High Sensitivity of Film Bulk Acoustic Resonator Sensors Based on Nonlinear PT Symmetric System

This work proposes a sensitivity-enhanced film bulk acoustic resonator (FBAR) humidity sensor based on a nonlinear parity-time (PT) symmetric system, which comprises three key components: an FBAR sensor, a series LC network, and a negative resistance circuit implemented with an operational amplifier. The PT -symmetric system operates at the exceptional point (EP), characterized by coalesce eigenfrequencies, leading to enhanced responsiveness to asymmetric perturbations. The nonlinear gain of the negative resistance drives the perturbed PT-symmetric system into a stable oscillatory state. Theoretical analysis demonstrates that the EP-operated PT-symmetric configuration significantly amplifies frequency shifts compared with a traditional single FBAR sensor. Experiments using an electrospun cellulose acetate/ graphene oxide (CA/GO) nanofiber-modified FBAR humidity sensor validated the theoretical predictions, with a 4 %RH perturbation inducing frequency deviations 16-fold higher than those observed in conventional configurations.