Thin films of SmCo have been produced by electrodeposition in a Hull cell from aqueous solution. ... more Thin films of SmCo have been produced by electrodeposition in a Hull cell from aqueous solution. The composition of the films is dependant on the supplying mode - continuous or pulsed current. The influence of the cobalt concentration in the electrolytic solution, as well as the presence of a supporting electrolyte has been also studied. A systematic study allowed determining several operating points leading to the functional compositions of 11% or 16% Sm/(Sm+Co) ratio.
Reducing the size of power supplies raises the problem of new elements which could be better cand... more Reducing the size of power supplies raises the problem of new elements which could be better candidates to integration. In this field, electromagnetic transformers may be replaced with significant profits by piezoelectric transformers (PT). In a piezoelectric transformer (PT ...
Proceedings of SPIE - The International Society for Optical Engineering, 2004
The damping of vibration resonance is a crucial problem for light and elongated structures. Diffe... more The damping of vibration resonance is a crucial problem for light and elongated structures. Different kinds of solutions have been developed in order to address the problem of volume or mass, or temperature dependence which are common to the passive approach. In the semi-passive technique proposed here, damping is obtained through the use of piezoelectric patches bonded on the structure.
This paper presents simulations and microfabrication of different parts of high fidelity electrod... more This paper presents simulations and microfabrication of different parts of high fidelity electrodynamic MEMS loudspeakers with high electroacoustic conversion efficiency. The originality of the structure lies on the use of rigid silicon membranes suspended by a whole set of silicon beams instead of flexible polymer membranes usually found in MEMS loudspeakers. The microspeaker structure includes a planar copper microcoil electroplated
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2013
ABSTRACT This paper introduces a novel energy harvesting technique and an associated packaged dev... more ABSTRACT This paper introduces a novel energy harvesting technique and an associated packaged device aimed at powering intracardiac active medical devices by scavenging energy from ordinary blood pressure variations. We present the innovative concept of a micro-bellows packaged implant that deforms due to cyclic blood pressure variations in the cardiac cavities. This bellows transmits stresses on a spiral-shaped piezoelectric transducer that converts mechanical deformations into electric energy. The particular shapes of the different components (bellows and spiral) are designed to dramatically increase the mechanical energy that is harvested. The miniature bellows design, fabrication through electrodeposition for high compliance and hermeticity, and experimental characterization are presented. The specific challenges that arise in spiral shapes piezoelectric harvesters working in bending mode are discussed and we present a method to predict the non-trivial optimal electrode placements for maximum efficiency. This design process is completed by an associated microfabrication method and three types of piezoelectric bimorph spiral samples with doubled-sided microstructured electrode patterns are presented. The experimental performances of these prototypes are confronted to numerical simulation. A power of 4.15 μW/cm3 at 1.5 Hz has been obtained for the best design and we predict that tens of micro-Watts per cubic centimeter could be obtained using similar design process and material.
Carbon Nanotubes, Graphene, and Associated Devices Iii, 2010
ABSTRACT In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine th... more ABSTRACT In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine the growth of silicon nanowires (SiNWs). High-density arrays of parallel, straight and organized SiNWs have been realized, by Hot Wire Chemical Vapor Deposition (HW-CVD) growth process inside PAA templates with electrodeposited copper as catalyst. The PAA was made by the anodization of an aluminium layer, followed by the catalysts electrodeposition at the bottom of the pores. Subsequently, SiNWs were grown in a modified HW-CVD reactor with SiH4 as the precursor gas. The morphology and the structure of the wires have been investigated by SEM and TEM, and their collective electrical behavior has been characterized with a 2-probes device.
Conference on Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems V, 2006
The integration of autonomous wireless elements in health monitoring network increases the reliab... more The integration of autonomous wireless elements in health monitoring network increases the reliability by suppressing power supplies and data transmission wiring. Micro-power piezoelectric generators are an attractive alternative to primary batteries which are limited by a finite amount of energy, a limited capacity retention and a short shelf life (few years). Our goal is to implement such an energy harvesting
Thin films of SmCo have been produced by electrodeposition in a Hull cell from aqueous solution. ... more Thin films of SmCo have been produced by electrodeposition in a Hull cell from aqueous solution. The composition of the films is dependant on the supplying mode - continuous or pulsed current. The influence of the cobalt concentration in the electrolytic solution, as well as the presence of a supporting electrolyte has been also studied. A systematic study allowed determining several operating points leading to the functional compositions of 11% or 16% Sm/(Sm+Co) ratio.
Reducing the size of power supplies raises the problem of new elements which could be better cand... more Reducing the size of power supplies raises the problem of new elements which could be better candidates to integration. In this field, electromagnetic transformers may be replaced with significant profits by piezoelectric transformers (PT). In a piezoelectric transformer (PT ...
Proceedings of SPIE - The International Society for Optical Engineering, 2004
The damping of vibration resonance is a crucial problem for light and elongated structures. Diffe... more The damping of vibration resonance is a crucial problem for light and elongated structures. Different kinds of solutions have been developed in order to address the problem of volume or mass, or temperature dependence which are common to the passive approach. In the semi-passive technique proposed here, damping is obtained through the use of piezoelectric patches bonded on the structure.
This paper presents simulations and microfabrication of different parts of high fidelity electrod... more This paper presents simulations and microfabrication of different parts of high fidelity electrodynamic MEMS loudspeakers with high electroacoustic conversion efficiency. The originality of the structure lies on the use of rigid silicon membranes suspended by a whole set of silicon beams instead of flexible polymer membranes usually found in MEMS loudspeakers. The microspeaker structure includes a planar copper microcoil electroplated
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2013
ABSTRACT This paper introduces a novel energy harvesting technique and an associated packaged dev... more ABSTRACT This paper introduces a novel energy harvesting technique and an associated packaged device aimed at powering intracardiac active medical devices by scavenging energy from ordinary blood pressure variations. We present the innovative concept of a micro-bellows packaged implant that deforms due to cyclic blood pressure variations in the cardiac cavities. This bellows transmits stresses on a spiral-shaped piezoelectric transducer that converts mechanical deformations into electric energy. The particular shapes of the different components (bellows and spiral) are designed to dramatically increase the mechanical energy that is harvested. The miniature bellows design, fabrication through electrodeposition for high compliance and hermeticity, and experimental characterization are presented. The specific challenges that arise in spiral shapes piezoelectric harvesters working in bending mode are discussed and we present a method to predict the non-trivial optimal electrode placements for maximum efficiency. This design process is completed by an associated microfabrication method and three types of piezoelectric bimorph spiral samples with doubled-sided microstructured electrode patterns are presented. The experimental performances of these prototypes are confronted to numerical simulation. A power of 4.15 μW/cm3 at 1.5 Hz has been obtained for the best design and we predict that tens of micro-Watts per cubic centimeter could be obtained using similar design process and material.
Carbon Nanotubes, Graphene, and Associated Devices Iii, 2010
ABSTRACT In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine th... more ABSTRACT In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine the growth of silicon nanowires (SiNWs). High-density arrays of parallel, straight and organized SiNWs have been realized, by Hot Wire Chemical Vapor Deposition (HW-CVD) growth process inside PAA templates with electrodeposited copper as catalyst. The PAA was made by the anodization of an aluminium layer, followed by the catalysts electrodeposition at the bottom of the pores. Subsequently, SiNWs were grown in a modified HW-CVD reactor with SiH4 as the precursor gas. The morphology and the structure of the wires have been investigated by SEM and TEM, and their collective electrical behavior has been characterized with a 2-probes device.
Conference on Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems V, 2006
The integration of autonomous wireless elements in health monitoring network increases the reliab... more The integration of autonomous wireless elements in health monitoring network increases the reliability by suppressing power supplies and data transmission wiring. Micro-power piezoelectric generators are an attractive alternative to primary batteries which are limited by a finite amount of energy, a limited capacity retention and a short shelf life (few years). Our goal is to implement such an energy harvesting
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Papers by Elie Lefeuvre