High resolution transforms

The introduction of phased arrays opens-up a range of new possibilities for ultrasonic inspections. Arrays come in various shapes ranging from linear arrays for weld inspection to circular arrays emitting guided waves for permanent monitoring applications. For this kind of applications, the data is best displayed as angle versus time to locate the position a defects. However, the data is normally measured as function of a certain spatial coordinate and time. A transformation is then applied to convert data from the spatial domain into the angle domain. The simplest example is a spatial Fourier transform. Unfortunately the resolution obtained by this kind of transforms is determined by the size of the array compared to the wavelength. The longer the array is compared to the wavelength, the higher is the resolution. The reason for this is the increased phase rotation along the aperture. A new iterative approach is proposed to overcome the shortcomings of the traditional plane wave decomposition. This is a so-called high resolution transform. The new approach yields at least a five times higher resolution and can deal easily with irregular sampling or missing data. The approach will be illustrated on numerically modeled.