The field of horizontally polarized ultrasonic shear wave radiated by a 2/2 piezoelectric composite normal probe was studied. The strictly analytic field solutions for two different surface forces were deduced and the field distribution and directivity patterns were given by numerical calculations. The vertical radiated field of shear wave was obtained theoretically and compared with experiment. The experimental result of directivity pattern conformed the theoretical prediction, which provided the theoretical basis for the engineering application of the transducer.
Two ultrasonic methods were studied for determining the parameters of a composite consisting of a soft thin film attached beneath a hard plate substrate from resonant frequencies and amplitude spectra in low frequency region,respectively.Analyses of the sensitivity function, the objective function and the error transfer function were presented for discussing the effects of the two methods for both single parameter and two-parameter inversion.Two techniques were employed in experiment to characterize a composite consisting of a film attached beneath an aluminum plate substrate with a 7 MHz center frequency broadband transducer.It was observed that the results were similar for single parameter inversion and the method based on resonant frequencies got better result for two-parameter inversion under the same condition. The relative errors of the method based on resonant frequencies for inversing acoustic impedance and time-of-flight were 3.4%and 4.7%,respectively,and the method based on amplitude spectra got no results.
The proper frequency is experimentally chosen to be the operation frequency of the electromagnetic acoustic transducer. The instantaneous amplitude, phase and frequency of the detected ultrasonic echoes from a multilayer adhesive sample of steel and rubber materials are calculated and composed to form three-dimensional instantaneous spectrum which is successful to distinguish the testing signals from different adhesive states qualitatively. Then, average instantaneous parameters in sensitive time window are picked up and used as the input eigenvectors for the BP artificial neural network. Identified results in both training and testing volumes demonstrate that the detected electromagnetic ultrasonic interracial echoes can be identified and classified automatically with the correctness ratio larger than 95%.
The electromagnetic ultrasound is used in the detection of interfaces of the adhesive multilayer structures to solve the unstable coupling problem in ultrasonic testing by traditional piezoelectric transducers. Based on the analysis of the transforming mechanism of electromag-netic ultrasound energy and the resultant dead zone from mutual inductance of the transducer, the wavelet filtering by soft-thresholding and adaptive noise canceling methods are used simul-taneously to the detected electromagnetic ultrasonic signals to overcome the drawbacks of the low signal to noise ratio （SNR） and the wide intrinsic dead zone of the transducer. Processed results in the interface detection of a three layered adhesive sample of steel and rubber materials demonstrate that the wavelet filtering enhances the SNR about 12dB while the adaptive noise canceling narrows the dead zone effectively.
