WANG Yang  MAO Jie  LI Mingxuan  WANG Xiaomin

(National Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences 　Beijing  100190)

Received Jan. 10, 2008

Revised May 13, 2009

Abstract Two ultrasonic methods were studied for determining the parameters of a composite consisting of a soft thin film attaches beneath a hard plate substrate form 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 methods 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.　　

PACS numbers: 43.35, 43.60