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In the paper there is considered the impact of nickel alloy addition upon the process of titanium carbide phase formation during the realization of self-propagating high-temperature synthesis in aluminum melt. The regularities of structure formation and optimum conditions for an engineering process for Al-4%Ni-10%TiC composite manufacturing are defined.

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.

A mesoscopic dielectric cuboid antenna (DCA), which can be connected to a standard waveguide, is proposed to achieve high directivity with a simple-structure and low-profile antenna compared with that of a horn antenna of same dimensions. We optimized the antenna dimensions based on simulation to maximize the antenna gain of 14.22 dBi, which is 1.9 dB higher than that of the horn antenna with the same dimensions. Simulation was performed both at 300 and 24 GHz. As a proof of concept, we designed and fabricated a scaled DCA with dimensions of 1.2 $\lambda \,\times \,1.2\lambda \,\times \,1.36\lambda$ and experimentally evaluated the radiation pattern at 24 GHz band. The full-width at half-maximum (FWHM) values were approximately 21% and 34% narrower than those of the horn antenna in the E -plane and H -plane, respectively. The frequency characteristic of sensitivity enhancement using the DCA as the reception antenna shows that the DCA is a nonresonant antenna with a wide bandwidth. Narrower FWHMs of the DCA have been discussed with respect to a two-dimensional near-field phase distribution measured using the electrooptic sensing technique.

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 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.

A variant of a broadband antenna is proposed, which can combine up to four antennas with different polarizations and operating frequencies in one design. The antenna is formed in the shape of an annular slot (annular magnetic current) excited at four points through a quarter of the slot perimeter. The characteristics of directivity and VSWR obtained as a result of numerical simulation using the 4NEC2 software product are presented.

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.

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.

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.

A compact portable device has been proposed for three-dimensional (3D) radio tomography, comprising a planar ultra-wideband (UWB) antenna array, a system for generating and receiving UWB signals, a switching block for the UWB antennas, and a program for tomosynthesis of the radar images. Results of numerical modeling and processing of experimental data are presented, confirming the efficiency of the device.

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 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.

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.

The device relates to the field of radar techniques for locating or objects detecting using reflection or reradiation of radio waves. This device can be used to detect and identify the objects containing non-linear electrical contacts. The non-linear radar contains two sources of signals that generate the signals in close frequency rangers, and a signal combining scheme associated with the antenna. The source of the first signal is provided with a low-frequency modulator. A vector reflectometer is included between the source of the second signal and the signal combining circuit. The design is simplified and the detectability of the non-linear radar is improved due to these design features.

In this paper, a method for detecting and mapping inhomogeneities in biological tissues using the radio-wave tomosynthesis method is presented. The proposed method of radio-wave tomosynthesis allows us to calculate the three-dimensional distribution of the permittivity of the space under study and, thereby, to detect tissue inhomogeneities and to determine their location and size. Due to their harmlessness for humans, these methods are suitable for dynamic observation of changes in the size of formation, in contrast to x-ray methods, for which regular doses of ionizing radiation are contraindicated. Therefore, the development of non-invasive methods for the search for inhomogeneities in biological media based on radio-wave sounding, which makes it possible to identify pathological formations, is now very relevant.

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.

Within the limits of a linear model based on processing of data of direct calibration measurements with semiconductor multisensors, a method of their calibration by standard levels of gas concentration is substantiated for its subsequent application for small concentration levels. On an example of data for nitrogen dioxide, the notion of the normalized surface density of the gas is introduced, and its relationship with the volume concentration is established. On this basis, the feasibility of increase in the sensitivity and selectivity of the multisensor system by several orders of magnitude compared with the existing instrumental methods is substantiated by imitational modeling using mathematical methods of modern algebra and regularization theory.

Simulation results of the antenna system of the radar of subsurface sounding intended for contactless investigation of the road condition are presented. The elements of the antenna system of ground penetrating radar with extended bandwidth made as a combination of electric and magnetic type radiators have been designed. The transmission coefficient between the elements of the antenna array determining their mutual influence has been calculated. Despite the close arrangement of the elements in the array, the level of mutual influence of the elements is not critical. The developed antenna array can be used both for excitation with short ultrawideband pulses and for frequency steering in the range of 0.8-4 GHz.

It's considered the principle possibility of creation the managed reflectors for formulation of given field distribution in the focus area. Reflectors change the reflect ratio in dependence of the external control. The proposed theoretical modeling of such controlled focused device which provides focuse to a specific point in a given distribution of the reflectors. On the basis of numerical simulation it's considered the application of this approach for the solution of the problem of radiotomography.

The research of various parameters influence on the Fresnel reflector focusing properties in particular spatial sizes, the focal point position, etc. is conducted. The version of using a flat Fresnel reflector for receiving ultra-wideband signals with the use of Wiener filtering is suggested.

Subsystems of the design of a complex security system for premises under conditions of large volume of passenger traffic are considered. These subsystems provide video- and thermal imaging control, radio wave tomography, and gas analysis. Simultaneous application of all examined variants will essentially increase the probability of timely prevention of dangerous situations with the probability of false alarm as low as possible. It is important that finally, this will provide protection of population and will facilitate the work of intelligence services.

Different approaches of the recognition of metal objects sounded with ultrawideband (UWB) pulses are investigated. The main consideration is given to cross-polarized components of the scattered field. The suggested approaches have been tested by means of numerical and physical experiments.

Active methods for investigation of different objects suggest sounding by pulses of different waveforms with subsequent receiving and processing of the passed or reflected signal. Linear systems in which the input and output signal relation is determined by the convolution Y(t) = h(t) ⊗ X(t) are considered in this paper. Here, Y(t) is the output signal, h(t) is the impulse response (IR) of the investigated object, X(t) is the sounding pulse. The IR completely reflects the properties inherent to this object in the sounding pulse frequency band and can be used for its recognition.