Christophe Martinsons - Academia.edu (original) (raw)

Papers by Christophe Martinsons

La radiometrie infrarouge photothermique est utilisee pour analyser les proprietes thermiques de ... more La radiometrie infrarouge photothermique est utilisee pour analyser les proprietes thermiques de couches dures ceramiques sur substrat d'acier. La technique consiste a induire un echauffement periodique par une source laser modulee et a detecter le rayonnement infrarouge synchrone avec l'excitation. Pour resoudre le probleme inverse, les donnees experimentales sont d'abord calibrees precisement. Puis, la modelisation est optimisee et la procedure d'estimation de parametres est adaptee aux problemes inverses mal poses apparaissant en thermique. L'introduction de la fonction de transfert photothermique, tenant compte de la non linearite du signal avec la temperature, permet d'aboutir a un modele simple dont l'application numerique est rapide. L'analyse dimensionnelle du probleme direct fournit un ensemble minimal et complet de parametres modeles. La non satisfaction d'un critere statistique, le critere k, signale l'impossibilite d'accomplir leur identification simultanee. L'approche developpee dans ce travail consiste alors a determiner les parametres les mieux resolus par l'inversion des donnees. Ces parametres optimaux, mutuellement independants, sont recherches de maniere iterative sous la forme de combinaisons lineaires des logarithmes des parametres modeles. Apres inversion des donnees, les proprietes thermiques dimensionnelles du revetement, de l'interface et du substrat sont estimees. Les resultats experimentaux conduisent a une estimation assez precise de l'effusivite thermique des revetements et la detection de tres faibles resistances thermiques d'interface (10#-#7w#-#1m#2k). En relation avec la microstructure, l'interpretation des proprietes thermiques d'echantillons d'acier revetus de nitrure de titane tin et de nitrure de titane carbure ti(n,c) montre que la resistance thermique d'interface n'est pas correlee a l'adherence, telle qu'elle est mesuree par le test de rayure ou des essais fonctionnels. En revanche, les resultats du test de rayure sont relies a la dispersion des mesures photothermiques, provoquee par des variations d'epaisseur et de diffusivite thermique du revetement.

International Journal of Environmental Research and Public Health, Jun 13, 2019

Background and Objectives: With the spread of Wifi networks, safety concerns have arisen, with co... more Background and Objectives: With the spread of Wifi networks, safety concerns have arisen, with complaints of somatic disorders, notably in traditional libraries and media libraries. The aim of the present study was to describe the conditions and levels of exposure to radiofrequency electromagnetic fields in the real-life occupational conditions of those working in traditional libraries and media libraries. Methods: Dynamic measurements, using an exposimeter, were taken in 20 radiofrequency bands from 88 to 5850 MHz. The activity of 28 library workers was analyzed on a space-time budget. An audit of exposure sources and static measurements enabled the workplaces to be mapped. Results: In seven libraries, 78,858 samples were taken over the 20 radiofrequency bands from 88 to 5850 MHz. Exposure was described for 28 working days. The median total field was 0.071 V/m (10th percentile: 0.022 V/m, 90th percentile: 0.534 V/m) and for Wifi the median field was 0.005 V/m (10th percentile: 0.005 V/m, 90th percentile: 0.028 V/m). Median individual exposure to Wifi frequency waves ranged from 0.005 to 0.040 V/m. Conclusions: Overall, the occupational exposure in this sector was close to the exposure in the general population. Peaks were due to the use of walkie-talkies by security staff. Exposure due to external sources depended on geographic location. Exposure in this occupation is well below the general occupational exposure levels, notably as regards Wifi.

Thin Solid Films, Apr 1, 1998

The study of the thermal properties of hard coatings offers great practical interest to better un... more The study of the thermal properties of hard coatings offers great practical interest to better understand the heat transfer which occurs between the coated tool and the piece. A non-destructive and non-contact method, based on thermal waves, has been especially designed for the analysis of hard coatings. The thermal effusivity, also called the heat transmission coefficient, and the thermal diffusivity are estimated. These properties describe the dynamic thermal behavior of the coating during its use. The technique is also sensitive to the thermal contact resistance which measures the thermal barrier effect of the coating-substrate interface, providing an estimation of the quality of the contact. q 1998 Elsevier Science S.A.

This paper describes a new optical spectroscopy instrument achieving lock-in detection in all its... more This paper describes a new optical spectroscopy instrument achieving lock-in detection in all its spectral output channels in a parallel and simultaneous fashion. It is based on two identical compact array spectrometers working in phase quadrature thanks to optical modulators synchronized with an external reference signal. In the application example, the optical lock-in spectrometer was used to perform spectral irradiance measurements with commercial LED lamps exhibiting temporal light modulation at different frequencies. A remote sensing optical device was designed to measure from a distance the temporal luminous waveform of a specific LED lamp and send it to the reference input of the optical lock-in spectrometer. When the lamps were operating together on top of a large continuous luminous background, the optical lock-in spectrometer successfully retrieved the respective spectral irradiance distributions and color parameters of each lamp, allowing their characterization to be performed independently of the other light sources illuminating the sensor during the measurements.

Lighting Research & Technology, Jul 16, 2021

The spectral responsivity of a photometer is usually measured using very narrow optical excitatio... more The spectral responsivity of a photometer is usually measured using very narrow optical excitations, provided by a monochromator or a tuneable laser. This article describes a technique to measure the spectral responsivity using an arbitrary number of optical excitations having any type of spectral distribution. The problem is formulated as an inverse problem which is solved using a probabilistic approach based on Bayes’ theorem. The method requires a prior knowledge of the spectral responsivity, which can be proportional to the standard photopic function, with an uncertainty level related to the spectral match index of the photometer. Using this method, the estimation can be performed from data provided by a simple experimental set-up. The numerical application provides a stable and unique solution to the inverse problem, along with the estimation uncertainties. Using a tuneable LED source, the method was applied to an illuminance measurement head, giving an estimation of its spectral responsivity from 380 to 780 nm with a step of 1 nm. The results were in good agreement with data obtained by a monochromator-based technique. Our measurement had larger uncertainties towards the red and blue limits of the spectrum as the light source provided very little light at these wavelengths.

High Temperatures-high Pressures, 1999

ABSTRACT

Inverse Problems in Science and Engineering, Apr 1, 2005

This article presents a method to solve parameter estimation problems by finding an optimal param... more This article presents a method to solve parameter estimation problems by finding an optimal parameterization of the mathematical model. The pi-theorem of dimensional analysis is used to establish a formulation of the model based on dimensionless products and scaling parameters, together with the rules of a parameterization change. Logarithmic parameters are introduced for the purpose of working in a linear parameter space in which a given base corresponds to a specific parameterization. The optimal parameterization is assumed to yield uncorrelated estimators. A statistical independence criterion based on the Fisher information matrix is derived for maximum-likelihood estimators. The method allows one to solve inverse problems with highly correlated model parameters by identifying well-resolved parameters, leading to a solution expressed in terms of correlation laws between physical quantities.

Buildings

As attention to indoor environmental quality (IEQ) grows, a systematic strategy for assessing IEQ... more As attention to indoor environmental quality (IEQ) grows, a systematic strategy for assessing IEQ in schools needs to be developed. For this purpose, this paper presents a summary of parameters measured in school classrooms to characterize the quality of thermal, acoustic, and visual environments and indoor air quality (IAQ). The summary is based on a review of published literature reporting measurements in schools in Europe and North America in the past ten years. It also summarizes the measurement protocols and measured concentrations. Eighty-eight papers describing measurements in schools were identified and analyzed. No unique standardized measuring method was used in the reviewed studies and different parameters were measured. The most often measured parameters were those describing the thermal environment and IAQ. The former mainly comprised air temperature and relative humidity. The latter mainly comprised concentrations of carbon dioxide, particulate matter, radon, formaldeh...

IEICE Proceeding Series

In a context where energy is valued, the use of Compact Fluorescent Light bulbs with low energy c... more In a context where energy is valued, the use of Compact Fluorescent Light bulbs with low energy consumption (CFL) tends to generalize. However, the radio noise produced by these sources is currently the subject of many discussions, particularly about the issue of human exposure. This paper is dedicated to the characterization of the electric and magnetic fields radiated by various models of lamps. For this purpose, we have carried out tests in the immediate vicinity (near field) of these CFLs in order to identify the frequencies involved, and the EM fields produced at very short distance. These measurements were conducted insitu to study the evolution of the electro-magnetic field over several minutes.

Radiation Protection Dosimetry, 2001

Electromagnetic radiation, which is used by broadcasting and mobile telephone systems to transmit... more Electromagnetic radiation, which is used by broadcasting and mobile telephone systems to transmit information, permeates the city environment. In order to properly evaluate population exposure to electromagnetic fields, knowledge of their intensity and spectral components is necessary. In this study the results of radiofrequency field monitoring carried out in Torino, a large town located in the north-west of Italy are shown: the variation of the electromagnetic field strength is evaluated as a function of the height from the ground, the location in the urban area and the frequency. separating the contributions of the different sources (broadcasting antennas and radio base stations for mobile phones). Furthermore, the contribution of the radio base stations is theoretically evaluated, adding the emissions off all installations situated in Torino and examining the field strength maps calculated, considering the orography, for different heights. The theoretical values are also compared with those measured in the frequency range of mobile telephony emissions.

Cyclic variations in lighting system luminous flux, known as temporal light modulation (TLM), may... more Cyclic variations in lighting system luminous flux, known as temporal light modulation (TLM), may have visual, neurobiological, and performance and cognition effects on viewers. Researchers have derived a Stroboscopic Visibility Measure (SVM) to characterize the TLM signal in a manner that is thought to predict the visibility of the stroboscopic effect. An SVM of 1 means that the average person would detect the phenomenon 50% of the time. If there exists a broad range of visual sensitivity in the general population, setting a limit based on the average person might lead to an unacceptable risk of an adverse consequence for the most sensitive individuals. There is an absence of published data concerning the relationship of SVM to stroboscopic visibility among the general population. This experiment was conducted to provide such data, using commercially available lamps to provide a range of SVM conditions (SVM: 0; 0.4-0.6; 1.0; 1.6; and >2.0).

Lighting Research & Technology, Feb 12, 2020

The advent of LED lighting has renewed concern about the possible visual, neurobiological, and pe... more The advent of LED lighting has renewed concern about the possible visual, neurobiological, and performance and cognition effects of cyclic variations in lighting system luminous flux (temporal light modulation). The stroboscopic visibility measure (SVM) characterises the temporal light modulation signal to predict the visibility of the stroboscopic effect, one of the visual perception effects of temporal light modulation. A SVM of 1 means that the average person would detect the phenomenon 50% of the time. There is little published data describing the population sensitivity to the stroboscopic effect in relation to the SVM, and none focusing on people subject to visual stress. This experiment, conducted in parallel in Canada and France, examined stroboscopic detection for horizontal and vertical moving targets when viewed under commercially available lamps varying in SVM conditions

Lighting Research & Technology, 2021

Archives Des Maladies Professionnelles Et De L Environnement, Sep 1, 2017

Leukos, Jul 21, 2021

ABSTRACT In lighting simulations, a luminaire is usually modeled using a luminous intensity distr... more ABSTRACT In lighting simulations, a luminaire is usually modeled using a luminous intensity distribution emitted by a single-point source. This so-called far-field approach is valid as long as the dimensions of the luminaire are much smaller than the distance to the calculation surface. This assumption is generally not met in standard indoor lighting and may lead to significant errors in the prediction of illuminances and discomfort glare. This work describes a practical near-field approach based on splitting the luminaire into N point sources. The errors in relation to the near field (infinite value of N) are evaluated as a function of N. This approach generates a more accurate assessment of the Unified Glare Rating in the case of luminaires with non-uniform emission.

Analytical Sciences/Supplements Proceedings of 11th International Conference of Photoacoustic and Photothermal Phenomena, 2002

An experimental setup was developed at the NPL with the goal of improving the accuracy of phototh... more An experimental setup was developed at the NPL with the goal of improving the accuracy of photothermal measurements. The principle is to perform accurate measurements of the experimental boundary conditions during a photothermal radiometry experiment. A numerical 3D heat diffusion model based on thermal transfer functions has been developed to use the measured boundary conditions. To prove the validity of this methodology, the thermal diffusivities of pure metal samples were estimated from experimental thermal radiance data by a least-squares fitting to the model. Experiments carried out at about 900K demonstrate good agreement between the theoretical and experimental data and accuracies of about 1.5% for thermal diffusivity measurements.