The generation and evolution of bubble clusters in ultrasound fields were studied using high-speed photography. The transition of a spherical bubble cluster to a layer-like bubble cluster was demonstrated in detail. At a distance of half a wavelength to the water surface, the rising spherical cluster oscillated strongly and its equilibrium size grew. The speed was about ~0.4m/s and had a tendency to decrease. A jet caused by the last collapse of the spherical cluster rushed to the water surface, creating a bulge on the surface. Subsequently, due to the primary acoustic field, bubbles accumulated again below the bulge, and a layer-like bubble cluster gradually formed. The effects of acoustic frequency and intensity on the layer-like cluster are considered. It is found that the clusters located at a distance-to-wavelength ratio of about 0.08 to 0.13, very close to the water surface. The flickering bubble clusters are easy to be observed at 28kHz and 40kHz, while the accumulation of bubbles and their flicker are relatively weak at 80kHz. The higher the frequency, the shorter the wavelength, the closer the structure to the water surface. However, at 80 kHz, the cavitation threshold is supposed to be higher and the resonance size of the bubbles is smaller, so the bubble oscillations and their interactions are weaker, and the phenomenon is different from the cases of 28 kHz and 40 kHz. Multiple structures mainly exist at 40 kHz. The formation and evolution of the layer-like cluster are closely dependent on the adequate supply of bubble nuclei from the water surface and the surrounding liquid. A Y-shaped bifurcation is used to model the branch streamers, which provided a path of bubbles accumulate into the clusters. The secondary Bjerknes forces between bubbles are adapt to analyze the interactions, and the results proved that it plays an important role in the appearance of the substructures.
The longitudinal-torsional composite transducer with slanting slots was studied. The equivalent circuit for the vibrational system was derived. The effect of the slanting angle of the slots on the resonance frequency of the vibrational system was analyzed. It is concluded that when the slanting angle of the slots was increased, the resonance frequency was decreased. Experimental results show that the measured frequencies are in good agreement with the predicted results.
The coupled vibration of piezoelectric ceramic disks was studied when the piezoelectric effect is considered. Based on the piezoelectric and motion equations, introducing themechanical coupling coefficient the electric admittance and the frequency equation werederived, the relation between the axial and radial vibrations was analyzed. The resonantfrequencies of the vibrators were computed' Compared with the measured frequencies thecomputed results of this paper are better those computed by one dimensional theory.
The cylindrical piezoelectric transducer has the advantages of large radiation area, high electromechanical coupled coefficient, and omni-direction radiation along the radius. In this paper, a piezoelectric transducer consisting of a radially polarized piezoelectric cylinder and an outer metal cylinder of varying height is presented. The metal cylinder of varying height is approximated as the radial superposition of multiple uniform height metal cylinders, and the equivalent impedance of the transducer's coupled vibration is obtained by using the impedance matrix method, and then the resonance frequency, anti-resonance frequency, effective electromechanical coupled coefficient, and displacement amplification coefficient are obtained. In this paper, the relationship between the vibration characteristics of the cylindrical piezoelectric transducer and its geometric dimensions is studied. An experimental sample of the transducer is fabricated and assembled, and its electrical impedance curve is measured. The measured results are in good agreement with the simulation results and the theoretical calculation results. The displacement distribution of the radiation surface of the transducer at resonance frequency is measured, which verifies that the two coupled vibration modes of the transducer can be effectively excited.
Based on the theory of coupled vibration and flexural vibration of a long thin bar with rectangular cross section, we studied the flexural vibration of rectangular plates, derived out the frequency equation when the boundaries of plates are free, studied the relation between resonant frequencies and vibrating modes. Experiments show that the measured results of resonant frequencies agree well with their calculated results, the ultrasonic cleaning tank with the rectangular plate of flexural vibration as ultrasonic radiators has the advantages of uniform acoustic field, large acoustic radiating surface and easy adjustment of exciting frequencies over traditional ultrasonic cleaning tank, the rectangular plate of flexural vibration proves to be a promising high power ultrasonic radiating source.
The majority of existing piezoelectric transducers work at a single resonant frequency, and their applications in scenarios with multi-frequency or frequency variation are not fully considered. Moreover, emitting high-energy ultrasound at different frequencies is also crucial. Here, we propose the three-frequency coupled vibration piezoelectric transducer, which exhibits higher emission performances. The proposed transducer is comprised of two rectangular piezoelectric ceramics, which are cut from a piece of rectangular piezoelectric ceramic. We derive the three-dimensional coupled vibration electromechanical equivalent circuit of the proposed transducer. Then, the characteristics of the transducer are numerically simulated. And comparison experiments between the proposed transducer and a piece of rectangular piezoelectric ceramic transducer were done. An ultrasonic water tank measurement system was used to measure their sound field, axial sound pressure, and transmitting voltage response. Experiments are conducted to verify the electromechanical and sound field characteristics of transducers, which are in good agreement with the simulated results and theoretical predictions. The proposed transducer can generate stable and stronger energy ultrasonic waves at three resonant frequencies. And this study can provide the theoretical and experimental references for multi-frequency conversion and high-energy ultrasonic radiation of the transducer.
Tetracycline (TC) has received a great deal of interest for the harmful effects of substance abuse on ecosystems and humanity. In this paper, the sonochemical yield under the action of single-frequency and dual-frequency ultrasound (DFUS) was measured using the KI dosimetry method, and DFUS showed a significant synergy with a synergy factor of 3.24. The effects of different processes on the degradation of TC were compared, with DFUS in combination with peroxymonosulfate (PMS) being the most effective for the TC degradation. Free radical scavenging experiments showed that SO4•-and •OH were the main reactive radicals in the degradation of TC. According to the major intermediates of TC degradation identified, three possible degradation pathways were proposed, which are of significance for translational studies of TC degradation. Notably, these intermediates were found to be significantly less toxicity. The number of active bubbles in the degradation vessel was calculated using a semi-empirical formula, and a higher value of 1.44 × 108 L-1s-1 of bubbles was obtained when using dual-frequency ultrasound at 20 kHz (6.333 × 105 Pa) and 80 kHz (2.458 × 105 Pa). Therefore, although the yield of strong oxidizing substances from individual active bubbles decreased slightly, a significant increment of the number of active bubbles still resulted in a higher synergistic effect, and the combination of DFUS and PMS should be effective in promoting the generation of reactive free radicals and providing a method for efficient removal of TC from wastewater.
Based on the wave equation of longitudinal vibration of variable cross-section rod,the frequency equation and some important parameter formulas of an power function horn are deduced.Compared with other type of ultrasonic horns,the results show the amplitude factor of power function horn is the same as that of the exponential type and the resonance length is equal to that of stepped type.Meanwhile,it is discovered that this kind of ultrasonic horn has no cut-off frequency. Finally,the modal analysis is obtained and the resonance frequency is determined by using finite element software Ansys.It is shown that the simulation result is consistent with that of the theory.
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