On Hole-Shaped Resistive Flexible Strain Sensor For Human Motion Detection

With the rapid development of artificial intelligence,electronic technology and new materials subject,as a new wearable device,flexible strain sensors attract lots of attention in the field of medical health,human motion detection and robot skin.In order to conform to the trend of intelligent times and provide more convenient services for the mass production and life,a porous resistance variant flexible strain sensor based on carbon black and multi-wall carbon nanotubes is designed and developed in this thesis.The main work of this thesis is as follows:(1)Preparations of flexible strain sensor.With the help of the high water solubility of white granulated sugar,polydimethylsiloxane is selected as the substrate,white granulated sugar is used as the pore-forming agent to acquire the porous flexible matrix,which adopts ultrasonic dispersion and high temperature heating.In addition,mechanical experiments are carried out on six kinds of flexible matrix.When the mass fraction ratio(n=m(sugar)/m(PDMS))is 30%,the best performance parameters(strain range of 130%,tensile strength of 0.83MPa,Young's modulus of 0.62MPa)are provided by the flexible matrix.The carbon black and the multi-walled carbon nanotube are selected as conductive fillers,and the conductive composite is prepared by solution blending method(carbon black and multi-walled carbon nanotube are 1.00wt%respectively).Finally,a sensitive material layer is formed on the surface of the porous matrix by economical and efficient spraying process,after that a porous resistive flexible strain sensor with an inner diameter of 2.25mm and a height that can be cut is produced.SEM is used for microscopic characterization and the conductive mechanism of the flexible sensor in the strain process is introduced.(2)Testings and analyses on static and dynamic performance of flexible strain sensors.Through the performance test experiments,what is shown is that the flexible sensor has the characteristics of high sensitivity(GF is as high as 61.82),good linearity(y as low as 13.6%)and wide output(0?60 ?).In 10 cyclic tensile tests under the strain of 2%,25%,50%and 75%,the stable waveform without drift is output stably,which shows excellent repeatability.In different stretching rate tests under the step strain of 2%,20%,40%,50%,75%and the strain of 30%,the high stretch property,low creep property and fast dynamic response are shown.In 100 cyclic tensile tests under the strain of 2%,50%,the excellent reliability is shown.In 45 tests of the bending cycle of 30?,there is a slight hysteresis which decreases with the increase of the number of cycles.In temperature sensitive characteristic tests within 22??51 ?,there is a small temperature drift and changed resistance rate of 0.12 ? around,which can satisfy the operation requirement of complex environment.(3)Applications of flexible strain sensor in human motion detection.After the characteristics of the output signal of the flexible sensor are analyzed and summarized,the Coif4 wavelet basis function,3 level decomposition,Rigrsure threshold and hard threshold function are selected as the wavelet domain denoising parameters by the control variates to denoise of the flexible sensor signal with the wavelet threshold.Finally,the flexible sensor is worn on each joint of the tester to measure the movement trend of human body and analyze the output curve of the flexible sensor.Through analysis,what is confirmed is that the flexible strain sensor changes in real time followed the body joints and respiratory variations of the tested,which shows that flexible strain sensors have a great application prospect in the field of human motion detection and medical health.