LUO Chungou TA De’an LI Wei WANG Weiqi

(Department of Electronic Engineering,Fudan University  Shanghai 200433)

Received May 8, 2009

Revised May 25, 2009

Abstract The ultrasonic signals in long bones contain multiple guided modes which are mutual superposed. The velocities of guided waves in long bones are very sensitive to cortical thickness (CTh). In this paper, Hilbert-Huang transform (HHT) was proposed to analyze multi-mode guided waves, which can decompose superposed waves into many independent modes. Then the group velocity of each mode was obtained at corresponding frequency, which was compared with the results of short time Fourier transform (STFT). The CTh was also obtained by comparing with the theoretical calculation. The results showed that the experimental determined thickness was in agreement with the actual CTh, indicating that measuring the velocity of the guided mode can be used to estimate the CTh. The HHT is an effective method to identify multimode guided waves.

PACS numbers: 43.35,43.40