Evaporation studies of VOCs using surface acoustic wave (SAW) devices

Abstract

Surface Acoustic Wave devices are very famous in the application of filters but they are also playing an important role as a sensor for the measurement and control of several physical parameters such as –temperature, pressure, humidity, strain etc. They are also useful for the effective detection of different gases, bacteria and water vapors. The performance of these devices is mainly contributed by the mass loading and acoustoelectric coupling. This paper presents the evaporation studies of VOC (Volatile Organic Compounds) using SAW delay line devices. The SAW Delay line device is designed and developed for the resonance frequency of 78 MHz using SAW grade single side polished 128° YX cut LiNbO3 substrate. The maximum insertion loss of the device is -27dB with a quality factor of 40.002. Here we studied the evaporation of ethyl alcohol (AR grade) at room temperature in dry air for different quantities of it. Polyaniline film of 1 µm thickness is deposited on the delay line area of SAW device to verify the change in evaporation rate of the compound. As the amount of ethyl alcohol on the delay line area changes, the frequency and insertion loss are get changed. The frequency decreases initially and after a typical time interval it regains its original value. The frequencies get changed due to the change in mass on delay line. As ethyl alcohol evaporates the mass reduces and the frequency increases towards its initial value. The practical sensitivity of the device is ∼75KHz/µl with the maximum evaporation time of 45 ±5 seconds for 20 µl of ethyl alcohol in dry air with room temperature range of 27-30 °C.