Franck Teston

A multiscale model for array of capacitive micromachined ultrasonic transducers

A model is developed for studying the acoustic behavior of a cMUT array. This model is based on separate calculations of the terms describing the behavior of a single cMUT on one hand, and those corresponding to acoustic mutual coupling on the other hand. The terms are combined into an equivalent circuit with matrix terms which displays only one degree of freedom per cell. This approach allows the simulation of several dozen cMUTs considered individually with a very short computer time. A Finite Difference model is used for the simulation of an isolated cell radiating acoustic energy and the determination of its equivalent electromechanical circuit. It is shown for various mutual coupling situations that the coupling between cells can be correctly approximated using a very simple mutual impedance term. The model is compared with experimental results, using a set of different cMUT configurations. Experimental results were obtained with electrical impedancemetry and laser interferometry techniques performed in fluid immersion.

A polytyramine film for covalent immobilization of oligonucleotides and hybridization

Abstract The electrooxidation of 4-hydroxyphenylethylamine in perchloric acid gives thick polymer films presenting one reactive amine group per moiety. Polytyramine (PTyr) film structure was determined by several techniques (SEM, EQCM, XPS, FT-IR). Oligonucleotides bearing a phosphate terminal function were immobilized on these particularly reactive PTyr films via a phosphoramidate covalent bond, yielding a high surface concentration of bound oligonucleotides. A washing protocol was set up to discriminate adsorption from real covalent grafting. Preliminary measurements showed a high hybridization capacity of probes-modified PTyr films with good discrimination properties between native and mismatches containing sequences.

Investigation of cross-coupling in 1-3 piezocomposite arrays

Plate waves inside the piezoelectric layer are much involved in the element cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using a network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S/sub 0/ mode is responsible for the inter-element coupling, whereas the S/sub 3/ mode widens the effective width of the excited element.

Fast time-domain modeling of fluid-coupled cMUT cells: from the single cell to the 1-D linear array element

We report a fast time-domain model of fluid-coupled cMUTs developed to predict the transient response-i.e., the impulse pressure response-of an element of a linear 1-D array. Mechanical equations of the cMUT diaphragm are solved with 2-D finite-difference schemes. The time-domain solving method is a fourth-order Runge-Kutta algorithm. The model takes into account the electrostatic nonlinearity and the contact with the bottom electrode when the membrane is collapsed. Mutual acoustic coupling between cells is introduced through the numerical implementation of analytical solutions of the impulse diffraction theory established in the case of acoustic sources with rectangular geometry. Processing times are very short: they vary from a few minutes for a single cell to a maximum of 30 min for one element of an array. After a description of the model, the impact of the nonlinearity and the pull-in/pull-out phenomena on the dynamic behavior of the cMUT diaphragm is discussed. Experimental results of mechanical displacements obtained by interferometric measurements and the acoustic pressure field are compared with simulations. Different excitation signals-high-frequency bandwidth pulses and toneburst excitations of varying central frequency-were chosen to compare theory with experimental results.

Characterization of cMUT by Dynamic Holography Microscopy

The comparison of numerical simulations to real cMUT behavior is essential to assess and optimize the process. For a complete characterization multiple devices (FIB, SEM, impedancemetry, laser interferometry, ...) are needed. In this context, we propose to use a full-field measurement device, a Digital Holography Microscopy (DHM Lynceetec®), which acquires static and dynamic in-plane and out-of-plane information of membranes population in a single acquisition and then provides most of required parameters. This paper presents the principle of this device, its performances comparing to other ones and its limits.

A strategy to predict and reduce baffle effects in linear array of CMUTs

This paper presents a cMUT array model based on matrix formulation like for the theory of linear systems. The model is compared with experimental data from which the baffle effect phenomenon in cMUT arrays is clearly identified. We propose to use the eigen-mode decomposition of linear matrices to understand and interpret origins of these phenomena. The impact of normal modes on the radiation directivity of cMUT array is clearly analyzed. The role of some geometric parameters on the baffle effect is studied too.

P2P-8 Characterization Standard of CMUT Devices Based on Electrical Impedance Measurements

A procedure for an electrical impedance characterization standard in air of CMUTs was reported. The electromechanical coupling factor was calculated by the low and high frequency capacity and the resonance and antiresonance frequencies measurements. The CMUT will be able to analyze and compared in terms of effective spring and mass with 1D model. The 1D model described the general behavior of the CMUT quite well, as long as first resonance/antiresonance mode and tensions below collapse were concerned

P2P-9 Collective Behavior of cMUT Cells for the Prediction of Electroacoustic Response and Directivity Pattern

This paper describes the development of numerical model of a cMUT array element. The array is modeled in the same way than piezoelectric plates, i.e. using an equivalent linear matrix transfer. Radiation conditions of collective cMUT are discussed, in the baffle plane and far from the baffle. Finally, example of pulse is given and compared with experimental results

Non-linear dynamic response of cMUTs population: modeling and characterization

This paper presents a time domain model for simulating cMUT in fluid. Non linearity is taking into account and the collapse / snapback phenomena are modeled with a ¿thrust¿ model. Confrontation with another simulation tool is performed and comparison with experimental results is done.

P4M-5 Accurate Assessment of CMUT Devices Through Precise Electrical Impedance Measurement in Air

This paper reports a technique to exploit results from electrical impedance measurement of cMUT devices in air. An analytical ID model has been used as a fitting function. The accuracy of this model has been theoretically analysed.