Additional radar signature for waterborne object recognition

Subject and Purpose. The article is devoted to the radio recognition of moving waterborne objects (sea-going ships). The problem lies in the lack of radar signatures, which is especially true for coherent radar in continuous mode, implying that more signatures for the waterborne object recognition is highly needed. An additional signature can be gained just by means of a simple mathematical processing of target reflection signals. This is particularly important for radio recognition systems in current use because this will hardly complicate the system structure. Hence, it will not affect its cost either. Methods and Methodology. The method developed for the retrieval of an additional radar signature characteristic of waterborne objects moving across a rough sea surface is based on a simple mathematical processing of a signal reflected from the moving waterborne object and taken from the phase output of coherent radar. The method approbation is by the mathematical modeling of signals at the phase detector output in the event of three waterborne objects such that have identical scattering cross sections but different periods of the side and keel vibrations. Results. Based on the mathematical modeling results, it has been shown that each of the local scattering centers keeps the ratio of the linear speeds of side and keel vibrations approximately the same for the same object. But the employed ratio takes different values for different objects. Conclusion. Having a single standard coherent radar in continuous mode and guided by the developed methodology, one can gain an additional signature for the target recognition, which is a ratio of the linear speeds of side and keel vibrations of the target. The suggested methodology can be used for the radio recognition of waterborne objects moving across a rough sea surface.

Electromagnetic wave tunneling through an asymmetric three-layer structure containing a conductive negative-permittivity layer

Subject and Purpose. In the context of growing anticipation of fundamentally new optical and radiophysical devices, the present study is concerned with the total electromagnetic wave tunneling through an asymmetric three-layer structure such that contains a conductive negative-permittivity layer. The aim of this work is to recognize how the asymmetry property of this three-layer structure acts on the effect of total wave tunneling with the frequency dispersion of the conductive negative-permittivity layer taken into account. Methods and Methodology. The frequency-dependent conditions of the total electromagnetic wave tunneling through an asymmetric three-layer structure are sought by numerical simulations. A universal approach based on the introduction of dimensionless frequencies and dimensionless layer thicknesses allows us to numerically investigate conditions of the total electromagnetic wave tunneling for any desired frequencies and geometric parameters of the asymmetric three-layer structure. Results. It has been shown that the asymmetry property of the three-layer structure can significantly change the total electromagnetic wave tunneling conditions. It has been demonstrated that parameters of the asymmetric three-layer structure can be selected in such a way as to modify the total electromagnetic wave tunneling conditions toward a desired practical application of the structure. It has been found that a proper choice of the parameters can minimize the action of the three-layer structure asymmetry on the electromagnetic wave tunneling effect. Conclusion. Asymmetric three-layer structures can be of use to effectively change conditions of the total electromagnetic wave tunneling in an effort to provide devices under development with desired characteristics.

Active media based on polyurethane doped with a binary dye mixture

Subject and Purpose. The article is concerned with the spectral-luminescent and lasing characteristics of the radiation from solid-state active media based on polyurethane activated by a binary mixture of dyes. The purpose of these studies is to demonstrate a possibility of the spectral range expansion of the emission from solid-state dye lasers with polyurethane active elements. Methods and Methodology. Specially prepared samples of polyurethane active media having the same donor (Rhodamine 6G) concentration but various acceptor (Sulforhodamine 101) concentrations are experimentally studied for their spectral-luminescent and lasing characteristics. Results. The main spectroscopic characteristics of Rhodamine 6G and Sulforhodamine 101 in polyurethane have been measured, the nonradiative energy transfer parameters in this molecular pair estimated. It has been demonstrated that the matrix emission spectrum can be purposefully transformed by selection of relative concentrations of dyes in the mixture. In a broadband resonator, either a single- or two-band emission with different positions and various intensities of spectral bands is observed depending on the acceptor concentration. In a dispersive resonator under the same conditions, the tuning range of the lasing spectrum expands and extends to the longer wavelengths. Conclusion. The prospects of using donor-acceptor dye mixtures for improving spectral characteristics of polyurethane active elements in solid-state dye lasers have been confirmed. It has been shown that signatures of the emission characteristics of these media are governed by the mechanism of the excitation energy transfer between dye molecules. Lasing has been obtained on polyurethane matrices with the emission wavelength tuning throughout the “green-red” region of the spectrum.

Laser rangefinder of relatively eye-safe wavelength range

Subject and Purpose. The development and prototype making of a laser rangefinder operating in the 1.50…1.70 μm spectral region is reported. This wavelength region is attractive to both laser producers and laser users for, first of all, relative eye-safety of radiation. Methods and Methodology. The paraxial scheme of rangefinder construction is used, involving a software-controlled power supply of laser radiation with technical arrangements providing its adaptation to varying operating conditions. The alignment of the transceiver channels is provided with laser beam visualization methods. Results. A pulsed laser rangefinder operating at a 1.54 μm wavelength has been developed, a prototype has been made. The rangefinder essentially consists of the transmitting and receiving channels and the visual channel for targeting. The radiation source is a pulsed laser on ytterbium-erbium glass with semiconductor diode pumping and modulated Q-factor. The laser provides a 6 mJ power pulse of 25 ns duration and 5 mrad radiation divergence. A laser light spot of a required aperture is formed using a Galilean telescope system. For the photodetector of the reflected radiation, a pin-photodiode with a photosensitive area diagonal of 0.3 mm and a 2.5 ns time resolution is used. The echo signal processing module has been developed and performed, providing a high-precision registration of a time delay between the starting and reflected pulses. An effective method with the use of a charge-coupled device and an LCD monitor has been proposed and implemented for the alignment of all the three rangefinder channels. The rangefinder can operate in a single-pulse or repetitive-pulse mode with a probing pulse repetition rate of 1 Hz. Conclusion. A pulsed laser rangefinder operating in a relatively eye-safe spectrum region has been developed, a prototype has been made. The field tests have shown that the created rangefinder measures an object distance within 140…7 000 m with a measurement error no worse than 3 m.

A magnetoactive metamaterial based on a structured ferrite

Subject and Purpose. The use of spatially structured ferromagnets is promising for designing materials with unique predetermined electromagnetic properties welcome to the development of magnetically controlled microwave and optical devices. The paper addresses the electromagnetic properties of structured ferrite samples of a different shape (spatial geometry) and is devoted to their research by the method of electron spin resonance (ESR). Methods and methodology. The research into magnetic properties of structured ferrite samples was performed by the ESR method. The measurements of transmission coefficient spectra were carried out inside a rectangular waveguide with an external magnetic field applied. Results. We have experimentally shown that over a range of external magnetic field strengths, the frequency of the ferromagnetic resonance (FMR) of grooved ferrite samples (groove type spatial geometry) increases with the groove depth. The FMR frequency depends also on the groove orientation relative to the long side of the sample. We have shown that as the external static magnetic field approaches the saturation field of the ferrite, the FMR frequency dependence on the external static magnetic field demonstrates "jump-like" behavior. And as the magnetic field exceeds the ferrite saturation field, the FMR frequency dependence on the groove depth gets a monotonic character and rises with the further growth of the field strength. Conclusion. We have shown that the use of structured ferrites as microwave electronics components becomes reasonable at magnetic field strengths exceeding the saturation field of the ferrite. At these fields, such a ferrite offers a monotonically increasing dependence of the resonant frequency on the external magnetic field and on the depth of grooves on the ferrite surface. Structured ferrites are promising in the microwave range as components of controlled filters, polarizers, anisotropic ferrite resonators since they can provide predetermined effective permeability and anisotropy

Dielectrometry of hydration of fl avin mononucleotide and DNA

Subject and Purpose. The elucidation of the molecular mechanisms of action of biomolecules is necessary for the development of state-of-the-art means of diagnosing and treatment. Dielectric studies in the millimeter wave range are effective for puzzling out the nature of the interaction of biomolecules with a surrounding aqueous solvent. Flavin mononucleotide (FMN), which can kill microorganisms and destroy cancer cells, is of particular interest. The aim of the work is to recognize hydration effects (changes in the state of water molecules) in FMN solutions. Methods and Methodology. The complex dielectric permittivity (CDP) is measured in the EHF range. Knowing the difference between the CDP of FMN solution and the CDP of water we find the difference, D es , between the effective dielectric permittivities in terms of the Debye theory of polar liquids. Since the relaxation time of dipoles of bound water is one or two orders of magnitude longer than that of free water, the amount of the difference D es characterizes the hydration of biomolecules. At low concentrations, this difference is proportional to the number of bound water molecules. Results. It has been shown that approximately18 water molecules are bound to the FMN molecule. Groups of atoms as the most probable hydration centers (primarily due to the hydrogen bonds) have been indicated. As the pH decreases, the number of water molecules bound to the Flavin mononucleotide increases to 21. The study of the FMN–DNA solution has shown that one nucleotide accounts for 25–26 bound water molecules in total. However, composing hydration numbers assumes a quantity of components less than 20. An assumption is made that the additional components are due to the cooperative nature of the hydration, leading to the fact that even if some solvent molecules do not come into a direct contact with hydration centers, they are under the influence of biomolecules all the same. Conclusion. Extremely-high-frequency dielectrometry is an effective method of research into the interaction of biomolecules with a water-ionic solvent. A FMN hydration model has been proposed, which indicates probable hydration centers and tells a measure of their effect on the solvent. It has been found that the FMN with DNA interaction increases the number of bound water molecules per one nucleotide of the DNA. The obtained results have been compared to the existing models of the DNA with FMN interaction.

Suppression of postpulse oscillations in active bow-tie antennas

Subject and Purpose. This theoretical and experimental research is devoted to peculiarities of the ultra-wide bandwidth (UWB) pulse radiation from active bow-tie dipoles. The focus is on the relationship between the amplitude-time dependences of electromagnetic fields produced by active UWB pulsed antennas and the configuration of the conductive components for temporally short (less than 0.5 ns), ultra-wide-bandwidth pulse radiation. Methods and Methodology. Analysis of the radiator geometry action on the emitted pulse parameters is performed by numerical simulation with the use of the finite-difference time-domain (FDTD) method. The experiment involves specially made, variously shaped bow-tie radiators tested with different resistive loadings in radiation mode. The numerically simulated characteristic curves of the radiated field amplitude shape versus radiator geometry are confirmed by experiment. Radiation field parameters versus load resistance are experimentally studied, too. Results. Conditions for the effective pulse radiation with a largest-possible pulse amplitude have been determined, the post-pulse oscillation amplitude and duration reduced to a minimum. Conclusion. It has been shown that the resistive loading in the excitation area significantly reduces amplitudes and durations of post-pulse oscillations in signals radiated by active dipole antennas.

Electromagnetic and acoustic technologies in antibacterial preparation development

Subject and Purpose. The present paper is concerned with the use of wave technologies in the development of antibiotics-alternative approaches for pathogenic microflora suppression. Lactobacilli strains picked in different ecological niches and their activity against pathogenic strains are studied with a focus on a targeted modification of adhesive and antagonistic properties of lactobacilli by exposing them to low-intensity electromagnetic (EM) fields and the ultrasound. Methods and Methodology. Lactobacilli picked in different ecological niches are experimentally studied, including (1) standard strains from probiotic preparations and (2) circulating strains picked in humans and bees. For the ultrasonic and electromagnetic radiation sources, G3-109 and G3-F and G4-141 and G4-142 generators are taken, respectively. The adhesive properties of Lactobacillus spp. strains and their antagonistic activity are estimated against C. diphtheriae, S. aureus and yeast-like fungi of Candida genus in aerobic and microaerophilic culture conditions. Statistical technology is employed in the data processing and analysis. Results. It has been established that L. plantarum strains picked in the gut of healthy bees are most antagonistic towards pathogens. It has been demonstrated that the priority culture conditions for lactobacilli are microaerophilic conditions simulating their stay in vivo. It has been shown that it is possible to modify properties of microorganisms by their exposure to ultrasound and low-intensity electromagnetic fields in narrow bands of the EHF range. The effect efficiency versus frequency has a dispersion character. Individual features of various pathogenic strains have been recognized. Conclusion. The obtained results open up prospects for electromagnetic and acoustic technologies in the development of safe alternative means to antagonize persisting pathogens and increase human body resilience.

Сonsideration of the signal attenuation in double-frequency sensing for rain intensity retrieval

Subject and Purpose. Precipitation is the main source of agricultural land moisture. The knowledge of its amount, especially during the growing season, is important information to justify necessary agronomic and land reclamation measures. The purpose of this work is to solve by regularization the inverse problem of double-frequency sensing of precipitation in the microwave range with the signal attenuation considered and analyze the influence of radar cross-section (RCS) calculation errors and the total signal attenuation measuring precision on the rain intensity retrieval results. Methods and Methodology. Numerical simulation is used in double frequency retrievals to solve the integral scattering equation by regularization methods. Results. Numerical simulation has been performed for the rain intensity retrieval with a uniform spatial profile of rain intensity in the range 1…20 mm/h. Direct and inverse iterative procedures were used for having the signal attenuation at 0.82 and 3.2 cm operating wavelengths. It has been shown that the direct iterative procedure is less effective than the inverse one. Thus, when the rain intensity exceeds 20 mm/h or when it is within 10…20 mm/h and a rain spatial extent goes over 500 m, the direct iteration scheme causes significant errors in the rain intensity retrieval. Conclusion. The analysis of the results has shown that the use of the inverse iterative procedure makes it possible to retrieve a uniform-profile rain intensity with a 25 % error for rains with a 20 mm/h intensity and a 4 km spatial extent and ± 20 % errors in the total signal attenuation and specific RCS calculated.

Directional radiation properties of two impedance monopoles mounted on a perfectly conducting rectangular screen

Subject and Purpose. Two impedance resonant monopoles of electric length 0.2 £ l / l £ 0.3 are mounted on a rectangular screen perpendicularly to the screen surface and studied for the directional radiation properties (directive gain and radiation patterns) depending on the monopole separation and the side length and aspect ratio of the screen. Methods and Methodology. A three-dimensional diffraction vector problem of two impedance monopoles mounted on a perfectly conducting rectangular screen is solved in terms of the uniform geometric theory of diffraction. Allowances are made for the diffracted field asymptotics of the secondary diffraction at the screen edges and for the electric current distribution asymptotics of a thin impedance dipole in the free space. Results. For a lattice of two impedance monopoles mounted on a rectangular screen, 3-D programs have been developed for calculating its radiation patterns, directive gain Dmax at a radiation maximum, and radiation resistance in view of the secondary diffraction at the screen edges. The radiation pattern shaping for the diffraction and total fields and the directive gain Dmax have been analyzed depending on the monopole separation x / l  0.1...1, the screen side length x / l  1.2…4, and the screen aspect ratio W / L  0.5…3. It has been shown that the so obtained optimum separation x opt  0.65, optimum length Lopt and optimum ratio (W / L) opt make Dopt three times greater than the lowest Dmax value. Conclusions. The three-dimensional vector problem of field diffraction of two impedance monopoles mounted on an ideally conducting rectangular screen has been solved. It is of interest that given an optimum monopole separation xopt and an optimum side length Lopt of the square screen, a lattice of two monopoles offers a greater radiation resistance and a two times larger Dopt than a single monopole on the same screen does. The developed computational programs and the obtained numerical results enable efficient actual wireless communication systems to be modelled for both ideally conducting and impedance resonant monopoles.