Rectangular Piezoelectric Transducers Research Articles

Theoretical and experimental investigation of Lamb waves excited by partially debonded rectangular piezoelectric transducers

The paper proposes a new hybrid approach technique to simulate acousto-ultrasonic wave excitation and propagation due to operation of the partially debonded piezoelectric transducer attached to a plate-like structure. The semi-analytical boundary integral equation method is applied to calculate guided waves propagation in the unbounded structures and to separate different guided waves in the piezo-induced wave-fields. The obtained model is verified experimentally using the scanning laser Doppler vibrometry. Eigenfrequencies are calculated and analysed for various sizes of the transducer and for different bonding conditions between the transducer and the waveguide. The impact of the transducer’s height, size and debonding area on symmetric and antisymmetric Lamb waves excitation is analysed. The paper demonstrates that one-sided debonding of the transducer exerts intense influence on the distribution of the wave energy among the excited Lamb wave modes, while center debonding has a sizable impact only at relatively high frequencies.

A three-dimensional analysis of natural vibrations of rectangular piezoelectric transducers

A computer program for the three-dimensional analysis of natural vibrations of rectangular piezoelectric transducers of arbitrary dimensions has been developed on the basis of the finite-element method (FEM). The analysis of natural vibrations of transducers was performed for several first modes. The results make it possible to substantiate the choice of the optimal geometric dimensions for a rectangular piezoelectric transducer that operates in the first mode.

Fluid property evaluation by using transversal effects of piezoelectric transducer

In this paper, we describe a highly sensitive device that utilizes the transversal effect of rectangular piezoelectric transducer to measure the viscosity of water-based and ionic MFs. This device could monitor the differences in MF types and also have overcome the design limitations of the conventional viscometer for measurements in external magnetic fields.

The directivity pattern of an interferometer for measuring thermal acoustic radiation

The directivity patterns of a pair of piezoelectric transducers for measuring the spatial correlation function of sound pressures produced by sources of thermal acoustic radiation in the megahertz frequency range are calculated. Sources in the form of a heated plane or strip are considered. The signal detection by two circular or rectangular piezoelectric transducers and by focusing transducers is studied. It is demonstrated that, for measuring the correlation function, the piezoelectric transducers must partially overlap. To determine the directivity pattern with a strong dependence on the distance between the heated object and the pair of piezoelectric transducers, focusing piezoelectric transducers should be used. The results obtained offer possibilities for a noninvasive measurement of the absorption coefficient of a medium and also for the realization of the previously proposed [20] passive acoustic thermotomograph, which does not use a priori information on the absorption coefficient of the medium.

Measurements of pulsed velocity field generated by circular and rectangular piezoelectric transducers directly coupled to a block of aluminum

A new computational tool Discrete Representation Acoustic Modelling/Solid (DREAM/S), has been developed for computing the displacement field generated by a pulse-excited transducer, directly coupled to an elastic half-space. It allows the separate determination of different components (shear, compressional, radial, axial) of displacement. This method is based on the spatial pulse response approach and gives directly the transient time-domain field. DREAM/S has already been validated mathematically in regard to analytic and exact methods. The main objective of this paper is to show the experiments performed in order to validate this software. First, a brief presentation of DREAM/S and elementary examples of computing are given. Afterward, the experimental results obtained in the case of circular and rectangular transducers directly coupled to a block of aluminum are presented and compared with the ones obtained by DREAM/S. This comparison displays a good agreement and confirms the high precision of this approach. In order to facilitate the interpretation of multichannel records, including the direct and edge waves and the reverberations from the borders of the model, both computed and recorded signals are displayed in specific format, usually applied in the geophysical imaging.

A piezoelectric pseudoshear multilayer actuator

A type of high strain piezoelectric ceramic actuator, namely, pseudoshear multilayer actuator, is described. In this structure, a stack of prepoled rectangular piezoelectric transducer ceramic sheets are conductively bonded at alternate ends, while the bottom layer bonded on a fixed base. When driven, alternate layers elongate or shrink in the same direction through converse piezoelectric effect, which results in the actuator structure developing a strong shear motion about the face perpendicular to the bonding direction. Experimental results indicate that more than 50 μm displacement can be achieved from the top layer for an actuator consisting of 18 layers with dimensions of 25.57 mm×4.02 mm×0.51 mm (1×w×t). By reducing ceramic sheet thickness and using more layers, even large displacement can be obtained, and driving voltage can also be reduced while keeping the same field level. Nonlinear piezoelectric response under high driving field further enhances the displacement level.

New implanted doppler sensors for the assessment of the main fetal hemodynamics

If the fetal Doppler examination during human pregnancies provides useful information to the obstetrician, it does not allow us to collect all the biological and haemodynamic data required to understand the physiopathological mechanisms involved in the development of intrauterine growth retardation (IUGR) and hypoxia. With the animal model, it is possible to have access to the blood pressure, the blood velocity and volume, to collect blood sampling and to perform pharmacological tests, or to simulate some human pathology. Several studies have been already carried out on lamb fetuses using electromagnetic flowmeters placed around the cord and catheters, with pressure sensors placed inside the fetal aorta. Most of the time only the umbilical flow was assessed on the fetal side. The aim of the present work was to develop a new Doppler system able to monitor in real time and simultaneously, the fetal cerebral and the umbilical arterial flows as well as the uterine circulation. New flat Doppler probes have been designed, to be implanted on the fetus and on the mother, which makes possible the atraumatic assessment of fetal and maternal flows during approximately 20 days. The 4-MHz CW Doppler probe consists of two rectangular piezoelectric transducers of 13-mm wide, preoriented at 45° from the surface of the probe, placed in a 6-mm-high plastic case in which small holes are made to sew the probe on the fetal skin. The sensors are fixed on the fetal skin, facing the umbilical cord, the fetal cerebral arteries and in front of the uterine arteries. The output wires and the fetal catheter connectors are stowed in a pocket fixed on the back of the ewe, and at each measurement session the fetus is connected during one or two hours (without any anesthesia) to the Doppler and pressure system. From the Doppler waveforms we can calculate the blood flow volume and the vascular resistance changes in the area supplied by the vessel (placenta, brain) and the fetal heart rate. This system has been tested on normal gestation, during simulated fetal hypoxia and pharmacological treatments.