Fast imaging algorithm in frequency domain for ultrasonic immersion testing

A one-step phase-shifting method is developed in this paper for its applicability to the fast frequency-domain algorithm in ultrasonic immersion testing,which allows one to virtually move the transducer array to the interface between the immersion water and the samples by multiplying a phase-shifting factor in the frequency-wavenumber(f-k) domain.The time consumption for calculating the refraction points on the water-sample interface is thus reduced compared to time-domain imaging algorithm.A grid matching method is proposed for normal-angle inspection.By adjusting the number of Fourier transform points,it is able to make the sampling grids of array signals in f-k domain approximately coincident with that of image in frequency domain,which effectively reduces the interpolation errors and corresponding artifacts,and further reduces the calculation amount.Experimental results indicate that the computational complexity of the developed grid-matching frequency-domain algorithm is only 1/60 of that of the time-domain algorithm,which provides promising feasibility for practical real-time ultrasonic immersion testing.