Excitation Spectrum & Mode Excitability Analysis of Comb and Annular Phased Array Transducers for Guided Wave Mode Control Applications

Open Access
Author:
Borigo, Cody J
Graduate Program:
Engineering Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 11, 2011
Committee Members:
  • Joseph Rose, Thesis Advisor
  • Joseph Lawrence Rose, Thesis Advisor
Keywords:
  • wave mechanics
  • transducer
  • array
  • comb
  • annular
  • guided waves
  • mode selection
Abstract:
The goal of this research is to investigate the excitation spectra of annular array and linear comb array transducers for guided wave mode selection. The approach used will be to analyze the spatial influence of the array transducer on the wavelength and wavenumber of the excited guided wave modes. While this approach does not produce results that are fully optimized for a given structure, it yields a complete independence from the material or waveguide to be inspected and thus is valid for any structure to which the transducer is applied. This makes it more versatile in that it can be easily applied to various structures and to structures for which the entire wavestructure solution or material properties are not fully known. A comparison of the excitation spectra between comb and annular arrays will be performed to determine the similarities and differences between the two. The properties of the excitation spectrum are analyzed to determine optimum annular array transducer design parameters including inner radius, element width, width-spacing ratio, and number of elements, as well as to determine how these various parameters ultimately affect the excitation properties of the transducer considering features like primary wavelength excitation, main peak separation, sidelobes, and effective range of wavelength control. Methods will be developed to determine the applied time delays required to preferentially excite various regions of the dispersion curve using the excitation spectrum alone. In addition to this, the wave mode excitability for various types of transducer loading will be considered, and the effect of this factor will be taken into account to predict optimum mode excitation with linearly phased annular array elements, considering both excitation spectrum and mode excitability. It will be shown that very good agreement exists between predicted waveforms and FE results. FE and experimental validation is provided. A design flow chart is also included which outlines the general process for designing phased array transducers for guided wave applications.