Ultrasonic characterization of porous silicon using a genetic algorithm to solve the inverse problem

International audienceThis paper presents a method for ultrasonic characterization of porous silicon in which a genetic algorithm based optimization is used to solve the inverse problem. A one dimensional model describing wave propagation through a water immersed sample is used in order to compute transmission spectra. Then, a water immersion wide bandwidth measurement is performed using insertion/substitution method and the spectrum of signals transmitted through the sample is calculated using Fast Fourier Transform. In order to obtain parameters such as thickness, longitudinal wave velocity or density, a genetic algorithm based optimization is used.A validation of the method is performed using aluminum plates with two different thicknesses as references: a good agreement on acoustical parameters can be observed, even in the case where ultrasonic signals overlap.Finally, two samples, i.e. a bulk silicon wafer and a porous silicon layer etched on silicon wafer, are evaluated. A good agreement between retrieved values and theoretical ones is observed. Hypothesis to explain slight discrepancies are proposed

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Non destructive characterization of porous silicon using ultrasonic method

Le silicium poreux est un matériau qui est actuellement utilisé dans de nombreux domaines, tels que la biologie ou la microélectronique, grâce à ses propriétés remarquables. De nombreuses applications sont étudiées au sein du laboratoire GREMAN, telles que la fabrication de vias électrique ou de capacités 3D. Le matériau étudié au sein de cette thèse est du mésoporeux, qui est utilisé comme substrats dans les applications RF. La caractérisation non destructive de ce matériau est encore limitée, soit selon l’épaisseur de la couche poreuse, soit selon la taille des pores. Cela limite ainsi l’industrialisation des procédés de fabrication de silicium poreux. Une technique ultrasonore de caractérisation est proposée dans cette thèse afin de permettre un suivi de la gravure in situ et en temps réel. Ainsi les variations de gravure peuvent être contrôlées.Porous silicon is a material that is currently used in many fields such as biology and microelectronics, thanks to its remarkable properties. Non-destructive characterization of this kind of material is still limited, mostly due to thickness of porous layer and pore size. The aim of this work is the development of an ultrasonic characterization method to allow monitoring of in situ etching in real time. First, the study of electrochemical etching and tanks where it is made to have the estimated microgeometric parameters of the porous layer. Through knowledge of the pore size and orientation, the mechanical constants md the values of permeability and tortuosity are estimated. Second, propagation of the ultrasonic waves within the material bi-porous Si-Si layer is examined. Modelling of the porous i layer is performed through the Biot model to estimate the longitudinal speed to calculate the theoretical spectrum transmission through the etched wafer. A measurement using an insertion-substitution method allows a determination of transmission spectrum. The parameters of the porous layer (thickness and porosity ) are determined by an inverse problem resolution, based on a genetic algorithm. A comparison with destructive measurements shows the interest of the ultrasonic measurement

Study of polarization state during high electrical loading

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Determination of piezoceramic microscopic parameters using phenomenological modeling of hysteretic behaviours

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Towards higher machine-tool eco-efficiency with an Information Sharing Platform

Poor information exchange between machine-tool manufacturers and the end users of machines imposes severe limitations on the optimized production of many manufactured goods and drastically increases the ecological impact of their production. An Information Sharing Platform is proposed as a suitable tool to overcome this limitation. The Platform processes information from an online data-acquisition system monitoring working machines and from the ERP system of the machine-tool manufacturer. It can automatically perform several programmed tasks to provide useful outputs, in order to improve the eco-efficiency of the machine-tools. The operation of this Information Sharing Platform has been tested on a milling machine manufacturer. A case study outlines various 3D representations and useful conclusions that can improve the eco-efficiency of present and future machines.Peer reviewe

Thickness evaluation of mesoporous silicon layer using ultrasonic method

International audienceThe manufacturing processes of porous silicon (PoSi) now allow samples with variable depths and porosities to be obtained. Thickness can be critical to ensure reliability as for microelectronic applications. However, thickness measurement methods are generally destructive or strongly limited by thickness or pore. Therefore in this study a non-destructive ultrasonic method based on an immersion insertion-substitution technique is investigated. Yet wavelength in ultrasonic method is much larger than optical ones, allowing to observe porous silicon layers having larger pore diameter or higher thickness. Total thickness of the wafer (550 microns) and high sound speed in pure silicon (8450 m.s-1) require transducers with high centre frequencies. The acoustic parameters of these samples, such as velocity and attenuation, are measured using time domain analysis. These measurements are compared with those obtained through a one-dimensional multilayer model of the wafer, using a homogenization approach for the porous layer based on Biot’s Theory