SAW sensor without the reference channel based on the two path delay line

The surface acoustic wave (SAW) sensor without the reference channel is proposed. It uses the single two path SAW delay line with one path covered with the sensitive film and connected to additional external phase shifter. The phase difference between paths determines the amplitude of the open-loop signal of such a feedback and the control voltage of the phase shifter determines the process of oscillation initiation and suppression. It is this voltage which is used as the sensor output. The feasibility of the proposed approach is experimentally proved by measurement and analysis of the open-loop circuit transmission parameters for the case of graphene oxide sensitive film deposited onto the surface of one path of the delay line. The sensitivity of such a sensor for wide range of relative humidity is presented.