Development Of The Automatic-Recovery Inertial Switch Based On The Galinstan Marbles

The inertial switch made by the MEMS process is a sensor and actuator used to monitor acceleration signals and react in time.According to the contact mode between the moving electrode and the sensing electrode,the inertial switch can be divided into solid-solid contact type and solid-liquid contact type.The traditional solid-solid contact type inertial switch is based on the mass-spring system to monitor acceleration signals,which cause problems such as contact wearing and signal bouncing when the moving electrode contacting with the sensing electrode,and seriously affect the long-term and stable use of the switch.In recent years,the solid-liquid contact type inertial switch was proposed,using the working liquid as the moving electrode,which can effectively solve many problems caused by the rigid contact between the moving electrode and the sensing electrode.Galinstan is a kind of ideal working fluid,but oxidized rapidly in the air.The oxide layer formed on the surface of galinstan will adhere to the substrate and affect its surface tension,making it moving difficult in the microchannel of the inertial switch and cannot recover after deformation,which seriously affects the performance of galinstan as a moving electrode.To solve this problem,we coated the galinstan droplets with PTFE and graphene powder to make the galinstan marbles.The results of performance testing shows that both galinstan marbles owns high surface tension and can move freely on various substrates.At the same time,the galinstan marbles coated with graphene powder also have ideal electrical conductivity.On this basis,we used a graphene coated galinstan marbles as the moving electrode and two PTFE coated galinstan marbles as the supporting structure,imitating the working principle of the mass-spring structure to enable the inertial switch with self-recovery performance.Meanwhile,the structure of the microchannel on the substrate and the sensing electrode on the cover sheet are designed based on the working principle of the inertial switch.Moreover,the diameter of the galinstan marble as the moving electrode is parameterized,and the relationship between the threshold acceleration and the central parameter was revealed based on the Young-Laplace equation.As the result,the PDMS substrate with a microchannel structure was fabricated using the soft lithography technology based on the SU-8 mold,the glass cover sheet with the metal thin film sensing electrodes was fabricated using the photolithography patterning technology,and the PDMS substrate was bonded with the glass cover sheet based on the oxygen plasma surface modification.The working performance of the inertial switch was tested by a drop hammer testing system.The results shows that the inertial switch has good self-recovery performance and can work stably for a long time,and the response time and conduct time at the threshold acceleration of 23 g are 6.62 ms and 0.99 ms,respectively.