Quantification and mitigation of the effect of resynchronization errors in ultrasound sensor network for passive imaging in elastic plates.

The problem of signal desynchronization in passive imaging based on noise correlation for defect detection in elastic plates is investigated. Although a post-processing resynchronization process relying on the symmetry of noise correlation functions can be applied prior to the imaging algorithm, perfect synchronization might not be achieved experimentally. Effect of such residual synchronization errors on the defect detection performance is quantified as a function of their probability density function.

Electrical and Optical Characterization of SAW Sensors Coated with Parylene C and Their Analysis Using the Coupling-of-Modes (COM) Theory.

In this paper, we present how complementary characterization techniques, such as electrical measurements with a vector network analyzer (VNA), optical measurements with a laser Doppler vibrometer (LDV), and numerical simulations with the finite element method, coupled with spectral domain analysis (FEMSDA), allow us to independently access different properties of a SAW device and fully characterize its operation using the coupling-of-modes theory (COM). A set of chemical SAW sensors coated with parylene C layers of different thicknesses (1, 1.5, and 2 µm) and an uncoated sensor were used as test samples.

Dispersion of surface acoustic waves in thin films at extreme wavelength-to-thickness ratios.

Surface acoustic waves (SAWs) are sensitive to the presence of a layer on the surface of a material, even if this layer is extremely thin compared to their wavelengths. Given the very slow propagation velocities of SAWs compared to electromagnetic waves, their wavelengths are on the order of 40 μm for acoustic frequencies on the order of 100 MHz. However, it has been shown that these waves are dispersive for coatings whose thicknesses are more than 1000 times smaller than their wavelength.

Development of a Broadband (100-240 MHz) Surface Acoustic Wave Emitter Devoted to the Non-Destructive Characterization of Sub-Micrometric Thin Films.

In the ultrasonic non-destructive evaluation of thin films, it is essential to have ultrasonic transducers that are able to generate surface acoustic waves (SAW) of suitably high frequencies in a wide frequency range of between ten and several hundred megahertz. If the characterization is carried out with the transducer in contact with the sample, it is also necessary that the transducers provide a high level of mechanical displacement (>100 s pm). This level allows the wave to cross the transducer−sample interface and propagate over the distance of a few millimeters on the sample and be properly detected.

Effect of Partial Ba Substitutions on the Crystallization of SrTiSiO (STS) Glass-Ceramics and on the Generation of a SAW Signal at High Temperatures.

Because of their characteristics, including a d of 10-15 pC/N and high stability up to temperatures over 1000 °C, polar glass-ceramics containing fresnoite crystals can be regarded as highly effective materials for applications requiring piezoelectricity at high temperatures. In the present paper we investigate barium substitutions in an Sr-fresnoite (STS) glass-ceramic. Two aspects are studied: first, the effect of the substitution on the preferential orientation of the crystallization, and second, the ability of the glass-ceramics to generate and propagate surface acoustic waves (SAW) at high temperatures.

Pump-probe localization technique of varying solid contacts.

A baseline-free defect localization method in thin plates is proposed and tested. In this proof-of-concept work, a steel ball pressed against an aluminum plate is used to mimic a surface contact defect. The technique takes benefit of a repetitive nonlinear pump-probe interaction with a backpropagation imaging algorithm.

A micro-transducer matrix design for the detection of flexural guided waves.

In this paper, a new approach is proposed for the detection of ultrasonic guided waves using a LiNbO single crystal-based micro-transducer matrix. This matrix was designed, manufactured, and then used to detect Lamb and Pochhammer-Chree guided waves in plate- and cylinder-like structures. This study highlights the identification of the first flexural mode F(1,1) in cylinders at low frequencies.

Spatially selective manipulation of cells with single-beam acoustical tweezers.

Acoustical tweezers open major prospects in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing since they are biocompatible, label-free and have the potential to exert forces several orders of magnitude larger than their optical counterpart at equivalent power. Yet, these perspectives have so far been hindered by the absence of spatial selectivity of existing acoustical tweezers - i.e.

Local damage detection by nonlinear coda wave interferometry combined with time reversal.

Coda wave interferometry (CWI) is a sensitive ultrasound method for the detection of weak and local changes in complex inhomogeneous media. In a nonlinear modification of the method discussed here, a high-frequency probe coda is compared to its replica obtained in the presence of low-frequency pumping. If, after the filtering-out of low frequencies, the coda signals are different, this is attributed to nonlinear pump-probe interaction induced by contact acoustical nonlinearity in the damaged zone.

3D FEM Analysis of High-Frequency AlN-Based PMUT Arrays on Cavity SOI.

This paper presents three-dimensional (3D) models of high-frequency piezoelectric micromachined ultrasonic transducers (PMUTs) based on the finite element method (FEM). These models are verified with fabricated aluminum nitride (AlN)-based PMUT arrays. The 3D numerical model consists of a sandwiched piezoelectric structure, a silicon passive layer, and a silicon substrate with a cavity.

An autonomous low-power management system for energy harvesting from a miniaturized spherical piezoelectric transducer.

A new spherical vibrational energy harvesting device with an additional low power management circuit for optimizing the power transfer from the mechanical vibrations to a storage capacitor is presented. The device is devoted to underwater wireless sensor network applications due to its broadband vibrational energy harvesting, sensing, and communicating facilities. The sensing node container consists of two acrylic glass (PMMA) half-spherical shells and a Pz26 piezoelectric ring clamped between the shells.

Folding a focalized acoustical vortex on a flat holographic transducer: Miniaturized selective acoustical tweezers.

Acoustical tweezers based on focalized acoustical vortices hold the promise of precise contactless manipulation of millimeter down to submicrometer particles, microorganisms, and cells with unprecedented combined selectivity and trapping force. Yet, the widespread dissemination of this technology has been hindered by severe limitations of current systems in terms of performance and/or miniaturization and integrability. Here, we unleash the potential of focalized acoustical vortices by developing the first flat, compact, paired single electrode focalized acoustical tweezers.

Non-destructive characterization of surfaces and thin coatings using a large-bandwidth interdigital transducer.

This paper deals with non-destructive testing of thin layer structures using Rayleigh-type waves over a broad frequency range (25-125 MHz). The dispersion phenomenon was used to characterize a layer-on-substrate-type sample comprising a thin layer of platinum 100 nm thick on a silicon substrate. The originality of this paper lies in the investigation of different ways of generating surface acoustic waves (SAWs) with large bandwidth interdigital transducers (IDTs) as well as the development of a measuring device to accurately estimate the SAW phase velocity.

Generation of broadband surface acoustic waves using a dual temporal-spatial chirp method.

Wideband surface acoustic wave (SAW) generation with a spatial chirp-based interdigital transducer was optimized for non-destructive characterization and testing of coatings and thin layers. The use of impulse temporal excitation (Dirac-type negative pulse) leads to a wide band emitter excitation but with significantly limited SAW output amplitudes due to the piezoelectric crystal breakdown voltage. This limitation can be circumvented by applying a temporal chirp excitation corresponding in terms of frequency band and duration to the spatial chirp transducer configuration.

[Transformation of cortical functional systems during the process of motor habit formation and disruption].

Specific cortical functional systems with synphasic and coherent activities were revealed in the left hemisphere as reflecting the motor program by means of the topical specifics. Diminishing of the activity synchronous character in the precentral and prefrontal areas and its increasing in the precentral and parietal inferior areas occurred in the course of motor automatization, i.e.

[Classical and current aspects of the formation of motor dominance in man].

In the paper, significance of driving phenomenon for formation of motor dominant is considered and experimentally corroborated with the aid of autocorrelation and spectral analysis of the working man's EEG. The A.A.