Stéphane Serfaty

Lamb Wave Sensor for Viscous Fluids Characterization

This paper is a study of a new sensor for fluid characterization. This sensor is composed of a stainless steel plate in contact with a viscous material. The aim is to characterize the material viscosity by using reflected Lamb waves at the boundary interface. In order to identify the effects on the Lamb reflected modes by the viscous material, a complete study of the propagation wave in the alone plate is first presented. The propagation modes of the loaded plate are then investigated. By monitoring the mechanical impedance, the viscosity of the material in contact is extracted. In order to validate the experimental setup, the mechanical impedance variation is measured for different water-glycerol mixtures. Results are in good agreement with those obtained by other techniques in the literature.

Study of the bending modes in circular quartz resonators

An experimental and theoretical study of bending modes in a partially electroded circular piezoelectric quartz (AT-cut) with free edge is presented. The quartz is excited by a voltage pulse applied on the electrodes, and its surface is scanned by a laser vibrometer that measures the out-of-plane displacements. The classical theory of bending of thin disks is used to describe the flexural modes at frequencies lower than the first thickness shear resonance (6 MHz). A fairly good agreement is found between experimental and theoretical results for the forced mode shapes and for the resonance frequencies. However, it appears that the two springs used to maintain the disk in position introduce extra clamping conditions. Several source shapes were studied, among which a collection of an arbitrary number of forces is particularly useful. The two-dimensional wavenumber representation shows the presence of anisotropy related to the crystallographic axes at higher frequencies, which is not predicted by the model. The experimental phase velocities are compared to those given by the classical theory of disks and to those of Lamb A0 mode. This study confirms the correspondence at low frequencies between the A0 mode and the bending eigenmodes of a disk with finite size

Viscosimetry using a new electromagnetic‐acoustic microbalance

The nanostructure evolution of gels, biomaterials or porous media can be characterized by its mechanical properties. Few nondestructive techniques are developed to investigate the viscosity evolution. This paper present a new electromagnetic‐acoustic technique using a wireless thickness shear mode transducer. A suitable model of the measurement is also presented to characterize the viscosity of the nanostructure in contact with the transducer. This transducer is a double copper‐clad PVDF substrate resonator, designed to operate over a wide radiofrequency range without lumped tuning capacitors. This architecture constitutes an alternative solution to design a high‐Q ultrasonic microbalance. To characterize the material at the surface of the transducer, the evolution of the induced complex impedance is measured. From this evolution, the mechanical energy storage and dissipation in the material can be extracted. In order to validate the lumped element model used, a series of glycerol/water mixtures is studie...

Gel formation monitoring by acoustic spectroscopy

An acoustic technique in the audible range has been developed to characterize the sol–gel process. Resonances appear at the sol to gel transition of a sol–gel matrix when submitted to an acoustic wave. The range of the associated resonance frequencies leads to a very low propagation speed of sound (about 20 m/s). The resonance frequencies versus time curves, corresponding to the harmonic propagation modes, converge to a unique intersection point with the time axis corresponding to the gelation time tg. The temporal evolution of the resonance frequencies features the formation of the network. Actually, the evolution of the matrix is independent of the initial conditions (precursor concentration, hydrolysis rate). Depicting the ‘‘reduced frequency’’ fi/fi(∞) [fi(∞) is the long‐term resonance frequency for the harmonic mode i] versus the ‘‘reduced time’’ t/tg for various Si concentrations and hydrolysis rates results in a unique curve, revealing the insensitivity of the matrix formation process to the input ...

Inductive magneto-acoustic technique for viscous fluids monitoring

The optimization of new soft hybrid materials elaborated from liquid phase needs an “on line” monitoring during the first steps of their formation. Up to date, few ultrasonic techniques ensure a complete tracking of the material characteristics. They often require a wired excitation particularly unsuited for hidden areas monitoring. This work presents an innovative magneto-ultrasonic sensor remotely controlled by an RF induction (at 100 MHz) in order to extract rheological properties of hidden complex fluids. An equivalent electrical model of the interactions between the developed wireless sensor and the complex fluid in contact is also presented. The validation study of this model using well-known viscous fluids (water-glycerol mixtures) is furthermore achieved.

Effects of materials conductivity on the viscosity measurement using a QCM

Quartz crystal microbalance (QCM) is commonly used to characterize the viscosity of soft materials. For biomedical applications the modified BVD model of QCM is unsuitable due to the conductivity of the biomaterial. In order to take into account the electrical effects, a new model including a static lossy capacitor is proposed. A theoretical study of the shear wave propagation in the quartz shows that these effects modify the static and the motional branches of the BVD circuit. The conductivity effects of the material at the surface of the QCM can be modeled by same parallel elements added in both branches. In the motional branch the electromechanical coupling factor is applied to these elements. To validate the new lumped element model measurements for KCl mixtures are achieved. The results show that an accurate extraction of viscosity (<5%) can be obtained for a middle of conductivity less than 0.3 S/m. In addition for water/glycerol mixtures the resonant frequency shift and damping follow an accurate l...

Non-Invasive Evaluation of Yogurt Formation Using a Contactless Radiofrequency Inductive Technique

The paper reports on the implementation of an inductive RF sensing technique dedicated to the non-contact evaluation of the dielectric properties of organic materials. The technique lies on the use of a high quality-factor RF resonator, electromagnetically coupled to the material under evaluation, and distantly monitored by an RF bobbin coil connected to a network analyzer. A lumped element electrical model of the set-up is proposed and used to estimate the complex permittivity of the material, starting from the complex impedance read out at the ends of the monitoring coil. The contactless measurement technique is implemented for the dielectric monitoring of yogurts during their gelation process. Results obtained under various operating conditions and yogurt preparation parameters are discussed and compared with results obtained with a conventional open ended coaxial contact probe. The obtained preliminary results open the way to the development of easy-to-implement and non-invasive dielectric monitoring techniques of organic materials, with many prospects in agrifood as well as health monitoring applications.

Caractérisation RF sans contact des changements structurels de milieux organiques

The paper reports on the implementation of an inductive RF sensing technique dedicated to the non -contact evaluation of the dielectric properties of organic materials. The contactless measurement techni que is implemented for the dielectric monitoring of eggs and acidified milk solutions during jellification. The obtained results are compared to results provided by conventional invasive techniques and open the way to the development of easy to-implement and non-invasive dielectric monitoring techniques of organic materials, with many prospects in agrifood as well as health monitoring . MOTS-CLÉS : capteur inductif résonant, caractérisation diélectrique radiofréquence, capteur sans contact , mesure non invas ive, milieu organique.

New ultrasonic technic for on-line encapsulation monitoring

This presented work shows the ability for this method to monitor the encapsulation process for fragrance delivery. The encapsulation is based on the coacervation principle which consists in the chemical reaction between two water soluble polyelectrolytic polymers with opposite charges. An experimental protocol is performed with precise conditions of temperature and acidity to form, during the process, elastic micro-shells encapsulating the fragrance. Thus, in this paper, the new ultrasonic technic is presented. It is based on the resonance of an AT cut quartz sensor. When the sensor is loaded, using the shear wave propagation in the complex fluid, the mechanical impedance of the material is extracted from the modification of the resonance parameters [1]. A complete on-line monitoring can then be carried out during the encapsulation process. The obtained results allow focusing the different steps of the encapsulation. This new system is inexpensive and easily adaptable to industrial conditions. It is robust in aggressive conditions. The evolution is to make this system remotely controlled.

Wireless implementation of high sensitivity radiofrequency probes for the dielectric characterization of biological tissues

The paper reports on an original wireless inductive radiofrequency probe dedicated to the distant sensing of the dielectric properties of biological tissues, with noninvasive, non-contact, and easy-to-implement diagnosis of tissues in view. The sensing technique lies on the distant monitoring of a high-quality factor radiofrequency resonator electromagnetically coupled to the investigated tissue. The sensing if carried out through the measurement of the modifications of the resonator impedance with the changes of the tissue properties. Firstly, a method dedicated to the wireless measurement of the resonator impedance is proposed and discussed. Secondly, the method is implemented for the sensing of dielectric liquids standing for tissue phantoms. Preliminary sensing results show that the electrical conductivity and the permittivity of the considered phantoms can be distantly and separately sensed. These results open the way to new easy-to-implement tissue characterization techniques.