Fast contactless vibrating structure characterization using real time field programmable gate array-based digital signal processing: Demonstrations with a passive wireless acoustic delay line probe and vision

International audienceVibrating mechanical structure characterization is demonstrated using contactless techniques best suited for mobile and rotating equipments. Fast measurement rates are achieved using Field Programmable Gate Array (FPGA) devices as real-time digital signal processors. Two kinds of algorithms are implemented on FPGA and experimentally validated in the case of the vibrating tuning fork. A first application concerns in-plane displacement detection by vision with sampling rates above 10 kHz, thus reaching frequency ranges above the audio range. A second demonstration concerns pulsed-RADAR cooperative target phase detection and is applied to radiofrequency acoustic transducers used as passive wireless strain gauges. In this case, the 250 ksamples/s refresh rate achieved is only limited by the acoustic sensor design but not by the detection bandwidth. These realizations illustrate the efficiency, interest, and potentialities of FPGA-based real-time digital signal processing for the contactless interrogation of passive embedded probes with high refresh rates

Un oscilloscope pour le traitement de signaux radiofréquences : gr-oscilloscope pour GNU Radio 3.7 et 3.8

International audienceGNU Radio, environnement libre de traitement de signaux radiofréquences, encourage le développement de blocs de traitements dédiés (Out Of Tree modules – OOT). Alors qu’une multitude d’interfaces matérielles dédiées sont supportées par GNU Radio [1], elles ont toutes en commun de fournir un flux de données continu de bande passante limitée par les débits de communication vers l’unité de traitement – Ethernet ou USB le plus souvent. Lors de traitements RADAR de distance de cibles, deux conditions sont respectées par les oscilloscopes radiofréquences : le flux de données n’a pas besoin d’être continu, nous n’avons besoin que de traiter une profondeur mémoire déterminée par la plus grande distance (temps de vol)de la cible à détecter ; et plus la bande passante est grande, meilleure est la résolution. Une bande passante B d’un GHz permet d’espérer une résolution en distance∆R=c/(2B) de l’ordre de 15 cm, objectif typique pour des mesures de glissement de terrain par exemple. Or aucune interface de radio logicielle accessible au grand public ne fournit une telle bande passante – alors que “n’importe quel” oscilloscope radiofréquence fournit actuellement allègrement quelques Géchantillons/s.De plus, nombre d’oscilloscopes fournissent 4 voies, permettant donc 4 flux d’acquisition, propices aux mesures de direction d’arrivée des signaux

Utilisation de la radio logicielle pour la caractérisation d’oscillateurs ultra-stables

International audience<font face="null"&gt<span style="font-size: 13px;"&gtUtilisation de la radio logicielle pour la caractérisation d’oscillateurs&nbsp; ultra-stables</span&gt</font&g

Real time GNSS spoofing detection and cancellation on embedded systems using Software Defined Radio

International audienceGlobal Navigation Satellite Systems have become ubiquitous to most daily activities requiring Positioning, Navigation and Timing and yet have become increasingly subject to spoofing and jamming, partly due to the availability of affordable software defined radio platforms allowing such functionalities.<br&gtDespite novel modulation schemes and broader frequency bands, GPS L1 at 1575.42 MHz remains the main signal source for most consumer grade receivers. We address here real time spoofing and jamming mitigation using a software defined radio approach in which the raw (I, Q) coefficients collected by the radiofrequency frontend are analyzed for spoofing detection by assessing the phase difference of the GPS signals collected by different antennas. These signals are possibly cleaned from the interfering sources by null-steering when spoofing or jamming is detected, and the cleaned signal are used for real time Position and Navigation information extraction using the opensource<br&gtgnss-sdr framework. The application to other frequency bands is considered for redundancy and detecting spoofing attacks.<br&gtTiming information is under consideration as well

Software-Defined Radio Implemented GPS Spoofing and Its Computationally Efficient Detection and Suppression

International audienceThis article demonstrates global positioning system (GPS) spoofing with a commercial, off-the-shelf software-defined radio (SDR) emitter fitted with a local oscillator exhibiting a stability consistent with the medium-term (0.01-1 000 s) stability of atomic clocks on GPS satellite systems. Computationally efficient means of detecting spoofing is then addressed, namely codeless spoofing detection by phase-difference measurement of the signals received from a two-antenna array. We conclude by using a simple and effective method to suppress spoofing to restore positioning and time-transfer capabilities, and extend the demonstration to jamming cancellation. Experiment results demonstrate the performance of the proposed methods with an emphasis on computational efficiency for real-time execution on embedded single-board computers

Implementation of a tunable hybrid system with coupled high Q-factor resonators based on mode localization for sensing purposes

International audienceIn this paper, we present a fully tunable system able to generate mode localization between a 170 000 Q-factor quartz crystal microbalance at 1 MHz and a digital device (field programmable gate array) simulating in real time the presence of an identical and weakly-coupled second resonator. Indeed, this method allows to precisely select each parameter value and thus to reach the optimal configuration with the maximum sensitivity to perturbations. In addition, this design gives a perfect adaptability to the geometry of the piezoelectric resonator, that allows to work with much higher frequencies and Q-factors than conventional cantilevers or tuning-forks usually selected for the design of mode-localized sensors. The experimental sensitivities reached in this work are at least two orders of magnitude higher than the ones found in the literature, which is promising for the design of a new generation of ultrasensitive sensors based on Anderson localization

Filter Optimization for Real-Time Digital Processing of Radio Frequency Signals: Application to Oscillator Metrology

International audienceSoftware-defined radio (SDR) provides stability, flexibility, and reconfigurability to radio frequency signal processing. Applied to oscillator characterization in the context of ultrastable clocks, stringent filtering requirements are defined by spurious signal or noise rejection needs. Since real-time radio frequency processing must be performed in a field-programmable array to meet timing constraints, we investigate optimization strategies to design filters meeting rejection characteristics while limiting the hardware resources required and keeping timing constraints within the targeted measurement bandwidths. The presented technique is applicable to scheduling any sequence of processing blocks characterized by a throughput, resource occupation and performance tabulated as a function of configuration characteristics, as is the case for filters with their coefficients and resolution yielding rejection and the number of multipliers

Passive RADAR acoustic delay line sensor measurement: demonstration using a WiFi (2.4 GHz) emitter and WAIC-band (4.3 GHz)

International audienceWe demonstrate passive RADAR interrogation of passive sensors: the non-cooperative signal source is analyzed to detect time-delayed copies of the reference signal generated by the cooperative target. The acoustic sensor is designed to introduce a delay dependent on a physical quantity under investigation, so that analyzing the echoes generated by the cooperative target allows for recovering the measured quantity. We demonstrate the passive RADAR principle for probing SAW cooperative targets acting as sensors using a WiFi emitter. Furthermore in the context of aeronautical deployment, we demonstrate the interrogation of a sensor operating in the 4.2–4.4 GHz WAIC (Wireless Avionics Intra-Communication) frequency band using a noise RADAR following principles similar to those implemented in a passive RADAR approach

Digital Control of Residual Amplitude Modulation for Ultra-Stable Optical Cavity

International audienceIn this work, we present one of the main limitations of the performance of cavity stabilized laser. Optical phase modulators (EOM) are essential devices in stabilized lasers. The residual amplitude modulation (RAM) generated by its EOM is partly due to the mismatch between the polarization axis of the laser beam and the extraordinary axis of the modulator. Using digital control system, we have developed a simple and robust technique for an active reduction of the RAM. It is based on temperature control and the addition of a DC offset on an EOM and it reduces the RAM to a few 0.25 ppm

Residual amplitude modulation at the 10−710^{-7} level for ultra-stable lasers

The stabilization of lasers on ultra-stable optical cavities by the Pound-Drever-Hall (PDH) technique is a widely used method. The PDH method relies on the phase-modulation of the laser, which is usually performed by an electro-optic modulator (EOM). When approaching the $10^{-16}$ level, this technology requires an active control of the residual amplitude modulation (RAM) generated by the EOM in order to bring the frequency stability of the laser down to the thermal noise limit of the ultra-stable cavity. In this article, we report on the development of an active system of RAM reduction based on a free space EOM, which is used to perform PDH-stabilization of a laser on a cryogenic silicon cavity. A RAM stability of $1.4 \times 10^{-7}$ is obtained by employing a digital servo that stabilizes the EOM DC electric field, the crystal temperature and the laser power. Considering an ultra-stable cavity with a finesse of $2.5\times 10^5$, this RAM level would contribute to the fractional frequency instability at the level of about $5\times 10^{-19}$, well below the state of the art thermal noise limit of a few $10^{-17}$.Comment: 6 pages, 4 figure