An equivalent circuit for simulating Love mode acoustic wave transducers: comparison of simulation and results

A simulation was performed using the equivalent circuit previously developed for a Love mode surface acoustic wave transducer. The present model is based on the Mason equivalent circuit for inter-digital fingers. A Love mode SiO2/ST-cut quartz transducer with operating frequency at 96 MHz was fabricated and the transfer function and input impedance were measured. Simulation results were compared with the experimental measurements and they showed close agreement

Optimum sensitive area of surface acoustic wave resonator chemical and bio-sensors

A model is developed to map the variation of sensitivity of a surface acoustic wave (SAW) resonator sensor over its surface, in order to find the region with maximum sensitivity. The model is based on a combined coupling of modes (COM) and periodic Green's function analysis. In order to extend the analysis to layered media, a new efficient technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique the sensitivity calculations are found to be in good agreement with measurements. It is also shown that whilst changes in other parameters influence the sensitivity, it is the velocity change which most strongly determines the overall frequency change

A ZnO/SiO2/Si(100) Love mode transducer

ZnO/SiO2/Si[100] Love mode transducers were fabricated. SiO2 films were deposited using electron beam evaporation. ZnO films were deposited using r.f. magnetron sputtering. ZnO and SiO2 films were examined by SEM and the performance of the transducers was examined by their acoustic response. The observation of the SAW Love mode delay line was performed under untuned conditions. Operating frequencies of the transducers were around 85 MHz

Vehicle cabin air quality monitor using gas sensors for improved safety

A vehicle cabin air quality monitor using carbon monoxide (CO) and oxygen (O2) gas sensors has been designed, developed and on-road tested. The continuous monitoring of oxygen and carbon monoxide provides added vehicle safety as alarms could be set off when dangerous gas concentrations are reached, preventing driver fatigue, drowsiness, and exhaust gas suicides. CO concentrations of 30 ppm and oxygen levels lower than 19.5% were experienced whilst driving

Spatial sensitivity distribution of surface acoustic wave resonator sensors

The sensitivity distribution of surface acoustic wave (SAW) resonator sensors is investigated by theoretical and experimental means. It is shown that the sensitivity to mass loading varies strongly across the surface due to the confinement of acoustic energy toward the center of the device. A model is developed for this phenomenon based on the extraction of coupling of modes parameters from a rigorous boundary element method analysis based on a periodic Green's function. As SAW sensors for many applications include a layer covering the electrodes, a new technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique, the sensitivity calculations are found to be in good agreement with measurements. It is also shown that while changes in other parameters influence sensitivity, it is velocity change that most strongly determines overall frequency change

Love mode SAW sensors with ZnO layer operating in gas and liquid media

Novel layered surface acoustic wave (SAW) sensors, based on a ZnO/90° rotated ST-cut quartz crystal structure, were fabricated. They were employed for liquid and gas sensing applications. Their mass detection limit in liquid media is as low as 100 pg/cm2. Furthermore, these sensors are able to sense oxygen gas concentrations as low as 0.2 ppm in nitrogen gas

Modelling of a thin film thermoelectric micro-Peltier module

A micro Peltier cooler/heater module has been modelled. The module consists of n-type bismuth telluride and p-type antimony telluride thermoelectric materials. The commercial software package CFD-ACE+ has been used to implement and analyse the model. A two-dimensional coupled electrical and thermal simulation was performed. This software includes the possibility to incorporate the Peltier effect. The temperature, electric field intensity and wall heat flux distributions were simulated for different applied potentials. The variation in temperature difference with respect to the Seebeck coefficient of the material was calculated and analysed

A layered surface acoustic wave gas sensor based on a polyaniline/In2O3 nanofibre composite

A polyaniline/In2O3 nanofibre composite based layered surface acoustic wave ( SAW) sensor has been developed and investigated for different gases. Chemical oxidative polymerization of aniline in the presence of finely divided In2O3 was employed to synthesize a polyaniline nanofibre/In2O3 nanoparticle composite. The nanocomposite was deposited onto a layered ZnO/64 degrees YX LiNbO3 SAW transducer. The novel sensor was exposed to H-2, NO2 and CO gases. Fast response and recovery times with good repeatability were observed at room temperature

A layered SAW device based on ZnO/LiTaO3 for liquid media sensing applications

Surface Acoustic Wave (SAW) sensors comprising a zinc oxide guiding layer deposited on a 36°-YX lithium tantalate substrate were developed. They were found to have greater mass sensitivity than other LiTaO3 based SAW sensors, such as the -SiO2/LiTaO3 configuration. In this paper, the fabrication of the ZnO/LiTaO3 sensor is described and micro-characterisation of the deposited films is presented. Sensitivity of these devices to surface mass and dielectric perturbations is then presented, followed by an analysis of temperature stability