THz Imaging Technology Trends and Wide Variety of Applications: a Detailed Survey

Terahertz (THz) imaging is a non-invasive and high spatial-resolution technique that uses non-ionizing electromagnetic signals in a frequency range of 0.1-10 THz. Hence, this article focuses on diverse THz imaging techniques, THz antennas and designing methods, image reconstruction algorithms, and its applications. The antennas include planar patch, photoconductive, dielectric-resonator, substrate-integrated waveguide, wire, and wave guide. In this study, it is noted that antennas with high efficient conducting materials having a compact size, high gain, and high directional properties are required for THz imaging. The image reconstruction algorithms cover back-projection algorithm, range migration algorithm, phase-shift migration algorithm, single-band compressed sensing reconstruction and compressed sensing hyper spectral image reconstruction. High-resolution image reconstruction algorithms and challenges are also reported. From this study, it is noted that a multi-input-multi-output-based phase shift migration algorithm is used for THz imaging due to its high-accuracy and low computation time. It is also noted that the image quality can be enhanced by introducing an inverse fresnel diffraction algorithm into THz images retrieved by compressed sensing. Applications of THz imaging focus on cell detection (tissue-detection, cancer-detection, and bacteria-detection), concealed objects detection, food safety and quality inspection, and monitoring the water level of plant leaves.