Acousto-ultrasonic input-output characteristics for contact-type transmitting and receiving transducers coupled to a thin orthotropic composite plate are analyzed in this paper. By introducing the point source/point receiver assumption, the governing equations of the problem, which relates to wave generation, wave propagation and wave reception, are first established. Using the multiple integral transform method, contour integration technique and some complex function theories, a spectral analysis method which is completely different from the present wave path tracing method for this problem is developed. From this approach, the spectral response of the normal contact force between the receiving transducer and the plate, due to an arbitrary input interrogation pulse excited by the transmitting transducer, is expressed in explicit form. Based on this, some physical properties involved with the output of the receiver are examined in the frequency domain. Finally, combining the fast Fourier transform (FFT) technique, some time domain numerical results are calculated to show the input-output characteristics of the AU system considered.

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For the purpose of understanding and improving the acousto-ultrasonic (AU) technique, the AU characteristics for an isotropic plate is investigated in this paper. Unlike the previous wave tracing method, a spectral analysis approach is presented, which can take into account the effects of the transducers’ characteristics. Using this approach and introducing the point source/point receiver assumption, the input–output frequency spectrum relationships for the cases of one transmitter/one receiver and one transmitter/multiple receivers coupled to an isotropic thin plate are expressed in explicit forms. Based on this, a wave scattering parameter to bridge two different sensing types of the receiving transducers is presented, and a new type stress wave parameter for the AU technique is developed, which eliminates the influence of the complex mechanic-electron transduction characteristics of the receivers and also separates to some extent the effects of some other external factors such as transducer masses and locations. Finally, some numerical simulations are carried out and conclusions drawn concerning the AU technique.

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