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

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

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 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

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

Palladium nanowire hydrogen sensor based on a SAW transducer

Palladium (Pd) nanowires were synthesized by electro chemical deposition technique. Pd nanowires were transferred onto a ZnO/36deg LiTaO3 surface acoustic wave (SAW) transducer with an approximate operating frequency of 100 MHz. This operational frequency approximately corresponds to the device's highest conductometric sensitivity. These devices were investigated for hydrogen (H2) sensing at the room temperature. It was observed that the device exposure to the H2 gas resulted to a measurable increase in the device operating frequenc

Polyaniline nanofiber based surface acoustic wave gas sensors - effect of nanofiber diameter on H2 response

A template-free rapidly mixed reaction was employed to synthesize polyaniline nanofibers using chemical oxidative polymerization of aniline. Hydrochloric acid (HCl) and camphor sulfonic acid (CSA) were used in the synthesis to obtain 30- and 50-nm average diameter polyaniline nanofibers. The nanofibers were deposited onto layered ZnO/64 degrees YX LiNbO3 surface-acoustic-wave transducers. The sensors were tested toward hydrogen (H-2) gas while operating at room temperature. The dopant for the polyaniline nanofiber synthesis was found to have a significant effect on the device sensitivity. The sensor response was found to be larger for the 50-nmdiameter CSA-doped nanofiber based sensors, while the response and recovery times were faster for the 30-nm diameter HCl-doped nanofibers

A layered structure surface acoustic wave for oxygen sensing

A novel layered structure surface acoustic wave (layered SAW) transducer has been employed for an oxygen sensing application. It is a SiO2(0.36 µm)/ST-cut quartz crystal transducer. The dominant mode propagating in the transducer is a combination of Rayleigh and Love modes. Such a structure has the advantage of confining the acoustic wave energy to the top selective layer, which increases the sensitivity of the device. A TiO2 thin film deposited by the sol-gel process has been used as the oxygen sensitive layer