Design of Dual-Frequency Alternating Current Field Measurement Instrument Based on FPGA

Aluminum alloy is widely used in aerospace because of the advantages of low density, high strength, and corrosion resistance. Due to the harsh service environment and the influence of complex forces, it is easy to produce surface cracks at arbitrary angles. In this paper, based on dual-frequency ACFM technology, a crack detection instrument based on FPGA is designed. The dual-frequency ACFM detection model is established by using the finite element software COMSOL, and the cracks at different angles are simulated. The distribution of the induced current on the surface of the specimen at different time is shown. The distribution and interference of the induced current on the surface of the specimen at different angles are analyzed, and the Bz magnetic field signals of the cracks at different angles are extracted. The quadrature excitation coil is printed on the PCB. Two sinusoidal signals with different frequencies are loaded in the excitation coil to generate a rotating current on the surface of the specimen. Based on FPGA platform, a detection instrument for dual-frequency ACFM is constructed, and the functions of excitation signal generation and detection signal acquisition, processing and display are realized. A crack recognition algorithm based on characteristic signal Bz is proposed to display the end point of the crack. Experimental and simulation results show that the crack detection instrument based on dual-frequency ACFM has high sensitivity to any angle cracks on the surface of the specimen.