Subsecond-response SAW humidity sensor with porphyrin nanostructure deposited on bare and metallised piezoelectric substrate

Abstract

The surface acoustic wave (SAW) humidity sensor based on the Meso-tetra (4 sulfonatophenyl) porphyrin (TPPS4) nanostrip structure deposited on a bare or metallised surface of the piezoelectric YZ LiNbO3 substrate has been investigated. The SAW attenuation, which greatly increases with humidity in sensors with TPPS4 layers on bare substrates, is almost humidity-independent in devices with TPPS4 layers on metallised substrates. For both types of sensors, the SAW velocity exhibits close-to-linear decrease with growing humidity. The sensor exhibited fast response and recovery times of from 0.8 to 0.5 s in both amplitude and phase of the output signal. The real-time monitoring of human breath with the help of the sensor was demonstrated.