Ultrasonic sensor for the presence of oily contaminants in water

The determination of the complex reflection coefficient of ultrasonic shear-waves at the solid-liquid interface is a technique employed for the measurement of the viscoelastic properties of liquids. An interesting property of the measurement technique is the very small penetration depth of the shear-waves into the liquid sample, which permits measurements with liquid films of some micrometers thick. This property, along with the adhesion of oily substances to surfaces, can be used for the detection of oily contaminants in water. In this work, the employment of the ultrasonic shear-wave reflection technique to the detection of oily contaminants in water is proposed and the theoretical and experimental concepts involved are discussed. Preliminary experimental results show the measurement technique can detect SAE 40 automotive oil in water in volume proportions less than 0.5%

Analysis of 1-3 piezocomposite and homogeneous piezoelectric rings for power ultrasonic transducers

Some power ultrasonic transducers, such as Tonpilz transducers, require high-power transmitting capability as well as broadband performance. Optimized vibrational modes can achieve these requirements. This work compares the resonant characteristics and the surface vibration modes between a homogeneous piezoelectric ring and a 1-3 piezocomposite ring, both used in power ultrasonic transducers. This is the first step in the design of power transducers. Analytical models and finite element results are validated by electrical impedance measurements and the surface acoustic spectroscopy method. Excellent agreement between theoretical and experimental results was obtained. Results show that using piezocomposite ceramics minimize superposition of undesirable modes and increase the bandwidth, as shown in sonograms

Nonlinear Dynamic Modeling of Langevin-Type Piezoelectric Transducers

Langevin transducers are employed in several applications, such as power ultrasound systems, naval hydrophones, and high-displacement actuators. Nonlinear effects can influence their performance, especially at high vibration amplitude levels. These nonlinear effects produce variations in the resonant frequency, harmonics of the excitation frequency, in addition to loss of symmetry in the frequency response and “frequency domain hysteresis”. In this context, this paper presents a simplified nonlinear dynamic model of power ultrasound transducers requiring only two parameters for simulating the most relevant nonlinear effects. One parameter reproduces the changes in the resonance frequency and the other introduces the dependence of the frequency response on the history of the system. The piezoelectric constitutive equations are extended by a linear dependence of the elastic constant on the mechanical displacement amplitude. For introducing the frequency hysteresis, the elastic constant is computed by combining the current value of the mechanical amplitude with the previous state amplitude. The model developed in this work is applied for predicting the dynamic responses of a 26 kHz ultrasonic transducer. The comparison of theoretical and experimental responses, obtained at several input voltages around the tuned frequency, shows a good agreement, indicating that the model can accurately describe the transducer nonlinear behavior.We would like to thank the research agencies: PEDECIBA and CSIC of Uruguay, FAPESP and CNPq from Brazil and ‘Ministerio de Economía y Competitividad’ of Spain (Projects: DPI2012-37466-C03-01 and PTQ-09-02-017691).We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Water-in-oil emulsions separation using an ultrasonic standing wave coalescence chamber.

The offshore extraction of crude oil produces stable water in oil emulsion. To separate this emulsion into oil and water phases, the oil/water interfacial film is commonly destroyed by the addition of chemical demulsifiers. The use of an ultrasonic standing wave force field could be an alternative to reduce the dosage of chemical demulsifiers in the coalescence process. In this work, an ultrasonic separator of water in crude oil emulsions is investigated through the use of a high frequency ultrasonic standing wave coalescence chamber. The coalescing chamber uses the acoustic radiation force to induce the coalescence of water droplets at the pressure nodes of a standing wave field. Due to temperature fluctuations, the excitation frequency is controlled to maintain the resonance in the coalescence chamber and the voltage amplitude is controlled to deliver a given acoustic power. Experimental tests using standardized emulsions of water in oil were carried out in a laboratory processing plant. The effects of ultrasound application, flow rate, initial water content, demulsifier dosage and chamber inlet temperature were analyzed. The results show that the use of the acoustic radiation force improves the emulsion separation in all the conditions analyzed, when compared with the gravitational separation technique

Application of one-bit time reversal technique to mechanical strain monitoring in plates

This paper presents the application of the one-bit\ud time reversal technique to a longitudinal strain sensor. The setup\ud consists of a pair of piezoelectric transducers bonded in the\ud extremities of a strip of aluminum plate. When the plate is\ud subjected to traction, time reversal focalization is performed, the\ud mismatch between the impulse response at initial and strained\ud levels causes loss in the focusing quality. The strain can be\ud evaluated by measuring either the time of flight shift or the\ud amplitude decrease in the focused signal. One-bit time reversal\ud can simplify the electronic device to perform the proposed\ud technique. In this work, the results using one-bit and normal time\ud reversal implementation were compared. Experiments were\ud performed using three different 2-2 piezocomposite transducers\ud pairs at 500, 1000 and 2250 kHz. The longitudinal strain was\ud applied up to 150 u- strain using a strain gauge as a reference.\ud The time reversal energy efficiency was used as a spectrum figure\ud of merit and obeys the sensitivity behavior. The one-bit time\ud reversal variation provided good focused signal for all\ud experiments and no significant loss in focus quality. Moreover,\ud every configuration showed a higher sensitivity than its normal\ud time reversal version, at least 10% depending on the transducer.\ud The one-bit technique reveals an important enhancement for the\ud method; it holds the natural advantage of being simpler and the\ud benefit of higher sensitivity.CNPq, FAPESP, and PETROBRAS/AN

Caracterización de emulsiones de agua y aceite por ultrasonidos

[ES] En este trabajo se presentan resultados de medidas de pequeñas concentraciones de agua en aceite lubricante utilizando una célula de medida por ultrasonidos. Esta célula es compuesta por un emisor piezocerámico (5 y 10 MHz), y un receptor de PVDF de grande apertura, que elimina efectos de difracción. A través de la medida de la velocidad de propagación, se puede diferenciar cantidades de agua en aceite con una resolución de un 0,2% en volumen, en el rango comprendido entre 0 y 5%. El máximo error en la medida de la velocidad de propagación es 0,003% a través de la utilización de una técnica de procesamiento digital de señales precisa.[EN] This paper presents an ultrasonic method to measure small concentrations of water in lubricating oil. It uses an ultrasonic measurement cell composed by a piezoceramic emitter (5 and 10 MHz), and a PVDF receiver of large aperture that eliminates the effect of diffraction. The concentrations of water of the samples were in the range of 0 to 5% in volume, and the results showed that these low concentrations can be discriminated within a resolution of 0.2% in the studied range. The maximun error obtained in the measurement of the propagation velocity is 0.003% by using an accurate signal processing method.6 pp.-- PACS nr.: 43.35.Zc.-- Comunicación presentada en los siguientes congresos: II Congreso Iberoamericano de Acústica. XXXI Congreso Nacional de Acústica – TecniAcústica 2000. II Jornadas Iberoamericanas de Ultrasonidos. II Congreso Ibérico de Acústica. EAA Symposium on Architectural Acoustics (Madrid, 16-20 Octubre 2000). Publicado también en número especial de la Revista de Acústica, Vol. XXXI, año 2000.Peer reviewe

Acoustic beam modeling of ultrasonic transducers and arrays using the impulse response and the discrete representation methods

La respuesta al impulso del potencial de velocidad y los métodos de representación discreta se utilizaron para modelar el campo acústico irradiado por transductores y matrices ultrasónicos. El primer método se ocupa del cálculo de la respuesta exacta al impulso, en el que las soluciones solo son posibles para geometrías simples, como el pistón circular. El segundo método es una solución aproximada basada en la discretización de la apertura acústica en pequeñas áreas elementales, cada una de las cuales irradia una onda esférica. Mediante el uso de transductores circulares, que pueden considerarse pistones circulares, se llevaron a cabo muchas simulaciones comparando los métodos. Se analizó la relación entre el costo computacional y la precisión, estableciendo así los niveles de discretización temporal y espacial. Las simulaciones se realizaron utilizando el software Matlab y los resultados se compararon con mediciones experimentales que mostraban una buena concordancia. Los resultados experimentales se obtuvieron mediante un sistema de escaneo. Se midió el campo acústico irradiado por un transductor circular de 1 MHz, así como una matriz de 3,5 MHz de 16 elementos sumergidos en agua. El campo acústico irradiado por el arreglo fue simulado y medido con focalización en un radio de 30 mm con deflexiones de 0º y 20º.The impulse response of the velocity potential and the discrete representation methods were used in order to model the acoustic field radiated by ultrasonic transducers and arrays. The first method deals with the calculation of the exact impulse response, in which solutions are possible only for simple geometries, such as the circular piston. The second method is an approximated solution based on the discretization of the acoustic aperture in small elementary areas, each of them radiating a spherical wave. By using circular transducers, which can be considered circular pistons, many simulations comparing the methods were carried out. The relation between the computational cost and the precision was analyzed, thus establishing the time and space discretization levels. The simulations were made using the Matlab software and the results were compared to experimental measurements showing good agreement. The experimental results were obtained using a scanning system. The acoustic field radiated from a 1 MHz circular transducer was measured as well as a 3.5 MHz array of 16 elements both immersed in water. The acoustic field radiated by the array was simulated and measured with focalization on a radius of 30 mm with deflections of 0º and 20

Ultrasonic material characterization using large-aperture PVDF receivers

This work describes the use of a large-aperture PVDF receiver in the measurement of liquid density and composite material elastic constants. The density measurement of several liquids is obtained with accuracy of 0.2% using a conventional NDE emitter transducer and a 70-mm-diameter, 52-mu m P(VDF-TrFE) membrane with gold electrodes. The determination of the elastic constants is based on the phase velocity measurement. Diffraction can lead to errors around 1% in velocity measurement when using alternatively the conventional pair of ultrasonic transducers (1-MHz frequency and 19-mm-diameter) operating in through-transmission mode, separated by a distance of 100 mm. This effect is negligible when using a pair of 10-MHz, 19-mm-diameter transducers. Nevertheless, the dispersion at 10 MHz can result in errors of about 0.5%, when measuring the velocity in composite materials. The use of an 80-mm diameter, 52-mu m-thick PVDF membrane receiver practically eliminates the diffraction effects in phase velocity measurement. The elastic constants of a carbon fiber reinforced polymer were determined and compared with the values obtained by a tensile test. (C) 2009 Elsevier B. V. All rights reserved

Flexible linear array with curvature sensor

In this work a 2-MHz flexible transducer probe more compact and capable of being attached directly over the surface was developed. An extra curvature sensor based on strain gauge construction embedded in the same flexible polymer matrix of the transducer was developed. This sensor is used to measure the curvature of the unknown non-planar surface in an attempt to determine the correct position of the emitter/receiver ceramics during scanning, in order to give a focal delay time law. This avoids problems related to beam distortions, enhancing the sensitivity of the transducer

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.CNPqCAPESPetrobras/AN