Fig. 1. Flow chart of ultrasonic signal processing.超声信号处理流程图

Fig. 2. Envelope of ultrasonic echo model: (a) [a, b, T ] = [1.5, 2.5, 1]; (b) [a, b, T ] = [3, 3, 1]; (c) [a, b, T ] = [1.7, 3.2, 1]; (d) [a, b, T ] = [1, 3, 1]. 超声回波模型包络　(a) [a, b, T ] = [1.5, 2.5, 1]; (b) [a, b, T ] = [3, 3, 1]; (c) [a, b, T ] = [1.7, 3.2, 1]; (d) [a, b, T ] = [1, 3, 1]

Fig. 3. Simulation of ultrasonic echo: (a) Ideal ultrasonic signal; (b)noisy ultrasonic echo.仿真超声回波　(a)理想超声信号; (b)含噪超声回波

Fig. 4. Comparison of de-noising by different methods: (a) Noisy echo plotted in a black solid line, original signal plotted in a red dotted line; (b) signal de-noised by our proposed method; (c) signal de-noised by wavelet method; (d) signal de-noised by EMD method不同方法降噪结果对比　(a)黑色实线为含噪回波, 红色虚线为原始信号; (b)本文方法处理结果; (c)小波方法处理结果; (d) EMD方法处理结果

Fig. 5. Ultrasonic echo acquisition device.超声回波采集装置

Fig. 6. Comparison of different ultrasonic signal models.不同超声信号模型对比

Fig. 7. Comparison of measured ultrasonic echo processing results: (a) Measured ultrasonic echo; (b) measured ultrasonic echo contaminated by system noise; (c) echo processed by our proposed method; (d) echo processed by wavelet method; (e) echo processed by EMD method.实测超声回波处理结果对比　(a)实测超声回波; (b)混入系统噪声后的实测超声回波, 信噪比为–10 dB; (c)本文方法结果; (d)小波方法结果; (e) EMD方法结果