Fabrication And Properties Of Ni Nanowire Arrays Based Flexible Strain Sensor

Joint movement is the key to human movement.Real-time monitoring of human joint movement is helpful to establish personalized medical assistance system.The rapid development of flexible electronic technology promotes the construction of human joint motion monitoring system,and puts forward extensive demand for flexible strain sensor of its core component.With high flexibility,high sensitivity,high stability and wide adaptability,the resistive flexible strain sensor plays an important role in the field of motion monitoring.However,there still have some chanllenges in the monitoring of joint motion: the complex joint motions such as in-plane bending,rotation and twisting cannot be accurately monitored;the problem of incompatible detection of small motion and large deformation motion.To these problems,based on the high-aligned Ni nanowire(Ni NW)arrays in this paper,we have designed a resistance flexible strain sensor with the tripleasymmetric structures,and proposed a strain zoning detection technology.The main research contents and results are as follows:1.The influence of the structure of Ni NW array,Ni NW density and the thicknesses of polydimethylsiloxane(PDMS)substrates on the properties of the strain sensor were studied.The results show that: 1)the high-aligned structure of Ni NW arrays endows the in-plane tensile strain sensing anisotropy of the strain sensors;2)With the increase of Ni NW density and PDMS substrate thickness,the sensitivity of the device decreases,but the strain detection range increases.3)The optimum PDMS substrate thickness was 360 nm.2.Different from most resistance flexible strain sensors,the sensing mechanism of the composite structure with Ni NW arrays and PDMS is not from the separation effect or crack effect,but from the tunneling effect.Meanwhile,the ability of the strain direction detection comes from the anisotropic structure of the device.3.A flexible strain sensor with triple asymmetric structure is designed and fabricated,and its sensing performance and application are analyzed.The triple asymmetric structures are the high alignment of Ni NWs,the asymmetric distribution of the sensing layer in the thickness direction and in the device width direction.The results show that: 1)under the tensile strain parallel to and perpendicular to the aligned direction of Ni NWs,the resistance change of the device are obviously different,and the maximum sensitivity factors in both directions are-1.68 and-35.16,respectively;2)when the out-of-plane bending tensile and compressiive electrical responses,and the maximum sensitivity factors are 1500 and-20 respectively;3)the movements of in-plane tension,out of plane bending and inplane bending are successfully monitored.In joint multi-dimensional motion monitoring,the up and down bending,left and right swing and rotation of wrist joint are detected.At the same time,it also realizes the distinction of handwritten English letters and the recognition of stroke order of Chinese characters.4.To realize the compatibility of joint large strain and small strain monitoring,based on the tunnel effect,we propose the strain zoning detection technology;i.e.,the resistance change rate was used in the small strain detection region,and the current change rate was used in the large strain detection region.The results show that the maximum sensitivity and the minimum resolution of the sensor in the small strain range(ε≤5%)are 35 and 0.2%,respectively;the maximum sensitivity is 9.43×106 in the high strain area(5%≤ε≤45%).The movements of knee joint,finger joint,respiration,cough and sneeze are successfully mointored.