Frédéric Polet

Single-mode rib optical waveguides on SOG/SU-8 polymer and integrated Mach-Zehnder for designing thermal sensors

This paper presents a successful design, realization,and characterization of single-mode rib optical waveguides on SOG/SU-8 polymers in order to highlight a new approach to designing heat sensors. The basic principle of this new thermal-sensing method relies on the differential thermal behavior regarding both acting arms of a micro Mach-Zehnder Interferometer(MZI). First, two families of single-mode straight rib waveguides composed of SOG/SU-8 polymers are analyzed. Hence, optical losses for TE00 and TM00 optical modes for structures on Si/SiO2/SU-8 have been estimated respectively as 1,36 plusmn 0,02 and 2,01plusmn0,02 dBmiddotcm-1, while the second one composed of Si/SiO2 /SOG/SU-8 presented losses of 2,33 plusmn 0,02 and 2,95plusmn0,02 dBmiddotcm-1. Then, owing to modeling results, an experimental sensor is realized as an integrated device made up of SU-8 polymer mounted on a standard silicon wafer. When subjected to a radiant source, as a laser light (980 nm) is injected across the cleaved input face of the MZI, the significant change of output signal allows us to consider a new approach to measuring radiant heat flowrate. Experimental results are given regarding the obtained phase shift against the subjected thermal power. According to the modeling results, one can expect new highly sensitive devices to be developed in the next coming years, with advantageous prospective industrial applications

Fast Psychrometers as New SU-8 Based Microsystems

In this paper, a new approach to designing fast micro-psychrometers devoted to measuring relative humidity is presented. Such devices are based on a planar thermopile fitted with an appropriate set of microchannels arranged for monitoring the evaporation process as a Seebeck voltage. They are fabricated out of a glass substrate, sputtered metals, and near vertical side walls made of SU-8, according to standard microtechnology processes for MEMs. Considering classical psychrometers, the new design is aimed at reducing both size and response time. Thus, besides being far less invasive than a standard unit, fast measurements (tau=5 s) are enabled. A straightforward modeling, aimed at deriving the relative humidity, is given with a view to integrating the signal conditioner. As regards validation, a prototype is calibrated and compared to a reference probe, and a discussion on its enhancement is also presented

Metrological prospects for the assessment of transition plateaus

Heat flow transducers have been implemented within a thermometric fixed-point cell operated with indium. Then a local heat flow rate was monitored simultaneously with the classical temperature measurement. A specific configuration, so-called cell-within-cell, allowed us to control a melting transition plateau and to observe the behaviour of the heat exchanged during the whole process of the melting transition. Owing to their dynamic character, heat flow measurements prove to be the most appropriate for defining specific boundaries on a given transition plateau, and relevant sensors are found to be suitable tools to be coupled with enhanced temperature measurements. This piece of work is presented in two parts, with the description of the set-up and measurement results in this first paper and their subsequent thermodynamic implications in the following one.

Distribution-patterned radiometers: a new paradigm for irradiance measurement

This paper introduces a new approach to measuring infrared radiant flux density. Thermal sensors featuring a significant metering area from 3 mm2 to 25 cm2 can be achieved by way of distributing the sensing surface upon an appropriate plated-planar thermopile. Despite a low figure of merit regarding bimetallic structures, low noise, rugged, thin and even flexible devices are made in the laboratory. Such sensors have neither to be covered with a protective widow nor to be placed in an insulating gas, thanks to their inherent immunity against convection afforded by the differential behavior of their structure. Hence wide spectrum infrared measurements, and experiments undergoing a wide range of pressure, are allowed with distribution-patterned radiometers. Current techniques of manufacture are reviewed together with the philosophical arguments concerning the distributed layout of monolithic thermopiles. Since such devices can be directly deposited upon various dielectric materials, many an application in military and space research can be expected. As regards industrialization, those multipurpose sensors meet the necessary requirements of self-calibrating ability, good reproducibility, fast response (#20 ms), ruggedness, and low cost. It is expected that the versatility of the device will result in a wide number of industrial applications.

Towards a thermodynamic assessment of transition plateaus

This second part of the work is devoted to the thermodynamic implications of the results presented in the preceding paper, as heat flow meters (HFMs) were installed within a thermometric fixed-point cell operated with indium. Then, simultaneous measurements of both temperature and heat flow allow us to pinpoint the specific boundaries (solidus and melt-off points) of a given transition plateau. To the best of our knowledge, this work is the first experimental illustration being reported on how to consider a plateau as a specific thermodynamic regime marked with a minimum amount of generated entropy in a metrological fixed-point cell. As a result, a significant relationship linking the boundaries of the plateau and the melting temperature of the material studied is presented. In order to obtain a quantitative understanding of the quality of a given transition process, straightforward thermodynamic considerations allow us to consider both theoretically and experimentally an adimensional parameter defined as the ratio of the entropy generation over the entropy change.

Heat Flow metric Policy for Dynamic Monitoring of Fixed- point Cells

Topic In this paper, an original configuration, named as cell-within-cell, is described together with a specific measurement policy. To this end, concomitant temperature and heat flow assessments are carried out so as to obtain the exhaustive energy monitoring within the thermometric fixed-point cell. Two different melting schemes are investigated so as to consider an optimized control strategy in the near future. 1. General considerations regarding thermometric fixed-point cells The characterization of temperature transition processes associated with numerous pure materials is since a long time ensured by way of high grade Resistor Temperature Detectors, such as classical Pt 25 devices. Such a way to operate enables a well-known and reliable measurement policy as regard various fixed points defining the International Temperature Scale, especially EIT-90 [1]. Sensitivity and low-noise sensor structures are most fundamental prerequisites for best operation together with specific designs regarding the cell, so as to screen out any polluting materials. Moreover, a prominent issue is to be considered as the phase transition is most often associated with an unfortunate marked density variation of the material experimented with. Then, the dimensional parameters of the cell must meet specifications allowing to reduce any untoward temperature gradient highly susceptible to alter the quality of the measurement process.