Study On The Frictional Electrical Properties Of Flat-knitted Spacer Fabrics

At a time when traditional energy sources are gradually depleted and environmentally friendly energy sources are limited by the natural environment,friction nanogenerators as a new technology are stronger than electromagnetic generators in low frequency energy harvesting.This has a good application prospect for various mechanical energy harvesting scattered in life.In this paper,a spacer fabric AC friction nanogenerator(AC-TENG)and a spacer fabric DC friction nanogenerator(DC-TENG)are developed from the perspective of wearable smart products by combining the advantages of friction nanogenerators and spacer fabrics.The core of both is the interlayer weave of the spacer fabric.The key point is to change the number of stitches separating the front and back needle beds,and the thickness of the spacer fabric will be different by the number of stitches separating them.AC-TENG spacer fabric mainly uses PTFE monofilament as the lower surface yarn,silver-plated nylon as the upper surface yarn,and nylon monofilament and multifilament as spacer yarns.The frictional electrical properties of the vertical contact-separation pattern were studied depending on the dielectric properties of the materials used.The output of the spacer fabric with 7 stitches between the front and back of the spacer bed for loop collection was excellent,and the frictional electrical output was subsequently tested and compared under variations in frequency and pressure.The results showed that the output characteristics of the fabric showed a positive correlation link with frequency and pressure at a test area of 5×5 cm~2.Under the test conditions of 2.5 Hz and 5 k Pa,the short-circuit current of the fabric was 0.19μA and the open-circuit voltage was 32 V.Moreover,the output was almost constant after10,000 cycles of testing and after 5 times of washing,showing good stability.For energy harvesting,its output can light up 34 LEDs in the case of manual tapping.It can also be applied to monitor different strengths,the angle of the body’s bent elbow,and the accurate recognition of walking,running and the bending knee movements involved.The DC-TENG spacer fabric uses silver-plated nylon conductive yarn for both the friction and breakdown electrodes and polyester monofilament for the spacer.The number of spacers in the friction electrode area is 3,and the number of spacers in the breakdown electrode area is 1.This provides a structural basis for air breakdown by achieving a thickness difference between the two areas on the sample fabric.The DC output was verified by the sliding friction test data and the air breakdown discharge graph,and the excellent stability was demonstrated by 10,000 cycles and after washing and drying tests.The output performance was then investigated in detail by varying the motion parameters such as speed,acceleration,motion stroke,compression degree,and changing the structure such as friction electrode area,breakdown electrode area,breakdown electrode yarn number,breakdown electrode number,and multi-unit repetition structure.The results show that the DC-TENG output is best when the friction electrode is 5 units across and the breakdown electrode is 1 across for full bed knitting,and its current and voltage are proportional to the speed and the charge is proportional to the displacement.The more the fabric is compressed,the higher the output.By manually testing the DC-TENG with a 5-unit structure,the short-circuit current peaks at 26.5μA,the charge at 2.4μC and the voltage peaks up to 3000 V during a single motion cycle,with good DC output.In different load tests,its internal impedance was about 900 MΩ,and its power was highest when the external load was equal to it,up to 0.78 m W.And it successfully lit up 1392 light-emitting diodes,and the calculator was powered by it directly without batteries,and successfully started and performed calculations.The application of charging the capacitor first and then powering the electronic meter successfully demonstrates its good DC output capability and provides ideas for the future development of wearable electronics in energy harvesting.And based on its different degrees of compression corresponding to different outputs,this provides a possibility for its application in the field of sensing.