有限衍射X波非线性声场特性研究

Study on Property of Nonlinear Field of Limited-Diffraction X Waves

X波用于超声成像可以获得很高的帧率,但在线性成像模式下图像空间分辨率相对于传统的聚焦成像有所下降.本文通过时域数值方法求解KZK(Khokhlov-Zabolotskaya-Kuznetsov)方程,研究有限衍射X波的非线性声场特性.结果表明:无论宽带或限带X波,其非线性声场同样是有限衍射波,并且二次谐波具有比基波更窄的主瓣和更小的副瓣.采用X波的二次谐波进行成像能够在整个成像区域获得更高的分辨率.理论分析验证了数值计算结果.

X waves may be used in ultrasound imaging to obtain very high frame rate.But the spatial resolution of the image with a linear imaging mode decreases as compared to conventional focused imaging.The nonlinear fields of limited-diffraction X waves are calculated and studied by solving the KZK equation using a time-domain numerical method.The result indicates that the nonlinear fields of broadband and band-limited X waves are both limited-diffraction beams.Moreover,the second harmonic component has narrower mainlobe and lower sidelobes than the fundamental field.Utilizing the second harmonic of X waves in ultrasound imaging,higher spatial resolution would be obtained throughout the entire imaging range.A theoretical analysis verifies the numerical calculation result.