Dmitry A. Usanov

Correlation of emission capability and longevity of dispenser cathodes with characteristics of tungsten powders

The intercorrelation of tungsten powder properties, such as grain size, distribution and morphology, and porous matrix parameters with electron emission capability and longevity of Ba dispenser cathodes are investigated for three different grain morphologies. Best results of tungsten cathode life were found for isoaxis polyhedron morphology in combination with certain powder and matrix parameters.

Appearance of S-shaped sections on the current-voltage characteristics of p-n junction diodes exposed to microwave radiation

An experimental investigation was made of the influence of microwave irradiation on the low-frequency current-voltage characteristics of p-n junction diodes. It is shown that when the microwave power increases to a certain level, a clearly defined S-shaped section appears on the current-voltage characteristic of the diode. This section becomes broader as the microwave signal increases further and then disappears when the microwave irradiation ceases.

Resonance features of the allowed and forbidden bands of the microwave photonic crystal with periodicity defects

The resonance features of the allowed and forbidden bands of the microwave waveguide photonic crystals with periodicity defects are theoretically and experimentally analyzed. It is demonstrated that the number of resonances in the allowed band is determined by the number of identical elements whose periodic sequence determines the photonic crystal and the maximum Q factor is reached in the vicinity of the lower and upper boundaries of the allowed band. An increase in the size of the forbidden bands and a decrease in the size of the allowed bands of the microwave photonic crystal due to a decrease in the number of resonances in the allowed band are caused by violations of periodicity of the photonic crystal related to nonidentity of a single element.

Acoustic pressure induced period-doubling bifurcations in tympanic membrane oscillations

We demonstrate the possibility of using a quantum-confined semiconductor structure laser operating in the autodyne regime for the investigation of the amplitude-frequency characteristics of the tympanic membrane (TM). Using such a laser, it is established that an increase in the acoustic pressure leads to the appearance of subharmonics in the spectrum of TM oscillations at frequencies equal to one-half and one-quarter of the exciting signal frequency, which is evidence for period-doubling bufurcations.

Conditions for negative differential resistance and switching in a tunnel diode under the effect of an external microwave signal

Experimentally observed phenomenon of the origination of the mode of negative differential resistance and switching in a tunnel diode under the effect of external microwave signal is theoretically interpreted. The reasons for the existence of the ranges of bias voltages applied to the diode and the power levels of microwave signal for which the phenomenon is observed are clarified.

Appearance of negative resistance in p-n junction structures in a microwave field

The results of theoretical and experimental investigations of the appearance of negative differential resistance in p-n junction diode structures in the presence of a high level of microwave power are presented. The theoretical analysis of the influence of a high level of microwave power on the form of the current-voltage characteristic of a diode takes into account the variation of the constant component of the current flowing through the p-n structure due to the heating of the free charge carriers and the rectifier effect.

Microstrip Photonic Crystals and their Application for Measurement Parameters of Materials

The computer simulation and experimental investigation of frequency dependencies of the reflectance and the transmittance of photonic crystals based on the microstrip structures in the frequency band 0-20 GHz have been performed. The investigations were performed for the photonic crystal with irregularity introduced as changed geometry size of the stripline conductor or changed substrate permittivity of one of the sequence microstrip sections. Good quantitative fit between the calculations and experimental results have been obtained. The possibility of application of open microwave transmission lines - microstrip photonic crystals - for measurement parameters of a material which acts as irregularity in the photonic crystal has been demonstrated.

Determining distances to objects using a frequency-switched semiconductor laser autodyne

We present the results of theoretical justification of a method for determining distances to objects that makes use of a frequency-switched semiconductor laser diode operating in the autodyne regime. It is shown that, by determining the ratio of harmonics in the low-frequency spectrum of the current-modulated autodyne signal, it is possible to determine the distance to an object with a 1% accuracy.

Power suppression mode in semiconductor synchronized microwave oscillators

An experimentally discovered and theoretically analyzed mode of power suppression of the output signal in a Gunn diode-based oscillator is described. It is established that the explored mode of the synchronized oscillator has an extremely high sensitivity to change in the natural frequency of the Gunn diode. The possibility is shown of using the power suppression mode in a semiconductor synchronized microwave oscillator as a method for high-precision indication of parameters changing for objects that are placed into the generators resonator system.

Wideband Waveguide Matched Loads Based on Photonic Crystals with Nanometer Metal Layers

The possibility of creation of wideband matched loads based on waveguide photonic crystals consisted of alternating layers of dielectrics with different values of thickness and permittivity and nanometer-thin metals with different values of thickness and conductivity has been shown theoretically and proven experimentally.