Preparation Of Flexible Stretchable Fiber Membrane Sensor For Human Activity And Voice Monitoring

With the improvement of materials science as well as the more attention people pay to self-health care.Portability and simple wearable sensing electronic devices that can monitor human health have been extensively developed,enabling people to familiarize with their state of health in real time.Besides,routine checks such as blood pressure,blood glucose and heart rate can be detected at any time.In order to further satisfy the demands for the structure and performance of the detection instrument,wearable sensor electronic devices have developed from traditional sensors which are rigid into flexible stretchable sensors.Moreover,compared with the earlier wearable sensors,this new type of sensor can be directly adapted to the human skin,especially to the irregular surface of the human body.The flexible stretchable sensor can convert mechanical stimuli into electrical signals while subjected to external strain,achieving the purpose of monitoring human physiological activities.In this process,the sensor requires to have the deformability ensuring human physical activities,high sensitivity that can quickly sense and respond,as well as environmental stability.In addition,what should not be overlooked is the breathability of contact with the skin.Becasue the flexible sensor attached to the skin surface for a long time will affect the metabolism of the skin and cause skin problems.Also,the sweat produced will affect the measured data and lead to use experience lower than expected.Herein,based on the requirements with high elasticity,excellent sensing properties and comfortability,fiber materials are selected as flexible substrates and multi-walled carbon nanotubes are used as conductive materials to prepare fiber membrane resistance sensors for human activity monitoring.The main research contents are as follows:1.Based on the centrifugal-electrospinning technology,a flexible stretchable fiber membrane sensor was prepared through multi-walled carbon nanotubes(MWCNTs)were loaded onto the PU fiber membrane by cross-tension technique.It was found that a dense conductive network was formed between MWCNTs and PU fibers,and MWCNTs were still firmly attached to the PU fibers after 10,000 cycles of stretching.The excellent electrical conductivity and mechanical properties endow PU@MWCNTs fiber membrane with a low resistance value of 800 ?,a high elongation at break of 272%,and a response test range from 0%to 203%.The sensitivity coefficient under large strain reach to 4177,and the response time and recovery time are 94.34 ms and 94.36 ms,respectively.The prepared PU@MWCNTs fiber membrane sensor has high elasticity,high sensitivity,high tensile resistance,oxygen resistance,good stability and a wide sensing test range,good hydrophobicity and air permeability.The excellent performance ensures that the sensor can be used as a flexible wearable electronic monitoring device to detect the movement of different parts of the human body.In addition,a voice signal recognition system was constructed by establishing a voice database model and building a voice signal processor to monitor and recognize voice signals,which can be used for voice recognition and rehabilitation training for people with damaged vocal cords.2.In order to further explore the performance influence of the structure of the flexible substrate,two kinds of silk with different structures were emploied to simulate spider web.A polyurethane-polyethylene terephthalate(PU-PET)composite fiber membrane were fabricated by centrifugal-electrospinning using choose PU and polyethylene terephthalate(PET)as paw materials.The composite fiber membrane composed of fibers with different mechanical properties can not only perceive the tiny movement changes of the human body,but also respond to large-scale limb movements.The testing results of the super-depth microscope shows the surface of the PU-PET composite fiber film is rough,which can improve the sensor's strain sensitivity and enable the sensor to quickly perceive and respond to the external strain.A stretchable composite membrane with high elasticity and high sensitivity was prepared using PU-PET composite fiber membrane as a flexible substrate and MWCNTs as a conductive medium.The composite fiber membrane exhibits excellent properties,such as the breaking elongation is as high as 314%,the response time is 60.97 ms,and the sensing area is between 0%and 220%.When the tensile strain is less than 50%,the sensitivity is 10.62,While the tensile strain is higher than 200%,the sensitivity reaches 1970.86.The PU/PET@MWCNTs composite fiber membrane sensor can quickly sense and respond by detecting the movement of different parts of the human body,and shows hierarchical response capability.The two flexible stretchable fiber membrane sensors prepared have excellent performance,simple preparation process,reasonable price and environmentally friendly materials,which are expected to promote the development and application of carbon-based materials and fiber flexible substrates in the field of wearable sensor devices.