Research On Flexible Pressure Sensor With Hierarchical Microstructur

As an important part of intelligent wearable,flexible pressure sensor plays an important role in human health monitoring,motion detection,electronic skin and so on.The performance of the sensor is largely affected by its structure,so part of its performance can be improved by designing micro nano structure.The deformation state of microstructure after stress is one of the main reasons affecting the performance of piezoresistive sensor.In this paper,three different hierarchical scale nano column array structure models are constructed by finite element simulation.By analyzing the equivalent strain and pressure-strain relationship of the three models,it is found that the model with a grading ratio of 1200:900 has the best equivalent strain and good pressure-strain relationship under the action of external force.After that,the porous anodic aluminum oxide（AAO）hierarchical microstructure template was prepared by anodic oxidation method.The average height of the low column area of the template was about 888.9±4.7 nm,the average height of the high column area was about 1198.4±4.5 nm,and the pore diameter was about 358.4±5.02nm.Polypyrrole（PPy）conductive layer was grown inside AAO template by in-situ polymerization,and polyurethane（PU）solution doped with multi wall carbon nanotube（MWCNT）was cured into film in the template by spin coating method.According to SEM observation,the nano column array is orderly and upright.The average height of low nano column array is about 872.3±1.52 nm and that of high nano column array is about 1167.6±3.05 nm.The flexible interdigital electrode was prepared by screen printing technology,and the electrode and conductive film were assembled into a flexible pressure sensor.The performance of flexible sensors with different content of carbon nanotubes is compared.With the increase of the content of carbon nanotubes,the sensitivity of the sensor to force is improved to a certain extent.When the content of carbon nanotubes is 3 wt%,it has the most ideal sensitivity value and detection range.In order to further realize the combination of high sensitivity and wide detection limit,PPy/MWCNT/PU hierarchical microstructure flexible pressure sensor with different conductive mechanism,PPy/PU flexible sensor and MWCNT/PU flexible sensor are compared.It is found that PPy/MWCNT/PU hierarchical microstructure flexible pressure sensor has a sensitivity of 208.35 kpa^-1 in the extreme low pressure range of0-250 pa,It has a sensitivity of 55 kpa^-1 in the pressure range of 250-750 Pa.In the comparative experiment with the flexible sensor without hierarchical structure,it is found that the sensitivity value and response interval of the flexible pressure sensor with hierarchical structure are higher than those without hierarchical structure.The experimental results are consistent with the finite element analysis results.In addition,the sensor has good stability and repeatability,and can monitor pressure signals such as arterial pulse and vocal cord sound in real time.These tests can preliminarily prove that the sensor has the ability to capture and analyze human activity signals,which provides some support for the future intelligent wearable textiles.