Terahertz (>0.3THz) active imaging systems

İdikut, Fırat
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 continuous wave (CW) source is 880μm and measured output power was 7mW. The detector was Schottky diode based mixer and heterodyne detection method was used. The source and detector are constructed in a transceiver architecture using a directional coupler specially designed for this frequency. The leakage due to the directional coupler limited the dynamic range of the system to at most 20dB. The optical design of the active scan THz imaging system is based on Confocal Gregorian Geometry (CGG). In this geometry, the main elliptical mirror and secondary parabolic mirror were manufactured by machining bulk aluminum. The final optical system utilized 6 mirrors in total: a flat mirror to turn the beam, a short focal length parabolic reflector to collimate the beam, an XY scanning galvanometer mirrors assembly utilizing beryllium mirrors, and the main as well as secondary manufactured mirrors. Before testing the system, the output frequency of the source was determined by using dichroic filter, a metal mesh of patterned circular holes. The XY galvanometer mirror assembly allowed for imaging at 2 frames/s speed. The final constructed system allowed for imaging a 0.5m x 0.5m field of view with 1.5cm resolution at a standoff distance of about 6m. By using the prototype, it was shown that obscured objects causing specular reflections was successfully detected from standoff distance. A metal stick, behind clothes and having 3cm thickness, was imaged.


Characterization of a terahertz wave scanned imaging system for threat detection at standoff distances
YILDIRIM, İBRAHİM SONER; ÖZKAN, VEDAT ALİ; Idikut, Firat; Takan, Taylan; ŞAHİN, ASAF BEHZAT; Altan, Hakan (2016-07-01)
A terahertz active scanned imaging system is developed in order to acquire images of various targets at stand-off distances. The images are analyzed with respect to the experimentally obtained beam profile at the target plane using a commercially available mm-wave/terahertz camera. The active scanning system utilizes a heterodyne, continuous wave transceiver unit operating at 340 GHz and 2-D opto-mechanical scanning of the target plane is performed using two large area mirror coupled galvanometers. 340 GHz ...
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...
Absorbance Estimation and Gas Emissions Detection in Hyperspectral Imagery
Başkurt, Nur Didem; Gur, Yusuf; Omruuzun, Fatih; Çetin, Yasemin (2016-05-19)
Hyperspectral imaging in gas detection applications is a leading and widely studied research topic thanks to its high spectral resolution and remote detection ability. The main problems in these applications covers the leakage detection, gas identification, and quantification. The proposed algorithm aims to reach the transmittance and absorbance features of the gas and to detect the gaseous region by using the measured radiance data from the hyperspectral infrared sensors.
KIRAGI, H; Ersak, Aydın (1994-04-14)
In this paper an object recognition and localization system based on ultrasonic range imaging to be used in optically opaque environments is introduced. The system is especially designed for robotics applications. The ultrasonic image is acquired by scanning ultrasonic transducers in two dimensions above the area where objects are located. The features that are used for recognition and localization processes are extracted from the outermost boundaries of the objects present in the input scene. Experimental ...
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...
Citation Formats
F. İdikut, “Terahertz (>0.3THz) active imaging systems,” M.S. - Master of Science, Middle East Technical University, 2016.