Alain Sommier

Modern engineering, driven by the need to reduce CO2 emissions and improve energy efficiency, is increasingly turning toward the use of advanced composite structures, particularly sandwich material...

The detection of through cracks using thermal methods is crucial in order to replace penetrant testing methods, which are polluting and only qualitative. The flying spot thermal method has been developed, but only as a detection method. Methods for estimating the characteristics of this type of defect (estimation of thermal resistance and depth) have been developed by Salazar et al., but only in periodic mode, requiring long analysis time and inverse methods that need a 3D study of transfers. We propose a simplified method for estimating these characteristics, based on a laser spot operating in pulsed mode, placed near the defect. It allows the temperature fields (measured by IR thermography) to be separated and reduces the estimation problem to a 1D signal inversion. Preliminary results have been obtained with isothermal media in the case of 2D granular media. We will present results obtained under non-isothermal conditions in calibrated conditions. The experiment will consider two metal plates in contact and the dedicated instrumentation (pulse laser spot and IR thermography).

The “Heart of Voh”, immortalized by Yann Arthus Bertrand in his book The Earth from the Air, depicts a sparse, heart-shaped clearing in the mangroves of New Caledonia. This highly poetic image is also the physical representation of thermal diffusion phenomena disrupted by fluid flow. This type of figure is a basic figure for analyzing source fields in a microfluidic channel surrounded by solid walls. Here, several analytical solutions will be presented and used for the estimation of crucial parameters related to the thermal diffusivity of the walls around the channel and the fluid flow inside the channel.

Putting small particles in levitation and in transient thermal imbalance in a gas has several advantages. This avoids chemical and thermal pollution through contact with a solid wall. The large exchange surface between the particle and the surrounding gas and the small volume can be considered as microfluidic situations with acceleration of surface transfers, rapidly isothermal particles, low-cost thermal cycling, rapidly isothermal situations and extreme temperature conditions facilitated. Several results related to thermal characterization in the case of fluidic and acoustic methods of levitation are presented. It consists of recording and comparing the transient temperature response by using an infrared thermography device to a step convective or radiative heating.

Thermal considerations affect the performance of most microsystems. Although surface techniques can give information on the thermal properties within the material or about buried heat sources and defects, mapping temperature and thermal properties in three dimension (3D) is critical and has not been addressed yet. Infrared thermography, commonly used for opaque materials, is not adapted to semi-transparent samples such as microfluidic chips or semiconductor materials in the infrared range. This work aims at answering these needs by using the variations of transmittance with temperature to obtain information on the temperature within the thickness of the sample. We use a tunable mid-infrared light source combined with an infrared camera to measure these variations of transmittance in a glass wafer. We couple this technique with a thermal model to extract the thermotransmittance coefficient—the coefficient of temperature variation of the transmittance. We then introduce a semiempirical model based on Lorentz oscillators to estimate the temperature-dependent optical properties of our sample in the mid-IR spectral range. Combined with the measurement, this paper reports the spectroscopic behavior of the thermotransmittance coefficient in the mid-IR range and a way to predict it.

This work reports on a terahertz tomography technique using constant velocity flying spot scanning as illumination. This technique is essentially based on the combination of a hyperspectral thermoconverter and an infrared camera used as a sensor, a source of terahertz radiation held on a translation scanner, and a vial of hydroalcoholic gel used as a sample and mounted on a rotating stage for the measurement of its absorbance at several angular positions. From the projections made in 2.5 h and expressed in terms of sinograms, the 3D volume of the absorption coefficient of the vial is reconstructed by a back-projection method based on the inverse Radon transform. This result confirms that this technique is usable on samples of complex and nonaxisymmetric shapes; moreover, it allows 3D qualitative chemical information with a possible phase separation in the terahertz spectral range to be obtained in heterogeneous and complex semitransparent media.