Dominique Gross

Fabrication and characterization of wafer-bonded cMUT arrays dedicated to ultrasound-image-guided FUS

In this paper, the development of wafer-bonded cMUTs arrays, which will be implemented on a dual-mode probe dedicated to liposomes activation and high frequency imaging, is presented. The process flow is briefly described, and optical and electrical characterizations are reported. Then, experimental electro-acoustic tests confirming the expected performances of each array are presented and discussed.

Automatic Optimal Input Command for Linearization of cMUT Output by a Temporal Target

Capacitive micromachined ultrasonic transducers (cMUTs) are a promising alternative to the piezoelectric transducer. However, their native nonlinear behavior is a limitation for their use in medical ultrasound applications. Several methods based on the pre-compensation of a preselected input voltage have been proposed to cancel out the harmonic components generated. Unfortunately, these existing pre-compensation methods have two major flaws. The first is that the pre-compensation procedure is not generally automatic, and the second is that they can only reduce the second harmonic component. This can, therefore, limit their use for some imaging methods, which require a broader bandwidth, e.g., to receive the third harmonic component. In this study, we generalized the presetting methods to reduce all nonlinearities in the cMUT output. Our automatic pre-compensation method can work whatever the excitation waveform. The precompensation method is based on the nonlinear modeling of harmonic components from a Volterra decomposition in which the parameters are evaluated by using a Nelder-Mead algorithm. To validate the feasibility of this approach, the method was applied to an element of a linear array with several types of excitation often encountered in encoded ultrasound imaging. The results showed that the nonlinear components were reduced by up to 21.2 dB.

Ultrasound pre-clinical platform for diagnosis and targeted therapy

This study reports on the development and the first experimental assessment of a custom ultrasound pre-clinical platform developed for diagnosis and targeted therapy. Moreover, a specific dual-mode probe developed for our application is based on cMUT technology. The platform combines two operating modes: high frequency imaging in the 15-20 MHz frequency range and low frequency focused ultrasound at 1 MHz for local therapy.

Dual mode cMUTs fabricated with LPCVD sacrificial release process

This paper aims to develop an integrated dual mode ultrasonic transducers (based on cMUTs technology) for applications of targeted drug delivery dedicated to small animal experiments. Two functions are designed on the same transducer: one for high frequency imaging and the other for thermal activation of liposomes. Tests and performances evaluation are reported.

Electroacoustic response of cMUT-based linear arrays: Role of inactive elements

This paper presents a strategy to model a full cMUT-based linear array. All elements of the array, active and passive, are taken into account. Development focuses mainly on the introduction in our model of the longitudinal dispersive wave, which propagates only in the fluid and at the surface of arrays. Simulations are compared with experiments to assess model validity.

Control and monitoring of dynamic collapse event in cMUTs arrays for therapeutic applications

In this paper, the displacement behavior of the cMUT is analyzed thanks to a time domain model. The nonlinear components in the response spectrum with different excitation parameters are compared. A method based on the addition of a series impedance to the cMUT, which permits to decrease the harmonic components and enhance the maximum displacement swept by the diaphragm, is applied in a therapeutic context. The benefits of such a method are pointed out and discussed. After that, experimental measurements are performed to confirm these advantages, and discussed.

Assessment of imaging capability of 16×16 2D cMUT transducer arrays

Among the different transducers technologies suitable for medical imaging, the cMUTs are known to offer an attractive alternative to conventional piezoelectric ones, with features including wider bandwidth, wider directivity, and readiness for integration with electronics. This last point is of particular interest for 2D matrix arrays. Here, we present the acoustic and imaging performances of these devices initially dedicated for external cardiac imaging (frequency range [1.5–4 MHz]).

Modeling a CMUT covered with passivation layer by means of boundary element method

This paper presents the development of a model to predict the response of CMUTs arrays covered by a viscoelastic material layer, i.e. the passivation layer. Theoretical approach developed here combines two models: on one side a CMUT model based on boundary element method and, on the other side a model of propagation in elastic media for computing the Green function associated to the semi-infinite loading medium. A first confrontation between theory and experiments is presented through a set of electrical impedance measurements obtained with one prototype of CMUT array element. Several loading media with variable viscoelastic properties were tested. It results that for media which rheological behavior obeys to Newtonian model, even in the MHz frequency range, the model validation was achieved. For the others which rheological behavior is poorly understood, it was necessary to implement more complex models like Kelvin-Voigt or Maxwell, in order to improve concordance between theory and experiments.