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This paper considers two methods for improving the visibility of hidden objects in radar tomography using nonlinear time transformations of short ultra-wideband (UWB) pulses. The first method is based on selection of a digital coherent jitter formed by special nonlinear signal transformation. The resulting increase in the contribution of high-frequency components to the reflected signal spectrum improves the spatial resolution of images of hidden objects. The second method uses relatively powerful monochromatic side irradiation in the clocked mode to detect a target. This leads to a characteristic distortion of the radar sensing pulse reflected from nonlinear radio-electronic elements – parts of the target being located. The observed change in the radar pulse waveform allows selective tomography of nonlinear radio-electronic elements to be carried out.

Based on results of theoretical analysis, a new method of transmission tomography of pipeline surface defects using ultrasound waves propagating along the pipeline walls is proposed. The waves are excited by a source and received by sensors that are located on ring-shaped lines and spaced along the tube surface. These waves propagating along the pipe surface represent either left or right handed rectilinear cylindrical waves like torsion waves. When a defect arises on the pipeline surface, the resulting waves are accompanied by changes in their shadow projections at the controlled pipe end. The problem of defect tomography is to determine locations and forms of defects using the backward projections. The physical feature of this method is that unlike traditional tomography, these projections arise on mutually intersecting left and right handed trajectories. The problem is solved by multiple joining of cylindrical pipe sections unfolded onto the plane in which all wave paths become rectilinear. A number of examples given in the paper confirm the possibility of restoration of locations and forms of various defects by the proposed method.

In this paper, theoretical and experimental studies of physical processes occurring during the interaction of electromagnetic fields with biological tissues containing blood vessels with a small depth are given. A new approach is aimed at creating a near-field microwave sounding system for regular non-invasive monitoring of glucose levels. A feature of the proposed approach is the use of significant changes in the phase state of the near field in the vicinity of the so-called “causal surface”. At the first stage of the study, numerical simulation made it possible to obtain a picture of the interaction of near field of the wideband sensor of a special design with samples of biological tissues of various types. The most important thing in this work is that the geometry of the sensor provides the formation of an extended near-field zone with a high level of electric field near its aperture. A study of the near-field interaction of the sensor with various biological tissues was carried out on the basis of an analysis of the behavior of the real part of the radiation flux. Since a change in a blood the level of glucose leads to changes in dielectric permeability, the largest changes in signal level should be expected in the radiation passing through the blood vessels. The second stage – experimental studies of the possibility of real measurement of glucose in the phantom of biological tissue. During the experiment, the complex reflection coefficient from the sensor was measured as a function of the frequency. First, the reflection coefficient was measured for saline solutions containing dextrose. Then the same procedure was repeated for a pure saline solution. Then followed the normalization (in doing so, we fully took into account the recommendations, concerning the reduction of the influence of various negative factors). Of particular interest, in our opinion, is the signal in the range from 4.3 to 4.6 GHz. In this frequency range, a clear correlation is observed between signal magnitudes and solution concentrations.

PURPOSE This report proposes an approach to develop a method of microwave imaging for early, non-invasive diagnosis of breast tumors. Here we describe a data-processing method for obtaining radio images of biological heterogeneities and a new method for filtering static noise in received signals. METHODS A specialized radar system was developed in the present study and used to perform sounding of synthetic phantoms with the dielectric properties of breast tissue in the range of 2-8 GHz. Datasets thus contained synthetic structures that imitated the dielectric properties of breast tissues and tumors. The permittivity values of the created artificial materials were verified using a waveguide cell. Tumors were simulated via plastic balls with a diameter of 1 cm that were filled with saline. A special ultra-wide band (UWB) radar system developed at Tomsk State University was used to register radar responses from the phantoms. The radar system included the vector reflectometer, the UWB antenna, and the mechanical scanner that provided sounding in the hemisphere. We also used the time-domain signals processing method to obtain the radio image signals. In this method, all signals received during scanning in the hemisphere are added with calculated delay for the given focus point. Special filtering of the constant components of the signal at each of the angular sounding latitudes was used to eliminate clutter in the received signal. This solution allowed us to account for additive clutter in the received signal from structural elements during scanning in the hemisphere. The influence of the number of angles on the quality of the resulting radio image was evaluated. RESULTS The phantoms of a female breast and a malignant tumor from artificial materials with electrophysical characteristics close to those of real tissues have been developed. This facilitated verification of the proposed method for constructing radio images under more clinically relevant conditions. The proposed filtering of the constant components of the signal effectively doubled the signal-to-noise ratio in the resulting radio image compared with the standard algorithm of clutter filtering. The influence of different numbers of scan points on the quality of the final radio image are presented herein. It is concluded that it is sufficient to use not more than 600-800 sounding points for acceptable image quality. A further increase in the number of angles does not significantly improve image quality despite increasing the scan time. CONCLUSIONS Scanning in the hemisphere of the breast phantom using the proposed method of clutter filtering show that multi-angle microwave imaging can form accurate three-dimensional (3D) images with double the level of signal-to-clutter compared with the standard filtering approach. The images of artificial tumors were obtained when sounding in the range of 2-8 GHz with the resolution of about 5-7 mm.

Physical possibilities of remote diagnostics and manipulation with the state of the propagation medium by the methods of wave tomosynthesis are considered. This refers to the electromagnetic and acoustic waves as well as waves of other nature. Important are multi-position measurements with retention of phase information at each point of the medium that allows the technology of synthesizing a wide aperture with focusing to be implemented. Processing of wave projections of hidden objects makes it possible to restore their three-dimensional images. In this way, the effect of multiple wave re-reflections is reduced. In addition, the tomographic approach allows one to manipulate with the properties of the media being sounded. Thus, an increase in the radiation power at a chosen focusing point causes hyperthermia that can be used, for example, to treat oncological diseases. And creation of a minimum field and a preset phase distribution in certain regions of the medium opens the possibility of control over the motion of microparticles being trapped. The last circumstance is important, for example, for targeted delivery of medical preparations in medicine.

It is proposed to use the tomographic approach to the problem of detecting and imaging concealed utility networks. This approach is based on generating the three-dimensional radio images of the space being explored from the results of measuring its location wave projections in a dual-polarization measurement mode. The problem is solved by focusing radiation first on the “air–dielectric” interface and then inside the dielectric. Experimental data processing results and reconstructed threedimensional radio tomograms are provided for a “twisted pair” cable and a fiber-optic cable with no metallic inclusions. The results confirm the operability of the approach.

Based on an analysis of physics of the phase transition from the quasistatic state field to the running wave field of elementary electric and magnetic dipoles located in absorbing media, it is concluded that the skin layer is formed at the boundary of this phase transition. The possibility is considered of obtaining the diffractive hyperbola of the skin layer and its subsequent application for sensing of objects in strongly absorbing media.

A new look at the description of the phenomenon of electromagnetic wave radiation as a phase transition of a quasi-static field state (near zone) in the field of running wave (far zone) is suggested. It is demonstrated that the boundary of this transition, called the causal surface, is sufficiently localized. The position of the causal surface depends on the chosen radiation frequency. The skin layer in media with strong absorption is formed at the boundary of the causal surface, and this can be used for depth sensing of such media.

The effect of electromagnetic wave focusing by a plane metamaterial layer with arbitrary parameters is theoretically simulated. Results of focusing of radiation of two point-sized radiation sources obtained without and with taking into account multiple re-reflections of waves are presented.

A new method of increasing resolution of radio images due to nonlinear ultra-wideband data processing without any modification of the employed hardware is presented. The approach is applicable for stroboscopic filling of ultrashort impulses in which the error of triggering of a sensing impulse generator – a jitter – detected as noise in the gated data – is always presented. The nonlinear operation of selection of the coherent noise component in combination with the synthetic aperture radar (SAR) method provides a higher contrast of the radio image in comparison with operation of jitter smoothing. As a result, the physical effect of jitter occurrence that is typically negative yields a positive result. Examples of experimental data processing confirm this conclusion.

The word tomography consists of two separate Greek words: τομοσ (slice, section) and γροφοσ (to write). So, tomography is similar to a "write sections" procedure, that is, a division of the structure of the object under investigation into slices. Wave tomography records information on each element of the object under investigation by use of numerous integral projections under various angles with respect to the direction of the investigated object. Radio, optical, and acoustic wave tomography are separate novel directions of physical tomography, and have recently been used for sounding, visualization, and reconstruction of various objects, features, and processes presented and occurring in the environment, as well as anomalous occurrences on and in the human body. In all types of wave tomography, the wave nature of any radiation is usually used during investigations carried out to understand deeply the inner and outer nature of the objects under investigation.

An analysis of the most effective methods, techniques and scientific-research developments of induction mine detectors is performed, their comparative tactical-technical characteristics are reported, and priority avenues for further research are outlined.

The experimental ultra-wideband radio tomographic imagings inside and behind dielectric barriers with resolution near the diffraction limit are described. The problem is solved by the method of radio wave tomosynthesis using the theory of spatial spectra of the received signals. The ultra-wideband pulse sensing of the air—building structure medium, developed in Tomsk State University, are described. It has been shown that for the case of sensing with ultra-wideband pulses of 0.2 ns duration, the resolution is about 2 cm. The paper also shows the possibility of accelerating scanning of the investigated space through the use of the MIMO (timed or switched) antenna array technology. As in the timed mode the distance between the receiving and transmitting antennas varies from time step to time step, the algorithm of processing the data obtained from the array is to be modified. The modification itself is a nonlinear stretching of the received UWB signal in time. The signal transformation allows preparation of data for the above algorithm to receive three-dimensional images of the tested space. The paper presents the results of the processed experimental data which confirm the efficiency of the proposed method for MIMO arrays. The resulting image resolution is about 2 cm.

The following work is connected with a new solution of aerospace focusing problem for communication systems. It is offered to use an inflatable spherical lens-reflector which can be calculated by Fresnel zone theory application. The antenna focus is situated on its external surface that is very important for applications.

A new look at the formation of the skin layer is suggested. It is based on an analysis of forming the radiation field as a phase transition of the field in the near zone to the field in the far zone. In the near zone, the field is in the quasi-static state, and in the far zone, it is in the form of the travelling wave. The boundary of this transition, called the causal surface, is sufficiently localized and acts as a certain causal surface for the free travelling wave field. The field in the near zone is attenuated with distance by a power law; moreover, this is the case not only for nonabsorbing media, but also for strongly absorbing media. In the far zone, the field attenuation differs. In absorbing media, the field is attenuated fast following an exponential law and gives rise to a skin layer. Thus, the skin layer is formed on the causal surface rather than in the immediate proximity of the source. Manipulation with the position of the skin layer allows absorbing media to be sensed. This conclusion is important for applications, for example, for the development of ultradeep geolocation systems and new non-invasive treatment methods in medicine.

Radiowave tomography of dielectric objects containing metal inclusions is a rather complex problem, since the scattering of waves by dielectric inhomogeneities occurs against the background of substantially stronger reflections from metal parts, even if they are geometrically small. The arising features of obtaining a tomogram in such conditions, including overcoming of disguising by reinforcing ribbons and the appearance of locational shadows at different depths, are discussed in the paper. Herewith principled importance to achieve high focusing of UWB radiation by tomosynthesis is noted on the basis of direct experimental data.

It is shown theoretically and experimentally that in the field of an electromagnetic radiator located in an absorbing medium, there exists a virtual surface that encompasses the near-field zone and is referred to as causal in the present study at which the field undergoes a second order phase transition. This transition is characterized by a rapidly changing phase and conversion of the energy of the quasistatic/reactive field into the energy of the field in the state of radiation. Behind the causal surface, the law of phase change sufficiently quickly acquires a linear character, and the field strength decreases with an increase in the distance following either an inverse-square law or an exponential function depending on the absorption coefficient of the medium, which is manifested through the formation of an intensively absorbing layer. Within the near zone, exponential attenuation is not observed. The size of the near zone depends on the frequency and the refractive index of the medium. Based on the studies performed, a new approach to the problem of sensing of absorbing media is suggested.

The characteristics of the ultrawideband (UWB) timed antenna array developed by the authors are described. The efficiency of the system is confirmed by experiments processed with the use of focusing and aperture synthesis methods. Technical solutions used in this work allow us to proceed to the development of the UWB radio tomograph operating in real time.

Results of testing a tomographic system based on joint application of electromagnetic radiation and ultrasonic radiation for detection and visualization of hidden objects are presented.

This paper describes a method of studying the natural habitats of underground animals by the example of zokor. The purpose of the research is to find habitation of animals using unmanned aircraft and investigate networks of tunnels and burrows with ground penetrating radar "OKO-2". Geolocation data were processed by techniques developed by the authors.

This paper features the technology for identifying the location of real people behind the barriers in real time using the UWB sensing. The opportunity to obtain the radar images of moving and not moving people was presented in this paper. The oscillation rate of a human chest can be defined by the continuous recording the not moving person. The point of this technique is in calculation of the differential signal in successive periods of time. The range of application to be extended considering the particular conditions. The research results can be used in intelligence service as well as for searching people trapped under the rubble.

Article demonstrates possibility of monochromatic radiation usage for relief restoration. There is a problem with restoration when scanned object is not flat and it is not parallel to the scanning plane. It was discovered that two-dimensional phase distribution could be applied for distance determination. It is reliable way to solve problems listed above. In conclusion offered methods allow monochromatic microwave radiation usage for screening system development.

A method for restoring the images of remote objects with the system’s instrument function in ultrabroad-band (UBB) pulse sounding is considered. The system is a synthetic-aperture radar combined with a parabolic reflector. The aperture was synthesized via UBB scanning with a transceiver over the near-focus plane of a parabolic rereflector. Such a scheme allows the boundary of the maximum offset of a sounded object to be displaced at a distance equal to 2–3 diameters of the parabolic reflector. An additional advantage of the system that contains a parabolic reflector (rereflector) consists in the possibility of focusing radiation to a specified remote spatial region. In support of the validity of this method, we represent the results of numerical and physical modeling.

Results of theoretical and experimental investigations of artificial metamaterials based on composite of straight and circular conductors for radio wave range are presented. It is demonstrated that for small conductor sizes, nonresonant character of metamaterial properties of the artificial medium is retained. The possibility of application of metamaterials for increasing resolution in radio tomography is discussed.

In the work, an approach to reconstruction of radio images of objects behind dielectric barriers is considered. The approach is based on the method of mathematical focusing of reflected ultra-wideband signals. A sensing system is a radar with aperture synthesis. The possibility of improving the image quality by additional processing of received signals is demonstrated. The efficiency of the method is confirmed by numerical modeling and experimental results.

A method is proposed for reconstructing three-dimensional images of scattering inhomogeneities from the results of wideband multiposition radio sounding in the millimeter-wave range with the help of linear frequency modulated signals. An algorithm is devised that implements the method based on the fast Fourier transform algorithm and ensures the real-time data processing. Results of numerical simulations, processed experimental data, and reconstructed images of test objects are considered.

You can see the method of the synthesis of planar sources of concentrated magnetic field. Method defines the current distribution in the plane, which is required to produce a concentrated magnetic field at a distance from the source. Carried out a numerical calculation of the current distribution to create a point field localization. It is shown that the field concentration is achieved by minimizing the level of low spatial frequencies due to antiphase currents in concentric circular coils. The resulting field distribution is extremely sensitive to the slightest changes in the current distribution, which creates difficulties for the practical implementation of the system.

In this work influence of an electromagnetic field on lattices from close located ring conductors is shown. RCS is also calculated and shown that at 0 ≤ n2 < 1 there is the considerable decrease of an object.

Experimental results are presented on the nanosecond radar application for test site tomography with radar calibration by a corner-cube reflector. It is demonstrated that the presence of the corner-cube reflector leads to the occurrence of false targets that can be used for detection of weakly reflecting targets.

We propose a noncontact method for determining the mean refractive index of the medium in problems of subsurface tomography using ultra-wideband multi-position radio sounding in the case of a plane air-ground interface. The method is based on the computer oblique focusing of the radioimage of the sounded half-space containing buried objects. The proposed method does not require any a priori information on the position of the scattering objects in the medium. The feasibility of the proposed approach is verified experimentally.

In the approximation of a strongly refractive medium, we solve the inverse problem of subsurface-radar imaging of buried inhomogeneities using data of multiposition ultra-wideband radio sounding. The fast Fourier transform is used for synthesizing a large aperture with focusing. A mathematical model of the proposed subsurface-imaging system is presented and its accuracy is estimated. The feasibility of the proposed method is confirmed by numerical simulations and model laboratory experiments.

The efficiency of using ultra-wideband (UWB) signals for nonlinear radar is investigated. In the case at hand, it is necessary to see, based on scattered field disturbances, whether nonlinear inclusions are present in the field of view. The solution suggested is to compare the shapes of UWB signals reflected from the probe area under two conditions: an additional generator irradiating the probe area by intense monochromatic radiation is switched on and off. If a nonlinear electronic component is present in the probe area, the reflected UWB signals differ in shape. Thus, the difference in the shapes of the signals indicates the presence of a component with a nonlinear characteristic.