Researches On Elastic Strain Sensor Based On Liquid Metal Alloy

The elastic strain sensor can realize the monitoring of human motion and physiological parameters,the robot's force perception,etc.,which has important application prospects in the fields of medical rehabilitation,sports fitness and robot skin.Generally,the elastic strain sensor is used to detect the deformation generated by the movement of a human body or a robot,thereby sensing the movement state of a human or a robot.In practice,in addition to detecting deformation,it is necessary to know the magnitude of the force.Existing elastic strain sensors are generally composed of a polymer and a conductive material,and the modulus is fixed,which is suitable for force detection on the order of several N,and it is difficult to meet the requirements of wide-range variable load force detection.In addition,most of the currently reported elastic strain sensors require external power,large power consumption,cumbersome and heavy wear,and limited life.Therefore,there is an urgent need for a method with low cost and simple process to manufacture a stretchable,selfpowered elastic strain sensor.Liquid metal has the characteristics of low toxicity,variability and good conductivity,which is the preferred conductive functional material for preparing stretchable sensors.However,the surface of the liquid metal alloy has an oxide film with a large surface tension.Drops on the flexible substrate tend to form small balls,which is difficult to pattern on a flexible substrate.Based on the above challenges,the main work of this article is as follows:(1)In the paper,the liquid metal eutectic gallium indium tin alloy is obtained by water bath heating.Micron-level copper powder is incorporated into liquid metal through mechanical grinding to form a liquid metal slurry,which enhances its wettability when patterning a flexible substrate.Using the characteristics of spiral elastic tube,a conductive spiral liquid metal pattern was prepared.(2)In order to realize the self-powered elastic strain sensor,we started with the material selection and structural design of the elastic strain sensor,and prepared a spiral liquid metal pattern.Elastic conductive coils are used to provide a stable conduction path near a 90-degree angle.This structure is combined with Faraday's law of electromagnetic induction to achieve self-powering.And the built-in Co-based amorphous wire is used to increase the output voltage(35 mV),which can not only respond to stretching,but also respond to bending and vibration.The magnetic flux changes between the external magnetic field and the inner diameter liquid metal spiral coil.Real-time health monitoring for monitoring and distinguishing between finger joint motion and Parkinson's disease.(3)For the adjustable modulus of the strain sensor,we arrange two thermoplastic elastomer tubes filled with liquid metal in parallel to form a capacitive elastic strain sensor.Springs with different elastic coefficients are assembled in parallel with the elastic strain sensor to form an elastic strain sensor with adjustable modulus.The modulus of the elastic strain sensor is adjustable in the range of 0.78 to 10.3 MPa,and it exhibits excellent linearity,repeatability and fast response time(<50 ms)in a wide range force detection range of 0.07 to 74 N.In addition,the elastic strain sensor has good fatigue resistance during loading and unloading for more than 3500 cycles.Finally,a digital display system matching the sensor was developed,which can accurately display the weight of the load,which verified the application potential of the elastic strain sensor in the field of robot weighing.