Research And Development Of New Liquid Metal Pressure Sensor In Geotechnical Engineering Monitoring

Geotechnical engineering is a subject which takes rock-soil body as the research object.Obtaining information about the structure,composition and internal stress distribution of rock-soil body is very important for research and analysis various geotechnical engineering problems.As a technical means to obtain the internal stress value of rock-soil body,the pressure sensor can monitor the internal stress value of rocksoil body for a long time,long distance and all directions.It plays an important role in guiding the construction of geotechnical engineering and monitoring various geological disasters such as landslides and debris flows.In this paper,a new type of liquid metal pressure sensor applied in geotechnical engineering is designed and developed.The external pressure can be obtained by measuring the resistance change of the sensor.The designed pressure sensor is mainly composed of 40 CrMoV alloy steel shell and PDMS microfluidic chip inside.The 40 CrMoV alloy steel has high strength and low hysteresis elasticity.While protecting the internal PDMS chip from damage,it also Creatly improves the measurement range of pressure sensor and ensures the stability and reliability of test results.Inside the pressure sensor is a PDMS microfluidic chip packaged with liquid metal EGaIn,which can form a ?m-level microfluidic channel inside the PDMS chip by means of photolithoCraphy.The working principle of the liquid metal pressure sensor designed in this paper is: PDMS microfluidic chip is used as the sensitive element of pressure sensor,the crosssectional area of liquid metal EGaIn conductor changes when the cross-sectional area of the microfluidic channel inside the PDMS microfluidic chip shrinks under stress,and the resistance value of liquid metal EGaIn as the transforming element of pressure sensor increases with the decrease of its cross-sectional area.The liquid metal pressure sensor is to obtain the internal pressure value of rock-soil body by converting the pressure signal into electrical signal.This paper draws the following conclusions through research and analysis:(1)The pressure sensor developed in this paper mainly uses 40 CrMoV alloy steel,polydimethylsiloxane PDMS,liquid metal gallium indium alloy EGaIn and other materials.The pressure sensor is rectangular with a long side size of 32 mm,within the design range of 20 MPa,the resistance of the sensor changes to 800 m?,which realizes the design purpose of small volume and large range of the sensor.At the same time,liquid metal EGaIn has strong fluidity and high conductivity.As a conversion element of pressure sensor,it overcomes the shortcomings of traditional metal conductor,such as low sensitivity and easy damage.(2)With the help of finite element software FLAC3 D,this paper simulates and analyses the influence of the arrangement of micro-channels on the force and deformation of PDMS chips.The results show that the size and layout of micro-channel can meet the design requirements of pressure sensor well.It can increase the stress and strain near the channel,make the resistance of liquid metal conductor change obviously,increase the output intensity of pressure sensor signal.It have no obvious influence on the stress and strain of other parts of the chip,avoid damage of uneven stress and deformation of chip.(3)In this paper,we use reCression analysis to fit the sample reCression line between the sensor resistance change and the applied pressure data measured under repeated loading experiments.At the same time,we verify the high correlation between the two by means of significance test.In practical engineering applications,according to the resistance value of the pressure sensor output,it can be substituted into the sample reCression line to get the value of external pressure,so as to achieve the purpose of longdistance and long-term acquisition of the internal pressure value of rock-soil body.(4)In order to simulate the influence of different conditions on the output stability of pressure sensor signal,three different loading rates are used to exert pressure on the sensor.To ensure the repeatability of the test results,the pressure sensor is loaded three times at different loading rates.The results of three repeated experiments show that the pressure-resistance curves of the pressure sensor under three different loading rates are very close,which verifies that the output signal of the pressure sensor has good stability.