SBIR Phase II: Nondestructive Evaluation by Quantitative Dielectric Imaging

*9312746郭这个小型企业创新研究第二阶段项目将开发一种通过介电常数的三维定量成像进行无损检测和评估的技术。通过测量目标的微波散射场，利用散射反演算法重建目标的介电图像。预计它将产生不受波长限制的分辨率，而只受信噪比限制。为克服波长限制，将散射方程数字化为无远场近似的矩阵形式。为了稳定反演并降低其对噪声的敏感性，将近场散射数据的数量增加到超过目标体素的数量，并使用最小均方方法对方程进行拟合。这项研究有望推动低成本、可运输的定量无损检测和检测设备的开发。由于介电常数对各种材料的敏感性，它将提供比现有器件更鲜明的对比度。成像处理时间预计为毫秒，曝光时间在微秒量级，微波剂量在每克微瓦到几十微瓦的量级，比连续曝光的安全水平低两到三个数量级。该项目有望开发出一种微波介电常数的实时三维成像设备。商业应用包括非金属物体的所有非破坏性评估，如机场行李询问、混凝土和屋面材料中水分含量的测量以及材料缺陷的监测。***

*** 9312746 Guo This Small Business Innovation Research Phase II project will develop a technique of non-destructive testing and evaluation (NDT&E) by three-dimensional quantitative imaging of dielectric permittivity. The dielectric image of a target is reconstructed by measuring the microwave scattering field and utilizing a scattering inversion algorithm. It is expected to yield a resolution unlimited by wavelength, and only limited by signal-to-noise ratio. To overcome wavelength limitation, the scattering equation is digitized into a matrix form without far-field approximation. To stabilize the inversion and reduce its sensitivity to noises, the number of near-field scattering data is increased to more than the number of voxels in the target and a least-mean-square method is used to fit the equations. The research is expected to lead to development of low-cost and transportable quantitative NDT&E equipment. Owing to the sensitivity of dielectric permittivity to various materials, it will provide sharper contrast than existing devices. The imaging processing time is expected to be in milliseconds, the exposure time in the order of microseconds, with microwave dose in the order of microwatt per gram to tens of microwatt per gram, which is two to three orders of magnitude below the safety level of continuous exposure. The project is expected to lead to development of a real-time three-dimensional imaging apparatus for dielectric permittivities in the microwave regime. Commercial applications include all non-destructive evaluation of non-metallic bodies, such as airport luggage interrogation, measurement of moisture contents in concrete and roofing materials, and monitoring of material defects. ***