Crosstalk reduction in a piezoelectric phononic plate induced by electrical boundary conditions: Application to multi-element transducers.

This paper proposes a method of passive electrical decoupling which aimed at found application in reducing the crosstalk phenomenon in multi-element ultrasonic transducers. A homogeneous piezoelectric plate, covered on one side by a 1D periodic arrangement of thin metallic electrodes and on the other side by a full electrode, is considered. Finite element analysis and experimental measurements are performed to obtain the dispersion curves and normal displacements at the surface of the structure. It is shown that applying inductive shunts at the electrodes, band gaps can be created in the first Brillouin zone, which can prevent from the establishment of the first thickness mode in the plate. In that way the mechanical inter-element coupling can be lowered. Thus, the acoustic radiation in water from one sector excited at the resonance frequency is found to be closer to that of a piston mode. The transposition of this principle to the situation of a transducer including a rear medium and a front matching layer confirms the possibility of reducing the inter-element coupling. However, the physical effects at the origin of this reduction are different from those inherent to the cutting of a piezocomposite ceramic as it is done in most probes available in the market. As a result, we show that taking advantage of the electrical boundary conditions upon the passive elements in a transducer gives real opportunities for crosstalk reduction that may be implemented in ultrasonic systems for imaging in the medical field and in NDT.

Modelling nonlinearity in piezoceramic transducers: From equations to nonlinear equivalent circuits.

Quadratic nonlinear equations of a piezoelectric element under the assumptions of 1D vibration and weak nonlinearity are derived by the perturbation theory. It is shown that the nonlinear response can be represented by controlled sources that are added to the classical hexapole used to model piezoelectric ultrasonic transducers. As a consequence, equivalent electrical circuits can be used to predict the nonlinear response of a transducer taking into account the acoustic loads on the rear and front faces. A generalisation of nonlinear equivalent electrical circuits to cases including passive layers and propagation media is then proposed. Experimental results, in terms of second harmonic generation, on a coupled resonator are compared to theoretical calculations from the proposed model.

Comparison of several methods to characterise the high frequency behaviour of piezoelectric ceramics for transducer applications

Thickness mode resonances in commercial piezoelectric ceramics have been characterised as a function of frequency by two methods. The first is based on a fit on the electrical impedance for the fundamental and the overtones. This method has been applied to a large number of PZT ceramic samples and frequency dependence for all the parameters is investigated, in particular for the piezoelectric coefficient e33. The second is based on the measurement of the mechanical displacement at the centre of the surface of a PZT ceramic disk. With a modified KLM scheme, this displacement is modelled. The dielectric, elastic and piezoelectric parameters are extracted and compared for the fundamental and the third overtone. The results are found to be in good agreement.