Identification of Guided-Wave Modes in Pipings of Power Plants by using Air-coupled Transducer

In order to inspect the piping effectively, one of the important components in the facility of power plants, the ultrasonic guided wave was generated by a tomb transducer and was received in a non-contact fashion by using an air-coupled transducer. The guided wave modes that ran be generated by the comb transducer in piping are predicted from the theoretical dispersion curves and the element spacing of a comb transducer. Moreover, to receive the specific modes, the receiving angle of the air-coupled transducer is calculated from Snell's law between the phase velocities of guided waves and the sound velocity of air. The guided wave modes obtained in experiments are identified from the result of time-frequency analysis such as wavelet transform and two-dimensional fast Fourier transform.