This paper discusses the dynamics of MEMS structures; including a single cantilever, a single clampedclamped beam, and a mechanically coupled cantilever and bridge resonator; actuated by Aluminum Nitride (AlN) layer, exploring the potential of coupled systems in gas sensing application. The pure AC actuation is applied on the piezoelectric layer and the corresponding frequency response of three systems are discussed. The experiment results show different responses on different devices with same structures, revealing the existence of induced axial stress in AlN layer or contact surface, i.e., due to fabrication process; as varying the applied AC voltages. To explore the system capabilities on gas sensing application, the weakly coupled system is heated via joules heating effect near a bifurcation point. The sensing performance for increasing Helium concentration is measured experimentally and shows high sensing performance and good linearity with low power consumption, which is suitable for applications of IoT and wireless sensor networks.