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International audience; We focus on the question of real-time computation for optimal distributed filtering or control applicable to MEMS Arrays. We present an algorithm for the realization of a linear operator solution to a functional equation through its application to a Lyapunov operatorial equation associated to the heat equation in one dimension. It is based on the diffusive realization, and turns to be well suited for fined grained parallel computer architecture as Field Programmable Gate Arrays (FPGA). An effective FPGA implementation has been successfully carried out. Here, we report the main implementation steps and the final measured performances.

The need of Surface Acoustic Wave (SAW) sensors operating at high-temperature ( $\mathrm{T}\geqslant\ 600^{\ \circ}\ \ \mathrm{C}$ ) is increasing. Generally, such SAW sensors are based on langasite (LGS) family crystals, with noble metal as interdigital transducers (IDTs), and oxide/oxynitride as a cladding layer. In addition, a buffer layer is systematically used to promote the noble metal adhesion. At high temperatures, material instabilities lead to several issues related mainly to interdiffusion and agglomeration and consequently in frequency instability and irreproducibility. In this work, after having tested several buffer layers (metals or oxides), the platinum grown directly on LGS surface showed the best stability at high temperature. The effect of surface quality of the LGS crystal and Pt thickness on the agglomeration of Pt was studied, as well. The final optimized stack consisted only of 3 materials: LGS, Pt IDTs, and SiO2 cladding layer, and it did not show any degradation at 800°C. The frequency of such SAW devices remained stable in the limits errors over 16 days.

Long-term monitoring of organic pollutants in the soil is a major environmental challenge. We propose to meet this issue by the development of a polymer dedicated to selectively react with H2S, coating surface acoustic wave transducers designed as passive cooperative targets with the compound, and probing their response using Ground Penetrating RADAR, thus providing the capability to monitor the presence of H2S in the subsurface environment. The selectivity is brought by including lead(II) cation in a reticulated polymer matrix which can be deposited as a thin layer on a surface acoustic wave sensor. We demonstrate a signal enhancement mechanism in which water absorption magnifies the signal detection, making the sensor most sensitive to H2S in an underground environment saturated with moisture., 13 pages including supplementary material

We present an integrated, compact, lab on a chip (LoC) platform and protocol for rapid pathogen analysis in food samples. The proposed LoC is based on an oxygen plasma nanotextured polymeric chip combining in one microfluidic chamber bacteria immunoaffinity capturing on the chip surface, chemical lysis and DNA isothermal amplification, followed by label-free detection with a Surface Acoustic Wave (SAW) biosensor. The proposed operation protocol includes: 1) a short (3 h) off-chip pre-culturing step, starting from 1 to 5 CFUs in only 25 ml of spiked fresh or pasteurized milk, followed by a brief centrifugation step for concentration of the 25 ml down to 100 μl, and, 2) injection of the preconcentrated sample on chip for automated bacterial capture, lysis, DNA amplification and acoustic detection. The sample-to-answer analysis time was less than 4.5 h, which is at least 5-times faster compared to conventional methods. Label-free detection of four different bacteria Salmonella, B. cereus, Listeria and E. coli in milk is demonstrated with minimal off chip handling and record fast analysis time.

International audience; The fast and efficient detection of foodborne pathogens is a societal priority, given the large number of food-poisoning outbreaks, and a scientific and technological challenge, given the need to detect as little as 1 viable cell in 25 gr of food. Here, we present the first approach that achieves the above goal, thanks to the use of a micro/nano-technology and the detection capability of acoustic wave sensors. Starting from 1 Salmonella cell in 25 ml of milk, we employ immuno-magnetic beads to capture cells after only 3 h of pre-enrichment and subsequently demonstrate efficient DNA amplification using the Loop Mediated Isothermal Amplification method (LAMP) and acoustic detection in an integrated platform, within an additional ½ h. The demonstrated 4 h sample-to-analysis time comes as a huge improvement to the current need of few days to obtain the same result. In addition, the work presents the first reported Lab-on-Chip platform that comprises an acoustic device as the sensing element, exhibiting impressive analytical features, namely, an acoustic limit of detection of 2 cells/μl or 3 aM of the DNA target and ability to detect in a label-free manner dsDNA amplicons in impure samples. The use of food samples together with the incorporation of the necessary pre-enrichment step and ability for multiple analysis with an internal control, make the proposed methodology highly relevant to real-world applications. Moreover, the work suggests that acoustic wave devices can be used as an attractive alternative to electrochemical sensors in integrated platforms for applications in food safety and the point-of-care diagnostics.

International audience; Surface acoustic wave (SAW) resonators built on Langasite (LGS) are capable to withstand temperature in excess of 900∘ C and demonstration of wireless interrogation of packaged sensors up to 700∘ C has been achieved for several tens of hours. These promising results emphasize the need for an accurate characterization of the raw material in order to design SAW resonators with a high level of confidence in the prediction, particularly concerning the temperature coefficient of frequency (TCF). Several data set have been published for LGS, offering prediction capabilities but also a significant level of data dispersion. Therefore, the evaluation of the effective thermal properties of SAW under periodic gratings turns out less robust than expected. Based also on published data and on measurements achieved within the SAWHOT project, harmonic admittance calculations have been achieved for deriving the evolution of mixed matrix parameters allowing for accurate SAW device simulation at any temperature. Adjusting the temperature coefficients then yield improved sets of material coefficients for design purpose. Using these data, we have demonstrated the possibility to develop a differential temperature sensor operating at temperature up to 600°C.

International audience; Passive wireless transducers are used as sensors, probed by a RADAR system. A simple way to separate the returning signal from the clutter is to delay the response, so that the clutter decays before the echoes are received. This can be achieved by introducing a fixed delay in the sensor design.Acoustic wave transducers are ideally suited as cooperative targets for passive, wireless sensing. The incoming electromagnetic pulse is converted into an acoustic wave, propagated on the sensor substrate surface, and reflected as an electromagnetic echo. According to a known law, the acoustic wave propagation velocity depends on the physical quantity under investigation, which is thenmeasured as an echo delay. Both conversions between electromagnetic and acoustic waves are based on the piezoelectric property of the substrate of which the sensor is made. Investigating underground sensing, we address the problems of using GPR (Ground-Penetrating RADAR) for probing cooperative targets. The GPR is a good candidate for this application because it provides anelectromagnetic source and receiver, as well as echo recording tools. Instead of designing dedicated electronics, we choose a commercially available, reliable and rugged instrument. The measurement range depends on parameters like antenna radiation pattern, radio spectrum matching between GPR and the target, antenna-sensor impedance matching and the transfer function of the target. We demonstrate measurements at depths ranging from centimeters to circa 1 m in a sandbox. In our application, clutter rejection requires delays between the emitted pulse and echoes to be longer than in the regular use of the GPR for geophysical measurements. This delay, and the accuracy needed for sensing, challenge the GPR internal time base. In the GPR units we used, the drift turns out to be incompatible with the targeted application. The available documentation of other models and brands suggests that this is a rather general limitation. We solved the problem by replacing the analog ramp generator defining the time base with a fully digital solution, whose time accuracy and stability relies on a quartz oscillator. The resulting stability is acceptable for sub-surface cooperative sensor measurement.

International audience; Predictive maintenance predicts the system health, based on the current condition, and defines the needed maintenance activities accordingly. This way, the system is only taken out of service if direct evidence exists that deterioration has actually taken place. This increases maintenance efficiency and productivity on one hand, and decreases maintenance support costs and logistics footprints on the other. We propose a system based on wireless sensor network to monitor industrial systems in order to prevent faults and damages. The sensors use the surface acoustic wave technology with an architecture composed of an electronic interrogation device and a passive sensor (without energy at the transducer) which is powered by the radio frequency transmitted by the interrogation unit. The radio frequency link transfers energy to the sensor to perform its measurement and to transmit the result to the interrogation unit—or in a description closer to the implemented, characterize the cooperative target cross section characteristics to recover the physical quantity defining the transducer material properties. We use this sensing architecture to measure the temperature of industrial machine components and we evaluate the robustness of the method. This technology can be applied to other physical parameters to be monitored. Captured information is transmitted to the base station through multi-hop communications. We also treat interferences involved in both interrogator to interrogator and sensor to interrogator communications.

International audience; Ground Penetrating RADAR (GPR) is a suitable measurement candidate for the development of interrogative systems ofpassive buried transducers acting as cooperative targets in the field of sub-surface sensing. We address the compatibility ofGPR for monitoring chemical compounds in soil or in the water table. This has been achieved by using a chemical sensorbased on surface acoustic wave reflective delay lines interrogated by a GPR. As model target, we focus on hydrogen sulfide,which is a gas soluble in water causing health hazard and water pollution. After demonstrating the chemical functionalizationof acoustic delay lines with a polymer designed for hydrogen sulfide detection through the specific reaction of sulfur withlead, we have successfully achieved the detection of hydrogen sulfide in air by GPR. We then consider extending thisstrategy towards sensors operating in liquid phase.

International audience; The development of integrated platforms incorporating an acoustic device as the detection element requires addressing simultaneously several challenges of technological and scientific nature. The present work was focused on the design of a microfluidic module, which, combined with a dual or array type Love wave acoustic chip could be applied to biomedical applications and molecular diagnostics. Based on a systematic study we optimized the mechanics of the flow cell attachment and the sealing material so that fluidic interfacing/encapsulation would impose minimal losses to the acoustic wave. We have also investigated combinations of operating frequencies with waveguide materials and thicknesses for maximum sensitivity during the detection of protein and DNA biomarkers. Within our investigations neutravidin was used as a model protein biomarker and unpurified PCR amplified Salmonella DNA as the model genetic target. Our results clearly indicate the need for experimental verification of the optimum engineering and analytical parameters, in order to develop commercially viable systems for integrated analysis. The good reproducibility of the signal together with the ability of the array biochip to detect multiple samples hold promise for the future use of the integrated system in a Lab-on-a-Chip platform for application to molecular diagnostics.

International audience; This paper presents the investigation of the influence of wafer-level packaging (WLP) on the stress-sensitivity of 100 and 200 MHz delay lines aimed to wireless sensing of stresses. The devices were fabricated on YXl/128° cut of lithium niobate. The investigated WLP achieves the assembly of two wafers by a 50μm-thick layer of SU-8 photoresist. The delay line is micro-machined on top of the first wafer while the second wafer realizes the function of protective cap in a way that should not be detrimental to the stress-sensitivity of the device. The paper gives a comparison between the theoretical and experimental phase sensitivity of both packaged and raw devices submitted to a three-points bending test.

International audience; Stroboscopy provides an energy and computationally efficient means of sampling radiofrequency and microwave signals assumed to be reproducible under external excitation. While well known for impulse mode RADAR receivers, we here investigate its use for interrogating surface acoustic wave (SAW) transducers acting as passive cooperative targets. Amongst the originality of the implementation is the need to keep phase coherence between successive pulse generations which last up to tens of the radiofrequency periods to optimally transfer energy to the transducer. A two-chip receiver architecture is demonstrated, with a trigger signal compatible either with single-period avalanche transistor pulse excitation or frequency-agile direct digital synthesizer source.

International audience; The development of integrated, fast and affordable platforms for pathogen detection is an emerging area where a multidisciplinary approach is necessary for designing microsystems employing miniaturized devices; these new technologies promise a significant advancement of the current state of analytical testing leading to improved healthcare. In this work, the development of a lab-on-chip microsystem platform for the genetic analysis of Salmonella in milk samples is presented. The heart of the platform is an acoustic detection biochip, integrated with a microfluidic module. This detection platform is combined with a micro-processor, which, alongside with magnetic beads technology and a DNA micro-amplification module, are responsible for performing sample pre-treatment, bacteria lysis, nucleic acid purification and amplification. Automated, multiscale manipulation of fluids in complex microchannel networks is combined with novel sensing principles developed by some of the partners. This system is expected to have a significant impact in food-pathogen detection by providing for the first time an integrated detection test for Salmonella screening in a very short time. Finally, thanks to the low cost and compact technologies involved, the proposed set-up is expected to provide a competitive analytical platform for direct application in field settings.

International audience; Surface acoustic wave (SAW) sensor on ATquartz piezoelectric substrate has been designed and fabricated. Test devices were based on asynchronous single-port resonators operating near the 434-MHz-centered industrial, scientific, and medical band. Multi-Walled Carbon Nanotubes/Ceria (MWNTs/CeO 2 ) nanocomposites were used as sensitive layers. The MWNTs were synthesized by catalytic chemical vapor deposition method and coated with nanosized ceria oxide. The composites were deposited on SAW quartz resonator using air-brush technique. MWNTs/CeO 2 nanocomposites were characterized using X-ray diffraction, transmission electron and atomic force microscopy. The sensor responses were tested under acetone (C 3 H 5 OH) and ethanol (C 2 H 5 OH) gases. The output signal was done by S 11 parameter of the SAW device and was monitored using a network analyzer. Frequency changes were observed under acetone and ethanol vapors. These changes depended on the surface conductivity of the nanocomposites deposited on the sensor. The single-port SAW gas sensor coated with the MWNTs/CeO 2 presented the highest sensitivity in the case of acetone vapor interacting with these layers, with a frequency shift of 200 kHz at room temperature.

International audience; In this work, we propose a compensated temperature pressure sensor fabricated on compound LiNbO3/Quartz/Quartz substrates obtained by Au/Au bonding at room temperature and double face lapping/polishing of LiNbO3/Quartz stack and a final gold bonding with a structured Quartz wafer. This paper shows the possibility to obtain device which is intrinsically low sensitive to thermal effects, and even allowing a second order compensation thanks to the Quartz thermal stability Sensitivity of the final sensor to bending moments then is tested and results show pressure sensitivity of such devices.

International audience; Data compression is a technique used to save energy in Wireless Sensor Networks by reducing the quantity of data transmitted and the number of transmission. Actually, the main cause of energy consumption in WSN is data transmission. There exist critical applications such as delay constrained activities in which the data have to arrive quickly to the Sink for rapid analysis. In this article, we explore the use of data compression algorithms for delay constrained applications by evaluating a recent data compression algorithm for WSN named K-RLE with optimal parameters on an ultra-low power microcontroller from TI MSP430 series. The relevance of the parameter K for the lossy algorithm K-RLE led us to propose and compare two methods to characterize K: the Standard deviation and the Allan deviation. The last one allow us to control the percentage of data modified. Experimental results show that data compression is an energy efficient technique which can also perform in certain cases the global data transfer time (compression plus transmission time) compared to direct transmission.

International audience; Sensors able to operate with liquid phases are the key-point for the development of biochemical lab-on-chip devices. In this work, we present the design and manufacture of Love-wave sensors equipped with a liquid cell, at the wafer scale level, to allow operation with liquid media. Love-wave sensors are fabricated on AT-cut quartz plates (IEEE Std-176 notation (YXlt)/36/90) and passivated by a 2.5 mu m thick silica overlay. The fabrication process using the celebrated SU-8 epoxy-based photoresist combined with silicon or quartz machined covers is presented, revealing robust enough for ensuring a reproducible sensor fabrication and packaging. Results are reported emphasizing the efficiency of the proposed approach.

In the context of direct detection sensors with compact dimensions, we investigate the gravimetric sensitivity of High-overtone Bulk Acoustic Resonators, through modeling of their acoustic characteristics and experiment. The high frequency characterizing such devices is expected to induce a significant effect when the acoustic field boundary conditions are modified by a thin adlayer. Furthermore, the multimode spectral characteristics is considered for wideband acoustic spectroscopy of the adlayer, once the gravimetric sensitivity dependence of the various overtones is established. Finally, means of improving the gravimetric sensitivity by confining the acoustic field in a low acoustic-impedance layer is theoretically established., 9 pages, 10 figures in J. Appl. Phys. 2015