多相离散随机介质探地雷达波传输特性研究

Study on transmission characteristics of GPR in multiphase discrete random medium

混凝土是最常用的人工合成建筑材料,属于典型的多相离散随机介质,为研究探地雷达波在此类复杂介质中的传输特性,基于量化约束多相离散随机介质模型建模方法,通过精准调节混合物中各组成物质的体积含量百分比和自相关长度,建立不同空隙率和不同尺度的多相离散随机介质模型,进行探地雷达数值模拟,研究探地雷达波在多相离散随机介质模型中的传输特性及其影响因素.结果表明:多相离散随机介质模型可以直接表征多相混合物的空隙率,为数值模拟研究多相离散随机介质的空隙率与其探地雷达波场特征之间的函数关系提供了模型基础;与均匀介质相比,探地雷达波在多相离散随机介质中发生了明显的电磁散射,形成了大量的无规则扰动,造成了电磁波能量损失,致使其相同空间位置处的探地雷达波波前振幅小于均匀介质,且随机、无序传播的散射波相互干涉叠加,会降低探地雷达回波信号的分辨率;对于多相离散随机介质,其空隙率越大,则混合物等效介电常数越小,介质非均匀性越强,致使电磁波传播速度越快,电磁散射越强烈,能量损失越大,波前振幅越小;随着自相关长度的增大,其对应的多相离散随机介质模型中骨料粒径随之增大,电磁散射越强烈,波前到达距离相同点的走时差越大,振幅变化越大,波前形状扭曲变形越强烈.研究结果可为探地雷达无损检测混凝土工程质量提供指导和借鉴.

Concrete is the most commonly used synthetic building material, it belongs to typical multiphase discrete random medium. In order to research transmission characteristics of Ground Penetrating Radar(GPR) waves in such complex media, based on quantized constrained multiphase discrete random media modeling method, we establish multiphase discrete random media models with different porosity factor and scales through precisely adjusting the volume content percentage and autocorrelation length of each constituent in the mixture, so as to carry out the numerical simulation of GPR, and study the transmission characteristics of the GPR wave in the multiphase discrete random medium model and its influencing factors. It shows that the model of multiphase discrete random media can directly characterize the porosity factor of multiphase mixtures, and provides a model basis for the numerical simulation of the functional relationship between the porosity factor of multiphase discrete random media and the characteristics of GPR wave field. Compared with the homogeneous medium, the GPR wave has obvious electromagnetic scattering in multiphase discrete random medium, forming a large number of random disturbances, resulting in the loss of electromagnetic wave energy, causing the GPR wave front amplitude at the same space position is less than that of uniform medium. Moreover, random and disorderly scattered scattering waves interfere and superimpose with each other, which will reduce the resolution of the GPR echo signal;For the multiphase discrete random medium, the larger the porosity fraction, the smaller the equivalent dielectric constant of the mixture, the stronger the inhomogeneity of the medium, so that the faster the electromagnetic wave propagation, the stronger the electromagnetic scattering, the greater the electromagnetic energy loss and the smaller the wavefront amplitude. With the increase of autocorrelation length, the particle size of the corresponding multiphase discrete random medium model increases. The stronger the electromagnetic scattering, the larger the difference of travel time between the wavefronts reaching the same point, the stronger the distortion of the wavefront shape. It can provide guidance and reference for the non-destructive detection of concrete quality by GPR.