Theoretical And Experimental Research On The Performance Of Liquid Metal Pressure Sensors Under Low Temperature Conditions

In the field of geotechnical engineering monitoring,pressure is a very important indicator,which plays a vital role in the monitoring of key parts of the structure and the early warning of engineering safety.This article focuses on how to ensure the stable operation of pressure sensors in cold and low temperature environments,and studies a liquid metal pressure sensor suitable for low temperature conditions.It uses elastomer PDMS(Polydimethylsiloxane)as the base material,uses microfluidic soft lithography technology to carve holes in its interior,and fills Galinstan with good fluidity,low melting point,and strong conductivity as a conductor,and finally encapsulated by a spring steel(50Cr VA)shell.Simplify theoretical derivation through finite element simulation,calibrate the pressure sensor,and explore its performance in low temperature environment.The pressure sensor designed in this paper has three main components: spring steel shell,PDMS chip,and liquid buffer layer.The shell is the main load-bearing structure,and the material is spring steel(50Cr VA).Because of its good elastic properties and high yield strength,it can increase the sensor range to MPa level while ensuring low hysteresis.The PDMS chip uses microfluidic soft lithography technology to carve holes in its interior and fill it with liquid metal.In order to explore the influence of channel cross-section and metal materials on chip performance,four different PDMS chips were designed.Through the theory of contact mechanics approximate model and finite element simulation analysis of channel deformation,the relationship between compressive stress and metal resistance change is simplified and deduced,which provides a theoretical basis for the subsequent calibration of the pressure sensor.The liquid buffer layer is filled with alcohol with low melting point to ensure the good performance of the sensor at low temperatures.The finite element ABAQUS software simulation shows that the existence of the liquid buffer layer makes the stress transferred to the surface of the PDMS chip uniform,making the theoretical derivation more accurate.Through theoretical analysis and demonstration of experimental results,the main conclusions of this article are as follows:For PDMS chips,the cross-sectional shape has a great influence on the sensitivity of the chip output curve,which is mainly caused by the channel width-to-height ratio w/h.The squares have lower sensitivity than rectangular cross-sections,and the output curve is smoother,which is more suitable for the channel form of the chip.At room temperature,chips made of EGa In and Galinstan do not have much difference in performance,and both can be used as good liquid metal conductors.However,due to the difference in the melting points of the two materials in a low temperature environment,only the chip made of Galinstan can Maintain stable and good working performance.The finally designed spiral chip has the characteristics of smoother output curve,high sensitivity and good repeatability,and within the stress range of 0-31.8k Pa,the experimental results are in good agreement with the theoretical analysis.For the pressure sensor,the pressure sensor is calibrated through the derivation of the theoretical formula.The calibration coefficient K is 23.71 MPa at room temperature.The key performance indicators such as sensor curve compliance,repeatability,and hysteresis meet the requirements.The installation of the shell also reduces the hysteresis of the pressure sensor from 7.24% of the chip to 4.05%,and based on this,the performance of the sensor under low temperature and the influence of low temperature on the pressure sensor are studied.The introduction of the temperature coefficient Ct shows that the sensor at low temperature can still be calibrated by the same theoretical formula.In the low temperature range of-20℃～0℃,the temperature has little effect on the calibration of the sensor,and the calibration coefficient K is around 25.0MPa.However,compared with the room temperature environment,the low temperature output curve has obvious deviation,the maximum error reaches 20.52%,and the calibration coefficient is too large,indicating that the influence of low temperature on the sensor cannot be ignored.In addition,the low temperature environment will affect the repeatability and hysteresis of the sensor to a certain extent.In the end,the Galinstan liquid metal sensor studied has good working performance in low temperature environments.Compared with room temperature conditions,only the calibration coefficients at low temperatures need to be corrected,and the application range is wider.