Abstract
A double SAW resonator system was developed as a novel method for gas sensing applications. The proposed system was investigated for hydrogen sensing. Commercial Surface Acoustic Wave (SAW) resonators with resonance frequencies of 433.92 MHz and 433.42 MHz were employed in the double SAW resonator system configuration. The advantages of using this configuration include its ability for remote measurements, and insensitivity to vibrations and other external disturbances. The sensitive layer is composed of functionalized multiwalled carbon nanotubes and polyaniline nanofibers which were deposited on pre-patterned platinum metal electrodes fabricated on a piezoelectric substrate. This was mounted into the DSAWR circuit and connected in parallel. The sensor response was measured as the difference between the resonance frequencies of the SAW resonators, which is a measure of the gas concentration. The sensor showed good response towards hydrogen with a minimum detection limit of 1%.
Highlights
One of the main sources of air pollution comes from power generation as a result of the fossil fuel consumed by the power plants
A plot of S11 versus resonance frequency is shown with two resonant frequencies corresponding to the commercial Surface Acoustic Wave (SAW) resonators used in the fabrication
It could be observed that when the sensor was exposed to different hydrogen concentrations there is a decrease in conductivity of the functionalized MultiWalled Carbon Nanotubes (MWCNT)/polyaniline layer which causes an increase in acoustic velocity and an increase in resonant frequency [33]
Summary
One of the main sources of air pollution comes from power generation as a result of the fossil fuel consumed by the power plants. Gas sensing using a single SAW resonator is commonly employed and has proven reliable for the detection of different gases [12,13,14,15] in which the sensor response is expressed as upshift or downshift of resonance frequency. Carbon nanotubes (CNT) have been proved to be good sensing materials for gas detection due to their inherent properties like good electrical conductivity and their hollow structure Due to their highly metallic behaviour they caused short circuits in the IDTs. In order to deposit the sensing layer successfully, an insulating/guiding layer which needs to be sandwiched between the sensing material and the electrodes has to be created. It is of interest to investigate a novel less cumbersome technique for deposition of the sensing material which can prevent the IDTs from short circuiting as well as eliminate the fabrication of a guiding layer for SAW resonators. The system will be tested with different hydrogen gas concentrations and the differences between the two shifted resonance frequencies will be used to express the sensor response signal
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