Image reconstruction based on active scan techniques in the terahertz frequency range

Özkan, Vedat Ali
THz continuous wave (CW) imaging systems have attracted interest in the past decade since they have the ability to detect non-metal threats such as ceramic knives. Moreover due to low energy levels of THz signals, these systems are not harmful. Although various types of imaging systems have been developed, the nature of THz waves has prevented the scienti c community from producing a fast, high resolution and cost e ective imaging system. In this study we have investigated both experimentally and theoretically the application THz waves in various imaging system con gurations. The main goal was to understand the e ects of the optical system design as well as noise and other parameters that could impact the formation of images in an active THz imager based on frequencies near 340GHz. The designed optical system was simulated and the e ects of scanning the target eld were assessed in the simulated images of various targets. The results show that reliable target detection will be aided by post-processing the images using various techniques. Furthermore, to experimentally demonstrate an active imaging system, compressive sensing was used in a non-scanning re ection based optical geometry. In these experiments a mm-wave source near 120GHz was used to obtain the images. The obtained images were analysed and compared to that of simulations. The results show that compressive sensing methods can be implemented successfully to improve image acquisition in typically low-resolution THz imaging systems. Finally, the e ect of imaging in the terahertz frequency range was also investigated for passive imaging methods. A commercial system working in the mm-wave range was used to obtain raw images at stand-o distances. The goal was to process the images without using the routines supplied by the manufacturer. Using wellestablished routines these raw images were processed successfully. Throughout this study careful attention is paid on the limitations on speed and resolution of these imaging systems and discussions on the applicability of the methods developed within this thesis are discussed throughout.


Image Reconstruction and Optimization Using a Terahertz Scanned Imaging System
Yildirim, Ihsan Ozan; ÖZKAN, VEDAT ALİ; Idikut, Firat; Takan, Taylan; ŞAHİN, ASAF BEHZAT; Altan, Hakan (2014-09-23)
Due to the limited number of array detection architectures in the millimeter wave to terahertz region of the electromagnetic spectrum, imaging schemes with scan architectures are typically employed. In these con fi gurations the interplay between the frequencies used to illuminate the scene and the optics used play an important role in the quality of the formed image. Using a multiplied Schottky-diode based terahertz transceiver operating at 340 GHz, in a stand-o ff detection scheme; the e ff ect of image q...
Terahertz (>0.3THz) active imaging systems
İdikut, Fırat; Altan, Hakan; Department of Physics (2016)
Imaging systems based on terahertz waves are becoming an integral part of commercial and military screening applications. In this thesis, the prototype of active scan THz imaging system was constructed for detection of concealed objects at standoff distance longer than 5m. The system was mounted on a platform that can adjust in height, tilt and azimuthal angle. The methods of generation and detection of THz signal are based on Schottky diode rectifiers and Schottky diode mixers. The wavelength of the contin...
Novel methods in modulation and detection of terahertz waves for imaging applications
Takan, Taylan; Altan, Hakan; Department of Physics (2018)
Terahertz radiation, due to its unique properties offers a plethora of possibilities of applications in various domains including security & defense, communications, material characterization, product inspection and medical imaging. In all these fields, cost-effective, high-resolution, and high-speed terahertz imaging is a greatly desired technology. However due the inherent challenges associated with terahertz detection, building a terahertz imaging system that satisfies all these requirements necessitates...
Super-Resolution Image Reconstruction Applied to an Active Millimeter Wave Imaging System based on Compressive Sensing
Alkus, Umit; Ermeydan, Esra Sengun; ŞAHİN, ASAF BEHZAT; ÇANKAYA, İLYAS; Altan, Hakan (2017-09-11)
The development of passive and active millimeter wave imaging systems is progressing rapidly fueled by the need for many applications in the area of security and defense. Imaging schemes that may either utilize array detectors or single detectors in scan architectures offer suffer from poor resolution due to the longer wavelengths used and the limits of the optical system in terms of lens and mirror dimensions. In order to overcome this limit, super-resolution techniques can be employed to enhance the resol...
Compressive sensing imaging at Sub-THz frequency in transmission mode
Özkan, Vedat Ali; Menteşe, Yıldız; Takan, Taylan; Şahin, Asaf Behzat; Altan, Hakan (Springer, Dordrecht, 2017-01-01)
Due to lack of widespread array imaging techniques in the THz range, point detector applications coupled with spatial modulation schemes are being investigated using compressive sensing (CS) techniques. CS algorithms coupled with innovative spatial modulation schemes which allow the control of pixels on the image plane from which the light is focused onto single pixel THz detector has been shown to rapidly generate images of objects. Using a CS algorithm, the image of an object can be reconstructed rapidly....
Citation Formats
V. A. Özkan, “Image reconstruction based on active scan techniques in the terahertz frequency range,” M.S. - Master of Science, Middle East Technical University, 2014.