Results are presented for the propagation of circumferential acoustic waves around a thin-walled stainless steel tube. Sol gel lead titanate-zirconate ͑PZT͒ films and chirp interdigital transducer ͑IDT͒ electrodes were used to generate the A 0 mode from 0.8 to 6.0 MHz. Group and phase velocity measurements are in good agreement with the theory for the empty tube. When the tube is filled with water a large decrease of 21% in group velocity is observed. While there is as yet no theoretical explanation for this effect, the results show promise for liquid sensing applications.
A modified modal frequency spacing (MMFS) method is developed, which can be used to directly evaluate the coating density ρc and the longitudinal velocities of the substrate and of the coating, VLS and VLc, based on the measured cutoff frequency data. Numerical simulation results showed that the error in evaluating VLS and VLc is less than 0.4% and is less than 4% in ρc compared with the input data.
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