Research On Impedance Response Of Intrinsically Flexible Eddy Current Flaw Detection Sensing Element

In the field of defense industry,non-destructive testing plays an important role in finding defects in metal materials in time and preventing accidents.The engineering applications such as the artificial electronic skin and flexible wearable devices require the sensing probe to work under bending and stretching.However,the metal coil is used as the probe of the traditional flaw detection sensor,which results in that the sensor does not possess intrinsic flexibility.To break through the aforementioned limitations,an intrinsically flexible coil made of the conductive polymer composite as a flaw detection sensor probe,which utilizes the response characteristics of the coil impedance to defect to complete flaw detection has been designed.The main works are summarized as follows.(1)The mold for coil preparation is designed.The intrinsically flexible coil samples composed of carbon nanotube-filled silicone rubber composites are developed by solution mixing method,in which the mass ratios of the carbon nanotubes to the silicone rubber are 0.04,0.08,0.12,0.16,and 0.2,respectively.An experimental platform for metal flaw detection of intrinsically flexible coil is designed and built,which consists of a load-bearing module,a control module and an acquisition module.(2)The impedance characteristics of the intrinsically flexible coil flaw detection under different mass ratios and different frequencies are studied.The lower limit of the effective flaw detection frequency increases with the increase of the mass ratio,and the impedance amplitude of the intrinsically flexible coil increases with the decrease of the relative distance between the coil and the defect.For defects with a depth of 1-4mm,the impedance amplitude of the four mass ratio coils in the effective detection frequency range decrease with the decrease of the relative distance between the coil and the defect.When the excitation frequency is 30 kHz,the intrinsically flexible coil with mass ratio of 0.12 has the largest change in normalized impedance amplitude response to defect depth,and the largest change in normalized impedance amplitude response is 0.0705.(3)It provides guidance for the development of the intrinsically flexible flaw detection sensors.Using the flexible coil with a mass ratio of 0.12 to detect the defects with different depths(0-4mm)at a frequency of 30 kHz.Whether the defect exists is judged by whether there is a peak value in the coil impedance response curve,and the location of the defect is determined by the position of the peak value of the curve;and the defect depth is determined according to the peak value of the normalized impedance amplitude response of the coil to the defects of different depths.The experimental results show that the deviation of the intrinsic flexible coil to the defect depth is 0.267mm(the range of defect depth:0-4mm),and the sensitivity is 2.13kΩ/mm.The aforementioned research results have laid a preliminary foundation to use the eddy current effect of the intrinsically flexible coils to detect the flaw of the metal plates.