Design And Research Of Micropressure Sensor Based On Flexible Composite Material

Flexible electronic devices have attracted wide attention in the fields of electronic skin,artificial intelligence and medical health due to their softness and high performance.Among them,flexible pressure sensor is a very important sensor,which has the most extensive application fields,such as attaching to the human body surface to detect the pulse signal,or integrating the sensor on the robot surface to improve the human-computer interaction ability.According to the working principle,flexible pressure sensors can be divided into piezoresistive,capacitive and piezoelectric flexible pressure sensors.Among them,flexible piezoresistive sensor has been widely studied because of its high pressure range and high sensitivity.For flexible pressure sensors,researchers design micro structures to improve the sensitivity of the sensor,such as angle cone structure,spherical structure,but these methods often require complex process steps and high cost to prepare the mold.Considering that the flexible pressure sensor will develop in the direction of high performance,low cost and simple process.In this paper,a simple and feasible method for fabricating flexible piezoresistive sensors is presented,which is to fabricate flexible piezoresistive sensors using ground glass with different microstructures as templates.The work and innovations of this paper are as follows.First,the design method of micro structure flexible piezoresistive sensor is proposed.In order to illustrate the advantages of structure design,the stress-strain and pressure response of simulated structure of frosted glass are simulated by COMSOL Multiphysics finite element simulation platform.The simulation results show that the sensor based on the irregular structure of frosted glass surface has higher sensitivity than the regular structure sensor,and the sensor with small mesh structure has higher sensitivity than the sensor with large mesh structure.Second,in order to determine the selection and proportion of conductive composites in micro structure flexible piezoresistive sensor,the conductive and piezoresistive properties of carbon black/polydimethylsiloxane（CB/PDMS）composites and multi walled carbon nanotube/polydimethylsiloxane（MWCNT/PDMS）composites with different conductive filler mass fraction are studied.The results show that the percolation threshold of CB/PDMS composite is5wt%,and that of MWCNT/PDMS composite is 2wt%;both composites have positive piezoresistive effect,and have the highest piezoresistive sensitivity at the percolation threshold.Third,after determining the material selection and ratio of conductive composites,according to the design scheme,single and double layer structure sensors with different microstructure sizes are prepared by using 120 mesh,240 mesh,300 mesh frosted glass and plane glass respectively.The effects of microstructure size and single-layer and double-layer structure on the sensitivity of the sensor are studied.The sensor’s response time,low-pressure detection capability,hysteresis,pressure response,repeatability,temperature characteristics and other properties are tested,and it is applied to monitor swallowing actions.The results show that the sensor made of frosted glass with smaller mesh（larger microstructure size）has higher sensitivity;the sensitivity of double-layer structure sensor(15.7 k Pa^-1)is higher than that of single-layer structure sensor(7.4 k Pa^-1).In conclusion,the sensor prepared in this paper shows excellent performance in all aspects.It has fast response time（less than 4 ms）,good low pressure detection ability（200 Pa）,stable pressure response and good repeatability in 700 repeated tests.And it has achieved better signal feedback in the application of monitoring swallowing actions,which is expected to be applied in the medical and health field.