W. Daniau

Measuring the inner body temperature using a wireless temperature SAW-sensor-based system

In this work, the possibility to measure the temperature of the inner body is addressed. For the present study, we have used Rayleigh wave resonators built on (ST,X) quartz for validating the interrogation principle. These resonators must be packaged to enable ingestion and transit via the digestive canal. A particular antenna design is then proposed, allowing for reducing the whole sensor size down to a 3.5 cm long 0.8 cm radius cylinder that contains both the antenna and the SAW resonators. In vivo tests have been performed on a dog, demonstrating the capability of our setup to wirelessly interrogate the ingested SAW resonators. In the first section of the paper, we briefly introduce the gastro-intestinal system and the associated medical diagnostic problems. We also briefly recall the principle of our interrogation system. For in vivo tests, we have used an altuglass package previously developed at INSERM Strasbourg tested for different low invasive operations in the gastro- intestinal system. The efficiency of the system is reported and first tests on living animals are presented and discussed. Some simple analysis elements are finally proposed to simulate the response of the ingested SAW resonators.

Pure longitudinal plate mode excited by poled domains transducers on LiNbO3

In this paper, we present new results on the development of piezoelectric transducers based on periodically poled ferroelectrics domains. The fabrication of test devices operating in the range 50-500 MHz has been achieved. Pure longitudinal modes are excited, yielding high frequency operation of test devices with easily achievable lithography process (20 and 10 mum periods). The dispersion analysis of our devices is reported and the capability of the proposed waveguide to support pure longitudinal modes along the plate radial dimension is emphasized.

Wireless temperature sensor using SAW resonators for immersed and biological applications

In this paper, the possibility to measure temperature using a passive wireless SAW device is regarded as a solution for immersed and biological applications. The RF set-up implemented in that matter is described and results are compare to those provided by classical temperature sensors.

High overtone bulk acoustic resonators for high temperature sensing applications

High overtone Bulk Acoustic Resonators have been developed for radio-frequency application such as oscillator stabilization, but also as an alternative to surface acoustic wave resonator for sensor development. In the present work, the possibility to operate such devices at temperature up to 800°C is investigated experimentally. Devices built using Aluminum Nitride deposited on Silicon with Platinum electrodes have been manufactured and resonance frequencies near the 434-MHz centered ISM band have been characterized from room conditions to 800°C. Although the exposition to such a temperature yields changes in the device response, it turns out that the operation is partly reversible and that these HBARs could operate without major defects for several tens of hours at such regimes. The development of wireless temperature sensors on this base then reveals accessible.

Fabrication of a 4.4 GHz oscillator using SAW excited on epitaxial AlN grown on a Sapphire substrate

Surface Acoustic Wave (SAW) devices are still the preferred solution for the stabilization of on-board frequency source for radar control. The possibility for developing an oscillator delivering a frequency very close to the usual operating band of these devices is considered in this paper. Double-port SAW resonators are built on epitaxial Aluminum Nitride grown onto Sapphire to take advantage of one of the lowest visco-elastic loss material and a high structural quality piezoelectric layer to optimize the resonance of the acoustic wave device. Experimental test vehicles are built using electron-beam lithography, yielding devices operating near 4.5 GHz with Q factor in excess of 3000 and moderate insertion losses. These resonators are used to stabilized feedback loop oscillators yielding noise floor better than -150 dBc/Hz. Among the other possible application of these devices, high temperature sensors may be considered as the growth temperature of the layer is in the range 1000°C - 1600°C.

A 2D transducer structure for the excitation of surface acoustic wave

In this work, we propose a new 2D bi-periodic transducer fabricated on single crystal susbtrates allowing for complex wave polarization excitation. The structure has been theoretically analysed using a mixed finite element/boundary element approach, showing numerous acoustic-electric contribution on the harmonic admittance for quartz. An experimental device then has been built on LiNbO3 using SiO2 spacers for 2D interconnection purpose. The device has been tested successfully, allowing for a first demonstration of the transduction principle. More work now will be achieve to better understand the transducer operation and to propose actual application of this 2D transducer.

Sensitivity of STW resonators to radial in-plane stress effects: theory and experiments

The design and fabrication of high spectral purity resonators based on surface waves requires a good understanding of the influence of temperature and mechanical stress effects on their frequency stability. The aim of these paper is to present a perturbation model of Surface Transverse Waves (STW) sensitivity to stresses used to predict the frequency variations of STW resonators built on AT cut quartz plates submitted to radial compression. Comparison between theory and experiments is shown to validate the model and to check the stability of STW properties to the propagation direction of the wave.

A 2D model for bulk acoustic wave devices using a dyadic Green's function of laminar plate

We have presented a model dedicated to the simulation of acoustic devices built on laminar plates. The important aspect of this model is that it is based on the computation of a spatial Greens function which can be completely derived as spectral variables (slowness and angular frequency) are always separated and its singular behavior always integrable. Once this function obtained, we have shown how to simulate finite length electrode excitation of bulk waves. Computation delays may be large when computing the spatial Greens function, but this must be done only once. The spatial Greens function then can be interpolated, yielding notable computation gain. Consequently, a standard BAW device can be accurately simulated in a few seconds. We intend to extend this model to account for electrode mass loading and eventually to 3D problems.