Numerical study on optimum design of a clad waveguide for ultrasonic pulse-echo measurements with high signal-to-noise ratio

Ultrasonic waveguides have been widely used for material characterizations, flaw detections and health monitoring by ultrasonic pulse-echo methods. Although a clad waveguide consisting of a core rod and a cladding layer has been expected to be the most promising waveguide for practical applications, little is known about an appropriate material combination for the cladding and core. In this work, numerical simulations are performed to investigate an optimum combination of the materials for the cladding and core of a clad waveguide. Wave propagations are examined for a series of clad waveguides having different combinations of material properties using a two-dimensional finite different analysis. In the analysis, steel is used as the core material, and the density and ultrasonic wave velocity of the cladding material are systematically changed, and the signal-to-noise ratios (SNRs) of ultrasonic pulse waves propagating through the clad waveguides are estimated. It is found that the SNR changes drastically with the material combination for the cladding and core and the highest SNR is appeared when the velocity and density of the cladding are approximately 120% and 70% of the core, respectively. It should be noted that an appropriate SNR is obtained when the velocity of cladding is approximately 110% of the core regardless of the density value of the cladding on the condition that the density value is within the range from 75% to 150% of the core. This fact obtained here could be useful for designing desirable ultrasonic clad waveguides used for practical applications.