Jean-Yves Ferrandis

An acoustic sensor for simultaneous density and viscosity measurements in liquids

We studied theoretically the properties of a vibrating sensor, constituted of a cylindrical tip partly immersed in a liquid. The tip is driven axially by a stepped horn and by a piezoelectric element. Equations of the fluid flow around the tip are solved and show that longitudinal and transverse waves are emitted in the fluid. This allows the device to be sensitive to the density and viscosity of the fluid. It is shown that the properties of the fluid can be deduced by measuring the frequency shift at resonance and the corresponding electric impedance. The precision of the actual device is still low for several reasons, which are discussed. Then our apparatus seems to be more convenient to in situ reaction monitoring rather than for rheological precise measurements.

Evaluation of textural properties of mango tissue by a near-field acoustic method

A near-field acoustic (NFA) method was applied to characterize viscoelastic properties of mango pulp tissue. The developed sensor was a stepped horn consisting of a cylindrical body and a coupled cylindrical tip to be inserted into the pulp sample. The properties of the pulp altered the mechanical resonance of the horn and the electrical resonance of the piezoelectric element, which served as both input and output port. The measured acoustic parameters represented the shift of the resonance frequency (Δf) and the attenuation of the peak amplitude (Δ(l/Z)) of the probe when its vibrating tip was immersed in air, the reference medium, and then inserted into the pulp sample. Acoustic testing was carried out on each fruit at four locations evenly distributed in the middle parenchyma tissue of an equatorial section. The acoustic data were then compared to the 10 mm depth penetration force values obtained for the same four pulp locations. The results obtained for 45 mangoes with a wide range of maturity showed that Δf was very sensitive to the quality of the probe-medium interface, especially for unripe fruit, and poorly correlated with puncture test values. In contrast, the acoustic parameter Δ(l/Z) was significantly correlated with mango pulp firmness Fp (r = 0.92) assessed by puncture test. The relationship between these two parameters was slightly improved by a hyperbolic equation (r = 0.95). The NFA method developed appears to be a promising tool for assessing mango pulp texture and for following texture changes during fruit ripening.

Effect of intense neutron dose radiation on piezoceramics

Four grades of commercial PZT materials have been exposed to nuclear radiation during five months in an irradiation channel of the BR1 research reactor at SCKCEN (Belgium). This experimental study was performed in the framework of the Joint Instrumentation Laboratory with the CEA French Commission of Atomic Energy to validate these materials for future applications in severe conditions such as online measurements in irradiation experiments performed in research reactors. For this purpose, thin piezoelectric discs were irradiated while a remote network analyser continuously monitored the frequency response of their electrical impedance. The total neutron dose has reached a level of 1.5.1017 neutrons/cm2. Positive and negative shifts of the peak resonance frequency have been recorded but in any case with a variation lower than 1%. On the other hand, the amplitude of the electrical impedance at resonance frequency has largely decreased with even a reduction by factor two or three for some piezoelectric cell...

Image processing for resonance frequency mapping in atomic force modulation microscopy

It has been demonstrated that the resonance frequency of the cantilever in atomic force modulation microscopy can be used to study local mechanical properties. We developed a numerical method to achieve mapping of the resonance frequency without significant modification of the device. By making the assumption that the resonance spectrum can be approximated by a Lorentzian curve, we established analytical expressions of the resonance frequency and the width of the curve (damping) depending on the real and imaginary parts of the vibration at a single frequency. Then, resonance frequency and damping images were produced from the recording of both the real and imaginary part images of the complex amplitude. The results on a standard high-impact polystyrene sample are shown.

Acoustic sensor for in-pile fuel rod fission gas release measurement

Innovative in-pile instrumentation is crucial for advanced experimental programs in research reactors. In this field, we developed a specific acoustic sensor to improve the knowledge of fission gas release in Pressurized Water Reactor (PWR) fuel rods when irradiated in Material Testing Reactors (MTR). In order to perform experimental programs related to the study of the fission gas release kinetics, the CEA (French Nuclear Energy Commission) acquired the ability to equip a pre-irradiated PWR fuel rod with three sensors, allowing the simultaneous on-line measurements of the following parameters: 1) fuel temperature with a centreline thermocouple type C 2) internal pressure with a specific counter-pressure sensor, 3) fraction of fission gas released in the fuel rod with an innovative acoustic sensor. The third detector, which has been developed and is patent pending by CEA, SCK·CEN (Belgian Nuclear Research Center) and IES (French research laboratory of Montpellier II University and French National Research Center), is the subject of this paper. This original acoustic sensor has been designed to measure the molar mass and pressure of the gas contained in the fuel rod plenum. For in-pile instrumentation, the fraction of fission gas, such as Krypton and Xenon, in Helium, can be deduced on-line from this measurement. The principle of this non destructive and on-line acoustical sensor is the following: a piezoelectric transducer generates acoustic waves in a cavity connected to the fuel rod plenum. The acoustic waves are propagated and reflected in this cavity and then detected by the transducer. The data processing of the signal gives the velocity of the acoustic waves and their amplitude, which can be related respectively to the molar mass and to the pressure of the gas. The piezoelectric material of this sensor has been qualified in nuclear conditions (gamma and neutron radiations). The complete sensor has also been specifically designed to be implemented in MTR conditions. For this purpose some technical points have been studied in details: 1) fixing of the piezoelectric sample in a reliable way with a suitable signal transmission, 2) size of the gas cavity to avoid any perturbation of the acoustic waves, 3) miniaturization of the sensor because of narrow in-pile experimental devices, 4) appropriate cables to transmit high frequency signal under nuclear conditions.

Characterization of the cement setting by acoustic near field

Abstract The cement setting has been characterized by the acoustic near-field method. The process consists in studying the variation of the resonance curve of a horn whose tip is immersed in the sample. The sensor design has been adjusted in order to make it sensitive to the viscosity, as well as to the setting and to the modifications of the mechanical properties. The experimental measurements agree with the results expected from modelling. They display the stages of the setting and highlight the shear threshold.

Acoustic near-field process for the characterization of non-miscible liquids

Abstract A process based on the acoustic near-field technique is proposed to characterize the system constituted by two non-miscible liquids. The method consists of studying the variations of the conditions of resonance of a vibrating probe during its immersion in the sample. The results are interpreted according to the modelling of the interactions between the probe and the liquid medium. A methodology to characterize the thickness, the viscosity and the density of the upper layer, the viscosity and the density of the aqueous phase is described.

On-line characterization of silica gels by acoustic near field

Abstract The acoustic near field technique consists in studying the features of the resonance state of an acoustic horn. The alterations of the resonance curve are investigated as a function of the evolution of the rheological properties of the medium to characterize. The contact between the sample and the horn is obtained through the immersion of the terminal section, the probe, in the medium. Two resonance peaks appears, whose impedance alteration is representative of the viscosity of the medium. We used this technique to study silica gels obtained from silicon alkoxide. The higher frequency peak, very sensitive, is used to characterize the gelation step. This peak disappears during aging, characterized by the lower frequency peak. The influence of the preparation parameters of the sol (catalyst type, hydrolysis water amount, solvent amount and temperature) on gelation, aging and final rheological properties was studied.

Ultrasonic method for nuclear fuel rods pressure and gas composition released measurement

The objective of this work was to develop a non-destructive acoustic method giving an easy access to two important pieces of information in the irradiated fuel rods: the pressure and the composition of the internal gas mixture in the upper plenum of a standard LWR fuel rod. A first attempt started in 1993 made possible the development of a focused sensor, able to inject acoustic power from a piezoelectric transducer, through the fuel rod cladding and excite the internal gas mixture. This step was achieved in 1999 and covered by a first patent [1]. However, the initial problem was not totally solved because of the presence of the upper spring in the LWR fuel rod. This spring mainly induced a large decrease in the acoustic amplitude response and this solution was not applicable. The method has been revised recently for several aspects: the design of the sensor to optimize the acousmtic power injection through the cladding rod, and the entire experimental protocol, including the signal processing in the time and frequency spaces. A single λ/2 layer (instead of the standard solution in λ/4) of low impedance material (compared to the transducer and tube wall impedance) as water, was found to be a better matching layer.

Fabrication, characterization and test of acoustic sensors for detection of pollutants in aquatic environments

In this paper, we present an ultrasonic transducer for the detection of hydrocarbon pollutants with a given concentration threshold. The device is made by screen-printing using piezoelectric PZT (Lead Zirconate Titanate). The piezo device is used as an ultrasound emitter and receiver that allow the measurement of sound velocity in a liquid medium, the value of the sound velocity being modified by the presence of pollutants.