Enhancing mass sensitivity of SAW delay line sensors by chirping transducers

The paper proposes a new device design for enhancing the mass sensitivity of SAW delay line oscillator sensors. Considering implicit dependence of the phase condition of oscillation on SAW velocity and delay path length it is theoretically shown that a chirped delay line can either reduce or enhance the mass sensitivity depending upon the characteristics of the chirp function. It is found that a linear FM up-chirp always reduces the mass sensitivity. The linear FM down-chirp devices with commonly implemented chirp parameters for matched filtering applications also reduce the mass sensitivity, though they offer the possibility of enhanced sensitivity through steep chirp slope implementation. A nonlinear chirp consisted of sum of linear and sinusoidal terms is proposed for practical implementation of SAW dispersive delay lines that can dramatically enhance the mass sensitivity of SAW chemical sensors.