Millimeter wave/Terahertz detection of target signatures with low Infrared visibility

Date

2024-9-3

Author

Aytaç, Berat

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Infrared target detection is crucial for search, track and security systems, and today, advanced infrared (IR) cameras in a wide product range are being used successfully in this field. Due to many reasons targets can have a low IR signature, whether it be poor atmospheric conditions in the detection band or the use of IR signature suppression systems. The detection of targets with low IR visibility is one of the most challenging research topics in this field that still needs to be addressed. A natural solution is to develop methods of detection in other spectral regions. Terahertz (THz) region is of special of interest since THz emission is expected from almost all objects who have an IR signature. In order to examine the detectability of targets in the THz region, first atmospheric propagation in different THz bands is studied. Using publicly available databases, it is found that under poor atmospheric conditions which cause low IR visibility, target detection is still possible in low frequency THz bands at distances 500 m – 10 km. THz detection at these frequencies is still a challenge and the performance of two different types of detectors, one polarization sensitive and the other insensitive are evaluated with a blackbody source. Measurements show that polarization insensitive THz detection mechanisms are superior for detecting thermal emission in the THz band. These measurements not only show that thermal detection of THz is difficult using highly sensitive specialized THz detectors they also show that the THz emission from a thermal source is not detectable using state of the art IR cameras working in the mid-wave IR and long wavelength-IR regions. To address this problem a THz to IR upconverter is proposed where for the first time the proposed device is specifically optimized for incoherent detection of THz radiation. The device based on a metasurface absorber with a dual polarized cross shaped THz to IR converter unit cell structure is designed to combine advantages of detection in the THz and IR regions. Under coherent and incoherent source illuminations, notable temperature difference values were calculated and found to be well above the limit of the minimum resolvable temperature difference of the state-of-art IR cameras with response times around one second. These results show that for target detection under poor atmospheric conditions or IR suppression a dual polarized or multi-polarization sensitive metasurface THz absorber structure can be a significant tool that can overcome the difficulties with direct IR detection techniques.

Subject Keywords

THz to IR converter, atmospheric propagation, incoherent source, low IR visibility, IR target detection

URI

https://hdl.handle.net/11511/111389

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Graduate School of Natural and Applied Sciences, Thesis