We present a new approach to nondestructive evaluation that uses the transmission of noncooperative 5G signals of opportunity and a passive millimeter-wave interferometric imaging system. Interferometric imaging samples scene information in the Fourier domain and reconstructs the image via a two-dimensional Fourier transform, providing an imaging mechanism that does not require mechanical or electronic scanning. To accurately form an image, the incident fields must be spatially and temporally incoherent, a criteria that is satisfied by the transmission of multiple independent 5G communications signals. We demonstrate the ability to image cracks in conducting walls using a sparse interferometric receiver capturing the transmitted 5G signals from two independent transmitters. The 38 GHz interferometric array consists of 24 receiving elements and generates images in real time. We employ deconvolution to remove artifacts resulting from the system point spread function, demonstrating the ability to determine the location of cracks in conducting walls.
Active incoherent millimeter-wave imaging is a recently introduced technique that combines incoherent signal transmission with interferometric antenna arrays. This essentially minimizes coordination between transmit and receive apertures and reduces the very high sensitivity requirements found in passive interferometric antenna arrays which capture very low power thermal signals. In this work, we explore short-range image reconstructions of conductive and dielectric targets from a compact 24-element 38 GHz active incoherent imaging array emitting random noise. We include experimental measurements in a semi-anechoic environment.
Active incoherent millimeter-wave (AIM) imaging is a recently introduced imaging technique that combines the benefits of passive and active millimeter-wave imaging by using incoherent noise illumination to mimic the properties of thermal radiation. In this work, we investigate the performance of a video-rate AIM imager in an outdoor scenario. The use of active illumination overcomes challenges in other modalities such as sky reflections and other environmental signals. We use a 38 GHz active incoherent millimeter-wave camera with multiple noise transmitters to demonstrate imaging in outdoor scenarios at ranges of more than 9 m.
Active incoherent millimeter-wave imaging is an emerging technology that combines the benefits of passive and active millimeter-wave imaging by using incoherent noise transmission and passive receive interferometric processing. In this paper, we investigate computational image processing techniques to achieve enhanced image reconstruction with a small number of antenna elements and without the need for accurate calibration. We demonstrate enhancement of images through simulation and experimental data collected with a 38-GHz active incoherent millimeter-wave imager.
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