Impact of ambient humidity on surface acoustic wave attenuation and velocity in hematoporphyrin-on-LiNbO3 structure

Abstract

The impact of ambient humidity on a surface acoustic wave (SAW) propagation in the structure consisting of hematoporphyrin (Hp) film deposited on a piezoelectric lithium niobate substrate has been studied. The SAW transmission dependencies on frequency were measured using an RF network analyzer, and the variation in the SAW velocity was measured using SAW delay-line oscillator technique. The increase in the SAW velocity and decrease in the SAW attenuation with increasing ambient humidity was observed. Both dependencies exhibited exponential dependence on a humidity, and the relative velocity change was proportional to the squared change in the attenuation. This observation is in agreement with the conductivity related mechanism of the humidity impact on the SAW propagation parameters in a hematoporphyrin-lithium niobate structure. The results show that Hp - LiNbO₃ structure can be used as a SAW humidity sensor.