Humidity sensing by love wave detectors coated with different polymeric films

In this paper, an experimental investigation was performed on humidity sensing by using Love wave devices coated with different polymeric layers. The Love wave device consists of two interdigital transducers (IDTs) with a period of 28 μm, an ST-90 X quartz substrate. Three different films of SU-8, SU-8+PVA and PVA, were spin-coated on the substrate surface by a sol-gel process as the waveguide layer and the sensing film. A detailed description was presented for the preparation of the solution and coating and curing process of SU-8 and PVA. A network analyzer was used to measure the operation frequency and insertion loss of the sensor at different relative humidity. The absorption mechanism of polymeric layers was analyzed and the mechanism was successfully used to explain the experimental results of the humidity sensing of Love wave devices coated with SU-8, SU-8+PVA, or PVA layers.