External Harmonic Signal Research Articles

Stepwise current oscillations in tunnel and high-frequency semiconductor diodes

The response of tunnel and high-frequency diodes to an external harmonic signal of large amplitude has been studied. Stepwise current oscillations have been found on the current-voltage characteristics measured at a direct current when an external high-frequency signal is imposed simultaneously on the sample. The frequency of these oscillations decreases with increasing frequency of the external signal. Analogs of the appearance of stepwise current oscillations in semiconductor and other systems are indicated.

Nonautonomous noise-induced synchronization

Two uncoupled Van der Pol oscillators driven by a common external harmonic signal and common white noise have been considered as a sample system. It was shown that the length of the time interval preceding the synchronous mode arising is inversely proportional to the value of the noise intensity.

Bifurcational mechanisms of synchronization of a resonant limit cycle on a two-dimensional torus

We study synchronization of a resonant limit cycle on a two-dimensional torus with an external harmonic signal. The regime of the resonant limit cycle is realized in a system of two coupled Van der Pol oscillators; we consider the resonances 1:1 and 1:3. We analyze the influence of coupling strength between the oscillators. We show that the resonant limit cycle can be generally synchronized on the torus through the resonance destruction followed by the locking of one and then another one of the basic frequencies. We consider the bifurcational mechanism of the synchronization effect.

Specific features of operation of free-electron lasers with a short bunch

The physical specific features of a free-electron laser in the short-wave region in which the bunch length in the proper frame is smaller than the undulator length in the same reference frame are discussed. The regimes of amplification of the external harmonic signal and the induced amplification of proper noise with forming the quasi-coherent radiation, i.e. the self-amplified spontaneous emission (SASE) regime, are considered.

Experimental study of the effect of external signal on microwave oscillations in a nonrelativistic electron beam with virtual cathode

The effect of an external harmonic signal on the characteristics of microwave generation in a nonrelativistic electron beam with virtual cathode (VC) formed in a static retarding electric field (low-voltage vircator system) has been experimentally studied. A significant increase in the vircator generation power is observed when the frequency of the external signal is close to the frequency of VC oscillations. At large detunings, a broadband chaotic generation is observed.

Controlled chaos in a system of van der Pol generators with a capacitive coupling

A mathematical model of a self-oscillating system with chaotic dynamics is presented. The model is based on coupled van der Pol generators with a capacitive coupling. The system’s chaotic behavior is ensured by a sufficiently simple algorithm of an additional feedback that involves nonlinear conditions for switching the oscillations and equations for filtering devices. Results of the numerical analysis of a two-generator system are presented. As the oscillations became chaotic, the motion is shown to switch between two complementary domains of attraction that emerge owing to the algorithm of the chaotizing feedback. The influence of an external harmonic signal is considered.

Experimental Determination of an Nonlinear Microwave Reactance of a Commercially Produced Avalanche-Transit Diode

The experimental method for the determining the reactive component of an impedance of an avalanche-transit diode is considered. The method is based on synchronization of the avalanche-diode oscillator the impedance of which is being determined by an external harmonic signal. The obtained results are discussed.

Experimental research of complex dynamics of on-line multycavity klystron oscillator with delay

Complex dynamics of the on-line resonant microwave oscillator on a basis of multycavity klystron with delayed feedback is investigated. It is shown, that with the help of an external harmonic signal the control is probable of the klystron oscillations character. Depending on an operating mode of the autonomous generator by selection of frequency and power of an external harmonic signal the modes of dynamic chaos can be received at one-frequency autonomous oscillation and, on the contrary, one-frequency oscillation modes can be received at chaotic autonomous oscillation.

Quantum feedback control of a solid-state qubit

We have studied theoretically the basic operation of a quantum feedback loop designed to maintain a desired phase of quantum coherent oscillations in a single solid-state qubit. The degree of oscillations synchronization with external harmonic signal is calculated as a function of feedback strength, taking into account available bandwidth and coupling to environment. The feedback can efficiently suppress the dephasing of oscillations if the qubit coupling to the detector is stronger than coupling to environment.

Processes of synchronization, chaotization andamplification in a germanium oscillistor

The effect of an external harmonic signal on the screw instabilityof the current in the electron-hole plasma has been studiedexperimentally in Ge at 77 K and 300 K.The influence exerted byexternal signals with various amplitudes and frequencies, appliedto a sample both additively and multiplicatively, on thesynchronization, amplification and stability of the system inabsolute and convective modes of instability excitation has beeninvestigated at points of bifurcation in a wide region of theparametric space.

Chaotic Oscillations in a Nonlinear Lumped-Parameter Transmission Line

We present the results of numerical simulation of the complex dynamics of a nonlinear radio-technical line having reflections at the boundaries and excited by an external harmonic signal. It is shown that, with increase in the amplitude of the input signal, periodic oscillations at the external-forcing frequency become unstable and are changed to more complex regimes, either quasiperiodic or chaotic. The main scenarios of transition to chaos are studied. The influence of the modulation instability and soliton formation on the complex dynamics is discussed.

SIGNAL TRANSFER AND STOCHASTIC RESONANCE IN COUPLED NONLINEAR SYSTEMS

A model of coupled nonlinear oscillators is discussed, wherein Langevin-type bistable systems are combined with self-sustained oscillators. An external harmonic signal is coupled in a subthreshold manner into the bistable systems at the initial stage of the signal chain. Signal transfer through the oscillators is studied under the influence of noise. Different noise contributions, including spatially-incoherent and spatially-coherent noise sources are considered. Results reveal a stochastic resonance kind of behavior at different stages of the signal transfer, specifically the harmonic signal is transduced through the whole system of coupled oscillators. The combined action of spatially-incoherent and spatially-coherent noise exhibits constructive as well as destructive influences on signal amplification.

Modulation of output signal from a Gunn diode microwave oscillator under the influence of an external microwave signal

We analyze the characteristics of the output signal from a Gunn diode microwave oscillator under the influence of an external harmonic signal with a frequency close to that of the output signal. The dependences of the period and amplitude of the low-frequency envelope on the detuning value and the power of an external signal are studied. It is shown that the envelope of the external signal can either be almost harmonic or present a periodic sequence of pulses. The applicability limits of the proposed modulation technique are assessed.

Effect of lumped interference on a synchronized generator

Transients in a self-oscillator under biharmonic action are examined on the basis of an auto-parametric model of the synchronization phenomenon. It is shown that an external weak harmonic signal will influence the synchronization mode differently depending on the magnitude and detuning of the synchronizing emf.