S. P. Gavrilov

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).

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.

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).

Sommerfeld wave diffraction by the undulator wire segments

In this paper, the results of analysis and solving of the Sommerfeld wave diffraction problem by the wire segment of the given configuration are presented. It is assumed that the Sommerfeld wave supported by a one-conductor open line exited from one end by a local incident field and scattering segment located at a certain distance from the line. The configuration of nonmagnetic metal wire segment is described by a harmonic function. They are used as the transversely polarised broadside radiators. Also the use of one-conductor open line at creation such type radiators can have positive advanced features in contrast with early investigated UW structures. The solution of the given problem consists of two stages. At the first one the current equivalent sources of the scattered field are found. The separate problem on radiation by the found current distribution in the undulator is solved on second stage. Investigations of the undulator radiation charcteristics showed its efficiency at use as an basic element in different MM-wave devices, for example in antenna system as radiator of good-directed transversely polarized broadside electromagnetic wave. Modeling and experiments confirm the basic possibility of using of such system.

GPR and microwave tomography imaging of buried objects using short-term (picosecond) videopulses

In the given study the experimental results on detection and image processing of weakly scattering subsurface objects are presented. For acquisition of experimental data about scattered by the object field the 2D mechanically scanning pulse system connected to PC was used. A short rise time of a sounding pulse (< 50 ps) and corresponding wideband of a test signal have allowed to apply GPR and microwave tomography methods of experimental data processing. The obtained results allow to maintain, that both techniques of processing give ability to get the high quality images even for weakly scattering dielectric objects with the dimensions approximately 1 divided by 5 (lambda) of average wavelength of radiated pulse. Tomography allows to achieve less noisy images, though the processing in a time domain is much faster. The developed experimental methods and methods of processing are ready to practical application.

Experimental investigation of buried objects by microwave tomography method

In this paper the results of experimental investigation of buried objects are given. To find images of the objects the microwave multi-frequency diffraction tomography method was used. For image reconstruction of the objects we used a plane wave spectrum of diffracted field. A vectorial network analyzer measured real and imaginary parts of the diffracted field by its sin/cos converter. The wave incident near to the normal of the surface was used in our measurements at frequency range of 2.5 - 4.5 GHz. The experimental set-up allows to obtain the diffracted field data at 512 frequency points. It contains a mechanical scanner system that can move as well linearly as in 2-D space. In the inverse problem a complex function of space coordinates representing the normalized polarization currents was reconstructed. A module of the complex function is the image of the object under investigation. The reconstruction algorithm is based on Fourier inverse formulas. The images of dielectric and metallic objects of different shape and configuration were reconstructed. The results of investigation may be used for civil or medical science application.

Investigation of mm-wave radiation from the undulator type wire antennas

Currently, the traveling wave linear one-wire radiators of finite size with only one, longitudinal, electric current density component (linear uniform wire antenna -LWA) have been sufficiently well studied and are used practically. On the other hand, a number of theoretical and experimental works devoted to the radiation by electron flow moving along a curvilinear trajectory showed that the electron beam moving along the wave trajectory with velocity V<C radiates electromagnetic waves (space harmonics) mainly at an angle to the trajectory axis. Using this concept, a new type of mm-wave wire antenna (undulator type antenna) has been investigated, in the frequency band 26-38.5 GHz. The investigation results are presented in this work.

Millimeter wave imaging of thin metallic wire by using interaction of it with dielectric waveguide

The authors show that it is possible reconstruct an image of an object such as a metallic wire located in a dielectric waveguide after measurement of ratio P/P/sub 0/ (transmission coefficient) in accordance with the computer tomography scheme. The result of such image processing is presented. The aim of the work is to determine small conductivity inhomogeneities which are comparable with wavelength (3 mm) for different material. Thus, it will be possible to analyze about the quality of material in integrated millimeter wave technology.