Design and Fabrication of Low-Threshold Inertial Switches Using Metal Droplets as Sensing Elements

In this paper, we propose a novel design model for an inertial switch that utilizes metal droplets as the sensing element. The overall device model comprises three components: the substrate layer, the functional structure layer, and the cover layer, along with the liquid metal. The metal droplets within the liquid storage tank are drawn towards the fixed electrode due to inertial forces. When the acceleration exceeds a predetermined threshold, the metal droplet covers the fixed electrode, closing the switch and allowing current to flow through the external circuit. Conversely, when the acceleration load is removed, the metal droplet retracts to the liquid storage tank, disconnecting the fixed electrode. This design is characterized by its simplicity, low manufacturing cost, and stable dynamic response. To evaluate the threshold acceleration of the inertial switch, we developed a threshold evaluation equation through theoretical analysis and successfully fabricated an experimental prototype. Test results indicate that the threshold acceleration of the fabricated inertial switch is 0.76g, with a response time of 21 ms and a contact time of 10 ms. The overload test indicates that the device has excellent overload impact resistance and stable dynamic contact. Compared to traditional mechanical contact-type inertial switches, this research not only presents a new scheme for low-threshold inertial switches with a simple structure and low manufacturing cost, but also introduces the concept of deformable liquid metal electrodes into the field of inertial sensing for the first time, opening up a new technical path for applications such as consumer electronics and the Internet of Things that require low power consumption for triggering.