Magnetic SAW RFID Sensor Based on Love Wave for Detection of Magnetic Field and Temperature

Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths with and without magnetic field sensitive layer. The delay in path with sensitive layer leads to magnetic field detection and the one without enable temperature measurement and thus compensation for the first path. The developed sensor is based on a ZnO/LiNbO$_3$ Ycut (X-direction) layered structure as Love wave platform. Love wave as a shear wave being more favorable for magnetic detection. Co-Fe-B is considered as sensitive layer to detect magnetic field changes and is deposited on the top of ZnO, but only on one of the two paths. We combined an original configuration of connected IDTs with a high electromechanical coupling coefficient (K$^2$) mode to improve the signal amplitude. The achieved sensor exhibits a high temperature and magnetic field sensitivity of -63 ppm/$^\circ$C and -781 ppm/mT, respectively. The temperature compensation method for magnetic field measurement is demonstrated using a differential measurement by subtracting the delay times obtained for the two paths with and without the sensitive layer. Finally, The sensor exhibited good repeatability at various temperatures. Moreover, the device developed allows in addition to the multisensor functionality, the radio frequency identification (RFID) which is necessary for the deployment of sensor networks

SAW RFID devices using connected IDTs as an alternative to conventional reflectors for harsh environments

International audienceRemote interrogation of surface acoustic wave ID-tags imposes a high signal amplitude which is related to a high coupling coefficient value (K 2) and low propagation losses (α). In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the conventional configuration, i.e. one interdigital transducer (IDT) and several reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the detected signal using direct transmission between IDTs instead of the reflection from passive reflectors. This concept can therefore increase the interrogation scope of ID-tags made on conventional substrate with high K 2 value. Moreover, it can also be extended to suitable substrates for harsh environments such as high temperature environments: the materials used exhibit limited performances (low K 2 value and relatively high propagation losses) and are therefore rarely used for identification applications. The concept was first tested and validated using the lithium niobate 128°Y-X cut substrate, which is commonly used in ID-tags. A good agreement between experimental and numerical results was obtained for the promising concept of connected IDTs. The interesting features of the structure were also validated using a langasite substrate, which is well-known to operate at very high temperatures. Performances of both substrates (lithium niobate and langasite) were tested with an in-situ RF characterization up to 600°C. Unexpected results regarding the resilience of devices based on congruent lithium niobate were obtained. Index Terms-high temperature, lithium niobate, radio frequency identification (RFID), surface acoustic wave (SAW

Capteurs à ondes élastiques confinées, sans fil et étirables : application à l'électronique imperceptible sur peau

With the development of Internet of Things (IoT), the continuous monitoring of the human body parameters and the extreme miniaturization of devices are becoming major societal challenges. At the same time, surface acoustic wave devices (SAW devices) who are widely used in telecommunications for filtering are booming for their sensor function. It is precisely in this context, between the field of epidermal electronics and micro-acoustics that lies this thesis project. The goal is to develop a wireless temperature sensor that combines a device based on the acoustic wave technology with stretchable antennas. The use of a confined wave structure (WLAW) and a choice of suitable materials remove the need for encapsulation in the device. In the ultrathin and ultra-soft flexible format, the device can be harmoniously “tattooed” on the skin. A significant part of the work is focused on the development of the packageless devices and their optimization through different strategies (development of thin-film materials, designs). The remote interrogation is demonstrated using stretchable antennas made by transfer printing.Avec le développement des objets connectés et de l’IoT (Internet of Things), le suivi en continu des paramètres corporels et la miniaturisation extrême des équipements de mesures deviennent de réels enjeux de société. Parallèlement, les dispositifs à ondes élastiques de surface (dispositifs SAW), largement utilisés dans les télécommunications pour leur propriété de filtrage, connaissent aujourd’hui un essor pour leur fonction de capteur. C’est précisément dans ce contexte, à l’interface entre l’électronique sur peau et la micro-acoustique que se situe ce sujet de thèse. L’objectif est de développer un capteur de température sans fil qui associe un dispositif basé sur la technologie des ondes élastiques à des antennes étirables. L’utilisation d’une structure à ondes confinées (WLAW) et un choix de matériaux appropriés permettent ensuite de supprimer le besoin d’encapsulation du dispositif. Au format ultrafin et ultrasouple, l’ensemble peut être « tatoué » harmonieusement sur la peau. Une grande partie du travail est consacrée à l’élaboration de dispositifs autoprotégés et à leur optimisation par le biais de différentes stratégies (développement de matériaux en couches minces, designs). L’interrogation à distance est démontrée en utilisant des antennes étirables réalisées par transfer printing

Negative‐Index Acoustic Metamaterial Operating above 100 kHz in Water Using Microstructured Silicon Chips as Unit Cells

International audienceA major challenge for negative-index acoustic metamaterials is increasing their operational frequency to the MHz range in water for applications such as biomedical ultrasound. Herein, a novel technology to realize acoustic metamaterials in water using microstructured silicon chips as unit cells that incorporate silicon nitride membranes and Helmholtz resonators with dimensions below 100 μm fabricated using clean-room microfabrication technology is presented. The silicon chip unit-cells are then assembled to form periodic structures that result in a negative-index metamaterial. Finite-element method (FEM) simulations of the metamaterial show a negative-index branch in the dispersion relation in the 0.25–0.35 MHz range. The metamaterial is characterized experimentally using laser-doppler vibrometry, showing opposite phase and group velocities, a signature of negative-index materials, and is in close agreement with FEM simulations. The experimental measurements also show that the magnitude of phase and group velocities increase as the frequency increases within the negative-index band, confirming the negative-index behavior of the material. Acoustic indices from –1 to –5 are reached with respect to water in the 0.25–0.35 MHz range. The use of silicon technology microfabrication to produce acoustic metamaterials for operation in water opens a new road to reach frequencies relevant for biomedical ultrasound applications

Investigation of the limit operating temperature of LiNbO3 as substrate for SAW devices

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AlN/ZnO/LiNbO 3 Packageless Structure as a Low-Profile Sensor for Potential On-Body Applications

International audienceSurface acoustic wave (SAW) sensors find their application in a growing number of fields. This interest stems in particular from their passive nature and the possibility of remote interrogation. Still, the sensor package, due to its size, remains an obstacle for some applications. In this regard, packageless solutions are very promising. This paper describes the potential of the AlN/ZnO/LiNbO3 structure for packageless acoustic wave sensors. This structure, based on the waveguided acoustic wave principle, is studied numerically and experimentally. According to the COMSOL simulations, a wave, whose particle displacement is similar to a Rayleigh wave, is confined within the structure when the AlN film is thick enough. This result is confirmed by comprehensive experimental tests, thus proving the potential of this structure for packageless applications, notably temperature sensing. Index Terms-Surface acoustic wave SAW, temperature sensor, waveguiding layer acoustic wave WLAW, packageless, low-profile

AlN/ZnO/LiNbO<inf>3</inf> packageless structure as a low-profile sensor for on-body applications

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Diamond/ZnO/LiNbO3 structure for packageless acoustic wave sensors

International audience—This paper studies the Diamond/ZnO/LiNbO3 structure, numerically and experimentally, as a candidate for a packageless sensor based on the surface acoustic wave technology. The structure is compared with an AlN/ZnO/LiNbO3 structure, in order to highlight better performances of diamond with respect to AlN. Early experimental results of nanocrystalline diamond growth on ZnO/Si are presented