Lithium Niobate Micro-transducers matrix design

In this work, a two-dimensional (2D) Lithium Niobate (LiNbO3) 36°Y-cut micro-transducers (μTs) matrix design is presented. Two main steps define the fabrication process: electrode deposition and photolithography. These steps are preceded by the optical mask conception, which defines the 2D matrix pattern. In contrary to the one element case, this μTs matrix allows to automatically scan a desired structure in real time. The μTs matrix is characterized using an impedance analyzer. Furthermore, the experimental tests carried out in order to demonstrate the matrix functionality at low frequencies [200 - 800] kHz are presented

Distribution maps of vegetation alliances in Europe

Aim: The first comprehensive checklist of European phytosociological alliances, orders and classes (EuroVegChecklist) was published by Mucina et al. (2016, Applied Vegetation Science, 19 (Suppl. 1), 3–264). However, this checklist did not contain detailed information on the distribution of individual vegetation types. Here we provide the first maps of all alliances in Europe. Location: Europe, Greenland, Canary Islands, Madeira, Azores, Cyprus and the Caucasus countries. Methods: We collected data on the occurrence of phytosociological alliances in European countries and regions from literature and vegetation-plot databases. We interpreted and complemented these data using the expert knowledge of an international team of vegetation scientists and matched all the previously reported alliance names and concepts with those of the EuroVegChecklist. We then mapped the occurrence of the EuroVegChecklist alliances in 82 territorial units corresponding to countries, large islands, archipelagos and peninsulas. We subdivided the mainland parts of large or biogeographically heterogeneous countries based on the European biogeographical regions. Specialized alliances of coastal habitats were mapped only for the coastal section of each territorial unit. Results: Distribution maps were prepared for 1,105 alliances of vascular-plant dominated vegetation reported in the EuroVegChecklist. For each territorial unit, three levels of occurrence probability were plotted on the maps: (a) verified occurrence; (b) uncertain occurrence; and (c) absence. The maps of individual alliances were complemented by summary maps of the number of alliances and the alliance–area relationship. Distribution data are also provided in a spreadsheet. Conclusions: The new map series represents the first attempt to characterize the distribution of all vegetation types at the alliance level across Europe. There are still many knowledge gaps, partly due to a lack of data for some regions and partly due to uncertainties in the definition of some alliances. The maps presented here provide a basis for future research aimed at filling these gaps

Caractérisation des écoulements liquides par méthode de conjugaison de phase paramétrique des ondes ultrasonores

The object of this work is the investigation of parametrically phase conjugate waves propagation in moving media and the demonstration of their possible applications for liquid flow velocimetry. The investigation of nonlinear effects accompanying the propagation and interaction of phase conjugate waves in moving media such as higher harmonics generation and Brillouin scattering is made. A possibility of application of these effects for precision improvement of conventional acoustic systems of flow velocimetry is considered. It is shown that the phase synchronization principle for cascade generation of higher harmonics is still valid in moving media which allows to improve the sensitivity of measurement proportionally to the number of used harmonic. It is also shown that the phase shift of Stokes component of differential frequency generated in moving media by Brillouin scattering of phase conjugate wave with the reference one corresponds to the one of the phase conjugate wave. The effects of higher harmonics generation and Brillouin scattering can be used simultaneously to improve the sensitivity and precision of liquid flow velocity measurements. The possible applications of wave phase conjugation effect to liquid flows velocimetry are presented. A method of simultaneous measurement of mixture relative concentrations and flow velocity is elaborated.Le but du travail est l'investigation de la propagation dans les milieux mobiles des ondes conjuguées en phase paramétriquement et la démonstration de leurs applications possibles à la vélocimétrie des écoulements liquides. Une investigation des effets non-linéaires qui accompagnent la propagation et l'interaction des ondes conjuguées en phase est réalisée avec par exemple la génération des harmoniques supérieures et la diffusion Brillouin. La possibilité d'application de ces effets pour l'amélioration de la précision des systèmes conventionnels acoustiques de vélocimétrie des écoulements est considérée. Il est montré que le principe de synchronisation des phases des harmoniques supérieures générées successivement par l'onde conjuguée en milieu hétérogène reste valide pour les milieux mobiles, ce qui permet d'augmenter la sensibilité de mesure proportionnellement à l'ordre de l'harmonique utilisée. Il est également montré que le décalage de phase de la composante Stokes de fréquence différentielle générée dans le milieu mobile pendant la diffusion Brillouin de l'onde conjuguée par celle de référence correspond à celui de l'onde conjuguée en phase. Les effets de génération des harmoniques supérieures et de la composante Stokes de fréquence différentielle peuvent être utilisés conjointement pour l'amélioration de la sensibilité et de la précision des mesures de vitesse de l'écoulement. Les applications possibles de l'effet de conjugaison de phase paramétrique à la vélocimétrie des écoulements sont présentées. Une méthode de mesure simultanée des concentrations relatives de mélange et de la vitesse des écoulements en temps réel est élaborée

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

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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. In this paper, an emitter transducer formed of interdigitated chirp electrodes deposited on 128° Y-cut LiNbO3 is proposed. It is shown that this solution efficiently enables the generation of SAW (displacement level up to 1 nm) in a frequency range of between 100 and 240 MHz. The electrical characterization and a displacement field analysis of SAW by laser Doppler vibrometry are presented. The transducer’s significant unidirectionality is demonstrated. Finally, the characterization of two titanium thin films deposited on silicon is presented as an example. A meaningful SAW velocity dispersion (~10 m/s) is obtained, which allows for the precise estimation (5% of relative error) of the submicrometer thickness of the layers (20 and 50 nm)

Nouvelles applications de la conjugaison de phases magnéto-acoustique

Par ses propriétés d'invariance par retournement temporel et d'amplification géante, la conjugaison de phases magnéto-acoustique a déjà montrer de nombreuses potentialités d'applications. On montrera que lorsque que l'on brise cette symétrie temporelle, les déphasages induits peuvent être exploités pour d'autres applications comme la vélocimétrie non intrusive

Reference-free damage localization based on pump-probe measurements

National audienceNondestructive testing is often based on comparison between experimental data measured on damaged and intact samples. However, properties of intact samples can change with time, temperature or other external factors. An alternative approach discussed here solely uses data obtained on a damaged sample under varying loading conditions. In our experiments, a series of ultrasonic probe pulses excite a known Lamb mode in a thin aluminum plate subject to vibrations, while damaged region is modeled with a steel ball pressed against the plate. LF vibrations produce changes in contact stresses and displacements which, in turn, slightly modulate each HF reverberation record. By subtracting recorded HF signals from each other we get an array of data that finally allow us to localize the contact. To do so, we apply a backpropagation algorithm in which the differential data are multiplied by phase terms accounting for the Lamb wave propagation from the source to the receiver via a certain point on the plate (pixel). All different contributions from all the receivers are averaged producing a function having the dimension of energy. It was shown that if a pixel is located on an intact zone of the plate, particular contributions are summed up in an incoherent way which results in zero average. An essential peak is obtained only when the pixel is located at the contact. The eventual image was additionally enhanced by application of a special technique that includes random signs for each back-propagated contribution. Without changing the fact that the peak corresponds to a pixel located on damage, each set of random signs change contrast of the obtained image. The final image corresponds then to maximum contrast. The experimental procedure together with data processing are also applied in a passive mode in which ultrasound generation is replaced with an ambient noise

Design of Autonomous Miniaturized Spherical Acoustic Sensor for Complexe Media Characterization

International audienceIn this work, a spherical device (1 cm in diameter) composed of two assembled hemispherical shells integrating both the active element (piezoelectric ring) and the integrated electronics dedicated to coding, control and analysis was developed as an acoustic sensor. This autonomous sensor can operate simultaneously as a transmitter and a receiver around its fundamental frequency (32 kHz). Viewing these characteristics, operation within a sensor network could be envisaged and it will be possible to map the acoustic properties of a given medium characterized by a heterogeneous dispersion due to imposed dynamic motion

Effect of Partial Ba Substitutions on the Crystallization of Sr2TiSi2O8 (STS) Glass–Ceramics and on the Generation of a SAW Signal at High Temperatures

Because of their characteristics, including a d33 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. XRD analyses show that a 10 at.% substitution of Ba allows us to keep a strong preferential orientation of the (00l) planes of the fresnoite crystals down to more than 1 mm below the surfaces. Higher substitution levels (25 and 50 at.%), induce a non-oriented volume crystallization mechanism that competes with the surface mechanism. SAW devices were fabricated from glass–ceramic substrates with 0, 10 and 25 at.% Ba substitutions. Temperature testing reveals the high stability of the frequency and delay for all of these devices. The glass–ceramic with a 10 at.% Ba substitution gives the strongest amplitude of the SAW signal. This is attributed to the high (00l) preferential orientation and the absence of disoriented volume crystallization