Wireless Alarm Microsystem Self-Powered by Vibration-Threshold-Triggered Energy Harvester

A novel self-powered wireless sensing micro-system is proposed and prototyped. The micro-system can autonomously monitor the amplitude of concerning vibration when it reaches a preset threshold, and wirelessly transmit alarming/notification signals when the vibration lasts for a considerable period. The event-driven sensing/alarming function is enabled by a piezoelectric energy harvester that starts to generate electric power only when the monitored vibration level reaches a critical threshold. The harvester consists of two stages of vibratory structures that interact with each other via magnetic repulsion. The bistability leads to the threshold-triggered power-generating function. For adapting to various applications, the threshold can be preset by adjusting the gap-distance between the two magnets on the two vibration stages; thereby, the power-generating action can be switched on by the concerning vibration level. The working mechanism is verified by both theoretical analysis and test for the prototyped miniature harvesters. Based on the smart energy-harvesting function, an application specific electric-energy control circuit and an RF-transmitter are designed to form a nonsupply wireless alarming system. Experimental results validate the event-driven alarming function. The abnormal vibration event-induced wireless alarming signal is autonomously transmitted to over 2 km away when the vibratory excitation lasts for 1 min to generate electrical energy of about 2 mJ.