Monte Carlo study of impact ionization in n-type InAs induced by intense ultrashort terahertz pulses

Electron impact ionization induced in n-type InAs by single-cycle pulses of picosecond and subpicosecond duration has been investigated by Monte Carlo method. It is established that the rate of generation of electron–hole pairs decreases with the decrease of the pulse duration. The impact ionization threshold field is found to depend linearly on frequency for the fields oscillating at frequencies much higher than reciprocal momentum relaxation time. Good agreement between calculations and available experimental data has been obtained.     

Extended resonant feedback technique for controlling unstable periodic orbits of chaotic system

An improvement of the recently described resonant chaos control method is suggested. Negative feedback loop containing a notch-rejection filter, tuned to the main harmonic of the unstable periodic orbit, is supplemented with a set of notch filters tuned to the higher harmonics. The extended method is applied to an electrical circuit representing the Duffing–Holmes type non-autonomous two-well chaotic oscillator. Stabilization of the period-1 orbit is achieved with very small control force. The residual control signal is about 1% compared to the main variable. Mathematical model based on a two-well piecewise parabolic potential is presented and numerical simulation is performed. Numerical results are confirmed by hardware experiments.     

Chaotic Colpitts Oscillator for the Ultrahigh Frequency Range

PSpice simulation and experimental results demonstrating chaotic performance of the Colpitts oscillator in the ultrahigh frequency (300–1000 MHz) range are presented. Various combinations of the resonance tank parameters are considered to achieve a fundamental frequency as high as possible. Simulations indicate that chaotic oscillations observed experimentally at higher frequencies, e.g., at about 1000 MHz are caused by parasites, like wiring inductances, loss resistance appearing due to skin effect, and collector-emitter capacitance of the transistor. Reliable and reproducible chaos can be generated at fundamental frequencies up to about 500 MHz with the single-stage Colpitts oscillator using the microwave 9 GHz bipolar junction transistors.     

Numerical Investigation and Experimental Demonstration of Chaos from Two-Stage Colpitts Oscillator in the Ultrahigh Frequency Range

A hardware prototype of the two-stage Colpitts oscillator employing the microwave BFG520 type transistors with the threshold frequency of 9 GHz and designed to operate in the ultrahigh frequency range (300–1000 MHz) is described. The practical circuit in addition to the intrinsic two-stage oscillator contains an emitter follower acting as a buffer and minimizing the influence of the load. The circuit is investigated both numerically and experimentally. Typical phase portraits, Lyapunov exponents, Lyapunov dimension and broadband continuous power spectra are presented. The main advantage of the two-stage chaotic Colpitts oscillator against its classical single-stage version is in the fact that operating in a chaotic mode it exhibits higher fundamental frequencies and smoother power spectra.     

Two-terminal feedback circuit for suppressing synchrony of the FitzHugh–Nagumo oscillators

An extremely simple analog technique for desynchronization of neuronal FitzHugh–Nagumo-type oscillators is described. Two-terminal feedback circuit has been developed. The feedback circuit, when coupled to a network of oscillators, nullifies the voltage at the coupling node and thus effectively decouples the individual oscillators. Both numerical simulations and hardware experiments have been performed. The results for an array of three mean-field coupled FitzHugh–Nagumo-type oscillators are presented.