Development Of An Inertial Micro-switch Based On A Liquid Metal Marble

The liquid-solid contact of inertial micro-switch is a precise inertial device,which senses threshold acceleration by using fluid to realize switch's on-off state.This solid-liquid contact type solves the problems of traditional solid-solid contact,such as contact wear,signal jump and high contact resistance.Liquid metal is a liquid-state metallic material at room temperature,mainly including mercury and gallium alloy,which is usually used as the movable electrode in solid-liquid contact of inertial micro-switch owing to good conductivity,thermal conductivity and fluidity.However,mercury is toxic and volatile,and therefore is not suitable for wide applications.Gallium-base alloy has the advantages of low toxicity and low vapor pressure,but it is easy to oxidize in air and adheres to the most substrates.Liquid metal marbles are made by coating hydrophobic particles on the surface of liquid metal droplets,which have the advantages of non-adhesion,good stability and simple preparation.In this paper,to solve the adhesion of gallium-base alloy droplet served as the movable electrode,a liquid metal marble as the movabe electrode is applied to inertial micro-switch for the first time,and an inertial micro-switch based on a liquid metal marble is developed successfully.First,the method of preparing liquid metal marbles by graphene sheets coating Galinstan droplets was introduced,which is simple,convenient and can make volume be controlled accurately.And the properties of liquid metal marbles were studied,including the measurement of contact angle and sliding angle on the glass,ground glass,PDMS and Parylene substrates,the test of electrical conductive and its timeliness,and the measurement of effective surface tension.The results show that liquid metal marbles have nonstick properties,good conductivity and timeliness,and the effective surface tension is 0.265 N/m.These properties indicate that the liquid metal marble conforms to the condition of the movable electrode in the inertial microswitch.Next,the structure design,material selection and numerical simulation of inertial microswitch were carried out.The diamond-shaped microchannel is designed to achieve the automatic-recovery performance,and the whole structure of the switch is designed to be symmetrical to work bidirectionally.PDMS and glass are selected as the substrate and cover materials of the inertial micro-switch.Depositing a layer of Parylene film on the inner wall of the microchannel can improve the mobility of the liquid metal marble.According to the design of inertial micro-switch structure parameters and the liquid metal marble property parameters,the switch was numerically simulated by VOF model in Fluent software for simulating and analyzing the liquid metal marble's motion under 25 g designed threshold acceleration.The results show that the position of the sensing electrode is determined,which provides theoretical basis for the inertial micro-switch design.Moreover,the results also verifies the feasibility of the inertial micro-switch's structure and parameters in theory.Finally,the inertial micro-switch was fabricated by using MEMS processing technology,including soft lithography,chemical vapor deposition,metal pattern and oxygen plasma bonding.The dynamic and static performance of the inertial micro-switch were tested by the drop hammer experiment and the centrifuge experiment respectively.The performance test results show that the dynamic threshold value is 26.2 g,the response time and contact time are 1.2 ms and 1.1 ms respectively,the static threshold value is 26.8 g,the switch closure is stable and reliable,and the switch can realize the automatic-recovery performance.By comparing the dynamic threshold,the static threshold and the designed threshold,it shows that they have good consistency,which verifies not only the validity of the simulation model of the threshold,but also the feasibility of the inertial micro-switch based on a liquid metal marble.