Christine Barthod

Resonant force sensor using a PLL electronic

The working principle of resonant force sensors with double ended tuning forks (DETF) consists of measuring one of the resonant frequencies of the vibrating beams which depend on the force applied in the beams. Although the principle is simple, its practical application presents some problems. The principal difficulties in the design of such a structure lie in two principal points dealing with the mounting of the DETF on its support and with the mechanical resistance of the structure. In order to approach the ideal structure, the proposed force sensor is based on a DETF directly machined in a metallic circular plate. The force to be measured is applied on the plate by using a tube. The sensor has been designed using finite element simulations. An electronic circuit including both analog PLL and logic circuitry parts has been developed for frequency shift measurement, dedicated to this sensor. A prototype has been realized and tested which gives promising results; the principal technical features of the prototype are reported.

Design and characterisation of a new force resonant sensor

Abstract This paper describes the design and performance of a resonant sensor for static force measurement. This sensor directly measures compressive forces like weight. The sensor relies on a metallic plate and on piezoelectric disks used to excite and detect vibrations of the structure. The paper underlines the interest of the use of finite element analysis for the design of the sensor. The frequency variation of the sensor in response to the applied force allows to determine the force sensitivity (about 6.63 Hz N−1). General features of the prototype of the sensor are presented. The environment effect and its thermal behaviour are studied.

Design and optimization of a low frequency electric field sensor using Pockels effect

The present paper proposes an optical device for measuring low-frequency (50-60 Hz) high electric fields (0-200 kV.cm/sup -1/) using a LiNbO/sub 3/ crystal as sensing medium without any contacting electrode. Thus, a good galvanic insulation of material and person is obtained. An experimental setup is developed in the laboratory by using the electro-optical effect or Pockels effect, and several measurements are realized. Simulations are performed with the finite element method (FEM) to optimize the sensing medium of the device. Experimental and simulation results are presented and discussed. The sensor induces a weak disturbance of the local electric field to be measured. The sensibility of the sensor is about 4 /spl mu/A/(kV.cm/sup -1/).

Validation of a Light Aspiration Device for In Vivo Soft Tissue Characterization (LASTIC)

In vivo characterization of soft tissue is a key step towards accurate biomechanical simulation enabling planning and intra-operative assisted surgery. This chapter presents the new version of LASTIC, a device measuring soft tissue deformations using a negative pressure. Its capabilities are compared with standard tensile tests on five samples with different elastic properties, i.e. Young modulus, from 10 kPa to 1 MPa, in order to estimate its accuracy and define the functional measurement range. Results show that LASTIC overestimates Young modulus by an average of 24% compared to the tensile devices. This error, although rather large, allows a first estimation of the elastic modulus of different materials, especially living tissues, even during surgery. Directions for improvements are given that will allow for better patient-specific biomechanical simulations of soft tissues.

Measurement System for Gesture Characterization During Chest Physiotherapy Act on Newborn Babies Suffering from Bronchiolitis

Despite the lack of studies, chest physiotherapy (CPT) is widely used for newborn babies suffering from bronchiolitis. The limited data regarding this technique is mainly due to the difficulties making in situ measurements during the act. In the presented study, original instrumented gloves were designed and realized to perform measurements on babies during the CPT act. Custom-designed associated electronics and software were specially developed to monitor and record the forces applied by the physiotherapists hands on the infants chest and their trajectories. A prospective study, with babies in real situation, validates the principle measurement. Measurements with the system was led on babies in a referent physiotherapist consulting room between January and March 2007. The results are being analyzed and typical phases of the CPT act are highlighted.

▪Analyse de pratiques professionnelles en kinésithérapie respiratoire pédiatrique en vue de la conception d’un simulateur en santé

Resume La fragilite du nourrisson rend difficile la comprehension et l’acquisition des gestes techniques que necessite l’apprentissage de la kinesitherapie respiratoire. L’utilisation d’un simulateur pourrait faciliter l’apprentissage professionnel. La conception d’un simulateur adapte necessite une analyse des situations professionnelles. Nous avons utilise conjointement un systeme d’enregistrement des gestes de kinesitherapeutes experts lors d’une seance de kinesitherapie respiratoire et un enregistrement video, afin de donner un cadre de reference aux gestes kinesitherapiques et d’identifier les concepts mobilises dans l’action. Il apparait que les kinesitherapeutes experts utilisent une demarche hypothetico-deductive pour structurer leur action a partir d’indicateurs specifiquement kinesitherapiques. Cette demarche de raisonnement devrait etre enseignee pour ameliorer la qualite des soins. Ceci a permis d’envisager un modele adapte a la creation d’un environnement mecatronique pour l’apprentissage humain. Niveau de preuve : non adapte.

Variable compliance device for a respiratory physiotherapy training simulator

Semi active devices to modify the stiffness or the damping of systems received significant attention in the recent years. In this paper, two solutions of a variable compliance device to change the physiotherapists feeling of the thorax compliance of a 6-month old infant torso training simulator are presented. A first solution, using a variable orifice device which allows to change the compliance by changing the radius of a flow pipe is proposed. Another solution is to use a magnetorheological fluid damper. Both systems are presented in detail and discussed especially for their applicability to be integrated in the simulator.

Interfacial stresses in vibration of multilayer composite materials: experimental and theoretical analysis

In laminated composites, interfaces are the transfer spots of mechanical charges, mechanical over-stress adaptations and energy dissipations. In order to examine the dynamic effects of interface stresses, we have inserted a thin layer of piezoelectric material at the interface of composite plies of a multilayer cantilever beam excited in bending. The voltage signals generated by the piezoelectric elements are seen to be dependent on the expected interlaminar stresses. Moreover, the realized experimental set-up validates the parameters of finite element simulations. Using the implemented finite element model, two different piezoelectric materials are compared with regard to their possibility for interfacial stress measurement and for mechanical energy dissipation.

Implementation of new dry electrodes and comparison with conventional Ag/AgCl electrodes for whole body electrical bioimpedance application

Reusable electrodes, when embedded into devices, can provide new ways of physiological measurements, and improve the usability and comfort of monitoring systems using whole body electrical bioimpedance in the areas of medical, nutrition and sports. However, good electrical and mechanical contacts between electrode and skin are very important, as it defines the quality of the signal, requiring generally the use of consumable. This paper introduces innovative dry electrodes and compares their electrical behavior with those of a traditional Ag/AgCl electrolytic one. Thanks to the campaigns of measurements involving Caucasian healthy volunteers, three designs of experiments are conducted to lead to choose the optimized set: material, supply, using conditions.

Flow changing device for varying the compliance of a simulator dedicated to respiratory physiotherapy learning

Semi-active energy dissipation devices are used in various domains like the automotive industry or seismic protection structures. This article presents the design and the implementation of a cylinder/piston energy dissipation system in a 6-month old infant simulator for respiratory physiotherapy training. The system is supposed to modify the compliance of the simulators thorax by equipping it with a flow changing device connected between the two cylinder chambers. The principle consists in modifying the geometry of the flow pipe section. For that purpose, two solutions are proposed and implemented.