Multimode self-oscillating systems with a filter in a delayed feedback circuit

A chaotic self-oscillating system based on a delayed oscillator containing a filter in the feedback loop is considered. Results of the numerical analysis of equations describing such an oscillator are presented for symmetric and asymmetric amplitude characteristics enabling variation in their nonlinearity within wide limits. The mechanism of transition to chaos is considered. A two-stage delayed oscillator containing a filter between partial amplifiers is studied.     

Controlled oscillations in an autostochastic system

Processes in a nonautonomous autostochastic system possessing an attractor of the Chen type were analyzed by numerical methods. The system was described by a set of equations for coupled oscillators with inertia. It is demonstrated that autooscillations can be controlled when a regular signal acts unidirectionally upon chaotic oscillations or, vice versa, when chaotic oscillations act upon the regular ones.     

Controlled chaotic system with time delay

A chaotic autooscillatory system described by an equation with delayed argument is proposed, in which the oscillations are controlled by means of a chaotizing feedback algorithm. The results of numerical analysis of the proposed system are presented.     

Controlled oscillations in a system with a delay in the presence of parametric and autoparametric actions

New models of an oscillator with a delay are based on an anharmonic oscillator with a nonlinear restoring force. The parametric and autoparametric oscillation control modes are considered. Numerical analysis is used to demonstrate the excitation of developed chaos at a relatively weak nonlinearity of the amplitude characteristic.     

Bifurcation and chaos in a system with a variable structure

A mathematical model of a variable-structure system based on a second-order nonself-oscillation equation is considered. Chaotic self-oscillations are formed when a chaotization algorithm is applied to the system. A block diagram of the dynamic system with a variable structure and the results of numerical analysis of this system are presented. It is demonstrated that chaos is possible in systems with a variable structure that are based on the equations of both nonlinear and conventional (linear) oscillatory circuits.     

Controlled oscillations in chain of unidirectionally coupled bistable oscillators with chaotic dynamics

Equations of a chain of n (n = 1, 2, ...) unidirectionally coupled bistable oscillators possessing chaotic dynamics are presented. Numerical analysis has been performed for a system of three identical autooscillatory systems with nonlinear elements admitting cubic approximation. It is shown that, as the degree of coupling between units in the chain increases, their motions in the phase space become more complicated and even chaotization of oscillations may take place at the parameters with which separate oscillators exhibit regular motions in the autonomous regimes. The features of the influence of a driving oscillator on the motions of a driven bistable subsystem are related to filtration of the driving signal in the circuit of the driven subsystem.     

Chaotic dynamics of oscillator based on lossless circuit

Equations that describe a new autooscillatory system with chaotic dynamics based on a lossless oscillatory circuit are presented. This system is capable of generating chaotic oscillations with irregular variations in the amplitude (amplitude chaos) at a small change in frequency. Bifurcation diagrams (one- and two-parametric), time series of the oscillatory process, and power spectra of the proposed system are presented.     

Autostochastic system of coupled microwave generators

Equations are presented describing a system of coupled generators, taking into account the feedback delay and time lag in each partial generator. The delay in the coupling elements between the generators is also taken into account. A numerical analysis of the dynamics of one, two, and three generators is performed. It is shown that chaotization of the oscillations occurs more readily in a coupled system of two or three generators than in the case of a single generator. This is confirmed by the results of experiments on transistor microwave generators. It is found that noise fluctuations can be obtained in a system of three coupled transistor generators over a broad range of frequencies in the centimeter wavelength range. Pis’ma Zh. Tekh. Fiz. 25, 33–38 (April 26, 1999)     

Experimental study of useful signal separation from pulse-modulated fluctuation noise in application to hidden data transmission

Hidden data transmission at microwave frequencies has been experimentally carried out by masking the useful signal with a continuous random signal of the new type formed from two series of identical fluctuation-noise-carried pulses that are delayed relative to each other by a time equal to the pulse duration.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.