitation at 200°, 300° and 400℃. The test section used was a venturi with ID and OD of 6.5 mm and 21 mm, respectively. The results show that the onset of cavitation in water was influenced by dissolved oxygen (DO) concentration and temperature change. The increase of noise intensity in sodium was steeper as compared to water with higher DO, but it was relatively steep for lower DO. The onset cavitation coefficient of water was higher than in sodium, which could be caused by the relatively higher DO concentration due to higher solubility of air in water than argon in sodium. The dissolved air in water could increase the onset cavitation condition (coefficient) because gaseous cavitation was more dominance than vaporous cavitation. In both water and sodium, the increase of the noise spectrum in case of cavitation occurrences was higher for higher frequency region than at lower one which might be caused by the rapid formation and collapse of cavitation bubbles. From the numerical calculation, the results showed that temperature effect had large influence on the growth of the bubble.

INVESTIGATION ON CAVITATION BEHAVIOR AND NOISE IN HYDRAULIC VALUES

Cavitations inside hydraulic valves were investigated by using high-speed camera technology and noise spectrum analyzing method. The bubble flow’s morphological and flowing characteristics were converted into numerical information by the employment of image process, which made the two-phase flow easily identifiable. Based on this, cavitation’s distribution and shape characteristics were revealed. Combined with cavitation noise spectrum analyzing, it was found that the shedding process of cavitation had similar high frequency properties with cavitation noise spectrums. Typical noise curves of cavitations were obtained, and the second peak levels were found in low cavitation number conditions. In addition, it assumed that, the shedding frequencies played a good reflection to cavitation noise while using cavitation numbers as the only variable.

Experimental research into the cavitation noise spectrum in water solutions of high molecular weight polymers

The paper presents cavitation noise spectrum measurements results for water and a water solution of polyacryloamide with the 1.5×107gmol−1 particle mass. Cavitation noise spectrum characteristics were shown for different ultrasound intensity, with different sonification times (at a constant ultrasound intensity) as well as characteristics which enable comparing particular sonification parameters.

Study of low-frequency ultrasonic cavitation fields based on spectral analysis technique

A kind of new spectral analysis method for analyzing ultrasonic cavitation fields is brought forward in this paper. This method extracts the line spectrum and the continuous spectrum from the cavitation noise spectrum respectively, then obtains estimations of the energy intensities of different cavitation components such as the stable cavitation and the transient cavitation through corresponding calculations. The method is also applied to investigate low-frequency ultrasonic cavitation fields and is compared with spectral level analysis method. The results show that this method can provide adequate information on the course of the cavitation process, give the delicate analysis on the transient cavitation and the stable cavitation, and help to gain an insight into the nonlinear process of cavitation fields. Moreover, it also shows that the criterion for characterization of cavitation intensity presented by Frohly through studying the high-frequency ultrasonic fields can be used to evaluate the low-frequency ultrasonic fields.

Correlation between Acoustic Cavitation Noise, Bubble Population, and Sonochemistry

Quantitative studies of the correlation between sonochemical activity and acoustical noise spectra have been performed. The width of the second harmonic (fwhm2) of the acoustical signal in the frequency domain shows a sensitive dependence to the presence of small amounts (mM range) of an anionic surfactant in water. This sensitive dependence is also observed for other characteristics of the cavitation noise spectrum and in the sonochemical production of peroxides and correlates well with the sonoluminescence intensity observed by other researchers. Analysis of the experimental data shows that SDS probably modifies the coalescence phenomena.