时频方法分析长骨中的超声导波及皮质骨厚度

Analysis of ultrasonic guided waves in long bone and cortical bone thickness using time-frequency methods

超声导波在长骨中传播时,接收信号中含有相互叠加的多个导波模式。本文提出将希尔伯特-黄变换(HHT)用于分析叠加的多模式导波信号,将其分解成许多单个独立的模式,然后对分解出的模式求得其对应频率下的群速度,并与短时傅里叶变换所得的结果进行比较。通过与理论计算结果比较,可得到长骨皮质骨的厚度。研究结果表明,实验得到的厚度与实际厚度一致。说明通过测量导波模式的速度可以评价皮质骨的厚度,也说明HHT方法是一种识别叠加多模式导波信号的有效方法。

Received ultrasonic signals from long bone contain multiple superposed guided modes. In this paper, Hilbert- Huang transform （HHT） was applied to analyze multi-mode guided waves and decompose waves to many independent modes. Group velocity of independent mode was obtained at corresponding frequency and compared with the results with short time Fourier transform （STFT）. Cortical thickness was also obtained by comparing with the theoretical results. The results showed that the experimental determined thickness was in agreement with the actual cortical thickness. It is indicated that measuring the velocity of the guided mode can be used to estimate the cortical thickness. Also, the HHT is an effective method to identify multimode guided waves.