An Nguyen-Dinh

Specific Ultrasound Data Acquisition for Tissue Motion and Strain Estimation: Initial Results

Ultrasound applications such as elastography can benefit from 3-D data acquisition and processing. In this article, we describe a specific ultrasound probe, designed to acquire series of three adjacent imaging planes over time. This data acquisition makes it possible to consider the out-of-plane motion that can occur at the central plane during medium scanning, and is proposed with the aim of improving the results of strain imaging. In this first study, experiments were conducted on phantoms, and controlled axial and elevational displacements were applied to the probe using a motorized system. Radiofrequency ultrasound data were acquired at a 40-MHz sampling frequency with an Ultrasonix ultrasound scanner, and processed using a 3-D motion estimation method. For each of the 2-D regions of interest of the central plane in pre-compression data, a 3-D search was run to determine its corresponding version in post-compression data, with this search taking into account the region-of-interest deformation model chosen. The results obtained with the proposed ultrasound data acquisition and strain estimation were compared with results from a classic approach and illustrate the improvement produced by considering the mediums local displacements in elevation, with notably an increase in the mean correlation coefficients achieved.

Powering autonomous wireless sensors with miniaturized piezoelectric based energy harvesting devices for NDT applications

IoT (Internet of Things) is driving an intense research activity targeting novel consumer applications. It has also an industrial counterpart, where thousands of sensors can be connected together into a proprietary network, i.e. into a Wireless Sensor Network (WSN). Such Industrial WSN may exhibit various shapes for different kind of applications. It can indeed be used for Structure Health Monitoring (SHM) to survey bridges, railways, avionic or automotive structures, rotating machine maintenance prediction, it can also serve security purposes like fire forest detection, border security, etc. In this paper we presents the architecture of a miniaturized and low-frequency piezoelectric-based vibrational-energy harvesting device (PEH) and its advanced manufacturing process flow. This harvesting technique uses direct piezoelectric effect to transform mechanical vibrations into electrical power. Over the past decade, several MEMS architectures have been built and assessed to harvest such low frequency (50-75Hz) vibrations. MEMS based PEH use thin (<;5μm) and thick (<;50μm) piezoelectric films allowing a high degree of integration and miniaturization, but at low frequencies the amount of harvested energy is not enough to power sensing electronics which typically consumes 100μW in average during 200ms. To overcome this limitation, we have developed and optimized a thinning process that enable us to use ultra-thin bulk PZT material (<;20μm) and propose a performant and miniaturized PEH.

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.

Characterization of a thin piezoelectric material before integration into a cantilever-based mechanical energy harvester

This paper deals with advanced characterization approaches of thin piezoelectric materials enabling accurate modelling of low frequency (<;50Hz) bimorph-based cantilever beam. Such structures had been widely studied and actual devices using bulk PZT materials had exhibited the best FoM (Figure of Merit) compared to thin and thick piezoelectric films generally used in MEMS industry. Bulk piezoelectric cantilever beam are mostly assembled under serial bimorph topologies where the piezoelectric material is laminated around an inner shim material. The two PZT skins exhibit an individual thickness ranging from few tens to hundreds of micrometers according to the targeted application and its miniaturization requests. Designing such devices become a challenge and one needs FEM (finite element model) to properly define material thicknesses and overall piezoelectric energy harvester (PEH) geometries. Unfortunately, bulk piezoelectric material are characterized using thicker samples which provide results slightly different of the actual characteristics of thinned-bulk piezoelectric materials. We present here two approaches, one analytical and one numerical, to study the thin piezoelectric material layer relying on the electrical admittance analysis. By using these methods, the effective coefficients of thinned-bulk piezoelectric material are identified and compared with those of a thicker bulk material of the same composition. The set of parameters is then entered in a 3D FEM of the PZT layer, and the electrical admittance is calculated, showing a good agreement with the experimental measurements.

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.

High frequency row column addressed matrix array for volumetric ultrafast ultrasound imaging

Volumetric “ultrafast” imaging is one of the major trends in ultrasound imaging techniques. It indeed paves the way for novel modalities when combined with Doppler, elastography and contrast imaging [1]. Unfortunately, due to the complexity and the inherently unaffordable costs, fully populated matrix-based systems are facing to pricing problems that limit their commercial development. Recently, row-column addressed (RCA) matrix transducer approaches have been proposed to overcome both complexity and costs issues but in a limited frequency range, i.e. below 10MHz. However, there is also a tremendous need to deploy this solution to higher frequencies, typically 15MHz and above, mainly for brain functional ultrasound imaging investigation.

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.

1D multi-element CMUT arrays for ultrasound thermal therapy

Interstitial therapeutic ultrasound devices are a promising technology for performing thermal ablation in a wide variety of organs. In this study, the use of Capacitive Micromachined Ultrasound Transducers (CMUTs) for interstitial heating applications was investigated. CMUTs exhibit potential advantages for use in therapeutic ultrasound applications in comparison to standard piezo ultrasound transducer technologies as they have good characteristics in terms of miniaturization (cell size: few dozens of microns), bandwidth (several MHz) and high electro-acoustic efficiency. Two designs of CMUT arrays were studied: (1) a 1D 128-element planar-CMUT array originally dedicated to abdominal ultrasound imaging purposes (5 MHz, element size: 0.3 × 8.0 mm2); (2) a 12-element linear-array, 32.4-mm long and 0.8-mm wide, developed specifically for minimally-invasive interstitial therapeutic applications (6 MHz, element size: 2.7 × 0.8 mm2). Simulations were performed to evaluate the ability to generate thermal lesions...

Smart autonomous wireless acoustic sensors for aeronautical SHM applications

Ultrasound technologies are of great interest for aeronautical structure inspection. Mainly deployed through Phased Array (PA) ultrasonic transducer, ultrasound inspection is currently used as a complementary tool for the local examination of the structure to determine geometry, damage or composition of invisible flaws like cracks, delamination and corrosion. This approach cannot be easily automated since the access to the area of interest often requires to pass through the complex aeronautical structure. Moreover this approach relies on a high degree of human interaction, as the user often decides the spatial inspection sampling according to his intuition and experience of the structure composition and vulnerability. Structure Health Monitoring, namely SHM, overcomes these limitations by enabling rapid, automated, remote, and real-time monitoring of the structure to reduce operational costs and increase lifetime of structures. This inspection strategy gains its strength from the use of a large amount of individual embedded sensors with embedded intelligence (sensing, signal processing, communicating and storing relevant data in non-volatile memories) organized in dense network, a Neural Network. We present in this paper the developments of a novel autonomous wireless acoustic sensor node, including: a flat flexural acoustic sensor capable of working in transmit and receive, a custom vibrational piezoelectric energy harvesting device (PEH) charging a 0.5 Farad buffer supercapacitance through a commercial rectifying IC, an ARM based cortex M3 microprocessor driving digitization, signal processing, data storage and two ways RF communication. The main objective was to create a versatile hardware platform that can be embedded within the structure to monitor, and capable of hosting different acoustic inspection strategies.