Research On Flexible Tactile Sensors Based On Conductive Composites

With the development of the mobile internet and the internet of things technology,wearable devices will become an important entrance and application terminal of the internet of things.Tactile sensors can provide information of the human health conditions and the environment by measuring human physiological parameters and sensing surrounding environmental indicators.These sensing technologies with wearable devices will make significant contribution to the future healthcare and portable motion detector.Therefore,it is necessary to develop the flexible tactile sensor to enhance the performances,competitiveness and comfort of wearable devices.Due to the unique merits of relatively simple fabrication process,controllable structure in conjunction with easy doping and functional modification and low production cost,conductive polymer composites are widely used in the manufacture of flexible sensor.In this dissertation,a series of flexible tactile sensors was designed and constructed by using conductive polymer composites as flexible substrates and functional layer.We investigated their microstructure,sensing properties and potential wearable applications.The main contents and results are summarized as follows:1.Crack-enhanced flexible strain senors based on conductive polymer composite were designed and fabricated.A crack-enhanced flexible strain sensor based on polyimide(PI)/carbon black(CB)piezoresistive polymer composite was demonstrated.A simple,cost-efficient approach to introduce micro-cracks into the sensitive film was proposed.By periodically tearing the sensitive film from a supporting layer,the aligned micro-cracks were generated in the sensitive film,and the crack size and density were modulated by repeated tearing-off times and finally saturated.This crack-enhanced strain sensor exhibited high mechano-sensitivity with a gauge factor of?470 at 0.2%strain.In addition,a high-performance crack-based strain sensor based on printable polyvinyl chloride/carbon black(PVC/CB)composite material was successfully developed.Flexible conductive circuit and PVC/CB composite were screen-printed to a desirable geometry on a PI substrate.After 5000 bends,a stable cracked morphology formed on the PVC/CB surface,which greatly enhanced the sensitivity of a strain sensor:corresponding gauge factors were equal to 741 and 1563 gauge under the tensile and compressive strains,respectively.Additionally,we presented the application of these crack-based sensors for human activity detection to demonstrate their application prospects for flexible and wearable electronic devices.2.Flexible pressure sensors with high sensitivity,broad pressure range and a large array are highly desired for wearable applications.A flexible pressure sensor with a PVC/CB microgrid films was obtained by screen printing.These printed pressure sensors with microstructured grids have a broad pressure range up to 666.7 k Pa,an excellent sensitivity of typically 4.71 k Pa^-1 in the dynamic range between 0 and 15 k Pa,a fast response of typically 25 ms,a high stability,a good durability in a broad pressure range for more than 5300 cycles and long effectiveness.We showed that the printed pressure sensors can be customized to fit in a smart insole.Moreover,a wrist pulse could be detected accurately by a single sensor.The proposed printed pressure sensors will have a great potential as smart devices in health monitoring,for preventive health care,and in rehabilitation care.In addition,three-dimensional carbon nanotubes-polyurethane-polyaniline foam materials were designed and prepared via facile one-step foaming process and hydrothermal method.The flexible pressure sensor based on this three-dimensional conductive foam presented a broad pressure range(0-30000 k Pa),owing to its excellent compressibility and conductivity.3.A flexible negative temperature coefficient(NTC)temperature sensor based on PVC/CB film were constructed and investigated its microstructure,sensing properties and potential applications.PVC/CB functional slurry was screen printed onto a polyethylene terephthalate(PET)substrate as temperature sensitive layer.The prepared temperature sensor exhibited high sensitivity(-0.148%°C^-1),excellent linearity(R²=0.995),a fast response time(198?s),and good repeatability when used to measure temperatures between 18°C and 44°C.The tunneling effect was used to explain the negative temperature coefficient of the PVC/CB temperature sensor,and its temperature sensing mechanism was proposed.Additionally,the sensor was used to monitor human breathing rates and temperatures,demonstrating its potential for real?time skin or environmental temperature monitoring.