NEW APPROACHES TO NONLINEAR DIFFRACTIVE FIELD PROPAGATION
NEW APPROACHES TO NONLINEAR DIFFRACTIVE FIELD PROPAGATION
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DOI：
10.1121/1.401274
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发表时间：
1991-07-01
影响因子：
2.4
通讯作者：
PARKER, KJ
中科院分区：
文献类型：
--
作者：
CHRISTOPHER, PT;PARKER, KJ
在声场传播的许多领域中，例如医学超声成像、碎石冲击治疗和水下声纳，波束图案的实际计算需要处理来自有限源的衍射效应。 此外，介质内的损耗和非线性效应的机制通常是不可忽略的。 衍射，衰减和非线性效应的组合已被处理的一些配方和数值技术。 提出了一种新的模型，增量传播的字段的挡板平面源的子步骤，占衍射，衰减和非线性的物理。 该模型考虑了在通过多个平行流体介质层传播的情况下折射和反射（但不是多次反射）的影响。 轴对称源的模型的实施已经开发。 在实现的一个子步骤中，新的离散汉克尔变换与空间变换技术一起使用，以在具有衍射和衰减的短距离上传播场。 在另一个子步骤中，Burgers方程的时间频率域的解决方案，以考虑非线性的谐波吸积和耗尽。 这种方法产生了一个计算效率高的程序计算光束模式从一个挡板平面，轴对称源的条件下，从准线性通过冲击。 该模型不受通常的抛物波近似的限制，场的方向性在每一点上都被明确地考虑。 谐波限制方案的改进使得模型能够传播一些以前难以处理的高强度非线性场。 该模型的结果被证明是在一个未聚焦的2.25 MHz的活塞源的非线性场上进行的测量，即使在近场建立的抛物线波近似模型失败的非常好的协议。 接下来，该模型用于比较医疗超声设备的水路径和原位场。 最后，该模型被用来计算与非线性场相关的空间加热率，并模拟饱和引起的光束展宽现象。
In many domains of acoustic field propagation, such as medical ultrasound imaging, lithotripsy shock treatment, and underwater sonar, a realistic calculation of beam patterns requires treatment of the effects of diffraction from finite sources. Also, the mechanisms of loss and nonlinear effects within the medium are typically nonnegligible. The combination of diffraction, attenuation, and nonlinear effects has been treated by a number of formulations and numerical techniques. A novel model that incrementally propagates the fields of baffled planar sources with substeps that account for the physics of diffraction, attenuation, and nonlinearity is presented. The model accounts for the effects of refraction and reflection (but not multiple reflections) in the case of propagation through multiple, parallel layers of fluid medium. An implementation of the model for axis symmetric sources has been developed. In one substep of the implementation, a new discrete Hankel transform is used with spatial transform techniques to propagate the field over a short distance with diffraction and attenuation. In the other substep, the temporal frequency domain solution to Burgers' equation is implemented to account for the nonlinear accretion and depletion of harmonics. This approach yields a computationally efficient procedure for calculating beam patterns from a baffled planar, axially symmetric source under conditions ranging from quasilinear through shock. The model is not restricted by the usual parabolic wave approximation and the field's directionality is explicitly accounted for at each point. Useage of a harmonic-limiting scheme allows the model to propagate some previously intractable high-intensity nonlinear fields. Results of the model are shown to be in excellent agreement with measurements performed on the nonlinear field of an unfocused 2.25-MHz piston source, even in the near field where the established parabolic wave approximation model fails. Next, the model is used to compare the water path and in situ fields of a medical ultrasound device. Finally, the model is used to calculate the spatial heating rate associated with a nonlinear field and to simulate the phenomenon of saturation-induced beam broadening.