LAUSR

Microwave imaging has been investigated in various areas involving nondestructive testing, biomedical imaging, and radar ranging imaging. With a lower frequency than THz and visible light, microwaves penetrate deep in dielectric materials, which enables detection in depth and three-dimensional (3D) imaging. High and super lateral resolutions have been obtained with current techniques, while the depth resolution remains in centimeters or millimeters due to the limited bandwidth of microwaves. Therefore, it is a challenging and interesting issue to accomplish microwave super resolution 3D imaging in low frequency and limited bands. Herein, we proposed a zero-padding pseudo pulse algorithm (ZPPA) enabling super resolution in depth for microwave 3D imaging within the limited band. This algorithm was explained and demonstrated through resolving and reconstructing two separate reflection signals of adjacent interfaces that cannot be resolved from conventional time-of-flight profiles. A depth variation of 10 μm and a metal step with a height of 50 μm were accurately identified and reconstructed through both experiment and theoretical simulation, which greatly surpasses the depth resolution limitation of about 11.1 mm within 26.5 ∼ 40 GHz. Besides, a 3D nanometric step pyramid was theoretically simulated and reconstructed with each step of 1 nm-high accurately resolved. In summary, the depth resolution of ZPPA was compared with that obtained through current microwave methods and THz time-domain imaging methods, which verified that the ZPPA is feasible to obtain super depth resolution in 3D imaging for low frequency and narrow band microwaves.Microwave imaging has been investigated in various areas involving nondestructive testing, biomedical imaging, and radar ranging imaging. With a lower frequency than THz and visible light, microwaves penetrate deep in dielectric materials, which enables detection in depth and three-dimensional (3D) imaging. High and super lateral resolutions have been obtained with current techniques, while the depth resolution remains in centimeters or millimeters due to the limited bandwidth of microwaves. Therefore, it is a challenging and interesting issue to accomplish microwave super resolution 3D imaging in low frequency and limited bands. Herein, we proposed a zero-padding pseudo pulse algorithm (ZPPA) enabling super resolution in depth for microwave 3D imaging within the limited band. This algorithm was explained and demonstrated through resolving and reconstructing two separate reflection signals of adjacent interfaces that cannot be resolved from conventional time-of-flight profiles. A depth variation of 10 μm ...