  Exceptional points (EPs) refer to degeneracies in non-Hermitian systems where
two or more eigenvalues and their corresponding eigenvectors coalesce.
Recently, there has been growing interest in harnessing EPs to enhance the
responsivity of sensors. Significant improvements in the sensitivity of sensors
in optics and electronics have been developed. In this work, we present a novel
ultrasensitive surface acoustic wave (SAW) gas sensor based on EP. We
demonstrate its ability to significantly respond to trace amount of hydrogen
sulfide (H2S) gas by tuning additional loss to approach the EP, thereby
enhancing the responsivity compared to the conventional delay line gas sensors.
In addition to high sensitivity, our sensor is robust to temperature variation
and exclusive to H2S gas. We propose an innovative method for designing a new
generation of ultrasensitive gas sensor.
