| Currently,the increasing popularity of various intelligent terminals and the Internet of Things(Io T)has driven the rapid development of flexible and wearable electronic devices.As an indispensable branch of flexible electronics,flexible sensor has great application potential in many fields such as electronic skin,intelligent robot and health monitoring equipment by virtue of its unique advantages.However,this also puts forward more stringent requirements for the performance indicators of flexible sensors,which require flexible sensors with high sensitivity and excellent stability.However,the existing design principles of flexible sensors are difficult to achieve this requirement,which restricts the further development of flexible sensors.Therefore,we are in urgent need of flexible sensors with high sensitivity and high stability that can be quickly prepared by simple methods.The emergence of bionics provides a new way of thinking on how to solve the limitations of materials and engineering technology in manufacturing flexible sensors.Through billions of years of natural selection,countless creatures have evolved a variety of strange sensory organs,some of which are far superior to the current human senses.Therefore,the bionic flexible sensor with both sensitivity and stability can be produced by replicating the biosensory structure through the study of the biological excellent sensing mechanism.Heterometrus petersii,a rainforest scorpion,was chosen as the biological prototype in this paper based on the basic concepts and methods of bionics.The morphological characteristics of the surface silt receptors of scorpion were observed and analyzed with a combination of various microscopes,and the flexural slit structures of the surface receptors were extracted,and then the relevant structural parameters were obtained.It has been found that the fracture structure of the scorpion's silt receptors is not a simple straight parallel structure,but a complex curved structure.Compared with straight slits,curved slits are longer in a limited area,making it easier for the slit receptors to perceive external stimuli.So according to the obtained morphology and structural parameters of the curved silt structure,a scorpion silt receptor model was constructed.Subsequently,the sensory process of the receptor was analyzed by static analysis to reveal the perceptual mechanism of scorpion.Then,the model of the scorpion slit receptor was optimized and the concentric circle model was selected as the base structure of the bionic curved slit sensor.By organic reagent the dissolution effect,polystyrene petri dishes were dissolved with ethyl acetate to fabricate the initial template.In specific,the factors affecting the morphology of the template,including heating time and heating temperature,has studied.Afterwards,the optimal preparation conditions(heating temperature 25 ?,the heating time of 6 min)were selected to prepared the samples.Based on the corresponding substrate template as-prepared,the curved slit structure is transferred to the substrate of the sensor via a double template transferring method and the conductive layer connecting wires were anchored on the substrate of the sensor,yielding the generation of bio-inspired flexible strain sensors.After that,the microstructure of bioinspired sensor was characterized and its basic performance was also tested.It was found that the radius of the curved crack is between20.919?40.642 mm,and the average minimum radius of the curved crack is about23.28 mm.The cross section of the curved joint structure is composed of three arcs with the radii of 0.45 mm,0.1694 mm and 0.222 mm respectively.The basic sensing performance of the bionic sensor was tested: the response time was less than 162 ms,the drift was less than 1.52%,the vibration signal frequency was not higher than 140 Hz,the sensitivity characterization value GF(Gauge Factor)was 2614.5 under 2% strain,and the hysteresis was low.At the same time,the repeatable and reliable response with no evident degeneration within loading/unloading cycles up to 16500 was observed,implying long working life and reliability of this bio-inspired strain sensor.Furthermore,the bionic curved slit sensor exhibited tremendous utility for the detection of human physiological signals and motion activities,such as monitoring finger motion signal,pulse signal,voice signal and throat motion signal.It was found that the resistance change value produced by different motion signals is obviously different.All these results demonstrated the flexible strain sensor with curved patterns of microcrack arrays can be used in distinguishing subtle human motion for various potential applications.At the same time,the reason why the curved slit structure greatly improved the sensitivity of the sensing element was found,and the mapping relationship between the curved slit structure-deformation-sensitivity was established based on the conductive layer morphology.Finally,based on the test data of the sensor,the base model of the bionic curved slit sensing element was established,and the static mechanical theoretical analysis was carried out to analyze the influence of different structural parameters on its deformation by using the simulation software ANSYS.It turned out that the cross-section of the curved crack was similar to the semicircle,and the minimum radius of the curved crack was about 23 mm.There was no curved crack structure at both ends with small deformation,and the smaller the distance between adjacent curved cracks,the greater the deformation of the model.Thus,the optimal bionic curved slit sensing element model is determined. |
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