The multi-mode plane wave imaging in the Fourier domain: Theory and applications to fast ultrasound imaging of cracks

The Total Focusing Method (TFM) was generalized about ten years ago to form images with complex ultrasound paths involving reflections and mode conversions at the interfaces of a testing sample. The resulting multi-mode imaging allows to fully image the face of a crack-type defect. More recently, the Plane Wave Imaging (PWI) was revisited to perform multi-mode reconstructions with a small number of transmissions compared to the TFM. In order to further accelerate the imaging process, we propose here to combine plane wave emissions with a fast reconstruction algorithm in the Fourier domain. The method was developed in medical imaging with the pioneering works of J.-Y. Lu, and was studied in a recent paper to form images in solids with direct reconstruction modes. In the present paper, the theory is extended to various reconstruction modes (half-skip and one-skip modes with/without mode conversions), and the imaging method is evaluated with experimental results in a sample featuring different planar defects. We show that the method provides multi-mode images equivalent to those computed with the time-domain PWI, while reducing the computation times by a factor up to 13.