Ultrasonic Frequency Research Articles

Design and development of a variable ultrasonic frequency generator for rodents repellent

Rodent is one of the major stored pests in Bangladesh, which causes a huge problem in the food sector. They substantially harm to crops and other valuable items on a large scale. Chemically rodent repellents already exist, but because of their toxicity and high price, they are not recommended for use in food storage. The aim of the study was to develop an electronic rodent-repelling circuit that is capable of generating variable ultrasonic frequencies. These frequencies cause discomfort for pests including rats, and nocturnal insects, which affects their aural senses. A device was successfully designed and constructed by microcontroller, printed circuit board, passive infrared sensor, liquid crystal display, Relay module, and other relative components. The device was vigorously tested in Precision Lab, Bangladesh Agricultural University. Laboratory tests were conducted to evaluate the device's repellent efficacy, considering factors such as range, coverage area, power consumption, and durability. The device functioned as it detected the presence of rodents and then released frequency by the positive signal for 30 s. The device generated ultrasonic signals within the range of 20–125 kHz and detected signals from any live substances up to 4.5 m with an error of a maximum of ±0.428 %. The frequency range of rodent hearing is approximately 20 Hz to 300 kHz, with the greatest sensitivity between 30 and 70 kHz, affecting their aural senses and causing discomfort. Therefore, the developed ultrasonic rodent-repellent circuit can be a practical and sustainable solution for repelling stored rodents, which mitigates storage losses caused by rodent infestations.

Extraction of Phycocyanin and Chlorophyll from Spirulina by “Green Methods”

Phycocyanin is a pigment–protein complex from the group of phycobiliproteins obtained from Spirulina (Arthrospira platensis), with possibilities for various applications in food and pharmaceutical technologies. It is a natural colorant for food and cosmetic products. This study aimed to investigate the effect of ultrasonic and microwave extraction conditions on antioxidant activity (AOA), chlorophyll content, and the content and purity index of phycocyanin in aqueous and alcoholic extracts of Spirulina (Arthrospira platensis). For this purpose, ultrasonic extraction with water or ethanol was performed at 20 °C, 30 °C, and 40 °C for 1, 2, and 3 h at an ultrasonic frequency of 36 kHz, 40 kHz, and 45 kHz. Microwave water extraction was performed for 60 s, 120 s, and 180 s. For each of the obtained samples, three parallel measurements of antioxidant activity were made by DPPH and FRAP methods, and chlorophyll content and phycocyanin yield and purity index were determined spectrophotometrically. Ultrasonic extraction resulted in a higher yield and purity index of phycocyanin compared to microwave extraction. The highest yield of 14.88 mg g−1 with a purity index of 1.60 was achieved at a temperature of 40 °C for one hour and an ultrasonic wave frequency of 40 kHz. A relatively low yield of 4.21 mg g−1, but with a purity index of 2.67, was obtained at a temperature of 30 °C, a time of two hours, and an ultrasonic frequency of 40 kHz. Chlorophyll b content at 20 °C, for two hours and ultrasonic frequency 40 kHz was 1.400 mg g−1. The study proposes ultrasonic extraction as a green method to obtain phycocyanin of varying purity index that may be used for food, cosmetic, or biomedical purposes.

Experimental and Numerical Study of Forming Limit in 1060 Aluminum Ultrasonic Vibration Single Point Incremental Forming

Low formability, low productivity and forming quality are the main factors restricting the industrial application of single point incremental forming technology. Ultrasonic vibration was introduced into the single point incremental forming process to improve the forming limit of sheet metal by changing the deformation mechanism of material. A device combining ultrasonic vibration with plastic deformation processing technology and single point incremental forming was developed in this work. Taking cone parts of 1060 aluminum as the research object, the effects of ultrasonic vibration amplitude and frequency on equivalent stress and equivalent plastic strain in forming process were analyzed by combining numerical simulation and experimental research. Then, the forming angle of cone parts was used as the standard to study the influence of ultrasonic vibration parameters on formability. The results show that the equivalent stress decreased and equivalent plastic strain increased by superimposing ultrasonic vibrations, ultrasonic vibration can significantly change the formability and improve the forming limit of 1060 aluminum, the forming limit of 1060 aluminum can be maximized by selecting ultrasonic vibration parameters: amplitude 0.03 mm and frequency 30 kHz.

Fluidic Ultrasound Generation for Non-Destructive Testing.

Air-coupled ultrasonic testing (ACU) is a pioneering technique in non-destructive testing (NDT). While contact testing and fluid immersion testing are standard methods in many applications, the adoption of ACU is progressing slowly, especially in the low ultrasonic frequency range. A main reason for this development is the difficulty of generating high amplitude ultrasonic bursts with equipment that is robust enough to be applied outside a laboratory environment. This paper presents the fluidic ultrasonic transducer as a solution to this challenge. This novel aeroacoustic source uses the flow instability of a sonic jet in a bistable fluidic switch to generate ultrasonic bursts up to 60kHz with a mean peak pressure of 320Pa. The robust design allows operation in adverse environments, independent of the operating fluid. Non-contact through-transmission experiments are conducted on four materials and compared with the results of conventional transducers. For the first time, it is shown that the novel fluidic ultrasonic transducer provides a suitable acoustic signal for NDT tasks and has potential of furthering the implementation of ACU in industrialapplications.

Ultrasound assisted extraction of amino acids and nucleobases from clay minerals and astrobiological samples

The study of organic molecules in meteorite and return samples allows for the understanding of the chemistry that undergoes in our Solar System. The present work aims at studying ultrasound assisted extraction technique as effective extraction method for these molecules in extraterrestrial samples and analogs. Optimal conditions were selected from the investigation of ultrasonic frequency, irradiation duration and solvent effects on amino acids, nucleobases and dipeptides extraction yields from a model clay-rich mineral matrix. Optimal ultrasound-assisted extraction parameters were frequency of 20 kHz within 20 min irradiation time and methanol/water solvent ratio of 1. We then validated this protocol on Mukundpura and Tarda meteorite fragments and compared it to the reference extraction protocol used in astrobiology and based on 24 h extraction time at 100 °C in water We obtained similar quantitative results without any racemization with both methodologies.

Reconstructive interpolation for pulse wave estimation to improve local PWV measurement of carotid artery.

Ultrasonic transit time (TT)-based local pulse wave velocity (PWV) measurement is defined as the distance between two beam positions on a segment of common carotid artery (CCA) divided by the TT in the pulse wave propagation. However, the arterial wall motions (AWMs) estimated from ultrasonic radio frequency (RF) signals with a limited number of frames using the motion tracking are typically discrete. In this work, we develop a method involving motion tracking combined with reconstructive interpolation (MTRI) to reduce the quantification errors in the estimated PWs, and thereby improve the accuracy of the TT-based local PWV measurement for CCA. For each beam position, normalized cross-correlation functions (NCCFs) between the reference (the first frame) and comparison (the remaining frames) RF signals are calculated. Thereafter, the reconstructive interpolation is performed in the neighborhood of the NCCFs' peak to identify the interpolation-deduced peak locations, which are more exact than the original ones. According to which, the improved AWMs are obtained to calculate their TT along a segment of the CCA. Finally, the local PWV is measured by applying a linear regression fit to the time-distance result. In ultrasound simulations based on the pulse wave propagation models of young, middle-aged, and elderly groups, the MTRI method with different numbers of interpolated samples was used to estimate AWMs and local PWVs. Normalized root mean squared errors (NRMSEs) between the estimated and preset values of the AWMs and local PWVs were calculated and compared with ones without interpolation. The means of the NRMSEs for the AWMs and local PWVs based on the MTRI method with one interpolated sample decrease from 1.14% to 0.60% and 7.48% to 4.61%, respectively. Moreover, Bland-Altman analysis and coefficient of variation were used to validate the performance of the MTRI method based on the measured local PWVs of 30 healthy subjects. In conclusion, the reconstructive interpolation for the pulse wave estimation improves the accuracy and repeatability of the carotid local PWV measurement.

Ultrasonic Activation of Mineral Sorbents

Introduction. Medical clays are polymineral sorbents with a predominance of the underlying clay mineral, the concentration of which determines the quality of mineral raw materials and its adsorption activity. One of the methods of improving the quality of mineral raw materials is its activation by means of ultrasonic treatment.Aim. To study the effect of ultrasound on the activation and adsorption activity of mineral sorbents.Materials and methods. Clinoptilolite mineral raw materials of the Kholinsky deposit, montmorillonite mineral raw materials of the Belgorod deposit and kaolinite mineral raw materials of the Eleninsky deposit were used as objects of research. A high-frequency UZDN-1 unit was used for ultrasonic treatment. Determination of adsorption activity was carried out by methylene blue.Results and discussion. The effect of ultrasound on the activation of mineral sorbents at an ultrasonic wave frequency of 40 kHz for five minutes has been studied. It was found that the average content of Clinoptilolite, taking into account all fractions in the clay of the Kholinsky deposit, increases by 20 %, the average content of Montmorillonite, taking into account all fractions in the clay of the Belgorod deposit, increases by 14 %, the average content of Kaolinite, taking into account all fractions in the clay of the Eleninsky deposit, increases by 18 %. The effect of ultrasound on the adsorption activity of mineral sorbents has been investigated. The use of ultrasonic treatment increases the adsorption activity of mineral sorbents by 12–19 %.Conclusion. The developed method of activation of mineral sorbents by ultrasonic treatment can be used to activate mineral sorbents by increasing the concentration of the underlying mineral (Clinoptilolite, Montmorillonite, Kaolinite), as well as increasing their adsorption activity.

Ultrasonic tool shank with multiple vibration mode for micro-nano drilling: Design, optimization and experiment

The machining effects of hole drilling is limited by merely changing the amplitude. Adjusting ultrasonic vibration frequency to expand the matching range of machining parameters optimization is necessary to improve hole drilling effects. Therefore, the design, optimization, and experiment evaluation for a novel integrated, fined, low-cost dual-frequency ultrasonic tool shank is proposed, which can work in three vibration modes for micro-nano precision drilling. The principle of the dual-frequency ultrasonic transducer is introduced. The electro-mechanical equivalent circuit model with step horn is applied to study the dual-frequency characteristics. The transducer displacement equation model based on the wave equation theory is deduced to find the shared vibration node of the first and third frequency. Sensitivity analysis by equivalent circuit model and Finite element method (FEM) simulation of the key parameter is both conducted to optimize ultrasonic transducer geometry dimension. The vibration node of mounting flange is specified in an identical position for the dual vibration modes. A prototype of ultrasonic tool shank is fabricated and evaluated in experiments. It demonstrates that the dual working frequency of the ultrasonic transducer is 34.9 kHz and 104.5 kHz in the first and third mode resonant vibration, which is benefit to the low and high frequency drilling. Three working modes of the low, high, and coupling frequency vibration is measured by a self-developed ultrasonic generator. When 40 V voltage is excited, the vibration amplitudes of the low and high frequency are 17.8 µm, and 9.3 µm, respectively, which can meet with the drilling requirement. Moreover, the coupling vibration with the low and high mode are excited simultaneously, and the motion trajectory of the coupling vibration is observed in a “M” shape, which is a novel trajectory for the precision micro-nano drilling. Micro drilling experiments show that the 35 kHz ultrasonic vibration drilling can achieve better machining effect than conventional drilling (CD). The 105 kHz ultrasonic drilling outperforms the CD, 35 kHz and coupling ultrasonic drilling at cutting force reduction. The coupling ultrasonic vibration drilling achieves the lowest chipping diameter. It is to be noted that the 105 kHz-8 µm produce the fined smoothly surface. The 35 kHz, 105 kHz and coupling ultrasonic drilling can produce better surface micro morphology with less quantity and size of craters than that of CD.

Experimental and modeling study on liquid film thickness of horizontal gas-liquid annular flow using ultrasonic method

In horizontal annular flow, the high gas velocity leads to the strong randomness, rapidity and complexity of the structure and dynamic characteristics of gas-liquid interfacial wave. As one of the important parameters to describe the interfacial wave, the liquid film thickness is significant to study the hydrodynamic characteristics of the gas-liquid two-phase flow. In this paper, the ultrasonic echo resonance main frequency (UERMF) method and the ultrasonic reference signal elimination (URSE) method are compared by numerical simulation method. The minimum liquid film thickness measured by these two methods are 0.3 mm and 0.01 mm, respectively. Experiments are conducted on a stainless steel test section with an inner diameter of 50.0 mm to study annular air-water flow under five different pressure conditions (from 0.1 MPa to 0.7 MPa). The experimental data is processed using the URSE method to analyze the characteristics of the liquid film under different operating conditions. In addition, based on the aforementioned experimental dataset, a comparison is made regarding the performance of existing predictive correlations. It is found that the existing correlations have certain limitations in capturing the variations of liquid film thickness in annular flow, particularly at high pressures and for different pipe diameters. Therefore, a new liquid film thickness correlation suitable for different system pressures and pipe diameters is proposed. By expanding the range of fitted data points (220 data points), the 95 % relative error of improved model is within ±25 % error band for all available data (authors' and literature). The mean absolute percentage error (MAPE) is 11.08 %. The improved correlation has the applicability and extrapolation for different system pressure and pipe diameter conditions.

Experimental Study of Seismic Wave Attenuation in Carbonate Rocks

Summary Seismic wave attenuation has a great potential for studying saturated and fractured media, due to its high sensitivity to the physical properties of geological media. However, accurately estimating this parameter can be challenging due to its sensitivity to signal noise, particularly in heterogeneous media such as carbonate rocks. This explains the paucity of attenuation studies carried out in carbonate rocks compared with sandstones, and the ambiguity around its mechanisms and its relationship with petrophysical properties. To investigate further, we conducted an experimental study of ultrasonic waveform signals (0.5–3 MHz) reordered under dry and fully saturation conditions in 13 samples covering a wide range of petrophysical values and subjected them to differential pressure reaching reservoir pressure. The resulting increase in attenuation magnitudes and their variation with pressure due to brine saturation were more pronounced than in velocity magnitudes, confirming the higher sensitivity of attenuation to fluid content. However, understanding the relationship between attenuation and petrophysical properties required a careful examination of the results and more elucidation about attenuation mechanisms. We suggested that multiple attenuation mechanisms coexist, including scattering, cracks slipping, solid frictional relative motion, and global and squirt flow. This explains the frequency dependence of attenuation, with higher magnitudes at sonic frequencies, where the squirt flow mechanism may be dominant. In contrast to sandstone, the magnitude of compressional to shear attenuation ratio (QP−1/QS−1) was found to be greater than unity in both dry and brine fully saturated carbonate samples at ultrasonic frequencies. This result may be due to the complex porosity structure of carbonate rocks, which makes it not appropriate to the sandstone rock physics models.

Characteristics of Ultrafine Bubbles (Bulk Nanobubbles) and Their Application to Particle-Related Technology

Ultrafine bubbles (bulk nanobubbles), small bubbles less than 1µm in diameter, have attracted academic and industrial attention because of their numerous advantages, including their chemical-free nature and extraordinarily long lifetime. The long lifetime is related to the much higher Brownian motion velocity than buoyancy. The reason why ultrafine bubbles can endure under stable conditions is still unclear, even though their inside is highly pressured. They have several characteristics, such as pH-dependent surface charge and reduction in friction. They are also closely related to ultrasound. Ultrafine bubbles are generated and removed by selecting the ultrasonic frequency. Reaction and separation using ultrasonic cavitation and atomization, respectively, are enhanced by ultrafine bubbles. They can produce hollow nanoparticles, enhance adsorption on activated carbon, and clean solid surfaces. This review discusses the fundamental and ultrasonic characteristics of ultrafine bubbles and their application to particle-related technology: fine particle synthesis, adsorption, desorption, extraction, cleaning, and prevention of fouling.

Numerical and experimental study of ultrasonic seismic waves propagation and attenuation on high‐quality factor samples

AbstractWe propose an approach for measuring seismic attenuation at ultrasonic frequencies on laboratory‐scale samples. We use a Gaussian filter to select a bandwidth of frequencies to identify the attenuation in a small window and, by moving the window across the frequency content of the data, we determine the frequency‐dependent attenuation function. We assess the validity of the method with three‐dimensional numerical simulations of seismic wave propagation across different sample geometries, using free surface boundary conditions. We perform the simulations using viscoelastic media under various seismic attenuation models. Our numerical results indicate that we can successfully recover the representative viscoelastic attenuation parameters of the media, regardless of the sample geometry, by processing the seismic signal recorded either within the volume or at the boundaries. Due to the equipartition phenomenon, the energy of S‐waves is consistently higher in seismic records than that of P‐waves. Therefore, we systematically recover the attenuating properties of S‐waves in the medium. We also conduct experiments of seismic wave propagation on samples of aluminum and Fontainebleau sandstone to validate our approach with real data. The quality factor of the S‐wave in the aluminum medium increases from 300 to 7000 between 60 kHz and 1.2 MHz. The Fontainebleau sandstone, which is more attenuating, exhibits a that increases from 200 at 60 kHz to 1000 at 1.2 MHz. With our approach, we are not only able to recover the attenuation property but also identify the frequency‐dependent attenuation model of the samples. Our method allows for seismic attenuation recovery at ultrasonic frequencies in low‐attenuating media.

Dynamics of high-power coupled nonlinear oscillator arrays for electronic beam steering technique: case of the triode based van der Pol oscillator

This paper presents the dynamics of coupled nonlinear oscillator arrays (CNOAs) as phase shifter for electronic beam steering technique. The proposed phase shifter uses oscillators of van der Pol type with a fifth-order nonlinear resistance and is built on the two architectures based injection-locked oscillator array (ILOAs) and coupled oscillator arrays (COAs). The dynamics equations of the phase shifter are proposed in the frequency and time domain. With the help of mathematical tools such as bifurcation diagrams, maximum Lyapunov exponent and Hilbert transform, important cartography of different oscillating states is deduced over large range of system parameters. Different behavior of the CNOAs including chaos, 2D-torus, multistability, locked and unlocked states are depicted. The phase shift between output voltages of each pair of coupled oscillators is presented for both architectures. A detailed analysis of locked states shows that the required phase shift is synthesized by slightly varying the frequency of the injected signal, or simply by detuning the free-running frequencies of the edge oscillators in equal but opposite directions. The proposed circuit of the phased shifter is built using the original van der Pol oscillator based on a vacuum triode. The maximal phase shift reaches 63° and 75° respectively for ILOAs and COAs. With the presence of triode in the circuit, the output voltage of each oscillating element in the array reaches 100V around 60KHz and is boosted by increasing the value of the triode bias potential to more than 420V. This, therefore, increases the total power dissipation of a single oscillator in the array to more than 47dB ( 50.12W ). This circuit is a candidate for high-power electronics beam steering at ultrasonic frequency.

Extraction of Vitamin B12 from Aqueous Solution by using Solid- Liquid Extraction and Ultra Sonic Frequency

A new method to uptake vitamin B12 in aqueous solution as pharmaceutical preparations by adsorption on the solid phase surface by using a multi-layer graphene oxide derivative compounds while the ultrasonic frequency wave was used to increase the efficiency of the extraction of drug from aqueous solution. Interlayer drug extraction conditions were optimized by studying a number of conditions that affect the extraction rate, including pH, ultrasound frequency, residence time of the solution inside the ultrasound device, the effect of the amount of graphene oxide derivative, and vitamin B12 concentration. The effect of temperature was also studied and a number of thermodynamic factors were generated. From the results, it was found that the best weight for the economically useful graphene oxide derivative is 0.01 grams at a concentration of 20 ppm relative to the concentration of the vitamin using an acidic medium of 2.1. The best temperature is 40 0C and within 50 Hz of the frequencies of the ultrasound device during the incubation period of 50 minutes. The proposed method was also applied to pharmaceutical samples containing vitamin B12, and the extraction rate was 95.35 %, with a very small error rate of 0.0465.

Effective treatment of 2,4,6-trinitrotoluene from aqueous media using a sono-photo-Fenton-like process with a zero-valent iron nanoparticle (nZVI) catalyst.

In this study, we examine the effectiveness of using a combination of a sono-photo-Fenton-like procedure and nano zero-valent iron catalyst (nZVI) to treat 2,4,6-trinitrotoluene (TNT) in an aquatic environment. Zero-valent iron particles were generated by a chemical reduction technique. nZVI nanoparticles were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) to characterize the nanocatalyst. The resulting nZVI nanoparticles were used as an addition in a sono-photo-Fenton method to remediate an aqueous solution contaminated with TNT. Furthermore, influences of operational factors such as temperature, catalyst dosage, wavelength, ultraviolet power, ultrasonic frequency and power, pH level, H2O2/nZVI ratio, initial TNT concentration, and reaction duration on the treatment of TNT were investigated. Under the conditions of an ideal pH of 3, temperature range of 40-45 °C, concentration of 50 mg per L TNT, dose of 2 mM of nZVI, and ratio of H2O2/Fe0 of 20, a treatment efficiency of 95.2% was achieved after a duration of 30 minutes. The sono-photo-Fenton process combined with nZVI showed a higher TNT removal efficiency compared to the Fenton, sono-Fenton, and photo-Fenton processes under the same conditions. Moreover, it promises a potential solution to treat TNT at the pilot scale while allowing reuse of the nZVI catalyst and the limitation of sludge.

Simulation and analysis of elastic waves in partially saturated double-porosity media based on finite difference method

Double-porosity poroelastic model takes into account the effect of mesoscopic flow induced by rock heterogeneity on dispersion and attenuation of elastic waves, and has obtained good application results in the quantitative explanation of seismic data in heterogeneous reservoirs. Wavefield simulation based on double-porosity model not only helps visualize the propagation characteristics of the elastic waves but also lays the foundation for seismic imaging. In this work, we perform wavefield simulation and analysis based on the Santos-Rayleigh model which incorporates mesoscopic and global flow in a partially-saturated double-porosity medium. Specifically, the mesoscopic flow mechanism is represented with a Zener viscoelastic model. The comparison shows that the Zener model can accurately capture the propagation characteristics of fast P-wave, but fails to describe the attenuation characteristics of slow P3 wave in the low-frequency band. It implies that Zener viscoelastic model and slow wave modes follow different mechanisms. Then the staggered grid finite-difference method is used to simulate wave propagation in a double-porosity medium, and the stiff problem is solved with a time-splitting algorithm, which can significantly improve computational efficiency. Based on the above methods, the correctness of our algorithm is verified with derived analytical solution for a P-wave source in a uniform partially saturated poroelastic medium. Analytical and numerical solutions are in good agreement and mean error is 0.33%. We provide some examples of wavefield snapshots and seismograms in homogeneous and layered heterogeneous media at seismic and ultrasonic frequencies. The simulation results demonstrate the strong attenuation of fast P-wave and no change of S-wave in the seismic band due to mesoscopic flow mechanism, which is consistent with the theoretical prediction of double-porosity model. Moreover, the energy of fast P-wave is concentrated in solid phase while slow waves are stronger in fluid phase. This work contributes to the understanding of broadband elastic wave propagation in a heterogeneous partially saturated porous medium and can be applied to the reservoir imaging with broadband geophysical data.

A COMBINED ACTIVE (PIEZOS) AND PASSIVE (MICROSTRUCTURING) PARTIAL FLOW-BOILING APPROACH FOR STABLE HIGH HEAT-FLUX COOLING WITH DIELECTRIC FLUIDS

Controlled but explosive growth in vaporization rates is made feasible by ultrasonic acoustothermal heating of the microlayers associated with microscale nucleating bubbles within the microstructured boiling surface/region of a millimeter-scale heat exchanger (HX). The HX is 5 cm long and has a 1 cm × 5 mm rectangular cross section that uses saturated partial flow-boiling operations of HFE-7000. Experiments use layers of woven copper mesh to form a microstructured boiling surface/region and its nano/microscale amplitude ultrasonic (~1-6 MHz) and sonic (< 2 kHz, typically) vibrations induced by a pair of very thin ultrasonic piezoelectric-transducers (termed piezos) that are placed and actuated from outside the heat-sink. The ultrasonic frequencies are for substructural microvibrations whereas the lower sonic frequencies are for suitable resonant structural microvibrations that assist in bubble removal and liquid filling processes. The flow and the piezos' actuation control allow an approximately 5-fold increase in heat transfer coefficient value, going from about 9000 W/m<sup>2</sup>-°C associated with microstructured no-piezos cases to 50,000 W/ m<sup>2</sup>-°C at a representative heat flux of about 25 W/cm<sup>2</sup>. The partial boiling approach is enabled by one inlet and two exit ports. Further, significant increases to current critical heat flux values (~70 W/cm<sup>2</sup>) are possible and are being reported elsewhere. The electrical energy consumed (in W) for generating nano/micrometer amplitude vibrations is a small percentage (currently < 3%, eventually < 1% by design) of the total heat removed (in W), which is a heat removal rate of 125 W for the case reported here.

Surface microstructuring by Ultrasonic Vibration Assisted Deformational Machining (UVADM) – Simulation and experimental results

Polymer-metal hybrids are a lightweight solution for many industrial applications, especially in the automotive or aircraft sector. However, due to their poor chemical bonding the manufacturing of such compounds requires the use of adhesive layers or the conditioning of the metallic surface to achieve form closure and high joint strength. Ultrasonic Vibration Assisted Deformational Machining (UVADM) is a novel process that generates functional microstructures with high production rates, aiming to form defined burr structures with undercuts, that have a significant impact on the interlaminar strength of polymer-metal hybrids (PMH). A 3D FEM simulation using Abaqus/Explicit software was applied to design and analyze process conditions including tool geometry. Material deformation was described by the Johnson-Cook model. Simulation results were validated experimentally using two different MCD tools. For the UVADM experiments, specimens of the aluminum alloy EN AW-6082 were used. In the tests, a constant ultrasonic frequency (20.42 kHz), machining speed (100 m/min and 200 m/min), and peak-to-peak amplitude (7 µm) were used. Geometrical surface properties were analyzed by optical methods and SEM. The study demonstrates a conformity between simulated and experimental results, highlighting the potential of UVADM for an increased productivity in the surface conditioning for polymer-metal hybrids.

Improving acoustic wave propagation models in highly attenuating porous materials.

This article presents an improved and extended modeling approach for acoustic wave propagation in rigid porous materials, focusing on examples, such as plastic foams used for noise reduction in automotive applications. We demonstrate that the classical model (Johnson-Champoux-Allard) in the asymptotic high-frequency limit, widely employed in the literature, fails to accurately reconstruct the transmitted acoustic signal through high absorbent porous materials characterized by significant wave attenuation. The study focuses on the airborne ultrasonic frequency range (30-200 kHz). To address this limitation, we introduce new non-acoustic parameters Σ and V for viscous effects, and Σ' and V' for thermal effects, with surface and volumetric dimensions, respectively, allowing for the reconstruction of the transmitted signal and accurate modeling of the pronounced acoustic attenuation within the material. These parameters are incorporated into the expansion on skin depths of the dynamic tortuosity α(ω) and thermal tortuosity α' (ω) response functions, which describe the inertial-viscous and thermal interactions between the fluid and the solid, respectively. This novel modeling approach enables a more comprehensive study of high attenuating porous media, which are crucial for effective noise reduction. Additionally, it opens up new possibilities for characterization beyond the capabilities of current models.

Rheological investigation of bitumen, used for radioactive waste conditioning, with ultrasonic waves

In the context of bituminized radioactive waste storage and disposal, nucleation monitoring at room temperature and radiolysis bubbles migration at elevated temperature is crucial particularly in fire scenarios where bubble may impact thermal properties. Traditional methods are limited by the opacity of bitumen. To gain a deeper insight into bitumen rheology and ultrasonic wave propagation, we conducted a pilot study using ultrasonic testing cells spanning temperatures from 10°C to 60°C. Ultrasonic velocities and attenuations were measured at around 500 kHz in a 70/100 grade bitumen. Rheological information was deduced with the Time-Temperature Superposition principle and a behaviour model was proposed to describe bitumen across a wide frequency range. Notably, our study reveals a transition point around 50°C to 60°C, where bitumen’s liquid behaviour becomes dominant. The shear-thinning characteristics gradually give way to a more Newtonian response. Using the proposed model, ultrasonic attenuation and viscosity were estimated at 110°C. Acceptable ultrasonic frequencies for monitoring the nucleation and migration of radiolysis bubbles are discussed for future investigations. These findings have significant implications for safety measures and a deeper understanding of bitumen response within the realm of radioactive waste management.