International audienceSurface acoustic wave (SAW) devices are currently used as passive remote-controlled sensors for measuring various physical quantities through a wireless link. Among the two main classes of designs-resonator and delay line-the former has the advantage of providing narrow-band spectrum informations and hence appears compatible with an interrogation strategy complying with Industry-Scientific-Medical regulations in radio-frequency (rf) bands centered around 434, 866, or 915 MHz. Delay-line based sensors require larger bandwidths as they consists of a few interdigitated electrodes excited by short rf pulses with large instantaneous energy and short response delays but is compatible with existing equipment such as ground penetrating radar (GPR). We here demonstrate the measurement of temperature using the two configurations, particularly for long term monitoring using sensors buried in soil. Although we have demonstrated long term stability and robustness of packaged resonators and signal to noise ratio compatible with the expected application, the interrogation range (maximum 80 cm) is insufficient for most geology or geophysical purposes. We then focus on the use of delay lines, as the corresponding interrogation method is similar to the one used by GPR which allows for rf penetration distances ranging from a few meters to tens of meters and which operates in the lower rf range, depending on soil water content, permittivity, and conductivity. Assuming propagation losses in a pure dielectric medium with negligible conductivity (snow or ice), an interrogation distance of about 40 m is predicted, which overcomes the observed limits met when using interrogation methods specifically developed for wireless SAW sensors, and could partly comply with the above-mentioned applications. Although quite optimistic, this estimate is consistent with the signal to noise ratio observed during an experimental demonstration of the interrogation of a delay line buried at a depth of 5 m in snow
We fabricated a tunable surface acoustic wave resonator in the 2 GHz-frequency range by depositing and patterning 2 μm-wide pitch inter-digitated Al electrodes on SrTiO3 (STO) paraelectric substrate. We took advantage of the electrostrictive behavior of STO, whose properties are nonlinear with respect to the applied electric field, to induce tunability of the resonance frequency. The obtained frequency tunability reaches 0.7% at 0.5 MV/cm. Besides, the main advantage of this device is its high acoustic quality factor Q reaching 2450 at 2 GHz, thanks to the single-crystal nature of STO. This is one order of magnitude larger than the typical quality factor of its tunable bulk acoustic wave resonators counterparts.
1.5 and 2 inch LGT, langatate (La3Ga5.5Ta0.5O14) crystals along the X[100], Y[120] and Z[001]-directions were successfully grown by the Czochralski technique.
Surface acoustic wave (SAW) resonators can advantageously operate as passive sensors which can be interrogated through a wireless link. Amongst the practical applications of such devices, structural health monitoring through stress measurement and more generally vibration characteristics of mechanical structures benefit from the ability to bury such sensors within the considered structure (wireless and battery-less). However, measurement bandwidth becomes a significant challenge when measuring wideband vibration characteristics of mechanical structures. A fast SAW resonator measurement scheme is demonstrated here. The measurement bandwidth is limited by the physical settling time of the resonator (Q/π periods), requiring only two probe pulses through a monostatic RADAR-like electronic setup to identify the sensor resonance frequency and hence stress on a resonator acting as a strain gauge. A measurement update rate of 4800 Hz using a high quality factor SAW resonator operating in the 434 MHz Industrial, Scientific and Medical band is experimentally demonstrated.
In this work, we propose a compensated temperature pressure sensor fabricated on compound LiNbO 3 /Quartz/Quartz substrates obtained by Au/Au bonding at room temperature and double face lapping/polishing of LiNbO 3 /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 audienceThe capability to accurately handle liquids in small volumes is a key point for the development of lab-on-chip devices. In this paper, we investigate an application of surface acoustic waves (SAW) for positioning micro-droplets. A SAW device based on a 2x2 matrix of inter-digital transducers (IDTs) has been fabricated on a (YXl)/128� LiNbO3 substrate, which implies displacement and detection in two dimensions of droplets atop a flat surface. Each IDT operates at a given frequency, allowing for an easy addressing of the active channel. Furthermore, very low cross-talk effects were observed as no frequency mixing arose in our device. Continuous as well as pulsed excitations of the IDTs have been studied, yielding, respectively, continuous and step-by-step droplet displacement modes. In addition, we also have used these two excitation types to control the velocity and the position of the droplets.We also have developed a theoretical analysis of the detection mode, which has been validated by experimental assessment
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