Harun Cetinkaya

A Study on Millimeter-Wave Imaging of Concealed Objects: Application Using Back-Projection Algorithm

Millimeter-wave (MMW) imaging is a powerful tool for the detection of objects concealed under clothing. Several factors including difierent kinds of objects, variety of covering materials and their thickness, accurate imaging of near-fleld scattered data afiect the success of detection. To practice with such considerations, this paper presents the two-dimensional (2D) images of difierent targets hidden under various fabric sheets. The W-band inverse synthetic aperture radar (ISAR) data of various target-covering situations are acquired and imaged by applying both the focusing operator based inversion algorithm and the spherical back-projection algorithm. Results of these algorithms are demonstrated and compared to each other to assess the performance of the MMW imaging in detecting the concealed objects of both metallic and dielectric types.

The millimeter-wave imaging of concealed objects

In this study, two different applications are performed. An application of concealed object detection is firstly studied through millimeter-wave inverse synthetic aperture radar (ISAR) imaging. For this purpose, near-field W-band ISAR measurements of one centimeter metallic and dielectric cube targets covered by distinct textile materials are carried out in an anechoic chamber room. Then, the images are reconstructed by using back-projection ISAR imaging technique. Then, the performance of the technique is quantified from the resulted images by using the accuracy and quality metrics. An application of a concealed weapon is also handled using millimeter-wave tomography imaging. The tomography imaging of concealed weapon located behind styropor foam wall is performed. Then, the images are reconstructed by using a method which calculates polarization currents on the object surface. The results obtained are finally shown.

Back-projection algorithm for ISAR imaging of near-field concealed objects

In this study, the detection of metal objects concealed under clothes is investigated through millimeter-wave inverse synthetic aperture radar (ISAR) imaging. A metallic gun is selected as the target and W-band ISAR measurements for a two-dimensional scanning geometry are carried out in our anechoic chamber measurement facility. The ISAR images of concealed object are reconstructed using the near-field back-projection algorithm. The obtained images indicate the efficient detection and identification of the gun covered with different textile types.

Terahertz and sub-terahertz subsurface tomography

Development of millimeter and sub-millimeter wavelengths technologies is of great interest lately, especially for application in so called terahertz imaging. As a rule, two main approaches are used for this purpose based on employment of active and passive methods of visualization. In our paper we consider a tomography approach for obtaining 3-D imaging in frequency range from 100 GHz up to 325 GHz. We applied the method which we developed earlier for low frequency sub-surface tomography for extremely high frequencies. The considered method may be used for nondestructive testing. In the paper we present a theoretical model, experimental method and the results obtained.

The millimeter-wave ISAR imaging of concealed objects

The detection of concealed objects like weapon, explosives, and other dangerous items became very important problem for defending people against terrorist attacks. Recent time, many methods have been developed but number of methods are not efficient to effectively solve this problem. The main aim of the research in this work is devoted to the detection of concealed dangerous objects by increasing sensitivity and resolution in obtained images. In this paper, we propose to use inverse synthetic aperture radar (ISAR) technology for the detection of hidden items in the millimeter-wave length. The millimeter-wave ISAR imaging of concealed cubes and a gun are studied. The theoretical background employed for the reconstruction of measurement results is briefly described. The millimeter-wave ISAR measurement setup is presented. Then, measurements carried out for different scenarios are explained. Finally, the reconstructed results are shown for all conducted measurements.

A tomography approach to through wall microwave and millimeter-wave imaging

The detection and imaging of concealed objects like spy cameras, eavesdropping spy devices behind or inside a wall are important problems. As electronic technology is developed, dimensions of these devices are being decreased. For this reason, in this paper, we investigate a surface tomography method which is used in subsurface applications in the context of through wall imaging for a small object. The microwave imaging of the piece of a metal plate behind marble wall and drywall and the millimeter-wave imaging of a web camera behind a marble wall were studied. Theoretical background employed for the reconstruction of measured results is briefly described. The microwave and millimeter-wave tomography setups are presented. Then, measurements carried out are explained. The 2D and 3D reconstructed images are illustrated for all measurements in section 3. Finally, the conclusion is given in section 4.

Image reconstruction in SAR, ISAR and tomography applications at millimeter-wave band

The study is devoted to the representation of the millimeter-wave imaging technologies of tomography, ISAR, SAR, and Passive Radiometric Radar (PRR) in International Laboratory for High Technologies (ILHT) of TUBĐTAK-Marmara Research Center (MRC). Millimeter-wave measurement setups with their technical descriptions are introduced as well millimeter-wave reconstructed images obtained by the usage of tomography, ISAR and SAR algorithms are illustrated.

Subsurface tomography imaging at sub-terahertz and terahertz frequency

The dielectric objects are more difficult for measurement because of the scattered field produced by a dielectric object is much weaker than that produced by metallic object. We present the image reconstruction of a dielectric object, cardboard capital letter C at millimeter wave region. It demonstrates that accurate scattering data is able to be collected from dielectric target and high quality images can be generated.

Subsurface sensing at sub-terahertz and terahertz frequencies

Development of millimeter and sub-millimeter wavelengths technologies is of great interest lately, especially for application in terahertz imaging due to bringing high resolution. In our paper we consider a tomography approach for obtaining 3-D imaging in frequency range from 100 GHz up to 325 GHz. We applied the method which we developed earlier for low frequency sub-surface tomography, for extremely high frequencies. The considered method may be used for 3D imaging in non-destructive testing. In the paper we present a theoretical model, experimental method and the comparison of results obtained at terahertz and sub-terahertz frequencies.