Low-frequency Ultrasonic Waves Research Articles

Low-frequency ultrasound assisted contact-electro-catalysis for efficient inactivation of Microcystis aeruginosa

Frequent cyanobacterial blooms pose a serious threat to the aquatic ecosystem and human health, so developing an efficient algae removal method is a long-term goal for bloom management. Current technologies for algal bloom control need urgent improvement in terms of algicide recovery, eco-friendliness and cost. Here we propose a contact-electro-catalytic method, using polytetrafluoroethylene (PTFE) film as a reusable catalyst. This contact-electro-catalytic approach involves the generation of reactive oxygen species (e.g., O2•–, HO•, 1O2 and H2O2) through water-PTFE contact electrification under the low-frequency ultrasonic waves, facilitating the inactivation of algae. The removal rate of the cyanobacterium Microcystis aeruginosa (M. aeruginosa) exposured to the water-PTFE contact-electro-catalytic system is almost five times greater than that of ultrasound alone after 5 h. A mechanistic investigation revealed that the contact-electro-catalytic system damaged the photosynthetic activity, antioxidant system and membrane integrity of the cells. Additionally, LC-MS metabolomic analysis indicated that this system caused substantial significant disruptions in the TCA cycle, amino acid metabolism, purine metabolism and phospholipid metabolism. Three-dimensional fluorescence spectroscopy suggested contact-electro-catalysis could further availably degrade the organic matter. We anticipate that this method can provide an eco-friendly, highly efficient and economic approach for effective control of harmful algal blooms.

Application of low frequency ultrasonic waves for Calcon azo dye removal from wastewater: influence of operational parameters and mineral ions, kinetic study and analysis of by-products

Application of low frequency ultrasonic waves for Calcon azo dye removal from wastewater: influence of operational parameters and mineral ions, kinetic study and analysis of by-products

Lamination of Capacitive Micromachined Ultrasonic Transducer on a Piezoelectric Array: Process and Evaluation

Harmonic imaging plays a crucial role in medical ultrasound imaging, where the transducer probes are required to emit low-frequency ultrasonic waves into the tissues, and receive reflected signals at the higher, typically the second harmonic of the transmitted wave. We have designed a unique probe with a high-frequency capacitive micromachined ultrasonic transducer (CMUT) on top of a low-frequency piezoelectric array for harmonic imaging. This paper presents a lamination process between CMUT and piezoelectric array using epoxy. The bond-line between the two components was thoroughly investigated using mechanical and electrical methods. The resulting bond-line thickness was less than 2 μm, and shear strength fell within the range 4.8 – 5.1 MPa. Additionally, electrical impedance measurement of all elements in the low-frequency array exhibited resonance shifts before and after bonding, providing further insight into the bonding process.

Experimental analysis of heat transfer characteristics using ultrasonic acoustic waves

In this experimental work, heat transfer intensification using ultrasonic waves was investigated. A heat source, consisting in a parallelepiped aluminum block in which two electrical heating cartridges of 160 W each were mounted to heat four liters of distilled water contained in a tank made of Plexiglas. To demonstrate the effectiveness of heat transfer enhancement with the use of ultrasounds, three different configurations were analyzed. In the first one, considered as a reference case, the heat transfer was studied without ultrasound field. In the second configuration, ultrasonic acoustic waves were generated using one transducer vibrating at a fixed frequency of 40 kHz with a total power of 60 W. In the last configuration, ultrasounds were generated with two similar transducers mounted on two opposite walls of the water tank while maintaining the same power and frequency. The effect of the distance separating the heat source to the trans-ducers on the convective heat transfer coefficients and the average temperature of the water in the tank were analyzed in detail. The results revealed that the natural convection heat transfer in the water tank was intensified by means of low frequency acoustic waves. Indeed, it was shown, particularly, that more the distance between the transducer and the heater is low more the heat transfer improvement is better. The heat transfer enhancement factor was estimated to 2.5 on the surface facing the transducer while it was only about 1.2 on the opposite surface in C2 configura-tion. In C3 configuration, the heat transfer enhancement factor is nearly the same with, however, more homogenous water temperature. The acoustic cavitation and streaming were identified as the main phenomena leading to these results. This study successfully demonstrated the feasibility of heat transfer intensification using low frequency ultrasonic waves.

Modeling and Optimization Study on Decolorization of Reactive Blue 256 Exposed to Low Frequency Ultrasonic Waves: RSM and ANN Approaches

Modeling and Optimization Study on Decolorization of Reactive Blue 256 Exposed to Low Frequency Ultrasonic Waves: RSM and ANN Approaches

An experimental study on low-content crude oil in water emulsion using low-frequency ultrasonic waves

An experimental study on low-content crude oil in water emulsion using low-frequency ultrasonic waves

Surface defect-engineered CeO2−x by ultrasound treatment for superior photocatalytic H2 production and water treatment

We designed a CeO2−x photocatalyst under the influence of low-frequency ultrasonic waves to generate surface oxygen vacancies for efficient photocatalytic performance.

Effect of low-frequency ultrasonic waves on heat transfer of laminar water flow over a heating flat plate

This research investigates the effect of 40, 80, and 120 kHz ultrasound on heat transfer of laminar water flow over a heating flat plate using thin leaf thermocouples in a low turbulence water tunnel. The mainstream velocity was set at 0.127 m/s, corresponding to the local Reynolds number during 65,181 – 148,390 in the test section. The ultrasonic waves were released perpendicular to the mainstream and vertically from the upper wall at the distance of 0.15 m to the heating plate having constant heat flux of 1,040 W/m2. The results show that the ultrasound, having frequencies of 40 and 120 kHz provides the maximum Nusselt number up to 15% and 31%, respectively at the most downstream position of the test region. In the meantime, the 80 kHz waves slightly affect the heat transfer over a flat plate. Hence, in an attempt to employ the ultrasound for heat transfer enhancement over a flat plate, the distance and ultrasonic frequency must be well considered.

Characterization of heat transfer and friction loss of water turbulent flow in a narrow rectangular duct under 25–40 kHz ultrasonic waves

This study experimentally investigated the effect of low-frequency ultrasonic waves on the heat transfer augmentation of turbulent water flow in a narrow rectangular duct with a width of 5 mm. 25-, 33-, and 40-kHz ultrasonic transducers were set to release waves in a downward direction to disturb the flow, with Reynolds numbers (Re) of 10,000–25,000 at increments of 2500. The results indicated that the ultrasonic waves increased the friction loss by only 0.2–2% over the entire testing Re range, while an 8.1–48.6% enhancement of the heat transfer capability was obtained for the Re range of 10,000–15,000. The maximum Nusselt number occurred at a Re of 12,500 and frequency of 33 kHz. However, beyond Re values of 12,500, the thermal performance tended to decrease with an increase in Re. Consequently, the average Nusselt number ratios at ultrasonic frequencies of 25, 33, and 40 kHz over the tested Re range were 1.123, 1.039, and 1.033, respectively, while the thermal performance values were 1.108, 0.989, and 1.036, respectively. These results confirmed that ultrasound has significant potential for application in heat transfer augmentation of turbulent pipe flow. This paper also provides formulas to predict the friction factor and Nusselt number and discusses the mechanisms of heat transfer enhancement by ultrasonic waves at 25, 33, and 40 kHz.

Research on the characteristics of Klein–Cook parameter and diffraction efficiency of acousto-optic interaction for low-frequency ultrasonic in the liquid

We have investigated the characteristics of acousto-optic interaction for low-frequency ultrasonic wave in a liquid. Based on the coupling wave equation of acousto-optic interaction, the diffraction light characteristics for normal incidence at small parameter Q have been discussed. The parameter Q with respect to acousto-optic interaction length, ultrasonic frequency, water temperature, and the concentration of sucrose solution have been analyzed, which is an important physical quantity and reflects the degree of mismatch in the acousto-optic interaction. The diffraction efficiencies for different parameters Q, incident angles and phase shifts have been calculated. The results of our work provide theoretical basis for further study of the acousto-optic effect in the liquid.

Detection of Surface Breaking Cracks Filled With Solid Impurities Using a Baseline-Free NEWS-TR Method

The use of piezoceramic transducers for cracks identification via guided wave has attracted significant attention recently. Most studies assume that the medium in surface breaking cracks is only air. However, it is common that such cracks are filled with impurities (e.g. dust, grease) due to its exposure to the operational environment. The impurities may affect the propagation of the ultrasonic guided wave and hence it is of practical interest to develop detection methods for surface breaking cracks filled with impurities. This work investigates the possible effect of contact acoustic nonlinearity (CAN) on detecting surface breaking cracks filled with solid impurities. A baseline-free method is proposed to detect surface breaking cracks filled with solid impurities using the nonlinear elastic wave spectroscopy (NEWS) as a pre-treatment of time-reversal (TR). This method involves three key issues: selecting low-frequency swept signal modulated by Hanning window as an excitation signal, comparing the initial filtered response with the nonlinear time reversal response to determine the nonlinear feature related to such cracks, and determining the recommended low cut-off frequency to extract such nonlinear feature. The feasibility of the proposed method is experimentally and numerically verified using aluminum beams with surface breaking cracks. Results show that due to the existence of solid impurities, the crack interacts with low-frequency ultrasonic waves, which leads to nonlinear components in the response signal. It also indicates that after the time-reversal processing, the shifting of the maximum peak frequency from the second harmonic range to the third harmonic range can be used as a damage-sensitive nonlinear feature for detecting such cracks. The proposed method provides a promising way to identify surface breaking cracks filled with solid impurities without reference signal.

Heat transfer intensification by low or high frequency ultrasound: Thermal and hydrodynamic phenomenological analysis

The aim of this work is to quantitatively demonstrate the intensification of heat transfer in forced convection by mean of ultrasonic irradiation at low (25 kHz) or high (2 MHz) frequency. High frequency ultrasound induces convective acoustic streaming while low frequency ultrasonic waves produce mainly cavitation effects. These hydrodynamic phenomena are at the origin of strongly different observations in terms of flow pattern modification and thereby in Nusselt number values. A link is tentatively established between hydrodynamic behaviors at both ultrasonic frequencies and corresponding thermal results. Hydrodynamic approach was performed with a 2D-2C PIV device while thermal one was carried out under uniform heat flux conditions. It seems that thermal enhancement effect of acoustic streaming (2 MHz) decreases as flow rate increases. This behavior is consistent with the decrease of turbulent kinetic energy produced by acoustic streaming in the same conditions. In the contrary, thermal enhancement effect produced by acoustic cavitation (25 kHz), increases as flow rate increases. This result could be due to the increase of relative size of acoustic bubbles with respect to laminar boundary layer thickness as flow rate increases. In conclusion, the two different ultrasound frequencies, which lead to two different hydrodynamic effects, also lead to two different thermal and turbulence trend with respect to flow rate modifications.

Excitation and propagation of torsional T(0,1) mode for guided wave testing of pipeline integrity

Guided wave testing is one of non-destructive testing techniques for pipeline inspection using low-frequency ultrasonic waves. Guided wave testing uses a set of equally placed piezoelectric transducers around a pipe, and the number of transducers in the array is a key factor for suppressing higher order flexural modes. This paper presents an effective approach for the excitation and propagation of torsional T(0,1) wave mode for detecting defects in a steel pipe by using finite element numerical simulations and experimental studies. From the numerical and experimental results, the optimised design for transducer arrangement is investigated. The relationship between defect type, dimension and transducer arrangement is also investigated. To validate the finite element modelling, the numerical results are then compared to the experimental data. Finally, the sensitivity of reflected signal from defects to two types of transducer array design is evaluated, and circumferential displacement along the pipe is investigated by using polar plots at different axial positions.

Experimental and theoretical study of crude oil pretreatment using low-frequency ultrasonic waves

In this work, an ultrasound experimental setup was designed to investigate the feasibility of using low-frequency ultrasonic waves as a substitute to reduce the consumption of chemical demulsifiers in the pretreatment of crude oil. The experiments were planned to study the effects of irradiation time, ultrasonic field intensity and initial water content on the efficiency of separation. The results of experiments showed that by selecting a proper irradiation time and field intensity, it is possible to decrease the usage of demulsifiers by 50%. Moreover, a population balance model was proposed to explicate the experimental data. A hybrid coalescence model was developed to determine the frequency of aggregation. The parameters of the model were estimated by linear regression. The parameter estimation was performed using a parallel execution of the particle swarm optimization algorithm. The results of the model showed a decent agreement with the experimental data.

On the thermal characteristic of a heating flat surface under low frequency ultrasonic waves

This study investigates the heat transfer capability between the near-wall water and a heating flat surface under the low frequency ultrasonic waves. The experiment was conducted at the main stream velocities of 0.12, 0.14, and 0.17 m/s, corresponding with the local Reynolds number between 60,000 and 200,000. The ultrasound, having a frequency of 25, 33, and 40 kHz was released from a 60 W flat transducer in a downward direction to disturb a near-wall flow over the flat surface having a constant heat flux of 1875 W/m2. The temperature decrease due to the disturbance of ultrasound, detected by 7 thin-leaf thermocouples, led to the increase in the Nusselt number by up to 10%, 16.5%, and 20.8%, at the wave frequency of 25, 33, and 40 kHz, respectively. The use of the thermochromic liquid crystals on the heating surface, disturbed by the 40 kHz wave, revealed that the bound of the wave incident region was shaped like a spiky structure that alternately occurs following with time. This incident region moved further downstream when the mainstream velocity increased and caused a retardation of the near wall flow, leading to a worse heat transfer in the upstream region. Therefore, the inclination of the acoustic beam, occurring as a variation of mainstream velocity, must be considered in order to use the ultrasound to enhance the heat transfer. Finally, the predictive formulas for the local Nusselt number under the 25–40 kHz waves are also provided and the mechanism of heat transfer is discussed.

AUTOMATIC CONTROL OF THE ORE SUSPENSION SOLID PHASE PARAMETERS USING HIGH-ENERGY ULTRASOUND

Context. The authors have solved the urgent problem of controlling automatically the parameters of solid ore suspension aimed for conversion thus increasing the end product quality and facilitating the choice and adhearance to the concentration specifications. Objective. The research aims at developing the method of obtaining operational data as to iron ore characteristics while concentrating, namely distribution of solid pulp particles as to their sizes and estimated grade applying multi-channel ultrasonic measurements. Method. In order to solve the problem of controlling automatically the parameters of solid ore suspension, the authors suggest the method of measuring the intensity of high-frequency bulk ultrasonic waves covering a fixed distance in a measuring chamber containing ore suspension under the influence of ultrasonic vibrations and in case of their absence. The calculated correlations of the measured values make it possible to determine the parameters of solid ore suspension. Besides, while measuring we can observe the formation of gamma-radiation and low-frequency bulk ultrasonic waves in the ore suspension flow. It is possible to measure the intensity of gamma-radiation and lowfrequency bulk ultrasonic waves covering the fixed distance if the measuring chamber contains some reference fluid and the ore suspension flow under ultrasonic vibrations and in the absence thereof. The intensity of ultrasonic vibrations influencing the suspension flow is changed according to the relevant law. Results. The dynamic effects of high-frequency ultrasound provide a theoretical basis and a practical approval of the method controlling the solid phase of iron ore pulps in order to displace the particles of the required grain-size class to the measuring zone and to determine the grade in ore particles. The developed purpose-designed programme realizes a numerical analysis and graphical representation of simulation results of changing solid pulp particle-sizes under the controlled influence of high-energy ultrasonic radiation pressure. Conclusions. The authors have devised the method for controlling the distribution of the grade in crushed ore particle-size classes in the pulp flow by means of measuring the changes in the distribution parameters of high- and low-frequency ultrasonic waves as well as gamma-radiation. The method is different from the existing ones by the fact that in the course of measuring, the crushed ore particles of the required size and density are displaced to the measuring zone by exposing the pulps to the high-energy ultrasound influence thus increasing the measurement accuracy by 0.76%.

Development of methods for ultrasonic scanning of X-ray wavelength

The method for X-ray wavelength tuning using an adaptive element (a quartz monolithic resonator modulated by a standing longitudinal low-frequency ultrasonic wave) has been proposed and implemented. This method is characterized by high tuning accuracy and possibility of scanning X-ray beam parameters with a time resolution of up to 3 μs.

Focusing ultrasonic waves in a 2-D covered channel above the periodic array of Helmholtz resonators

This paper presents the numerical simulation and experiments on focusing low-frequency ultrasonic waves in a 2-D covered channel above acoustic metamaterials composed of the periodic array of Helmholtz resonators, in which the refractive index can be in a negative value. The 2-D channel above the acoustic metamaterials is covered by a plate to limit the area affected by the negative refractive index metamaterials. Ultrasonic waves propagated in the 2-D covered channel are found to be highly dependent on input frequency and the designed Helmholtz resonator structure, where its negative refractive index causes the focusing phenomenon in this channel. From the numerical simulation and experiments, an amplitude focus spot is observed in the peak-to-peak of the time domain signal and frequency response at 125 kHz by mapping a pressure field in the 2-D covered channel. Different focal points with several input frequencies are also identified. Our research demonstrates the possibility of applying the designed lens based on acoustic metamaterials to improve the focusing effect in ultrasonic testing.

Theoretical and experimental investigation of fiber Bragg gratings with different lengths for ultrasonic detection

In this paper, the response of fiber Bragg gratings (FBGs) subjected to the ultrasonic wave has been theoretically and experimentally investigated. Although FBG sensors have been widely used in the ultrasonic detection for practical structural health monitoring, the relationship between the grating length and ultrasonic frequency is not yet to be obtained. To address this problem, an ultrasound detection system based on FBGs is designed and the response sensitivity of different lengths gratings are detected. Experimental results indicate that the grating with 3 mm length has a higher sensitivity when detecting high frequency ultrasonic wave, and the amplitude can be up to 0.6 mV. The 10 mm length grating has better detection sensitivity for low frequency ultrasonic wave and the amplitude is 0.8 mV. The results of this analysis provide useful tools for high sensitivity ultrasound detection in damage detection systems.

Effect of low-frequency ultrasound waves on the hydrogen peroxide degradation process

Investigation of the activating effect of low-frequency ultrasonic waves on both fiber-forming polymer and chemicals and reagents used in bleaching processes of textile materials is an important objective. Comprehensive experimental studies on determination of the ratio of the treatment time and power of ultrasonic waves have been carried out in order to reach the optimal rate of hydrogen peroxide decomposition. The experimental results have shown that the optimal hydrogen peroxide degradation rate during ultrasoundassisted bleaching is observed at an ultrasonic power of 3 kW and a treatment time of 15–20 min.