基于随机场照射的最优微波成像

近年来,电磁计算成像的理论和技术得到了广泛的研究和发展,其中基于随机场照射的微波成像引起了诸多关注.与传统成像方法的连续波照射不同,基于随机场照射的成像方法以随机照射的方式获取多组非相关的目标散射测量值,经过反演计算就能提取散射目标体的轮廓和形状等信息.基于阵列天线理论,本文理论分析并实验验证了一种最优的二维微波成像系统,能够使用最少的天线单元实现随机照射,通过最少的测量次数完成矩阵求逆并得到重建图像.该系统主要有以下两个创新点:完全随机照射的获取和成像系统最优参数的选取.与基于超材料的成像系统相比,本文通过对1 bit相位调制器随机相位调制的方式获取随机场照射,使得每个天线单元都处于工作状态,因此整个系统的能量效率更高.此外,所述单频成像系统还具有频谱效率高、结构简单、成本低等优点,在安检、室内定位等不同场景中具有潜在的应用价值.

Optimal microwave imaging with random field illuminations

In the recent years, the theory and technologies of electromagnetic computational imaging have been well developed and several novel imaging methods have been proposed, one of which is known as the microwave imaging under random field illumination. In order to solve the matrix equation of imaging model, the key of such an imaging system is to generate the random electromagnetic radiation field distribution, implementing the independent measurements under random field illuminations. In this work, an optimal microwave imaging system for the desired imaging region and resolution is theoretically analyzed and experimentally implemented. In the randomness analysis, the correlation between different measurements is evaluated by the singular value decomposition, which is also adopted as a criterion for choosing the optimal parameters of the imaging system. Based on random field illuminations generated by the least number of antenna elements, a full-rank matrix equation can be used to reconstruct the object by direct matrix inversion, which can be completed in nearly real-time once the system calibration is implemented in advance. The numerical simulation and experimental investigation are performed, and the results prove the effectiveness of the proposed optimal imaging system. By using the traditional array theory, it is found that for an N-element phase array, N illuminations with each element excited by a single frequency, equal amplitude and randomized 0 or π phase signal will result in N independent measurements. Theoretically, any additional measurement under random illumination will be correlated with the previous N measurements. Since the random field illumination is obtained by array antennas with 1-bit random phase modulation, the power radiated by each transmitting element is not sacrificed, resulting in an optimal power efficiency of the imaging system compared with those of earlier metasurface-based imaging systems. Besides, a single frequency signal source is used in the system, which also realizes the optimal spectrum efficiency. In conclusion, there are two major innovations of the proposed imaging system:1) the completely random field illuminations based on 1-bit phase modulation; 2) the approach to optimizing the system on desired demand. The compact and low-cost imaging system promises to have various imaging applications, such as public security and indoor localization.