Synchronization problem in delay-line oscillator SAW sensors

Many surface acoustic wave (SAW) sensors are self-excited oscillators, where the self-excitation is a consequence of the time-delay in the propagation of the acoustic waves. In dual-delay-line oscillator sensors, differences in the lengths of delays are detected through differences in oscillation frequencies. In this paper, we identify synchronization as a potential problem that can cause the sensors to behave in an unexpected manner. We model SAW sensors with delay differential equations. Using the method of averaging and the stability analysis of the fixed points of the averaged equations, we show that stable synchronized solutions exist in dual-delay-line oscillator sensors consisting of one pair of fingers each. For dual-delay-line oscillator sensors with multiple-fingers, we use numerical simulation methods to show the occurrence of synchronization. We propose methods to reduce the possibility of synchronization. Moreover, we propose methods for sensing in the presence of synchronization.