M. Wilm

A full 3D plane-wave-expansion model for 1-3 piezoelectric composite structures

The plane-wave-expansion (PWE) approach dedicated to the simulation of periodic devices has been extended to 1-3 connectivity piezoelectric composite structures. The case of simple but actual piezoelectric composite structures is addressed, taking piezoelectricity, acoustic losses, and electrical excitation conditions rigorously into account. The material distribution is represented by using a bidimensional Fourier series and the electromechanical response is simulated using a Bloch-Floquet expansion together with the Fahmy-Adler formulation of the Christoffel problem. Application of the model to 1-3 connectivity piezoelectric composites is reported and compared to previously published analyses of this problem.

Finite-element analysis of periodic piezoelectric transducers

The need for optimized acoustic transducers for the development of high-quality imaging probes requires efficient simulation tools providing reliable descriptions of the behavior of real devices. The purpose of this work is the implementation of a finite-element model for the simulation of periodic transducer arrays. By using the assumption of harmonic excitation, the harmonic admittance of the studied structure can be derived. It is then shown how the mutual admittance is deduced from this feature, allowing one to estimate the amount of cross-talk effects for a given periodic transducer. Computation results are reported for standard linear acoustic probes, 2-2 (one-dimensional periodic) and 1-3 (two-dimensional periodic) piezocomposite materials. In the case of 2-2 connectivity composites, a comparison between nonperiodic and periodic computations of the mutual admittance is conducted, from which the minimum number of periods for which periodic computations can be trustfully considered can be estimated.

Periodic finite element/boundary element modeling of capacitive micromachined ultrasonic transducers

The possibility to excite and detect acoustic waves in fluids using capacitive transducers built on silicon using surface micromachining offers attractive opportunities in the manufacturing of high quality low cost imaging probes. As in the case of standard probe transducers, simulation codes are required to accurately design such devices. The periodic structures extensively used for these capacitive transducers has to be accounted for. In this work, a two-dimensional finite element analysis of capacitive micromachined ultrasonic transducers (cMUT) is proposed, taking into account periodicity and radiation in fluids. The convergence of the calculation is verified using different computation approaches. It is then shown that the periodic computations provide a rapid and precise analysis of the cMUT compared to non periodic calculations. The mutual displacements are deduced from the periodic harmonic calculation, providing an efficient estimation of cross-talk phenomena arising for cMUT radiating in water. ...

A FEA/BEM approach to simulate complex electrode structures devoted to guided elastic wave periodic transducers

A modelling approach able to address complicated SAW periodic structures with non homogeneous geometry has been developed and implemented. It is based on the combination of finite element analysis and a boundary element method. Validation of the computation is reported. An example of simulation of a passivated STW resonator is used for theory/experiment assessment.

Theoretical analysis of damping effects of guided elastic waves at solid/fluid interfaces

A theoretical description of ideal and viscous fluid media is proposed to address the problem of modeling damping effects of surface acoustic waves and more generally of any guided elastic waves at the interface between viscous fluids and solids. It is based on the Fahmy-Adler eigenvalue representation of the elastic propagation problem, adapted to provide Green’s function of the considered media. It takes advantage of previous efforts developed to numerically stabilize Green’s-function computation process. This function is used to compute a harmonic admittance according to the Blotekjaer approach. The influence of acoustic radiation and viscosity effects on different kinds of waves excited on various substrates is reported and discussed.

Fast FEM/BEM simulation of SAW devices via asymptotic waveform evaluation

The finite element method/boundary element method (FEM/BEM) computation model applied to surface acoustic wave devices requires the solution of a large linear system for each frequency point. An asymptotic waveform evaluation technique is used to obtain an approximate solution of the linear system that is valid over a large frequency bandwidth. The approximate solution was shown to be very accurate and vastly reduces the computation time.

A novel surface wave transducer based on periodically poled piezoelectric domain

A surface wave transducer using a thin ferroelectric film deposited atop silicon and periodically poled has been theoretically analysed. Fundamental guiding properties of such devices are extracted from numerical computations. A low frequency validation of the proposed principle is reported using a periodically poled PZT plate glued on a silicon wafer.

Periodic arrays of transducers built using sand blasting and ultrasound micromachining techniques for the fabrication of piezocomposite materials

Two technological approaches devoted to the collective manufacture of piezocomposite materials are investigated. Arrays of PZT pillars are built using sand blasting and ultrasound micromachining in order to manufacture 2-2 or 1-3 connectivity piezocomposites. Different structures built with both approaches are presented. Their efficiency is discussed in conclusion.

Simulation of cMUT radiating in water using a mixed finite element/boundary element approach

A 2D finite element analysis of cMUT is proposed, taking into account periodicity and radiation in fluids. The convergence of the calculation is verified using non periodic computations. The capability of cMUT radiating in water to generate low velocity wave guided at the fluid/silicon interface is theoretically pointed out.

Characterization and prediction of transverse plate resonators built using mixed strip and groove gratings

Two approaches are developed to model accurately the physical characteristics of plate mode devices, and more specifically of resonators. They are respectively based on pure finite element computation and on mixed boundary integral methods and finite element analysis (BIM/FEA). The main parameters of wave propagation (velocity, coupling factor, reflection, and so on) can be estimated, considering an infinite periodic structure and using the harmonic admittance, and can be inserted in a mixed matrix model to simulate the electrical response of devices. A comparison between theory and experiments is reported for transverse plate resonators built using mixed strip and groove gratings.