Preparation And Optimization Of Flexible And Wearable Sensors With Hermetic Structure

In recent years,smart wearable technology has become an emerging data flow portal by integrating technologies in information field and material field.Sensors,as the core of wearable technology devices,can convert physiological signals of human body or external environmental signals into electrical signals,thereby providing an interface for information transmission between the human body and electronic information systems.However,traditional sensors are large in size,rigid,and highly dependent on external power sources,which reduce the flexibility,comfort and biocompatibility of wearable devices.Therefore,designing a self-powered flexible sensor has become one of the research hotspots.The triboelectric nanogenerator(TENG)can continuously convert the small,low-frequency mechanical energy produced by human body into electrical energy to supply electricity for itself.It has advantages of simple preparation,high efficiency,environmental friendliness,wide material sources,and linear correlation between pressure and output voltage.So it can be used as pressure sensor for practical applications to get rid of the shackles of traditional batteries and truly realize passive sensing.The triboelectric sensor combined with textile substrate possesses both the excellent flexibility of the textile and self-driving performance of the triboelectirc nanogenerator.It can meet the requirements of lightweight,soft and comfortable for wearable devices.However,the triboelectrification effect is greatly affected by the external environment,especially the humidity,and most of the TENG structures are non-closed.When using them as pressure sensors,the output stability and sensitivity will be affected by the environment.In practical applications,it is greatly restricted by the environment,which restricts its development in the field of sensing.Although some researchers have proposed closed-structure triboelectric nanogenerators,most of them are rigid structures and focus on energy collection as their main working purpose.They have many disadvantages when used as sensors such as poor comfort and flexibility.This article introduces three kinds of triboelectric nanogenerators with balloon structure.The balloon hermetic structure is combined with the friction power generation function and pressure sensing function of TENG.The device,prepared by combining the highly resilient hermetic material with air as supporting material and spacer material,can isolate the external environment to maintain the stability of the internal environment of the balloon,ensure the output stability and flexibility of the sensor.It has the advantages of easy preparation,light weight and flexibility,which broadens the development potential of sensors based on triboelectric nanogenerators in wearable aspect.This research firstly uses nylon fabric as the substrate material,silver paste with excellent conductivity as electrode material,high resilience polydimethylsiloxane(PDMS)film as hermetic material,nylon fabric and waterborne polyurethane(PU)as positive and negative tribomaterials,add different thickness of polyimide(PI)film between PU and electrode layer as reinforced material.The silver paste is transferred to the fabric surface through screen printing process to prepare conductive fabric.The PDMS-based triboelectric sensor with the best output performance can be prepared under the process parameters of PI film thickness of 15?m,inflation volume of 1m L.Its effective friction area is 3.14 cm²,the weight is 1.39 g.Under the test conditions of 5 N,3Hz,the output voltage can reach 15 V;the output voltage has no obvious attenuation after 1000cycles of work,and has good mechanical stability;it still maintains stable electrical output performance after continuous immersion in deionized water for 3 hours;The sensitivity of the sensor is 0.34V/k Pa,and the linearity is good(R²=0.995).After that,thermoplastic polyurethane(TPU)composite fabric was used both as hermetic material and positive tribomaterial,PDMS doped with different mass fractions of Ba Ti O₃nanoparticles as negative friction material,conductive silver paste was used as electrode material,the balloon triboelectric sensor based on TPU composite fabric was prepared.The working area is16 cm² and the weight is about 3 g.The device uses the TPU film both as hermetic material and positive tribomaterial,which further simplifies the structure and preparation process of the TENG.The influence of the air volume on the triboelectric sensor with different Ba Ti O₃ doping ratios was discussed.Taking the device with no Ba Ti O₃ as example,the best air volume is 2.5 m L,and the output voltage can reach 25V under the test conditions of 23?,50%RH,force of about 10 N and2 Hz;the output voltage remains stable after 1000 cycles of continuous work;sensitivity is 1.494V/k Pa,the linearity is 0.912.In order to optimize the process,the TPU frosted film is directly used as the hermetic material and the positive tribomaterial,PDMS is used as negative tribomaterial,conductive copper foil tape is used as the electrode material to prepare the TPU film-based balloon triboelectric sensor with an effective friction area of 4 cm²,the weight of 1.10 g.When the air volume is 5 m L,the output voltage can reach 7.2 V under the test conditions of 25?,55%RH,about 3 N and 2 Hz.The output voltage remains stable after 1000 times of continuous cycle work.Its electrical output remains stable after 6 hours of continuous immersion in deionized water.The sensitivity is2.481V/k Pa,linearity is 0.967,and the sensing performance is greatly improved than the sensor based on TPU composite fabric.Finally,the practical application functions of these triboelectric sensors have been discussed.They are placed on the joints of the human body or under the feet,which can be used for gesture recognition and motion sensing.Through experimental analysis and discussion,it is proved that the hermestic wearable triboelectric sensors have the characteristics of high output performance,good mechanical stability,high flexibility.They have a wide range of application prospects in the fields of human energy collection,motion monitoring and sensing.