Adsorption of Water on Surface Acoustic Wave Gas Sensors
Abstract
Surface acoustic wave sensors SAWS respond to mass adsorbed onto chemically specific coatings put upon the acoustic wave transmission path. Target gas response is perturbed by naturally present atmospheric water vapour. This work measured the response of two particular coating materials, polyVINYL PYRROLIDONE, PVP and FPOL a polyfluorinated polyol. These were chosen for their particular responsive behaviour towards water PVP and phosphonate esters FPOL typified by dimethylmethyl-phoshonate DMMP. From the water adsorption isotherms measured at 30 and 40 C, a mathematical function would be deduced to describe the response behaviour of the SAWS over a range of relative humidity RH 5 to 85%RH. The work showed PVP and FPOL respond reversibly to water vapour, over the range 5-85% RH at 30 and 40 C. The isotherms are qualitatively described by classical adsorption theories and a mathematical relationship relating RH to SAWS response can be derived for PVP and FPOL. Work was undertaken to design SAWS oscillator circuit, method of variable relative humidity generation and method of SAWS coating. A circuit based on RS560C amplifiers yields stability better than 1 Hz/4 min and + or - 5 Hz/sec for microsensors systems 157 MHz dual SAW devices, without temperature compensation in 50% RH air at 30 C. Coating methods utilizing a fine hair brush or an air brush were found to be the best out of range of methods essayed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1988
- Accession Number
- ADA204726
Entities
People
- Christine G. Fox
- John F. Adler
Organizations
- University of Manchester