Cyril Meynier

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.

Piezocomposite and CMUT arrays assessment through in vitro imaging performances

Piezoelectric and capacitive micromachined ultrasound transducers (CMUT) are usually measured and compared in regards to acoustic and electro-acoustic performances. This paper is focused on the imaging performances of such transducers and propose a quantitative imaging assessment of B-mode images. In this purpose, fully integrated CMUT and piezocomposite-based probes were manufactured. Transducers were designed with close features (geometries, center frequency, interconnect and packaging) and plug on a clinical ultrasound system with a research interface. Major imaging performances (speckle to noise ratio, resolutions and contrast) of the probes are presented. Despite an environment dedicated to piezoelectric transducers, CMUT probe exhibits comparable image quality as compared to a state-of-the-art piezocomposite probe. Indeed, close resolutions are calculated, field of view is improved in phased-array imaging, and contrast is significantly improved.

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

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.

Performance assessment Of CMUTs in dual modality imaging/HIFU applications

In this paper, multi-element arrays based on cMUT and piezoelectric technologies, using the same geometry, have been realized. The first part of the paper is focused on comparing both in terms of imaging performances. The CMUT is shown to be lower in sensivity but better in terms of bandwidth and resolution. The second part of the paper investigates the ability of the CMUT array for HIFU applications. The dual imaging-HIFU capability of the cMUT array is demonstrated. This is a new feature of the CMUT technology, as piezoelectric transducers are designed with a trade-off between bandwidth and transduction efficiency.

pMUT for high intensity focused ultrasound

Capacitive ultrasonic tranducers, cMUTs rely on the electrostatic field between the membrane and a back plate for sensing andactuation. This is an excellent solution for small amplitudes. But the movement of the membrane is physically limited by the bottom plate (risk of collapse). Furthermore, pull-in and linearity considerations restrict the available range to about one percent of thegap. Piezoelectric micromachined ultrasonic transducers, pMUTs, on the other hand have no such restrictions. The excitation is basedon lateral contraction of a thin film of Lead Zirconate Titanate, PZT, deposited on top of the membrane. Then there is no need for abackplate, and the linear range is greatly increased. Therefore, pMUTs are ideally suited for applications demanding large excitationamplitude, such as high intensity focused ultrasound, HIFU. In this work, we present pMUTs designed for HIFU operation around 1MHz.

Micromachined probe performance assessment

In recent years, Capacitive Micromachined Ultrasound Transducer (CMUT) technology was widely investigated and functional prototypes have been released by several R&D teams. CMUT technology offers outstanding characteristics in acoustic, interconnect packaging capabilities or in integration features that are exciting criteria for new medical applications. We propose a full acoustic characterization report of a CMUT probe. A linear array was fully packaged with electronic preamplifier boards integrated. A complete acoustic characterization of the probe is then performed and presented. In a second phase, a linear probe with piezocomposite technology is realized. The conception is done in regard to the geometric characteristics and to the acoustic response of the micromachined probe. Then an electro‐acoustical benchmark CMUT / piezocomposite is realized in the closest conditions. Using a commercial ultrasound imaging platform, an image assessment is performed. The images are first analysed in a quantitative w...

5×128-Element array transducer for elevational motion consideration in strain imaging

Ultrasound is a widely used imaging modality, both for diagnosis and guidance of interventional procedures such as biopsies. Ultrasound imaging commonly provides 2D data, which can be a limitation for further data processing, since information like out-of-plane motion is inaccessible. In this study, a specific multi-row array transducer — developed for the elastography application — is presented. This prototype acquires series of three adjacent imaging planes over time and makes therefore possible to compute 2D strain images of the central plane, with consideration of out-of-plane motion.