On-command Control Of The Flexible Piezoresistive Composites Based On Magnetorheological Effect And Its Application In Sensors

Flexible piezoresistive sensors are widely used in wearable electronic devices,intelligent robot and aerospace,etc.However,pressure signal is complicated in real testing conditions,which requires pressure sensor to maintain stable,real-time and accurate response.In terms of conventional flexible piezoresistive materials,their piezoresistive properties(such as working range,sensitivity,etc.)are determined once produced,and thus unable to change in order to fit in test environment,which greatly limits their applications.In this paper,the on-command control of the piezoresistivity was realized by applying magnetic field onto the magnetorheological elastomer based flexible piezoresistive composite.The research results are presented as follows:(1)A novel flexible pressure sensor with a tunable and large pressure-detecting range was produced by simply infusing magnetic carboxyl iron particle(CIP)/silicone resin into carbon sponge(CS).Attributed to the magnetorheological effect,the upper pressure-detecting limit of the CS/CIP/silicone sensor in a frequency of 0.01-5 Hz is significantly increased from 180 to 330 k Pa in the prese nce of magnetic field,while a lower pressure-detecting limit of 70 Pa is obtained in the absence of magnetic field,thus covering the whole pressure-detecting range for various human activities.The CS/CIP/silicone sensor in monitoring various human motio ns with low to high-pressure stimuli is demonstrated by recording breathing,arm movement,walking,lifting and grasping,consecutively.(2)Due to the limited sensitivity of CS/CIP/silicone composite in low pressure range,a flexible porous CB/CNT/CIP/silicone composite was produced by using sugar particles(SP)as the sacrificial pore-forming agent.Results indicate the introduction of pores significantly decreases the compressive modulus of the composite especially at lower compressive strain.The combination of CNT and CB greatly decreases the threshold of the composite,whereas the sensitivity of composite at lower pressure range is still lower than that of bulk CS/CIP/silicone composite.Therefore,the current CB/CNT/CIP/silicone composite is inappropriate for the production of flexible pressure sensor with on-command controlled piezoresistivity.(3)To increase the sensitivity at lower pressure range,CNTs was coated onto SP and transferred onto the surface of pores after the removal of SP.Due to the porous structure and the synergistic effect between CNT and CB,the sensitivity of the porous CNT/CB/CIP/silicone composite sensor in low pressure range is significantly increased up to 0.1 k Pa^-1.Additionally,after the magnetic field is applied,the compressive modulus of the material is increased due to the magnetorheological effect,and therefore the upper limit of pressure measurement is increased from 200 k Pa to 380 k Pa,which is increased by 90%.As a result,the current flexible pressure sensor is able to monitor stimuli signal from low pressure level to medium pressure level and further to high pressure level.