Study Of Flexible Kirigami Films And Their Stress/strain Sensing Characteristics

The development of flexible electronic devices is a new trend in the development of electronic and optoelectronic devices.Flexible stress/strain sensors are a typical example among them,which have recently received considerable attention from researchers across the world.This paper aims to improve the sensing performance of flexible piezoresistive stress/strain sensing film under large strain(>100%),including working strain range,surface adhesion,sensing stability,linearity and sensitivity.Silver nanoparticle/polydimethylsiloxane(AgNP/PDMS)kirigami structure film was obtained by silver-mirror preparation method and laser cutting technology.The mechanical and piezoresistive properties of thin film as flexible strain sensor are systematically studied by combining finite element simulation with experimental means such as micro extensometer and electronic multimeter.Various kirigami structures such as honeycomb,rectangle and diamond are considered,and the quantitative relationship is discussed between the preparation process,structure type and geometric parameters of the film and the sensing characteristics of the film.Firstly,Yeoh model of high elastic material and finite element software ANSYS are used to simulate the tensile test of honeycomb,rectangular and diamond kirigami films.The material parameters of the third-order Yeoh model of high elastic material are obtained by fitting with the experiment,and the reliability of the model is verified by comparing it with the experiment.Then,through the simulated tensile test,the mechanical properties of different structural films and material films(unstructured films)in the tensile process are quantitatively characterized,such as the elastic modulus and strain ratio(i.e.the ratio of the overall strain of the structural film to the strain of the structural unit),and the paper-cut structural film with the best structure type,i.e.diamond film,is obtained.On this basis,the relationship between geometric parameters and mechanical properties of kirigami structure film is further studied in this paper.The geometric parameters considered here include diamond length L,width a,and structure edge widths x and y.It is found that the "strain ratio" proposed in this paper does not change with strain and thus reflects the unique deformation characteristics of structural film.It is an ideal characterization parameter of mechanical properties in the research of kirigami films.Under the guidance of simulation,diamond kirigami films made of AgNP/PDMS were prepared.The sensing film is prepared by laser cutting and silver mirror preparation.The method is simple and easy to operate,and can be produced in large quantities.Then,through the piezoresistive test system composed of universal micro tensile instrument and digital multimeter,the sensing characteristics of the sample under cyclic load are studied,in which the piezoresistive characteristics of the sensing film under different geometric parameters(diamond length L)and process parameters(silver deposition time t),namely the maximum working range,sensitivity,linearity and pressure retardation,and the research results are analyzed theoretically.Finally,based on the design of flexible AgNP/PDMS kirigami structure strain sensing film,the flexible strain sensor is prepared,and the prepared sensor is attached to different joint parts of the human body(fingers,wrists,arms and knees)for bending test.The peak value of relative resistance change caused by bending of different joint parts is observed to distinguish the bending degree of different joint parts,Secondly,the motion frequencies of different joint parts can be distinguished according to the frequency of relative resistance change.The sensor prepared in this paper can meet the technical requirements of sensing equipment,monitor the movement of different human parts,and provide health monitoring data after treatment and training for patients who need rehabilitation treatment after operation.In addition,the flexible sensing film can also have broader application prospects in other fields such as electronic skin and wearable electronic devices.In this paper,the concept of "strain ratio" is proposed.Its value does not change with strain and can accurately reflect the influence of structural parameters.It is an ideal mechanical parameter to characterize the mechanical properties of kirigami structural film.Compared with other kirigami materials,the kirigami structure proposed in this paper has the same flexibility and flexibility as that of other kirigami materials.The prepared flexible strain sensing film can provide a good material basis for practical engineering applications such as motion monitoring.