Etienne Gaviot

Experimental investigation of transient nonlinear phenomena in an annular thermoacoustic prime-mover: observation of a double-threshold effect

Thermoacoustic engines have been subjected to numerous studies for the past 10 years. Our current research is focused on the transient regime in an annular thermoacoustic prime-mover. It appears that several nonlinear phenomena can play a role in the amplification and saturation regimes. Indeed, acoustically induced conductivity, forced convection due to acoustic streaming, minor loss phenomenon, and saturation due to harmonic generation can be quoted among the others. The experiments presented here show for the first time a double-threshold phenomenon during the amplification regime. The first threshold, which corresponds to the setting of the thermoacoustic instability, is followed by a saturation regime. Then after a time delay, without any changes in the control parameters, a second threshold corresponding to an additional amplification has been observed.

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

Matrix formalism to enhance the concept of effective dielectric constant

By using a matrix formalism, a general framework describing the effective permittivity constants of an idealized free-standing superlattice (SL), composed of thin alternating layers is derived, as a function of the dielectric tensor of each of the N constituents. The versatile results are applied to superlattices with layers of all classes of the whole set of symmetries (triclinic, monoclinic, orthorhombic, hexagonal, tetragonal and cubic). Such an approach leads to only three new general prevalent laws for working out the whole dielectric tensor of any superlattice featuring N constituents of any symmetry. Moreover it is of noteworthy interest that such laws can be formulated as one general relationship related to the ‘Vegard rules’ in solid state physics.

Thin foil planar radiometers: application for designing contactless sensors

This paper is devoted to describing a new sensor allowing one to measure the net radiant flux exchanged by the wall surface it is mounted on. The device is constructed by mounting a thermopile-type radiometer on a larger thin metallic foil support. When the emissivity of the paint covering the support is the same as that of the wall surface on which the sensor is applied, a direct reading (positive or negative emf) of the radiant flux (absorbed or emitted) by the wall surface is given, whatever the convective losses. The calibration is carried out in a simple and useful apparatus designed to produce a prescribed total radiant exchange between two metallic plates at different temperatures and is estimated to be accurate to within two per cent. Simplicity and ruggedness make the radiometer appropriate for direct measurement of heat exchanged between surfaces heated up to 500 K. Notable applications include use as a traditional total hemispheric radiometer and a contactless temperature difference sensor.

Marcatili’s extended approach: comparison to semi-vectorial methods applied to pedestal waveguide design

This paper deals with a theoretical study of pedestal waveguides. An extension of the Marcatili method has been developed in order to adapt this analytical method to pedestal structures. Simulations are performed for two different T-pedestal waveguide (T-PW) configurations corresponding respectively to a high and a lower core to pedestal widths ratio (T-PW I and T-PW II). Each configuration is simulated considering two core widths (2 and 4 µm) and a core height ranging from 1 to 2 µm at a 670 nm wavelength. Then, this extended Marcatili method has been compared with a semi-vectorial finite difference method (SVFD) and a spectral method developed by Galerkin, both based on a numerical approach. The simulation of the T-PW structure with these three methods shows a good congruence since the relative differences between Marcatilis method and the numerical methods remain below 6%. Then, the three approaches are applied to study the modal birefringence minimization in the case of pedestal structures. Simulations are typically performed for waveguide height and width values ranging, respectively, around (1.6–2.6) µm and (1.8–6) µm, with pedestal widths ranging around (0.4–0.8) µm, at a 670 nm wavelength. The authors stress a specific property of pedestal configurations: by judiciously adjusting the dimensional parameters (core and pedestal width and core height), the birefringence can be completely screened out.

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

A new sensor to measure fluid velocities: the Peltier anemometer

This paper introduces a new approach to the measurement of low fluid velocities. A new type of anemometer is presented, resorting to a sensor directed to measuring low velocities ( in air) with a precision to the nearest . The device works owing to the thermoelectric effects, especially the Peltier and Seebeck ones. It is non-invasive since its increase in average temperature remains lower than 15 K. Therefore low-velocity measurements can be carried out without any significant perturbation. A coherent design rationale is formulated and the various stages in the technical development of the system are delineated. A compensating technique is described in order to provide reliable performance over temperature variations. In most cases this sensor can be instrumental in studying mechanisms of natural convection.

Integrated Mach-Zehnder interferometer on SU-8 polymer for designing pressure sensors

This paper describes a new integrated pressure sensor based on a Mach-Zehnder (MZ) interferometer made of SU-8 polymer. Such a device is designed with a view to working in a standard intensity modulation scheme. To this end, the device takes advantage of a differential measurement thanks to a sensing arm of the MZ structure arranged upon a thin membrane actuated by the pressure to be dealt with, while the second arm allows for a reference signal. The combination of both signals out of the optimized structure of the interferometer allows us to detect any change in the optical path as a result of the applied pressure. A prototype is characterized by way of a specific optical bench allowing an efficient end-fire coupling into the sensor. Practical results prove such a design to delineate a promising measurement approach

A laterally coupled UV210 polymer racetrack micro-resonator for thermal tunability and glucose sensing capability

Authors report and demonstrate the feasibility of a laterally coupled racetrack microresonator based on UV210 photoresist to act as a thermal and glucose sensor. The large thermo-optic coefficient and the detection principle based on the interaction of the evanescent field with different glucose concentrations demonstrate that this sensor displays high sensitivity on detection properties. Deep-UV lithography procedures allow us to develop a laterally coupled microresonator with submicrometer patterns. The thermo-optic response of the racetrack microresonator is interrogated by using a NiCr alloy tip positioned on the top of the device. Temperatures ranging between 19 and 33°C yield a red shift of the resonant wavelength with a linear sensitivity of 220 pm °C− 1. Additionally, the thermal tunability is successively demonstrated by covering the resonator with DI water. A blue shift of the resonant wavelength is obtained with a linear sensitivity of 200 pm °C− 1. The resonance optical properties under this top cladding conditions lead a Q-factor of 4000 with a finesse of 5.7. Glucose homogeneous sensing capability is also experimentally demonstrated. Different concentrations of glucose solutions result in a red shift of the resonant wavelengths with a linear sensitivity of 280 pm mg− 1 ml− 1. Finally, these results validate the laterally coupled racetrack microresonator as an operative photonic component for integrated optical devices such as optical filters applied on telecommunication, or transducer components devoted to assess biochemical interactions. Graphical Abstract

Integrated optical Mach-Zehnder on SU-8 polymer for designing thermal sensors

A new approach to designing heat sensors is presented. The basic principle relies on the differential thermal behavior regarding both active arms of a micro Mach-Zehnder interferometer (MZI). Based on modeling results, an experimental sensor is realised as an integrated device made up of SU-8 polymer mounted on a standard silicon wafer. When subjected to a radiant source, such as laser light (980 nm), 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 flow rate. 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 numerous prospective industrial applications.