Multi-functional Electronic Skin With Modulus Gradient-Distributed Structure For Tactile-Bending Perception

Electronic skin is a recent advancement in flexible biomimetic electronic devices that mimic the sensory functions of human skin.Benefiting from its flexibility,miniaturized units,and integrated system,various types of electronic skins have been developed for aerospace and aviation applications.Among them,flexible tactile electronic skin is the most extensively researched and applied type of electronic skin.The broad range of potential applications has led to the demand for high sensitivity and wide measurement range performance in flexible tactile electronic skins.However,current state-of-the-art technology struggles to meet these requirements.Moreover,most flexible tactile electronic skins require measurement circuits and display devices to communicate with users,which hinders efficient and convenient interactions.Additionally,owing to the excellent conformability of flexible electronic skin,the need to perceive the bending state of electronic skin in aerospace and aviation robotics applications is increasingly critical.However,single-function electronic skins often fail to acquire these crucial pieces of information simultaneously.In response to the aforementioned issues,this article proposes a modulus gradient-distributed structure for tactile-bending perception multi-functional electronic skin.This electronic skin not only achieves high-sensitivity pressure detection within a wide measurement range but also displays pressure magnitude in situ through color changes.Furthermore,it possesses the function of perceiving its own bending state.The specific research contents are as follows:（1）Research on the structure and working principle of a modulus gradient-distributed structure for tactile-bending perception multi-functional electronic skin.The research focuses on the development of a composite and flexible electronic skin structure with tactile and bending perception based on the modulus gradient-distributed architecture to meet the demand for high sensitivity and wide-range pressure sensing.The working mechanism of the pressure-resistive pressure sensing unit under pressure load is investigated,and the influence of structural design on the performance of the sensing unit is explored.The attenuation mechanism of the sensitivity of traditional micro-structured pressure sensing units under high pressure is revealed.A multi-layer pressure sensing structure based on the modulus gradient is proposed,and its impact on the sensitivity and measurement range of the sensor is analyzed.For the pressure display function of electronic skin,the force-electric-heat conversion relationship during the operation of the sensing unit is studied,and a pressure in-situ display sensing unit based on this relationship is proposed.The variation of the surface temperature of the sensing unit with pressure is analyzed,and the time-dependent pressure memory effect based on the heat transfer principle is explored,as well as the influence of the thermal conductivity of the encapsulation material on the pressure memory time of the sensing unit.In response to the bending detection needs of electronic skin,a method for detecting bending status based on distributed curvature information is proposed,and a distributed bending sensing layer is designed by establishing a mathematical model for distributed bending perception.（2）Preparation and material characterization of a modulus gradient-distributed structure for tactile-bending perception multi-functional electronic skin.In order to prepare the multi-functional electronic skin,the preparation processes and material preparation methods of each sensing unit were investigated,and key composite materials of the electronic skin were prepared,including graphene/carbon nanotube/polycaprolactone conductive composite materials,thermochromic composite materials,and liquid metal/Ecoflex composite materials.The influence of the conductive filler ratio and concentration on the conductivity of the graphene/carbon nanotube/polycaprolactone composite material was studied,and the permeability threshold of the conductive composite material was studied,as well as the morphological characteristics of the conductive composite material.The color-temperature change characteristics of the thermochromic composite material were investigated,and the effect of the liquid metal filling ratio on the thermal conductivity of the liquid metal/Ecoflex composite material was explored.（3）Research on performance testing of a modulus gradient-distributed structure for tactile-bending perception multi-functional electronic skin.First,the study tested the influence of modulus gradient and multilayer structures on the sensitivity and measurement range of pressure sensing units of the composite electronic skin,and optimized the structure of the pressure sensing unit.The study also tested the linearity,repeatability,dynamic response,and minimum detection limit of the pressure sensing unit of the composite electronic skin.Second,the study investigated the pressure display characteristics,repeatability,and hysteresis of the pressure display sensing unit of the composite electronic skin,and tested the effect of ambient temperature on the display function of the composite electronic skin.The study also tested the effect of the thermal conductivity of the packaging material on the pressure memory time of the electronic skin,and achieved the adjustment of the memory time of the electronic skin.Finally,the study compared the influence of pre-strain structures on the sensitivity of the curvature sensing unit of the composite electronic skin,and tested the curvature detection performance and repeatability of the curvature sensing unit in the bend sensing layer.The research results show that the tactile-bending sensing multi-functional electronic skin with modal gradient-distributed structure designed in this paper can not only achieve highly sensitive pressure measurement in a wide range,display the pressure magnitude and distribution in situ,but also detect its bending state.The specific performance indexes are:the modal gradient multilayer microstructure pressure sensing unit of the electronic skin has a sensitivity of 29.69 k Pa^-1 in the 0-500 k Pa range,a linearity error of 4.85%,a repeatability error of 2.18%,a dynamic response of 50 ms and 30 ms,and a lower detection limit of 30 Pa;the pressure display sensing unit of the electronic skin can display in situ the pressure changes in the 15-110 k Pa The pressure display sensing unit of the electronic skin can display the pressure change in the range of 15-110 k Pa in situ,while having adjustable pressure memory time;the curvature sensing unit in the bending sensing layer of the e-skin has a high sensitivity of 63.66%/cm^-1 in the range of 0.067-0.500 cm^-1,while the sensing unit has good consistency among them.The tactile-bending sensing multi-functional electronic skin with modulus gradient-distributed structure designed in this paper can realize pressure sensing,pressure display and bending sensing functions at the same time,which is suitable for a variety of application scenarios,including detection of micro-pressure and human body signals,pressure distribution detection and object shape detection.This thesis provides a new idea for the design of multi-functional electronic skin,which is of great scientific significance for the development of high performance and multifunctionality of electronic skin.