Determination of Partial Propagation Velocity and Partial Isentropic Compressibility Coefficient in Water-Ethanol System.

This study introduces an innovative approach to the layered model, emphasizing the physical-chemical characterization of miscible liquid systems through ultrasonic techniques, with a specific focus on the water-ethanol system used in pharmaceutical formulations. Traditional characterization methods, while effective, face challenges due to the complex nature of solutions, such as the need for large pressure variations and strict temperature control. The proposed approach integrates partial molar volumes and partial propagation velocity functions into the layered model, enabling a nuanced understanding of miscibility and interactions. Ultrasonic techniques are used to calculate the isentropic compressibility coefficient for each component of the mixture as well as the total value using an additive mixing rule. Unlike conventional methods, this technique uses tabulated and experimental data to estimate the propagation velocity in the mixture, leading to a more precise computation of the isentropic compressibility coefficient. The results indicate a significant improvement in predicting the behavior of the water-ethanol system compared to the classical layered model. The methodology demonstrates the potential to provide new physicochemical insights that can be applied to other miscible systems beyond water-ethanol. This research has implications for improving the efficiency and accuracy of liquid medication formulations in the pharmaceutical industry.

Error analysis of self-compensated ultrasound measurements of the thickness loss due to corrosion in pipe walls.

The ultrasonic pulse-echo technique is widely employed to measure the wall thickness reduction due to corrosion in pipelines. Ultrasonic monitoring is noninvasive and can be performed online to evaluate the structural health of pipelines. Although ultrasound is a robust technique, it presents two main difficulties arising from the temperature variation in the medium being monitored: the mechanical assembly must have high stability and the ultrasonic propagation velocity must take into account the temperature variation. In this paper, a detailed strategy is presented to compensate for changes in the propagation velocity whenever the temperature changes. The method is considered self-compensated because the calibration data is obtained from the ultrasonic signals captured using the pipe under evaluation. The analysis of systematic errors in the temperature compensation is presented, first considering that a reference initial pipe thickness is given, and second when a reference sound velocity is given. The technique was evaluated under laboratory conditions using a closed loop with accelerated corrosion through the use of continuous flow saline water containing sand. In this test, the ultrasonic results were compared with the traditional coupon method used to determine corrosion loss. The results show that the self-compensated method was able to compensate for temperature fluctuations, and the total thickness loss measured by the ultrasound technique was close to the value measured by the coupons. Finally, the measurement system was tested in a production pipeline exposed to sunlight. The results show that the self-compensated method can reduce the oscillations in the thickness loss readings, caused by temperature swings, but large temperature variations cannot be completely compensated for. This experiment also shows the effects of low mechanical stability, which caused completely invalid results.

Self-compensation methodology for ultrasonic thickness gauges.

There are many causes for the reduction of the thickness in pipelines, tanks and other mechanical structures. Corrosion, erosion, and abrasive wear cause degradation of mechanical structures and decrease their lifespan. These can be very slow processes that are difficult to track over time. Thickness gauging monitoring is commonly used as a way of preventive maintenance. The pulse-echo ultrasound can be a suitable technique to measure the thickness diminution in industrial facilities. Although ultrasound is considered a robust technique, in this particular application it presents two main difficulties: the mechanical stability of the assembly and the variation of the ultrasonic speed over time. Both mechanical assembly and acoustic propagation speed are strongly influenced by the temperature. In this paper, the implementation of a methodology that compensates for the temperature influences on the ultrasonic speed and the mechanical assembly is presented. The methodology can be applied in metallic structures to evaluate corrosion over long time periods. The temperature compensation data is obtained from the analysis of the ultrasonic signals. In this sense, the method can be called self-compensated. As initial data for the determination of thickness changes, the ultrasonic speed in the material at a reference temperature must be known. All results are evaluated at this temperature. An analysis of the uncertainty sources and limitations of the methodology is also included. To show the experimental application of the proposed technique, a rigid sample was designed in order to avoid mechanical instability. The results show that the methodology can compensate for the temperature, detecting a thickness reduction in the order of a few micrometers.

Water content monitoring in water-in-oil emulsions using a delay line cell.

The extraction process of crude oil requires addition of water, resulting in complex emulsions, in which the phases must be separated before the petrochemical processing starts. An ultrasonic cell may be used to determine in real time the water content in water-in-crude oil emulsions. The water content of emulsions can be related to parameters, such as propagation velocity, density and relative attenuation. The ultrasonic measurement cell developed here is composed of two piezoelectric transducers, two rexolite buffer rods, and a sample chamber. It is an inexpensive and robust system. The cell measures the parameters at different temperatures and flow conditions. The tests were performed using emulsions with water volume concentrations from 0% to 40%. The experimental results show that this cell is able to obtain more precise parameters, when compared to similar ultrasonic techniques. The data acquired in real time may be used to improve the emulsion separation, decreasing greenhouse gases and energy requirements.

Ultrasonic Monitoring of the Water Content in Concentrated Water-Petroleum Emulsions Using the Slope of the Phase Spectrum.

This work proposes the slope of the phase spectrum as a signal processing parameter for the ultrasonic monitoring of the water content of water-in-crude oil emulsions. Experimental measurements, with water volume fractions from 0 to 0.48 and test temperatures of 20 °C, 25 °C, and 30 °C, were carried out using ultrasonic measurement devices operating in transmission-reception and backscattering modes. The results show the phase slope depends on the water volume fraction and, to a lesser extent, on the size of the emulsion droplets, leading to a stable behavior over time. Conversely, the behavior of the phase slope as a function of the volume fraction is monotonic with low dispersion. Fitting a power function to the experimental data provides calibration curves that can be used to determine the water content with percentage relative error up to 70% for a water volume fraction of 0.06, but less than 10% for water volume fractions greater than 0.06. Furthermore, the methodology works over a wide range of volume fractions.

Water Content Monitoring in Water-in-Crude-Oil Emulsions Using an Ultrasonic Multiple-Backscattering Sensor.

This work shows the application of an ultrasonic multiple-scattering sensor for monitoring water-in-petroleum emulsions. The sensor consists of a commercial ultrasonic transducer with an array of cylindrical scatterers placed in the near field. The scatterers are thin metal bars arranged in rows in front of the transducer. The backscattering signals were analyzed by calculating the wave energy and by a cross-correlation between signal segments; they were also used to determine the propagation velocity in the emulsions. The tests performed used emulsions with water volume concentrations from 0% to 50%. The results showed that both the signal energy and propagation velocity strongly depended on the concentration of water in the emulsion. Therefore, the ultrasonic multiple-scattering sensor can be used for on-line and real-time monitoring of the water content in water-in-crude-oil emulsions.

Shear-wave corner retroreflector device for ultrasonic measurement of viscosity.

This work shows a novel ultrasonic viscosity measurement device with increased sensitivity. The measuring principle is based on the determination of the complex reflection coefficient of shear-waves at the solid-liquid interface. But the proposed approach is the replacement of the flat surface at the measurement interface with a grooved surface, which works in a similar way to an optical retroreflector. The complete reflection of the waves involves a double reflection with oblique incidence, where both phenomena increase sensitivity, in comparison with a plane surface. It is shown that a set of orthogonal flat interfaces reflects a well-defined ultrasonic pulse. The sensitivity is enough to measure the change in the magnitude and phase of the reflection coefficient even for the small portion of the energy transmitted to water. A model for calculating the viscosity and a calibration approach for the measurement were proposed. Results with samples of corn syrup-water mixture are reported.

Stepped-plate ultrasonic transducer used as a source of harmonic radiation force optimized by genetic algorithm.

Circular stepped-plates are often chosen to generate continuous waves in air due to their transmission efficiency, directive radiation patterns and capability to generate high-intensity airwave emission. Such features can be suitable for an acoustic radiator intended for the generation of harmonic radiation force, if the narrow bandwidth of the piezoelectric power transducer is not an obstacle to the application. This force has been used as the excitation source in noncontact modal analysis of mechanical devices, since it offers some advantages over the traditional impact method and the use of shakers. In this study, a directional stepped-plate ultrasonic device driven by a bolt-clamped Langevin-type transducer is used to excite the first flexural mode of a clamped-free beam by means of harmonic radiation force. The harmonic component was generated using an amplitude-modulated electrical input signal. The radiator design was done by solving a parametric optimization problem of finding a plate with the desired vibrational behavior using the genetic algorithm. Finite element analysis was used to obtain the dynamic behavior of the device and the airwave propagation was modeled using linear acoustic theory. Modal and harmonic analyses were conducted to obtain some of the electroacoustic parameters of the transducer. The acoustic field generated by the prototype is estimated by solving the Rayleigh integral and the obtained results are compared to experimental measurements.

Development of a 2-D Array Ultrasonic Transducer for 3-D Imaging of Objects Immersed in Water.

Most works that address 2-D array ultrasonic transducers for underwater applications are about the geometry aspects of the array and beamforming techniques to make 3-D images. They look for techniques to reduce the number of elements from wide apertures, maintaining the side lobes and the grating lobes at acceptable levels, but not many details about the materials and fabrication processes are described. To overcome these gaps, this paper presents in detail the development of a 2-D array ultrasonic transducer prototype that can individually emit and receive ultrasonic pulses to make 3-D images of immersed reflectors within a volume of interest (VOI). It consists of a 4 × 4 matrix ultrasonic transducer with a central frequency of 480 kHz. Each element is a 5 mm sided square cut into a 1-3 piezocomposite. The center-to-center distance of two contiguous elements (pitch) was chosen to be greater than half wavelength, to increase the amplitude of emission and reception of signals with larger elements. Artifacts generated by grating lobes were avoided by restricting the field of view in the azimuth and elevation directions within 40° × 40° and applying the sign coherence factor (SCF) filter. Two types of backing layer materials were tested, one with air and another made of epoxy resin, on the transducers called T1 and T2, respectively. The pulse echoes measured with T1 had 2.6 dB higher amplitude than those measured with T2, and the bandwidths were 54% and 50% @ -6 dB, respectively, exciting the element with a single rectangular negative pulse. The 3-D images obtained with full matrix capture (FMC) data sets acquired of objects from 0.2 to 1.15 m motivate the development of a 2-D array transducer with more elements, to increase the angular resolution and the range.

Ultrasonic measurement of viscosity: Signal processing methodologies.

This work deals with two alternative methodologies for data post-processing resulting from the ultrasonic shear-wave reflectance method used for liquid viscosity measurement. In the shear-wave reflectance method, the measurement principle is the small transference of energy to the liquid when the wave strikes a solid-liquid interface, causing a detectable change in the reflection coefficient. A measurement cell that uses mode conversion for the generation of the shear waves was employed and samples of five different substances were tested, covering a viscosity range of three orders of magnitude. Ultrasonic results were compared to the values obtained by conventional viscometry. Despite the wide range of viscosity and the different nature of the liquids, Newtonian behavior was observed with all samples at the working frequencies. This can be concluded from the coincidence between the values obtained by ultrasound and by the rotational viscometer. However, the viscosity values show an oscillating behavior when calculated for different frequencies along the band of the transducer. This oscillating behavior induces big errors when the viscosity is calculated at a single frequency, forcing the development of alternative methodologies. Two methodologies that calculate the reflection coefficient in a frequency band instead of a single frequency were analyzed, showing more accuracy and precision.

Numerical Characterization of Piezoceramics Using Resonance Curves.

Piezoelectric materials characterization is a challenging problem involving physical concepts, electrical and mechanical measurements and numerical optimization techniques. Piezoelectric ceramics such as Lead Zirconate Titanate (PZT) belong to the 6 mm symmetry class, which requires five elastic, three piezoelectric and two dielectric constants to fully represent the material properties. If losses are considered, the material properties can be represented by complex numbers. In this case, 20 independent material constants are required to obtain the full model. Several numerical methods have been used to adjust the theoretical models to the experimental results. The continuous improvement of the computer processing ability has allowed the use of a specific numerical method, the Finite Element Method (FEM), to iteratively solve the problem of finding the piezoelectric constants. This review presents the recent advances in the numerical characterization of 6 mm piezoelectric materials from experimental electrical impedance curves. The basic strategy consists in measuring the electrical impedance curve of a piezoelectric disk, and then combining the Finite Element Method with an iterative algorithm to find a set of material properties that minimizes the difference between the numerical impedance curve and the experimental one. Different methods to validate the results are also discussed. Examples of characterization of some common piezoelectric ceramics are presented to show the practical application of the described methods.

Transthoracic cardiac ultrasonic stimulation induces a negative chronotropic effect.

The objective of this study is to investigate cardiac bioeffects resulting from ultrasonic stimulation using a specific set of acoustical parameters. Ten Sprague-Dawley rats were anesthetized and exposed to 1-MHz ultrasound pulses of 3-MPa peak rarefactional pressure and approximately 1% duty factor. The pulse repetition frequency started slightly above the heart rate and was decreased by 1 Hz every 10 s, for a total exposure duration of 30 s. The control group was composed of five rats. Two-way analysis of variance for repeated measures and Bonferroni post hoc tests were used to compare heart rate and ejection fraction, which was used as an index of myocardial contractility. It was demonstrated for the first time that transthoracic ultrasound has the potential to decrease the heart rate by ~20%. The negative chronotropic effect lasted for at least 15 min after ultrasound exposure and there was no apparent gross damage to the cardiac tissue.

Matrix method for acoustic levitation simulation.

A matrix method is presented for simulating acoustic levitators. A typical acoustic levitator consists of an ultrasonic transducer and a reflector. The matrix method is used to determine the potential for acoustic radiation force that acts on a small sphere in the standing wave field produced by the levitator. The method is based on the Rayleigh integral and it takes into account the multiple reflections that occur between the transducer and the reflector. The potential for acoustic radiation force obtained by the matrix method is validated by comparing the matrix method results with those obtained by the finite element method when using an axisymmetric model of a single-axis acoustic levitator. After validation, the method is applied in the simulation of a noncontact manipulation system consisting of two 37.9-kHz Langevin-type transducers and a plane reflector. The manipulation system allows control of the horizontal position of a small levitated sphere from -6 mm to 6 mm, which is done by changing the phase difference between the two transducers. The horizontal position of the sphere predicted by the matrix method agrees with the horizontal positions measured experimentally with a charge-coupled device camera. The main advantage of the matrix method is that it allows simulation of non-symmetric acoustic levitators without requiring much computational effort.

Identification of elastic, dielectric, and piezoelectric constants in piezoceramic disks.

Three-dimensional modeling of piezoelectric devices requires a precise knowledge of piezoelectric material parameters. The commonly used piezoelectric materials belong to the 6mm symmetry class, which have ten independent constants. In this work, a methodology to obtain precise material constants over a wide frequency band through finite element analysis of a piezoceramic disk is presented. Given an experimental electrical impedance curve and a first estimate for the piezoelectric material properties, the objective is to find the material properties that minimize the difference between the electrical impedance calculated by the finite element method and that obtained experimentally by an electrical impedance analyzer. The methodology consists of four basic steps: experimental measurement, identification of vibration modes and their sensitivity to material constants, a preliminary identification algorithm, and final refinement of the material constants using an optimization algorithm. The application of the methodology is exemplified using a hard lead zirconate titanate piezoceramic. The same methodology is applied to a soft piezoceramic. The errors in the identification of each parameter are statistically estimated in both cases, and are less than 0.6% for elastic constants, and less than 6.3% for dielectric and piezoelectric constants.

Ultrasonic viscosity measurement using the shear-wave reflection coefficient with a novel signal processing technique.

Real-time viscosity measurement remains a necessity for highly automated industry. To resolve this problem, many studies have been carried out using an ultrasonic shear wave reflectance method. This method is based on the determination of the complex reflection coefficient's magnitude and phase at the solid-liquid interface. Although magnitude is a stable quantity and its measurement is relatively simple and precise, phase measurement is a difficult task because of strong temperature dependence. A simplified method that uses only the magnitude of the reflection coefficient and that is valid under the Newtonian regimen has been proposed by some authors, but the obtained viscosity values do not match conventional viscometry measurements. In this work, a mode conversion measurement cell was used to measure glycerin viscosity as a function of temperature (15 to 25 degrees C) and corn syrup-water mixtures as a function of concentration (70 to 100 wt% of corn syrup). Tests were carried out at 1 MHz. A novel signal processing technique that calculates the reflection coefficient magnitude in a frequency band, instead of a single frequency, was studied. The effects of the bandwidth on magnitude and viscosity were analyzed and the results were compared with the values predicted by the Newtonian liquid model. The frequency band technique improved the magnitude results. The obtained viscosity values came close to those measured by the rotational viscometer with percentage errors up to 14%, whereas errors up to 96% were found for the single frequency method.

Computational method to determine reflected ultrasonic signals from arbitrary-geometry targets.

A computational method based on the impulse response and on the discrete representation computational concept is proposed for the determination of the echo responses from arbitrary-geometry targets. It is supposed that each point of the transducer aperture can be considered as a source radiating hemispherical waves to the reflector. The local interaction with each of the hemispherical waves at the reflector surface can be modeled as a plane wave impinging on a planar surface, using the respective reflection coefficient. The method is valid for all field regions and can be performed for any excitation waveform radiated from an arbitrary acoustic aperture. The effects of target geometry, position, and material on both the amplitude and the shape of the echo response are studied. The model is compared with experimental results obtained using broadband transducers together with plane and cylindrical concave rectangular reflectors (aluminum, brass, and acrylic), as well as a circular cavity placed on a plane surface, in a water medium. The method can predict the measured echoes accurately. This paper shows an improved approach of the method, considering the reflection coefficient for all incident hemispherical waves arriving at each point of the target surface.

Finite element analysis and optimization of a single-axis acoustic levitator.

A finite element analysis and a parametric optimization of single-axis acoustic levitators are presented. The finite element method is used to simulate a levitator consisting of a Langevin ultrasonic transducer with a plane radiating surface and a plane reflector. The transducer electrical impedance, the transducer face displacement, and the acoustic radiation potential that acts on small spheres are determined by the finite element method. The numerical electrical impedance is compared with that acquired experimentally by an impedance analyzer, and the predicted displacement is compared with that obtained by a fiber-optic vibration sensor. The numerical acoustic radiation potential is verified experimentally by placing small spheres in the levitator. The same procedure is used to optimize a levitator consisting of a curved reflector and a concave-faced transducer. The numerical results show that the acoustic radiation force in the new levitator is enhanced 604 times compared with the levitator consisting of a plane transducer and a plane reflector. The optimized levitator is able to levitate 3, 2.5-mm diameter steel spheres with a power consumption of only 0.9 W.

Modeling of functionally graded piezoelectric ultrasonic transducers.

The application of functionally graded material (FGM) concept to piezoelectric transducers allows the design of composite transducers without interfaces, due to the continuous change of property values. Thus, large improvements can be achieved, as reduction of stress concentration, increasing of bonding strength, and bandwidth. This work proposes to design and to model FGM piezoelectric transducers and to compare their performance with non-FGM ones. Analytical and finite element (FE) modeling of FGM piezoelectric transducers radiating a plane pressure wave in fluid medium are developed and their results are compared. The ANSYS software is used for the FE modeling. The analytical model is based on FGM-equivalent acoustic transmission-line model, which is implemented using MATLAB software. Two cases are considered: (i) the transducer emits a pressure wave in water and it is composed of a graded piezoceramic disk, and backing and matching layers made of homogeneous materials; (ii) the transducer has no backing and matching layer; in this case, no external load is simulated. Time and frequency pressure responses are obtained through a transient analysis. The material properties are graded along thickness direction. Linear and exponential gradation functions are implemented to illustrate the influence of gradation on the transducer pressure response, electrical impedance, and resonance frequencies.

Viscosity measurement of Newtonian liquids using the complex reflection coefficient.

This work presents the implementation of the ultrasonic shear reflectance method for viscosity measurement of Newtonian liquids using wave mode conversion from longitudinal to shear waves and vice versa. The method is based on the measurement of the complex reflection coefficient (magnitude and phase) at a solid-liquid interface. The implemented measurement cell is composed of an ultrasonic transducer, a water buffer, an aluminum prism, a PMMA buffer rod, and a sample chamber. Viscosity measurements were made in the range from 1 to 3.5 MHz for olive oil and for automotive oils (SAE 40, 90, and 250) at 15 and 22.5 degrees C, respectively. Moreover, olive oil and corn oil measurements were conducted in the range from 15 to 30 degrees C at 3.5 and 2.25 MHz, respectively. The ultrasonic measurements, in the case of the less viscous liquids, agree with the results provided by a rotational viscometer, showing Newtonian behavior. In the case of the more viscous liquids, a significant difference was obtained, showing a clear non-Newtonian behavior that cannot be described by the Kelvin-Voigt model.

Ultrasonic density measurement cell design and simulation of non-ideal effects.

This paper presents a theoretical analysis of a density measurement cell using an unidimensional model composed by acoustic and electroacoustic transmission lines in order to simulate non-ideal effects. The model is implemented using matrix operations, and is used to design the cell considering its geometry, materials used in sensor assembly, range of liquid sample properties and signal analysis techniques. The sensor performance in non-ideal conditions is studied, considering the thicknesses of adhesive and metallization layers, and the effect of residue of liquid sample which can impregnate on the sample chamber surfaces. These layers are taken into account in the model, and their effects are compensated to reduce the error on density measurement. The results show the contribution of residue layer thickness to density error and its behavior when two signal analysis methods are used.