A spacing compensation factor for the optimization of guided wave annular array transducers

Abstract

Transducer arrays can be utilized in ultrasonic guided wave applications to achieve preferential excitation of particular points on a dispersion curve. These arrays are designed according to the principles of wave interference and the influence of the wavelength excitation spectrum. This paper develops the relationships between the peak wavelength in the excitation spectra and the element spacing of linear comb and annular arrays. The excitation spectra are developed by applying Fourier and Hankel transforms to the spatial loading distribution functions of the comb and annular arrays, respectively. Although the peak wavelength of excitation of a comb array is typically assumed to be equal to the element spacing, it is shown that this can be an inaccurate assumption for annular arrays. The ratio of element spacing to the peak wavelength in the excitation spectrum is termed the spacing compensation factor, and is dependent on the number of array elements and the inner radius. It is determined that the compensation factor is negligible for comb arrays but is crucial for annular arrays in order to achieve optimal mode selection. Finite element analyses and experimental data are used to verify the calculations and demonstrate the significance of the compensation factor.

Defects Detection inside the Rail Head by Ultrasonic Guided Waves

“…The multi-modes and dispersion characteristics make UGWsbased defects detection challenging. To eliminate, or at least reduce, those influence, specific excitation methods have been investigated by a host of researchers [26][27][28].…”

Time delay controlled annular array transducers for omnidirectional guided wave mode control in plate like structures

“…Similar to linear arrays, by controlling the spacing between the annular array elements the wave modes generated in a structure can be controlled. The relationship between the annular array element spacing and the desired excitation wavelength are slightly different in comparison to linear arrays and a compensation factor need to be used for optimum excitation, details of which can be found in [9,10]. By applying relative time delays (phase) between the annular elements in the transducer, guided wave modes at wavelengths other than that controlled by the element spacing can be generated.…”

Analysis of annular phased array transducers for ultrasonic guided wave mode control

“…The multimodality of guided waves at any given frequency means that generation techniques that selectively generate the chosen mode are important. There are several techniques for guided wave mode selection, including (a) fixed and variable angle wedges based on Snell's law [4], (b) one and two-dimensional transducer combs [5][6][7][8][9] and (c) phased array transducers [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Fixed and variable wedges can be bulky and are prone to mechanical wear and tear.…”

“…Ultrasonic guided wave mode control using phased array transducers (PATs) is an increasingly important research topic for (SHM) and (NDE) of plate-like structures [10][11][12][13][14][15][16][17][18][19][20][21]. PATs consist of an array of transducers similar to comb transducers, each of which is excited with a distinct time delay and by the principle of interference of waves; both mode selection and steering of guided waves can be accomplished and controlled electronically.…”

“…Annular PATs have been applied to SHM and to improve tomography in [13,14]. In [15,16], the optimization of various annular PAT parameters was attempted. The advantage of an annular PAT is that it generates waves omni-directionally, while on the other hand a linear PAT, due to its spectral characteristics, can be used to select and steer modes.…”