Abstract
Ultrasonic array imaging algorithms have been widely developed and used for non-destructive evaluation (NDE) in the last two decades. In this paper two widely used time domain algorithms are compared with two emerging frequency domain algorithms in terms of imaging performance and computational speed. The time domain algorithms explored here are the total focusing method (TFM) and plane wave imaging (PWI) and the frequency domain algorithms are the wavenumber algorithm and Lu’s frequency-wavenumber domain implementation of PWI. In order to make a fair comparison, each algorithm was first investigated to choose imaging parameters leading to overall good imaging resolution and signal-to-noise-ratio. To reflect the diversity of samples encountered in NDE, the comparison is made using both a low noise material (aluminium) and a high noise material (copper). It is shown that whilst wavenumber and frequency domain PWI imaging algorithms can lead to fast imaging, they require careful selection of imaging parameters.
Highlights
Ultrasonic arrays have been widely used for non-destructive evaluation (NDE) in recent years [1].Ultrasonic arrays have advantages over single-element devices such as the ability of one array to produce beams at a range of angles or focal depths, and the intuitive imaging of the interior of a structure that they produce as an output
Because the time domain approaches are based on a simple summation, the algorithms are readily parallelisable using graphics processing units (GPU) and field-programmable gate arrays (FPGA)
In a plane wave data set with Np transmitted plane waves, f (θ, v, t) represents the time domain signal transmitted with a plane wave steering angle of θ and received by an array element at (v, 0)
Summary
Ultrasonic arrays have been widely used for non-destructive evaluation (NDE) in recent years [1]. Delay-and-sum (DAS) algorithms [2], the amplitude of an image pixel is the summation of the amplitudes of the received signals after the application of time delays, typically set to represent a specific wave propagation path These imaging algorithms are relatively simple to implement and can be configured for a wide variety of inspection cases. Because the time domain approaches are based on a simple summation, the algorithms are readily parallelisable using graphics processing units (GPU) and field-programmable gate arrays (FPGA) Such approaches have been used for fast TFM imaging [8,9] and can achieve imaging speeds of frames/s for an image with 200 × 200 pixels and a 32 element array [9]. Note that given their widespread industrial application, this paper is limited to the application of 1D linear arrays for 2-D imaging on a 2-D structure
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