衰减匹配的超声Barker码激励方法

为增加超声穿透高声衰减介质的能力,提出了一种衰减匹配的超声Barker码激励方法。基于换能器高斯响应与材料非频散线性衰减的假设,得到了Barker码激励的信号模型,求解旁瓣抑制滤波后脉冲压缩的信噪比表达式可知,该方法仅需要根据材料衰减特性与轴向分辨率的要求,分别调整Barker码的中心频率与时长,便可以获得更高的信噪比。取衰减系数为1.4 Np/(MHz·cm)、厚度为5 cm的橡胶为试样进行验证。当与方波激励方法的轴向分辨率相近时,衰减匹配的Barker码激励方法比传统Barker码激励方法的信噪比增益提高接近5 dB;当牺牲一定轴向分辨率时,信噪比增益提高接近11 dB。结果表明,衰减匹配的Barker码激励方法可以降低依频率衰减对脉冲压缩的影响,有效提高衰减回波的信噪比。 

Ultrasonic Barker-coded excitation method with attenuation matching

In order to increase the ability of ultrasound to penetrate the high attenuation medium,an attenuation matching method of ultrasonic Barker-coded excitation is proposed.Based on the assumption of transducer impulse response with Gaussian shape and linear phase attenuation without dispersion in material,the signal model of Barkercoded excitation is obtained.By solving the expression of signal-to-noise ratio of Barker-coded pulse compression after sidelobe suppression,it can be seen the proposed method only needs to adjust the center frequency and time duration of the Barker-coded signal according to the material attenuation characteristic and the requirement of axial resolution.Take the rubber with attenuation coefficient of 1.4 Np/(MHz·cm) and thickness of 5 cm for example.When the axial resolution of square wave excitation method is similar to that of the Barker-coded excitation method,the signal-to-noise ratio gain of attenuation matching Barker-coded excitation method is nearly 5 dB higher than that of traditional Barkercoded excitation method.Furthermore,the increasement of the signal-to-noise ration gain grows to 11 dB at the cost of the axial resolution.The results show that the attenuation matching Barker-coded excitation method can reduce the influence of frequency-dependent attenuation on pulse compression and effectively improve the signal-to-noise ratio of the attenuated echo.