FPGA-based ultrasonic energy mapping with source removal method for damage visualization in composite structures

This paper presents the implementation of an ultrasonic energy mapping (UEM) method in a field programmable gate array (FPGA)-based processing board. This method is integrated into an ultrasonic propagation imaging (UPI) system for real-field application. UEM method involves two-dimensional Fourier transform and wavenumber filtering to capture the energy scattering waves. Performing multi-dimensional Fourier transform in FPGA is a challenging task because it cannot fit into a single FPGA chip, and therefore, external memory is required to handle a large amount of data. The row-column decomposition method is used to perform 2D Fourier transform using two DDR3 SDRAM memories. Additionally, a source removal function is added into the system to highlight the damage when high energy at the source location occurs. The UPI system was applied for inspection of a composite wing box with impact damages. The UEM results showed that a damage of 20x20mm(2) was detected successfully in the presence of the source inside the scan area. Moreover, the UEM result is produced in less than 5 s for 57,600 points, which is practical for a real-world, non-destructive testing application.