Detection And Recognition Of Physiological Information Based On Flexible Sensor

As an important device that converts external stimuli into electrical signals that can be measured and recorded,flexible sensors play a pivotal role in the monitoring of physiological information and human activities.With the continuous development of micro-nano processing technology and flexible electronics,it is possible for flexible sensors to monitor various human signals in real time with high accuracy.Flexible sensors with high sensitivity,fast response/recovery time,low detection limit and excellent stability can provide guarantee for meeting the current needs.Among them,the flexible sensor based on the template method is widely used in the monitoring of physiological signals due to its advantages of low cost,simple process,less time-consuming and large-area production.Anodic aluminum oxide(AAO)was first proposed as a template to replicate the sensing layer of flexible sensor,and assembled into a flexible tactile sensor and a flexible humidity sensor,which solved the problems of low sensitivity under small force and long response and recovery time respectively.In addition,through further research on the device structure,a supercapacitive tactile sensor based on a double interlocking structure was constructed by using a laser marking Cu template and an electric double-layer sensing mechanism,which successfully solved the problem of linear sensitivity in a high-pressure range.The relationship between the three parts of this paper is independent,and the main work is as follows:(1)Inspired by the interlocked microridges between the epidermis and dermis,herein,a highly sensitive capacitive tactile sensor by creating interlocked asymmetric-nanocones in poly(vinylidenefluorideco-trifluoroethylene)film is proposed.Particularly,a facile method based on cone-shaped nanoporous anodized aluminum oxide templates is proposed to cost-effectively fabricate the highly ordered nanocones in a controllable manner and on a large scale.Finite-element analysis reveals that under vertical forces,the strain/stress can be highly strengthened and localized at the contact apexes,resulting in an amplified variation of film permittivity and thickness.Benefiting from this,the developed tactile sensor presents several conspicuous features,including the maximum sensitivity(6.583 k Pa^-1)in the low pressure region(0-100 Pa),ultralow detection limit(?3 Pa),rapid response/recovery time(48/36 ms),excellent stability and reproducibility(10 000 cycles).These salient merits enable the sensor to be successfully applied to the monitoring and recognition of weak physiological signals including pulse,blinking,swallowing and voice,and realize functions such as spatial pressure distribution monitoring,finger bending state recognition,and artificial fingertip recognition of Braille.(2)A high-performance flexible capacitive humidity sensor by creating the arc-shaped hollow structure with the P(VDF-Tr FE)nanocone arrays is developed.Particularly,a facile method based on combining the hot-pressing method and the anodized aluminum oxide template transfer method is proposed to realize the large-scale preparation of the nanostructure arrays with controllable morphology.Benefiting from the open arc-shaped hollow structure and the large-area P(VDF-Tr FE)nanocone arrays,the proposed humidity sensor shows several conspicuous features,such as ultrafast response/recovery time(3.693/3.430 s),long-term stability(25 days),excellent bending stability(10000 cycles),unaffected capacitance response to humidity in a certain temperature range(20-50?)and high selectivity toward water vapor.The above-mentioned significant advantages enable the proposed humidity sensor to be successfully used to extract various humidity-related physiological signals,including breathing detection,skin noncontact sensing,and real-time monitoring of diaper wetting process and skin humidity,which reveals great potential value in prevention and diagnosis of many diseases.(3)Inspired by the skin external structure(hair-like structure)and internal structure(epidermis-dermis-subcutaneous double interlocking structure),a layered microcone structure Cu template was prepared by laser marking technology,and the bottom electrode of single-sided layered microcone structure array(Au/PDMS),dielectric layer of double-sided layered microcone structure array(Poly(vinylidene fluoride-hexafluoropropylene(PVDF-HFP)/1-Ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide([EMIM][TFSI])),and the double-sided heterostructure top electrode(PDMS/Au)were successfully replicated by skillful template transfer technology.Benefiting from the hair-like structure that effectively reduces the viscoelasticity of the PDMS surface and the double interlocking structure provides a large specific surface area,and increases the concentration of local stress,the developed tactile sensor has ultra-high sensitivity(8053.1 k Pa^-1)in the pressure range of less than 1 k Pa,linear sensitivity(3103.5 k Pa^-1)in the pressure range of 1-35 k Pa and ultra-short response/recovery time(<5.6 ms/<5.6 ms).The above-mentioned outstanding sensing performance enables it to be successfully applied to the extraction of physiological signals in a large pressure range,such as repeated bending of fingers,knee joints and elbow joints.Finally,a wireless capacitance signal transmission system based on physiological information monitoring is designed,which is of great significance for the development of personal health care.