Vol 61, No 1 (2016)

Periodic 3G lattices made of oriented magnetic nanowires are considered under the magnetic resonance in the millimeter-wavelength range. The propagation of electromagnetic waves in anisotropic nanostructured materials based on these lattices is mathematically modeled using the method of autonomous blocks with virtual Floquet channels. The real and imaginary parts of propagation coefficients of longitudinal (clockwiseand counterclockwise polarized) and transverse (ordinary and extraordinary) waves for the zero spatial harmonic of 26 GHz are electrodynamically calculated. These waves propagate in 3D lattices of magnetic (Co₈₀Ni₂₀, Fe) nanowires. The obtained results depend on the intensity of the external constant magnetic field and the lattice period. The methods of control of the frequency dispersion in the millimeter-wavelength range under the influence of the external magnetic field and under the change of the geometry of lattices are determined. It is considered that the direction and intensity of the magnetic bias, its orientation with respect to the nanowire axis, and the mutual orientation of the constant and high-frequency magnetic fields vary.

A mathematical model of the electromagnetic wave diffraction by specimens of anisotropic nanocomposite materials (3D lattices of oriented carbon nanotubes (CNTs) with magnetic nanoparticles and magnetic nanowires) in waveguides is developed. It is made with the help of a computational algorithm based on a multilevel recomposition and the method of autonomous blocks with the Floquet channels. The transmission coefficients of the H₁₀ wave with the frequency of 26 GHz that propagates through plates of magnetic nanocomposites in a waveguide are electrodynamically calculated as dependences of an external constant magnetic field (a magnetic bias field) and the number of magnetic nanoparticles filling the CNT.

The possibility of measuring simultaneously the thickness of the substrate of a semiconductor structure and the thickness and conductivity of a highly doped epitaxial layer is shown in the case when the semiconductor layer plays the role of a distortion of the periodicity of a microwave photonic crystal. For measuring the mobility of free charge carriers in the highly doped epitaxial layer, a modified method of microwave magnetoresistance based on solving the inverse problem with the use of frequency dependences of the transmission and reflection coefficients measured under the action of the magnetic field in the its absence is proposed.

A traveling-wave tube of the millimeter range belonging to the short-wavelength region with a sheet electron beam and a slow-wave structure of the double grating type is studied. Its dispersion characteristics and coupling impedances for various spatial harmonics are calculated. The issues of design of the electron-optical system are discussed. The focusing of a sheet electron beam with a high current density by a uniform magnetic field is modeled.

The decapsulation effect of nanocomposite liposomal capsules containing anisotropic gold nanoparticles (nanorods), which is caused by the action of ultrashort electric pulses on these capsules, is discovered. The mechanism of destruction of liposomal shells of the capsules near poles of conducting gold nanorods under the pulse electric action is described. An expression for the critical intensity of the pulse electric field, which determines the threshold of initiation of this effect, is obtained. Its numerical value is in agreement with the obtained experimental data. It is shown experimentally that the discovered decapsulation effect is caused by the presence of gold nanorods connected to the liposomal shell of the capsules and does not arise in the absence of nanorods.

Specific features of the interaction of terahertz radiation with nanometer-thick chromium films deposited on quartz substrates are analyzed. Optical coefficients of chromium films with thicknesses ranging from 1.5 to 40 nm are measured in a frequency range of 0.25–1.1 THz. Pulsed spectroscopic measurements employ a picosecond oscillator. A maximum absorption coefficient of 43% is measured at a film thickness of 10 nm. Theoretical calculations of optical coefficients are performed with the aid of expressions that take into account a phenomenological dependence of conductivity on film thickness. It is demonstrated that the conductivity of thick chromium films (20–40 nm) is less than the conductivity of bulk metal by an order of magnitude.

A mathematical model of the mechanical effect of nanosecond laser pulse radiation on brittle materials is suggested. An analytic technique is developed for estimating the strength of monolithic glassy carbon on formation on its surface of an emitting structure by a series of nanosecond laser pulses with high energy density.

Original superconducting quantum interference devices (SQUIDs) with a working temperature of 77 K based on high-temperature superconducting (HTSC) YBa₂Cu₃O_7–x films can be used for the measurement systems of nondestructive testing using magnetic and eddy-current methods. A dynamic range of 120 dB with respect to the amplitude of the measured signal and a spatial resolution of about 10 µm are reached for the measurement system with the HTSC SQUID in which a receiving loop with a size of 50 µm is placed at a distance of about 0.3 mm from the room-temperature object under study. The sensitivity with respect to magnetic field (4 fT/ \(\sqrt {Hz} \) at a temperature of 77 K) of the HTSC SQUID magnetometer with multilayer superconducting flux transformer is sufficient for applications in biomagnetic measurements in magnetocardiography and magnetoencephalography. HTSC SQUID gradiometers with multilayer superconducting flux transformers exhibit stable operation in magnetically unshielded space at a sensitivity of 15 fT/cm \(\sqrt {Hz} \) with respect to the gradient of magnetic field at 77 K. Such a sensitivity is sufficient for the detection of single magnetic particles with a size of about 10 µm at a distance of about 15 mm.

The effect of external chaotic oscillations on systems of coupled generators with chaotic dynamics is studied. Coupled self-oscillating systems, in which partial generators are characterized either by Lorentz equations or by Rössler equations presented in the form of subsystems with inertance, are used as examples. The case of identical external chaotic oscillations affecting partial generators is considered. It is demonstrated that the synchronism of interacting oscillations is enhanced for both Lorentz andRössler coupled oscillations if the influences of noise-like oscillations on partial generators are identical.

Temperature coefficients of delay of zero- and higher-order acoustic plate modes in the most widespread piezoelectric crystals are calculated and measured. It is shown that, along with the well-known dependence of these coefficients on material constants (typical of surface and bulk acoustic waves), their values for plate modes depend also on the mode number, plate thickness, acoustic wavelength, and thermal expansion coefficient of the crystal across the plate thickness, which allows one to change the temperature sensitivity of plate modes in wide limits without changing the material and orientation of the crystal. For some combinations of the aforementioned parameters, very small temperature changes Δt ~ 10^–3°C are detected.