A. A. Vertiy

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.

Through-wall and wall microwave tomography imaging

In the present work new results of experimental investigation on TWWI with using the microwave tomography technique are submitted. A tomographic algorithm is employed for the cross-section imaging of dielectric and metal objects on the other side of a concrete wall and within a concrete block. The cross-section restoration of studied objects is based on the tomography integral equation. The scattered field of the object is measured on a direct line parallel to the wall investigated. The solution of this integral equation gives the possibility to find the function representing the normalized polarization current distribution in the probing cross-section which is normal to the wall surface and in which the scan line lies (vertical cross-section). The normalized polarization current distribution depends on frequency and can be calculated for a set of frequencies. The image function is defined as modulus of the sum of the normalized polarization current distributions. If the wall material in vertical cross-section is not homogeneous because of the presence of defects or quests within the wall or on the other side of the wall, one can see these inhomogeneities. A set of images in different vertical cross-sections allows us to reconstruct a 3D image of the object. It is shown that advanced through-wall and wall images can be obtained by application of an indemnification procedure to the field caused by final sizes of the scanning line and also by using an algorithm allowing us to allocate from the complete field the scattering component.

Application of tomography method in millimeter wavelengths band II. Experimental

Tomographycal methods of image reconstruction of two-dimensional objects, surfaces or subsurface regions in millimeter wavelengths band are suggested and considered. Experimental images obtained using antennas and waveguiding lines of different types and radiation frequencyf≈33÷35GHz are represented. Volumetric dielectric objects and plane-parallel ferrite (or dielectric) plates distributed in free space or in homogeneous dielectric medium have been taken as objects under investigation.It is shown that in the frequency band under consideration, the images of investigated objects with characteristic dimensionA≈2λ÷7λ may be obtained by first-order diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for electromagnetic field).

Circular groove shaped resonator for millimeter waves

In millimeter wave lengths region semiconductor generators, amplifiers, mixers and other solid state UHF devices find a wide application. In our work, we suggested to use aCircular Through-Shaped Resonator for obtaining power combination using active elements at frequency region Δf≈20–40 GHz.The resonator is formed by two plane aluminum reflectors. The first reflector has a circular groove. The second reflector has coupling elements. The first and the second reflectors are considered as a ring groove shaped waveguide.A resonator spectrum was calculated and analyzed in the frequency range Δf ≈20–40 GHz. It is showed that, in the given frequency range the resonator spectrum has a complicated structure and is formed by a series of spectrum lines; a frequency range between the series increases with the frequency increasing.We studied on transmission coefficient of the resonator, frequency shifts of spectrum lines when inserting a thin (t/λ≈0.003) dielectric substrates into the resonator, and also attenuation constants of waves propagating in circular groove (due to losses in metal).

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.

A millimeter wave radio spectrometer for material analysis below T<1 K

A radio spectrometer set suggesting wide fuctional possibilities and operating in the shortwave part of the millimeter band at temperatures below 1 K is described. The set is intended for analyzing materials of polarized nuclear targets under the conditions close to actual operation, with the use of magnetic resonance methods. The potential of spectrometer allows employing it in semiconductor physics, physics of disordered media, biology, et.c.

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.

Diffraction Tomography Method Applications in Wide Frequency Range

Development of millimeter wave and microwave tomography for nondestructive testing and subsurface investigations is suggested. It may be manufactured as well in waveguide modification as in quasioptical one. Description of the main principles of creation of the tomographic system both for millimeter waves band and for microwaves is given below. The system combines possibilities as well of tomograph operating “on passage” as tomograph operating in regime of undersurface measurements. Using both of these approaches will allow us to create microwave or millimeter wave tomograph providing the image reconstruction of the object under investigation. The suggesting version of tomography is orientated towards applications in industry, medicine, detection and identification of abandoned objects and other fields.

Microwave tomography systems for investigation of the wave structure

In the present paper topographical methods of image reconstruction of two-dimensional cross-sections of volumetric objects, surfaces or subsurface regions in millimeter wavelengths band are suggested and considered. Experimental images obtained using antennas and waveguiding lines of different types and radiation frequency f approximately equals 33 divided by 38 GHz are represented. Volumetric dielectric objects and plane-parallel ferrite (or dielectric) plates distributed in free space or in homogeneous dielectric medium have been taken as objects under investigation. It is shown that in the frequency band under consideration, the images of investigated objects with characteristic dimension A approximately equals 2 (lambda) divided by 7 (lambda) may be obtained by first-order diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for scattered electromagnetic field).

Application of tomography method in millimeter wavelengths band I. Theoretical

Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths band are suggested and considered.It is shown that in the frequency band under consideration, the images of investigated objects may be obtained by first-order diffraction tomography method (Born, Rytov or high frequency approximation of the first-order for scattered electromagnetic field).