Research On Ultrasensitive Nanocrack-based Strain Sensor

In recent years,some scholars have found that nanocracks can be used to make nano-scale graphics and are used in many fields.For example,making an ultrasensitive strain sensor composed of a flexible polymer substrate and a metal film with nanocracks.The nanocrack pattern?density,length,shape?has a great influence on the performance of the sensor.Although the currently proposed method can achieve the patterning of nanocracks,it is necessary to sacrifice the bonding force between the metal thin film and the substrate,or to fabricate stress-concentrated microstructures on the substrate.In view of the difficulties in the current manufacturing process of nanocracks,this paper proposes a nanocrack patterning process based on photolithography technology.By building the area covered with no photoresist into a composite beam model and the area covered with photoresist into a shear lag model,the stress of the metal film at different positions during the patterning of nanocracks was analyzed.And produced uniaxial straight nanocracks of different densities,uniaxial straight nanocracks of different lengths,oscillating uniaxial nanocracks,biaxial straight nanocracks,and on four different metal films of platinum,gold,silver and copper,uniaxial straight nanocracks are produced.Then,uniaxial straight nanocracks strain sensors with different densities were fabricated,and the performance of the strain sensors was tested by tensile tester.The test results show that the strain sensor with a nanocrack density of 200 cm^-1 and a length of 5 mm has a gauge factor of up to 19883 in the strain range of 0-1.2%,so the strain sensor has ultrasensitive characteristics.In the strain range of 0-1.2%,when the strain sensor is stretched at a rate of0.1mm/min,the hysteresis of the strain sensor is only 4.92%.In the strain range of 0-1%,when the frequency test is performed at 0.125 Hz,0.25 Hz,0.5 Hz,1 Hz,the 10th cycle curve of the strain sensor at four kinds of frequencies has good repeatability,indicating that the frequency has little effect on the response of the strain sensor.In the strain range of 0-0.5%,the relative change of the maximum value of the strain sensor?35?R/R₀ was only 2.15%during 1000 cycles of fatigue testing at a rate of 4mm/min.Finally,this article first applies the ultrasensitive strain sensor to detect human physiological signals,including breathing signals,pulse signals and sound signals.Then sensors with uniaxial straight nanocracks and biaxial straight nanocracks are used to detect temperature signals.The density of the uniaxial straight nanocracks is 200 cm^-1 and the length of the uniaxial straight nanocracks is 5mm.The transverse density of the biaxial straight nanocracks is 200 cm^-1and the length is 10mm,the longitudinal density is 200 cm^-1 and the length is 5 mm.The performance of the strain sensors was tested by temperature test platform.The test results show that the sensor with uniaxial straight nanocracks has a resistance temperature coefficient as high as 1.20/?in the temperature range of 30?-60?.the sensor with biaxial straight nanocracks has a resistance temperature coefficient as high as 1.86/?in the temperature range of 30?-42?.And,the flexible array sensor is used to detect the pressure signal.The density of the flexible array sensor is 200 cm^-1,the length is 2 mm,and the array form is a four-point array.