Wideband chaotic microwave signal generation in a ring system with a nonlinear delay line on coupled ferromagnetic films

Various regimes of chaotic signal generation have been studied in an self-oscillating ring system with a wideband nonlinear delay line based on coupled ferromagnetic films, in which magnetostatic backward volume waves (MSBVWs) are excited. It is shown for the first time that the simultaneous excitation of two waves in the coupled films leads to the appearance of a falling part in the dynamic characteristic of the MSBVW delay line and the generation of a broadband chaotic signal with a continuous spectrum. Under certain conditions, the ring exhibits a regime of intermittency, in which broadband chaotic signals with both continuous and discrete spectra are generated.     

Influence of the amplitude and phase nonlinearity of a spin-wave delay line on the wideband chaotic microwave generation

Regimes of wideband chaotic microwave generation have been studied in a self-oscillating ring system with a nonlinear delay line, in which magnetostatic backward volume waves (MSBVWs) are excited. It is established that a change in length of the delay line influences on its amplitude and phase nonlineartity, thus making it possible to control the characteristics of the chaotic microwave signal generated in the ring. It is demonstrated for the first time that a wideband chaotic microwave signal with a continuous spectrum and a nearly Gaussian probability density distribution can be generated by exciting MSBVWs in a self-oscillating ring system with a nonlinear delay line based on single ferromagnetic film.     

隧道爆破振动信号混沌分形特征研究

为了分析隧道延时爆破时滞信号动力系统的非线性特征,在对新悬泉寺隧道爆破信号准确采集的基础上,运用混沌理论研究了经频率切片小波变换后各频带重构子信号的混沌动力学行为。通过子信号吸引子相轨迹特征对隧道爆破信号系统状态进行了直观描述和定量分析。结果表明:隧道爆破振动信号具有混沌特征,不同频带子信号吸引子在二维相空间一定区域内具有特定层次结构且永不封闭椭圆形轨迹。随着频率的增大,混沌吸引子在相空间的形态表现为椭圆轨迹的长/短轴之比逐渐减小,混沌吸引子在相空间沿长轴方向收缩,沿短轴扩展并最终趋于稳定,信号高频噪声具有弱混沌特征。混沌吸引子形态的演化过程有助于爆破信号幅值、能量信息的精确提取和主频有效判别,为隧道爆破信号非线性特征提取提供了新的思路。     

Leading Chaos to Period by Two Unfeedback Methods in a Two-degree-of-freedom Vibrating System with Two Rigid Constraints

The equations of the asymmetrical periodic motion in a two-degree-of-freedom vibrating system with two rigid constraints are constructed analytically.Its Poincaré mapping equation is established too.Periodic motions of the system and their routes to chaos are also illustrated by numerical simulation.The ranges of the system excited frequency from periodic motions to chaotic motions are obtained.The chaotic motions of the system are shown by diagrams of Poincaré mapping,phase portraits and diagrams of bifurcation.The chaos controlling methods by the addition of constant load and the addition of phase are dissertated and analyzed numerically by the numerical solution.The chaos of the system is controlled by the two methods.The allowable range controlling variables and the steady orbits of the controlled system are obtained.     

隧道爆破振动信号混沌分形特征研究

为了分析隧道延时爆破时滞信号动力系统的非线性特征,在对新悬泉寺隧道爆破信号准确采集的基础上,运用混沌理论研究了经频率切片小波变换后各频带重构子信号的混沌动力学行为.通过子信号吸引子相轨迹特征对隧道爆破信号系统状态进行了直观描述和定量分析.结果表明:隧道爆破振动信号具有混沌特征,不同频带子信号吸引子在二维相空间一定区域内...     

一类非线性振子中有界噪声诱发的混沌运动

研究谐和外力与有界噪声激励联合作用下的一类非线性振子的混沌运动。利用Melnikov方法，通过计算扰动系统的Melnikov积分，分析了系统在参数发生变化时的同宿分岔，得出系统产生混沌运动的参数阈值，并讨论了有界噪声激励对系统的混沌运动的影响。最后利用数值方法模拟了系统的安全盆的侵蚀状况，并进一步通过计算系统运动的Lyapunov指数，给出了由噪声诱发的混沌运动与噪声激励下非混沌运动之间的差别。     

Phase synchronization of switchings in stochastic and chaotic bistable systems

We study synchronization of switching processes in stochastic and chaotic bistable systems driven by a periodic signal in terms of phase synchronization. By introduction of instantaneous phases of transitions between metastable states and of the periodic forcing we show explicitly the effect of phase locking. The dynamics of phase difference appears to be qualitatively equivalent to that of a synchronized classical self-sustained oscillator. We have found that the degree of phase coherence between the input signal and the response estimated employing the effective diffusion constant is maximal at an optimal noise level in a stochastic bistable system or at an optimal value of a control parameter in a purely deterministic case. We also consider the effect of mutual synchronization of the switching processes in coupled stochastic and chaotic bistable systems.     

On the dynamic response of the hysteretic system

In this study, the jump phenomena and the chaotic motion are investigated. Firstly, it is found that the jump phenomenon occurs under the harmonic excitation by means of computer simulation, and that it occurs under the narrow band random excitation by the averaging method, too. And the conditions for the occurrence of jump phenomena, the probability density function of dynamic response and the resonance curves are shown, respectively. Furthermore, the phenomena are considered from the viewpoint of mean square value, where the statistical linearization method and Liapunov matrix equation are used. Consequently, it seems that the method of equivalent linearization for smooth hysteretic systems under random excitation is versatile and has a great potential in the analysis of hysteretic system, but that it is impertinent to the research of jump phenomena. Secondly, the occurrence of chaotic motion is disscussed by means of the method of mapping and the averaging method. As the results, it is found that the chaotic motion occurs under the various parameters.     

Transition to phase synchronization in a system with periodic dynamics under the action of a chaotic signal

Intermittent behavior has been studied near the boundary of phase synchronization in an autooscillatory system with periodic dynamics under the action of an external chaotic signal. It is shown that the intermittency obeys the same scenario as that observed in the case of interaction between two coupled chaotic oscillators.     

Stochastic and chaotic sub- and superharmonic response of shallow cables due to chord elongations

The paper deals with the non-linear response of shallow cables driven by stochastically varying chord elongations caused by random vibrations of the supported structure. The chord elongation introduces parametric excitation in the linear stiffness terms of the modal coordinate equations, which are responsible for significant internal subharmonic and superharmonic resonances. Under harmonically varying support motions coupled ordered or chaotic in-plane and out-of-plane subharmonic and superharmonic periodic motions may take place. If the harmonically varying chord elongation is replaced by a zero-mean, stationary narrow-band random excitation with the same standard deviation and center frequency, qualitatively and quantitatively completely different modes of vibration are registered no matter how small the bandwidth of the excitation process is. Additionally, the stochastic excitation process tends to enhance chaotic behavior. Based on Monte Carlo simulation on a reduced non-linear two-degree-of freedom system the indicated effects have been investigated for stochastic subharmonic resonance of order 2:1, and stochastic superharmonic resonances of orders 1:2 and 2:3. By analyzing the responses for two chord elongation processes with almost identical auto-spectral density function, but completely different amplitudes, it is shown that the indicated qualitative and quantitative changes of the subharmonic resonance primarily are caused by the slowly varying phase of the stochastic excitation. The superharmonic stochastic responses are dominated by random jumps between a single mode in-plane and a coupled mode attractor, which are caused by the variation of the amplitude of the random excitation. Such jumps do not occur in the subharmonic response, because the single mode in-plane attractor is unstable.     

Chaotic phase synchronization studied by means of continuous wavelet transform

A new approach to introduction of the phase of a chaotic signal is developed based on the continuous wavelet transform. The proposed method is applied to the study of phase synchronization of two chaotic dynamical systems with ill-defined phases.     

Stochastic resonance in a bistable system driven by a chaotic signal

The behavior of a bistable oscillator under the action of a chaotic signal from a Rössler oscillator with a spiral attractor is considered. The influence of the width of the main spectral line of the chaotic drive signal on the signal to noise ratio at the response system’s output has been studied.     

A Novel Method of Distance Measurement Based on Pulse Position Modulation and Synchronization of Chaotic Signals Using Ultrasonic Radar Systems

This paper deals with a novel method of transmission and receipt of a signal based on both the property of two chaotic systems generating the same chaotic signal when they are synchronized and the property of pulse position modulation (PPM) to be insensitive to the distortions of the transmission channel. The method is discussed in the context of ultrasonic radar systems, in which the transmitter and receiver, which consist of ultrasonic sensors, are near each other, and the received signal consists of the transmitted signal reflected by an obstacle. A reference sinusoidal signal is superimposed to a chaotic signal generated by a master chaotic system, and the whole signal is modulated according to the PPM method and transmitted by the sensor. The received signal is demodulated, and the demodulated signal forces a slave chaotic system to generate the chaotic signal embedded in it, which allows recovery of the sinusoidal signal by subtracting this chaotic signal from the demodulated echo. The difference of the phases of the reference sinusoidal signal and the recovered sinusoidal signal allows computation of the time of flight of the signal and, consequently, the distance of the radar system from the obstacle. The novel method is illustrated and tested by both simulation and experiments. The interference problem between the considered radar system and other radar systems ( crosstalk) is also addressed, and a solution is proposed to avoid it.     

Design of a low-cost optical instrument for pH fluorescence measurements

This paper describes the electronic design and the performance of a low-cost fiber-optic instrument for pH fluorescent measurements. The chemical sensing phase consists of an organic pH indicator (mercurochrome) immobilized in a sol-gel matrix placed at the end of a fiber optic by means of a steel grid. The active phase was excited by means of a high-intensity blue light-emitting diode. The light signal was modulated to avoid external interference. Fluorescence emission is detected by a low-cost photodiode. To avoid drifts in excitation light emission intensity, a ratiometric measurement was proposed. To perform such measurements, two fiber-optic measurement channels were used. One of them was employed to measure only the pH indicator fluorescent emission intensity. The second channel was employed to measure only the intensity of the excitation light reflected by the sensing phase. The ratio between both signals is only proportional to pH and proved to be independent of excitation light intensity. The sensor is useful over the pH range of 4-8, providing highly reliable results.     

Controlled stochastization of oscillations in a chaotic delayed-feedback system

A mathematical model of the ring autooscillatory system, which possesses chaotic dynamics and comprises a nonlinear amplifier with a differentiating element in the feedback chain, a nonlinear oscillatory circuit, and a delay line, is considered. Numerical analysis has been performed for irregularly varying initial conditions. These conditions were set by the solutions of equations describing chaos that simulated intrinsic noises of a real autooscillatory system. It is shown that the irregularly varying conditions of excitation can lead to stochastization of the chaotic oscillations, in which case the oscillatory process becomes irreproducible.     

一般支承条件下输流管道的非线性动力学特性研究

摘要: 研究两端一般支承垂直放置的输流管道系统,采用非线性动力学分析方法,研究其在自激、参数激励和外激励联合作用下的非线性动力学特性,分析系统出现混沌运动的参数条件和进入混沌运动的途径。数值仿真结果表明,随着平均流速和质量比的增大,系统响应交替出现周期和混沌运动两种形态。系统进入混沌运动的途径为倍周期分岔,由混沌转化为周期运动的途径为倍周期倒分岔。混沌运动和周期运动出现的参数与流体的平均流速和管道端部的支承/约束刚度有很大关联,随着管道端部约束刚度的增大,系统出现混沌运动的区域减小,说明管道端部的约束刚度有益于抑制混沌运动的发生。     

利用间歇混沌检测含噪未知频率信号的研究

研究发现被测信号频率和干扰噪声变化都会引起间歇混沌间隔的变化,通过仿真实验分析了被测信号频率和干扰噪声对间歇混沌特征影响的相互关联关系,从理论上分析了被测信号频率和相角变化对间歇混沌特征的影响,提出了一种利用间歇混沌特征变化测量含噪未知频率信号的方法,设计了有噪声和无噪声两种环境中对声波信号频率的检测实验。实验结果显示与Duffing混沌系统相比,利用Liu-cos混沌系统间歇混沌检测含噪未知频率信号的效果更好。     

Features of induced synchronization of a bistable oscillator with chaotic dynamics

The features of induced synchronization of a Chua oscillator with a nonlinear element admitting cubic approximation have been numerically simulated for a system where the autonomous operation admits regular or chaotic regimes determined by losses in the oscillatory circuit. The cases of deterministic synchronization (under the action of a harmonic external driving signal) and chaotic synchronization (chaotic control) have been considered. It is established that, outside the band of synchronous oscillations that corresponds to the deterministic synchronization, the external harmonic signal stimulates the transformation of regular oscillations into chaos with the motions switched between two attractors. In cases of chaotic synchronization, there is a residual “noise” in the form of differential chaotic oscillations, which grows with increasing non-identity of the driving and driven signals.     

拟脉冲激励下悬架振动的混沌特性

通过数值仿真和实验,研究拟脉冲激励下汽车悬架振动的混沌特性。建立拟脉冲激励下的2自由度汽车悬架模型,通过数值仿真,给出悬架振动的时间历程曲线、功率谱图、相轨迹和最大Lyapunov指数,从理论上说明汽车悬架振动是混沌的。采用三角木法进行振动实验,获取汽车悬架的振动加速度曲线图;通过Matlab对悬架振动的特性曲线进行计算分析,获得悬架振动的功率谱图和相轨迹,并对其计算最大Lyapunov指数,从而验证汽车悬架振动的混沌特征。     

Frequency division transmission imaging and synthetic aperture reconstruction

In synthetic transmit aperture imaging only a few transducer elements are used in every transmission, which limits the signal-to-noise ratio (SNR). The penetration depth can be increased by using all transmitters in every transmission. In this paper, a method for exciting all transmitters in every transmission and separating them at the receiver is proposed. The coding is done by designing narrow-band linearly frequency modulated signals, which are approximately disjointed in the frequency domain and assigning one waveform to each transmitter. By designing a filterbank consisting of the matched filters corresponding to the excitation waveforms, the different transmitters can be decoded at the receiver. The matched filter of a specific waveform will allow information only from this waveform to pass through, thereby separating it from the other waveforms. This means that all transmitters can be used in every transmission, and the information from the different transmitters can be separated instantaneously. Compared to traditional synthetic transmit aperture (STA) imaging, in which the different transmitters are excited sequentially, more energy is transmitted in every transmission, and a better signal-to-noise-ratio is attained. The method has been tested in simulation, in which the resolution and contrast was compared to a standard synthetic transmit aperture system with a single sinusoid excitation. The resolution and contrast was comparable for the two systems. The method also has been tested using the experimental ultrasound scanner RASMUS. The resolution was evaluated using a string phantom. The method was compared to a conventional STA using both sinusoidal excitation and linear frequency modulated (FM) signals as excitation. The system using the FM signals and the frequency division approach yielded the same performance concerning both axial (of approximately equal to 3 wavelengths) and lateral resolution (of approximately equal to 4.5 wavelengths). A SNR measurement showed an increase in SNR of 6.5 dB compared to the system using the conventional STA method and FM signal excitation.