Design And Research Of A General Enhanced Structure Of Flexible Strain Sensor

With the rapid development of science and technology,people's working environment is becoming more complex and diversified.The requirements for flexibility,portability,and wearability of electronic devices are getting higher and higher.Compared with traditional sensors,flexible sensors overcome the shortcomings of fragility and inflexible deformation of the substrate.They also have the advantages of small size,light weight,low power consumption,easy integration and resistance to harsh working environments,which have become the focus of many scientific researchers.The sensitivity of the strain sensor is directly related to the area deformation of the pressure-sensitive film.Most flexible substrates are positive Poisson's ratio materials.Therefore,the total effect of the area change will be weakened.Traditional methods of improving the sensitivity of flexible strain sensors focus on changing and optimizing sensitive materials.However,common pressure-sensitive film materials are generally positive Poisson's ratio.The sensitivity that can be improved is limited.This paper innovatively proposes the idea of increasing the sensitivity of the flexible sensor by adding an auxetic structure on the periphery.A concave hexagonal structure,which is one of mechanical metamaterial cell structures,is introduced.A new type of flexible strain sensor with negative Poisson ratio is designed.The sensor includes a base,structural pillars and a central groove.The four structural pillars are centered symmetrically and evenly distributed around the central groove.This paper studies in detail the factors that affect the Poisson's ratio of the concave hexagonal structure,the optimization of sensor parameters,sensor performance and applications.The specific research content is mainly divided into the following aspects:(1)This paper theoretically derives the influencing factor of the Poisson's ratio of the concave hexagonal structure.It is found that as the ratio of the length of the vertical support rod to the recessed support rod increases and the angle ? between the two support rods decreases,the Poisson's ratio becomes larger.Based on this discovery,the structure of a new type of sensor was designed,and the best structural parameters were optimized through simulation.According to the simulation results,when the aspect ratio of the structural column is larger,the aspect ratio of the central groove is smaller,Poisson's ratio is the larger.When the angle between the structural column and the horizontal direction is 35 degrees,the distance between the structural column and the central depression is 2 mm,Poisson's ratio is the largest.The sensor is prepared according to the above parameters.(2)It is found that the sensitive film prepared by coating CNTs on the flexible sink has the best sensitivity and tensile performance through experimental verification,thus preparing a complete flexible strain sensor.The strain sensor can form two linear ranges within a stable measuring range of 0-50%: the sensitivity factor(GF)is 28.3 in the 0-25% strain range,and the GF is 45.1 in the 25-50% strain range.It exhibits good voltampere characteristics under different strain tensions.The sensor maintains an approximate resistance response under different frequency tensions(0.07HZ-0.23HZ).the strain response time is about 200 ms.After 10,000 times of 40% strain tensile-release cycle test,it can still maintain good stability.(3)The flexible strain sensor with an auxetic structure is attached to the surface of the human skin to research applications as wearable devices for human motion detection and health monitoring.It is found that the strain sensor can effectively detect the movement of the limb joints of the human body such as the finger joints,wrist joints and knee joints.Besides,it can also monitor human body's vocal vibration,touch vibration,and carotid pulse.It demonstrates the flexible strain sensor fabricated by this method has potential applications in human motion detection and mobile healthcare,human/machine interaction,electronic skin,intelligent robots,and so on.In summary,in this paper,by introducing a mechanical metamaterial cell structure,a flexible strain sensor with negative Poisson's ratio characteristics is fabricated.The fabrication method is simple and the cost is low.The sensor shows excellent performance in sensitivity,stretchability,linearity,stability,hysteresis and response speed.It also realizes the function of body motion detection,vocalization,touch and pulse monitoring tests when attached to the surface of human skin,and demonstrates attractive prospects as wearable devices.