Flexible Wearable Pressure Sensor Based On Microstructure

There has been a rising demand for high-performance,flexible,and multifunctional sensors in the wake of the rapid advancement concerning artificial intelligence,Internet of Things,and wearable electronics.In particular,as one of the most widely adopted sensor devices,wearable flexible pressure sensors have gained extensive attention from researchers.Being a type of flexible intelligent electronic device,it detects pressure signals generated by the human body.Flexible pressure sensors can measure,document,and monitor physical parameters associated with human health such as blood pressure,pulse rate,skin stress,or respond to human activities such as movement status,physical movements,gestures,and expressions.They offer potential applications in areas such as intelligent skin,human-computer interaction,and medical surveillance,which have been evolving rapidly in recent years.There are various types of flexible pressure sensors in accordance with the sensing mechanism,including piezoresistive,capacitive,piezoelectric and optical observable types.In this regard,flexible piezoresistive pressure sensors are promising in applications owing to features such as simple structure,convenient signal reading,and low energy consumption.Optical observable sensors have also attracted the researchers'interests in recent years because of signal reading visualization,favorable dynamic response.In the construction of flexible pressure sensors,researchers have carried out micro-structuring of the sensing layer in flexible pressure sensors to enhance the linear range and sensitivity of flexible sensors.Further studies have demonstrated that the micro-structured sensing layer can enhance the sensing performance and modify the light transmission property by microstructure configuration,which offers the potential for constructing an optical observable sensor.This paper presents a scheme to streamline microstructure production to improve the sensitivity and linear range of flexible piezoresistive pressure sensors,along with a method to construct an optical observable sensor utilizing microstructures.A piezoresistive flexible pressure sensor and an optical observable flexible pressure sensing film have been fabricated,respectively,with the main research content as follows:1.A wide linearity range and high sensitivity flexible pressure sensor with hierarchical microstructures via laser markingFirst,acrylonitrile-butadiene-styrene(ABS)templates with multi-stage hemispherical structure arrays were manufactured by laser engraving,while arrays with multi-stage hemispherical structures were fabricated by flexible polydimethoxysilane transfer.Subsequently,a sensing layer was obtained by spraying a layer of graphene onto the multi-stage hemispherical structure.Eventually,the piezoresistive flexible pressure sensor was assembled from the sensing layer and the inte rdigital electrodes embedded with silver nanowires.The sensor features high sensitivity of 15.4 kPa-1 over an ultra-wide linear sensing range of 200 kPa,a low detection limit of 16 Pa,a rapid response time of 20 ms,and excellent stability at 7500 cycles under cyclic pressure application.By comparing the sensing performance for this sensor with a multi-stage hemispherical structure array,and that of a hemispherical array-based sensor,it has been evidenced that such a multi-stage structure is conducive to the enhancement of sensor sensitivity and linear range.Additionally,utilizing the in-situ observation method has further revealed the mechanism underlying the flexible pressure sensing performance enhancement based on the multi-stage hemisphere structure.Ultimately,the manufactured sensors have been successfully employed to monitor various human movement signals such as sound,pulse,gesture,and gait,which holds promising applications for studies in areas such as human-computer interaction systems,human health monitoring and electronic skin.2.Optical observable flexible sensing films based on polydisperse pore structureFirstly,polydispersed sodium chloride(NaCl)particles were produced by grinding NaCl particles with a ball mill,which were subsequently mixed into polydimethoxysilane(PDMS).After elution,observable flexible sensing films with strong scattering effect of polydisperse structure were yielded.Such sensing film exhibits a sensitivity of 0.067%kPa-1 over an ultra-wide linear range of 1200 kPa,with a remarkably robust stability at 5000 cycles of applied pressure and an outstanding responsive performance at high humidity temperature.The effect of polydispersity for pore structure on the light transmission of sensing film was explored by comparing the polydispersity of various sensing film pore structures.A finite element analysis was utilized to simulate the process of light transmission variations of sensing film upon stressing.The light transmission variation of sensing film was acquired with different compressive strains,validating this polydisperse structure's sensing characteristics.Eventually,the fabricated optical observable flexible pressure sensing film was adopted for pressure distribution testing,realizing the visualization and dynamic testing of pressure distribution.