Bruno Cavallier

Energy harvesting using vibrating structures excited by shock

Energy scavenging research shows a growing interest these last years. This paper aims to demonstrate the ability of micromachined vibrating structures to store mechanical energy and then to convert it into electrical energy through a piezoelectric plate. Such a micro power generator may be used as a mechanical to electrical energy transformer. The energy conversion consists in a mechanical shock enabling to convert low vibrating energy levels at very low frequencies (typically below 10 Hz for human being excitation source) to mechanical energy to the vibrating structure for which resonant frequencies are ranging from 10 kHz to 1 MHz. Moreover this basic low frequencies to high frequencies spectrum conversion enables to avoid frequency tuning designing that is required for adapting the frequency spectrum of the excitation source.

Thermoelastic modeling: application to superresolution in photothermal and thermoelastic microscopy

Photothermal and thermoelastic microscopies are nondestructive methods using optical excitation and detection. In photothermal microscopy, the photoreflectance is used to detect the dynamic component of the surface temperature. In our microscope, the normal component of the thermoelastic displacement is also detected with a laser probe, leading to thermoelastic images. Both methods are used to image surface and subsurface inhomogeneities of the investigated object. A thermoelastic model has been developed to calculate the temperature and the displacement fields in the bulk and at the surface of an isotropic solid. Modeling is applied to the case of limited size optical excitation, corresponding to super-resolution. Theoretical temperature profiles show that the resolution essentially depends on the radius of the excitation beam. Conversely, the thermoelastic displacement provides a lower resolution. Finally, experimental devices are presented.Some images of test samples are shown to place in evidence the different resolutions obtained with thermal and thermoelastic methods in the super-resolution case. An extrapolation of this study should allow to fix the values of the experimental parameters to optimize a microscope using a nanometer sized source.

Integrated Love Wave Device Dedicated to Biomolecular Interactions Measurements in Aqueous Media

Mass-sensitive electro-acoustic devices such as surface acoustic wave (SAW) micro-balances, capable to operate with aqueous media are particularly favorable for the development of biosensors. Their dimensions and physical properties offer a large potential in biological fluid investigations, especially for measuring physical phenomenon (mass deposition, adsorption, pressure…). In this work, we propose a specific grating configuration to lower the influence of viscosity of fluids which reduces the signal dynamics of the surface wave transducers. A dedicated liquid cell also has been developed to isolate the electro-active part of the device. The fabrication of the cell is achieved using theSU-8™ photo-resist, allowing for manufacturing thick structures preventing any contact between the tested liquids and the transducers. Furthermore, the sensing area has been optimized to optimize the sensor gravimetric sensitivity. The operation of the sensor is illustrated by detecting bovine serum albumin (BSA) adsorption in the sensing area.

W-Shaped Cantilevers for Scanning Force Microscopy

This paper deals with the tip tilt occurring in scanning force microscopy during contact. Tangential forces lead to affect the localization of the measurement and prevent the quantification of local contact stiffness. Both are crucial for an accurate mechanical characterization of materials with high spatial resolution. Specific W-shaped cantilevers, using a mechanical compensating mechanism, have been designed to keep the tip vertical and get around these problems. They have been simulated with finite-element softwares and validated experimentally on the scanning microdeformation microscope. The promising results show that the principle could be used in other types of scanning force microscopies.

P2E-4 Energy Harvesting Using Composite Silicon/Lithium Niobate Vibrating Structures

Energy scavenging research shows a growing interest these last years. This paper describes all the potential energy losses in an energy harvesting device. Such a micro power generator may be used as a mechanical to electrical energy transformer. A finite element piezoelectric optimization is performed on a cantilever structure and enables to show the best location for the piezoelectric plate.

Specific geometries of resonant cantilevers for scanning force microscopy

In this paper, specific geometries of resonant cantilevers for scanning force microscopy aimed to reduce sliding between tip and sample have been presented. These cantilevers have been designed for the scanning microdeformation microscope. Flexural and torsional vibration modes have been observed and compared to finite element simulations. Static deflections and dynamic sliding have been studied and the results have confirmed the efficiency of the cantilevers to keep the tip vertical during contact and to reduce the displacement of the tip on the surface.

9D-2 Numerical Modeling of the Cantilever-Tip Vibrations in Scanning Microdeformation Microscope

The Scanning Microdeformation Microscope, as many other scanning probe microscopes developed in the last years, is a kind of ac force microscope. The system consists in an electromechanical oscillator made of a silicon cantilever, a diamond or sapphire tip, associated with a bimorph piezoelectric transducer and a specific amplifier . The specificity of the system is the way of detection of the oscillation frequency performed electrically through the admittance of the piezoelectric transducer. In this paper, we describe the technique of detection involved in the microscope. A nonlinear finite element modeling under the LS-DYNA code of the complete behaviour of the electromechanical oscillator is presented. A comparison of both explicit and implicit algorithms is given. Finally a comparison between experimental and theoretical behaviour shows a very good agreement.