Preparation Of Flexible Carbon-based Fabric Strain/magnetic Dual-mode Sensors And Their Contact/noncontact Sensing

In recent years,with the constant technological improvement of flexible electronics,artificial intelligence and the integration of multifunctional devices,flexible strain sensors have developed rapidly,demonstrating great application values and market prospects in human-machine interaction,motion detection and intelligent robots.At present,a large number of scientific researches have been performed on flexible strain sensors and all kinds of sensors with excellent structure and performance have been prepared.However,it is still difficult to balance the sensitivity and strain range,and it is also a great challenge that the single mode sensor cannot satisfy the demands of people.In this paper,the textile structure of soft crepe de chine silk fabrics was used to obtain carbonized silk fabrics(CSF)with high conductivity under heat treatment by adjusting carbonization process.Then,using CSF as conductive sensing materials and Fe₃O₄ nanoparticles as magnetic sensing materials,a flexible strain/magnetic dual-mode sensor was successfully fabricated by combining polydimethylsiloxane(PDMS)with CSF and Fe₃O₄ nanoparticles.In addition,the sensing mechanisms were further analyzed through the performance test of the flexible sensors.Finally,the application of the sensor in some complex scenarios were simulated,and it was confirmed that the sensors could realize contact and non-contact response to strain and magnetic field.And the sensors also had the function of joule heating and electromagnetic shielding.The main research contents and conclusions are as follows:(1)The influence of different carbonization processes on the structure and properties of silk was investigated.Raman spectroscopy was used to study the structural differences of silk fabrics under different carbonization conditions such as carbonization time,heating rate and carbonization temperature.It was found that the area ratio of Raman D-peak to G-peak of CSF was 1.63 under the carbonization conditions with carbonization temperature of 1100?,heating rate of 5?/min and carbonization time of 60 min,indicating a higher degree of graphitization.During that carbonization condition,the resistance of CSF was 77?.The structural changes of the fabrics under the carbonization condition was further characterized by XRD and elemental analysis.It was found that the crystal structure was more complete and the content of C element increased from 44.92%to81%.The results showed that the carbonized silk fabrics had excellent electrical conductivity and could be used as the sensing material of strain sensors.(2)The strain sensing performance and mechanism of the fabric-based strain sensors were discussed.A flexible strain sensor with excellent performance was successfully fabricated by means of combining CSF with PDMS.It was found that the CSF/PDMS sensor had good flexibility,the maximum strain range was 60%,the gauge factor(GF)was 12.7,and the response time was only70 ms.It still had good cyclic stability at 20%,40%and 60%strain,respectively.The change of fabric structure by CSF/PDMS strain sensor under different strain was observed by ultra depth of field microscope,finding that the fabrics had obvious fiber fracture.The sensing mechanism was mainly dependent on the crack propagation effect of CSF in the tensile process.Irreversible cracks formed in the tensile process destroyed the conductive path,and the conductive path decreased with the increase of cracks.The island structure between the gaps also ensured a large strain range.(3)The dual-mode sensing performance of strain/magnetic sensors were studied.The Fe₃O₄ nanoparticles with saturation magnetization of 55.54 emu/g were successfully synthesised by the hydrothermal method.A CSF/Fe₃O₄/PDMS flexible strain/magnetic dual-mode sensor was fabricated by combining Fe₃O₄ nanoparticles with CSF and PDMS elastomers.The sensors exhibited stretchability with a strain range of 0-60%and a maximum GF of 9.49.The addition of Fe₃O₄ equipped the sensor with a response to low magnetic fields above 30 m T.When the addition of Fe₃O₄ was 25 wt%,the magnetic field sensitivity(GFm)could reach 39.73%/T.It was also proved that the strain/magnetic sensor had excellent response to strain and magnetic field,and could realize contact and non-contact sensing.(4)The application and multifunctionalities of the dual-mode sensor were explored.The flexible CSF/Fe₃O₄/PDMS sensors were not only applied to human motion detection of large deformation such as elbow and finger bending,but also were applied to detection of weak deformation such as pulse rates and breathing.And a smart mask was designed to monitor cough degree.Due to the response to the magnetic field,the sensors were also applied to the non-contact magnetic response switch.Nine small sensor units were used to create a flexible induction array that could respond to both pressure and magnetic fields.It was also found that the sensor could generate joule heat owing to the low resistance of CSF.At the same time,due to the synergistic effect of CSF and Fe₃O₄,the electromagnetic shielding efficiency of the sensor for X-band reached 23.5 d B,which had a good electromagnetic shielding effect.The CSF/Fe₃O₄/PDMS strain and magnetic sensor developed in this work realized multifunctional.In brief,a multifunctional flexible dual-mode sensor with response to strain and magnetic field was successfully fabricated by carbonized silk fabrics.The versatility would expand the application field of carbon-based flexible strain sensors.