Vol 61, No 10 (2016)

The specific features of meteorological radiolocation and its state of the art are discussed. The characteristics of weather radars manufactured by all companies leading in this field are compared. The problems facing weather radars and possible methods of their solution are determined. The further trends inherent to the development of the given field of science and technology are outlined.

The objective function for the optimization of frequency-selective structures with cross-shaped aperture elements is formulated. The electrodynamic characteristics of such systems are determined using a numerical model of a local section of a metasurface with periodic Floquet conditions, which demonstrates a good agreement with the experiments. The sizes of the aperture elements and the electrophysical properties of materials providing narrow-band filtering of electromagnetic signals in a given frequency range are found.

The paper shows the possibility of existence of a self-consistent solution in a system uniting the internal and external Sestroretskii cubes; this system simulates vacuum. An expression for estimating time for which half of the energy is radiated is presented.

An algorithm for improvement of the accuracy of small-sized phase direction finders by rejecting abnormally large errors in the process of resolving the measurement ambiguities is proposed. Design relationships that characterize the efficiency of the algorithm are obtained. The theoretical propositions are validated by digital simulation of the operation of a three-base direction finder and by its full-scale test.

The problem of decomposition of multicomponent Doppler signals in order to increase the operation efficiency of systems based on the use of Doppler radars for a wide range of applications is considered. To study the structure of these signals, a matched pursuit algorithm and its modification—matched pursuit with compensation, which have been developed for the analysis of signals represented by functions of time and their spectrograms, respectively, are used. Obtained and analyzed the Results of decomposition of a simulated three-component signal against the background of noise for a signal-to-noise ratio of 20 dB as well as actual Doppler signals by these algorithmsare obtained and analyzed.

Specific features of the Andronov–Hopf bifurcation in the model of brusselator in the presence of parametric noise are numerically and experimentally studied. Regularities of evolution of the probability distribution with an increase in the noise intensity are typical of the additive and multiplicative effect of the Gaussian white noise. The existence of bifurcation interval corresponding to the gradual transition to the generation regime is experimentally revealed for both additive and multiplicative noise.

The magnetic and magnetocaloric properties of Ni_1.81Mn_1.64In_0.55, Ni_1.73Mn_1.80In_0.47, and Ni_1.72Mn_1.51In_0.49Co_0.28 Heusler alloys are investigated. The magnetocaloric effect (MCE) is experimentally measured using the direct method with the help of different protocols. The phase transformation temperatures and the latent heat of metamagnetostructural transitions are determined from the temperature dependences of magnetization and via differential scanning calorimetry. In the case of Ni_1.81Mn_1.64In_0.55 and Ni_1.73Mn_1.80In_0.47 alloys, the temperature shift of martensitic transformation induced by external magnetic field is found. It is demonstrated that, in the Ni_1.72Mn_1.51In_0.49Co_0.28 alloy, added Co atoms raise the temperature of structural and magnetic phase changes and enhance the MCE. In addition, it is revealed that the MCE depends on measurement protocols near the first-order phase transition.

Stability of current characteristics of a field-emission cell is analyzed. Experimental and simulated results are presented.

A solution to the problem of formation of toroidal cuts from classic 1D Brillouin flows (solid, hollow, and electrostatic beams) and a 2D Brillouin flow in a nonuniform magnetic field is presented.

An upgrade of the structure of magnetic resonance flowmeter–relaxometer is proposed to improve the metrological characteristics. The improved structure of the magnetic resonance flowmeter–relaxometer is based on the modulation of static magnetic field Н₀ by ac magnetic field in the region of the nutation coil. The experiments show that the measurements of liquid flow q in the proposed regime make it possible to eliminate the effect of measurement errors related to variations in amplitude and phase of the NMR signal inverted by 180° under rapid variations in quantity q and increase the measurement dynamic range of quantity q by 30%.

The analysis of the current state of solid photoelectronics for thermal imaging and thermal direction-finding equipment of new generation is performed. The results of the latest development of photoelectronic modules for thermal imaging and thermal direction-finding in the spectral bands 1–3, 3–5 and 8‒12 μm, as well as for ultraviolet range are presented. The main physical and technological problems of the design of photoelectronic modules as well as production of photosensitive materials for them are considered. A forecast of the directions of development is presented.

The absorption coefficient of HgCdTe structures grown by the methods of liquid-phase epitaxy (LPE) and metalorganic chemical vapor deposition (MOCVD) is studied and calculated. The experimental data are compared to a theoretical absorption spectrum model, which is based on the fundamental absorption effect and the general theory of direct interband optical transitions, as well as other empirical dependences. The Fermi level shift in the studied HgCdTe structures and the slope of experimental absorption characteristics are calculated.

Principles of an analytical system of physical design of avalanche heterophotodiodes with separate regions of absorption and multiplication (AHPD with SRAM) are presented. The system is based on analytical expressions for the field of the avalanche breakdown of the p–n heterostructure and the interband tunnel current in it. This current determines the minimum noise level in the AHPD with SRAM based on direct band semiconductors. The considered method strongly facilitates optimization of the doping levels of the heterostructure layers and their thicknesses. In addition, it gives significantly more pronounced physical content to the optimization process.

Characteristics of external conditions are studied in spectral intervals of 0.4–0.9 and 1.4–1.7 μm. The advantages of photodetector arrays that are sensitive in a spectral interval of 1.4–1.7 μm are demonstrated for applications in night-vision devices.

The results of investigation of planar photodiodes (PDs) in a focal plane array (FPA) based on a heteroepitaxial InGaAs/InP structure are reported. The FPA has a size of 320 × 256 elements with a pitch of 30 μm, which are hybridized with various ROIC readout circuits. It is demonstrated that the PD reverse bias should be no lower than 2 V in order to suppress the FPA intercoupling at the room temperature. It is found that the dark current may be reduced considerably by cooling the FPA to–20°С with a two-stage thermoelectric cooler. The best average room-temperature dark current over the FPA planar photodiodes is 0.22 pA at an optimum PD bias of–2.4 V.