Frequency detection of self-adaption control based on chaotic theory

Low-order Duffing and high-order Rossler chaotic oscillator are connected together and new self-adaption frequency detection method is presented. The frequency difference control between unknown signal and the periodic driving force is realized in this paper and the self-adaption is obtained. Thus, the detection precision and speed are promoted. The limitation that there are too many chaotic oscillators in Duffing system is broken. Meanwhile the disadvantage that the detection speed is lower in R ssler chaotic control is overcome. The self-adaption choice of frequency difference control is realized using the Duffing and Rssler different chaotic oscillators to obtain unknown signal frequency. The simulation results show that the presented method is feasible and effective.

Lorentz Force Electrical Impedance Detection Using Step Frequency Technique

Lorentz force electrical impedance tomography（LFEIT） inherits the merit of high resolution by ultrasound stimulation and the merit of high contrast through electromagnetic field detection. To reduce the instantaneous peak power of the stimulating signal to the transducer, the sinusoidal pulse and step-frequency technique is investigated in LFEIT. The theory of application of step-frequency technique in LFEIT is formulated with the direct demodulation method and the in-phase quadrature demodulation method. Compared with the in-phase quadrature demodulation method, the direct demodulation method has simple experimental setup but could only detect half of the range. Experiments carried out with copper foils confirmed that LFEIT using the step-frequency technique could detect the electrical conductivity variations precisely, which suggests an alternative method of realization of LFEIT.

Effect of a preload force on anchor system frequency

The interrelationship between preload forces and natural frequencies of anchors was obtained from the structure of an anchor and its mechanical characteristics. We established a numerical model for the dynamic analysis of a bolt support system taking into consideration the working surroundings of the anchor. The natural frequency distribution of the system under various preload forces of the anchor was analyzed with ANSYS. Our results show that each order of the system frequency varied with an increase in preload forces. A single order frequency decreased with an increase in the preload force. A preload force affected low-order frequencies more than high-order frequencies. We obtained a functional relationship by fitting preload forces and fundamental frequencies, which was in agreement with our theretical considerations. This study provides theoretical support for the detection of preload forces.

Assessment of structural damage using natural frequency changes

The present paper develops a new method for damage localization and severity estimation based on the employment of modal strain energy. This method is able to determine the damage locations and estimate their severities, requiring only the information about the changes of a few lower natural frequencies. First, a damage quantification method is formulated and iterative approach is adopted for determining the damage extent. Then a damage localization algorithm is proposed, in which a damage indicator is formulated where unity value corresponds to the true damage scenario. Finally, numerical studies and model tests are conducted to demonstrate the effectiveness of the developed algorithm.

Intelligent Spectrum Detection Model Based on Compressed Sensing in Cognitive Radio Network

In view of the uncertainty of the status of primary users in cognitive networks and the fact that the random detection strategy cannot guarantee cognitive users to accurately find available channels,this paper proposes a joint random detection strategy using the idle cognitive users in cognitive wireless networks.After adding idle cognitive users for detection,the compressed sensing model is employed to describe the number of available channels obtained by the cognitive base station to derive the detection performance of the cognitive network at this time.Both theoretical analysis and simulation results show that using idle cognitive users can reduce service delay and improve the throughput of cognitive networks.After considering the time occupied by cognitive users to report detection information,the optimal participation number of idle cognitive users in joint detection is obtained through the optimization algorithm.

Cochannel interference cancelation for multiple access systems

Many properties of frequency-hopped spread-spectrum multiple access （FH/SSMA）, such as, robustness against frequency selective fading and jamming make it a preferred multiple access communication scheme. But cochannel interference （CCI） can seriously harm the system＇s performance. On the basis of the analysis of the CCI pattern of frequency hopped multiple access signal, a new multiuser detection algorithm for canceling the CCI in frequency hopped multiple access systems is proposed. In the proposed scheme, the CCI is canceled by first detecting the frequency hopping slot, and then classifying and regenerating the candidates of the interference pattern from the time-frequency matrix. Both the theoretical analysis and computer simulation results show that compared to the conventional detector and Mabuchi＇s detector, this new multiuser detector has lower complexity, better convergence stability, and is suitable for both additive white Gaussian noise （AWGN） channels and Rayleigh fading channels.

A Robust Acquisition Scheme for FH Signal in Adverse Environments

Both partial-band jamming and multitone jamming have severe effect on the acquisition of frequency-hopping （FH） signal in adverse environments. In this paper, an anti-jamming FH signal acquisition scheme based on cognitive correlation process is proposed to boost the robustness of acquisition. The main idea of this scheme is to utilize a priori knowledge of FH speed and FH pattern to distinguish jamming signal from received signal. Furthermore, theoretic analysis on detection probability and false probability is given to demonstrate the robust performance of the FH signal acquisition method compared with conventional acquisition scheme without any prior information on FH speed and pattern in adverse environments.

CVRgram for Demodulation Band Determination in Bearing Fault Diagnosis under Strong Gear Interference

Fault-related resonance frequency band extraction-based demodulation methods are widely used for bearing diagnostics.However,due to the high peaks of strong gear meshing interference,the classical band selection methods have poor performance and cannot work well for bearing fault type detection.As such,the CVRgram-based bearing fault diagnosis method is proposed in this paper.In the proposed method,inspired by the conditional variance(CV)index and root mean square(RMS),a novel index,named the CV/root mean square(CVR),is first proposed.The CVR index has high robustness for the interference of non-Gaussian or Gaussian noise and has the ability to determine the center frequency of the weak bearing fault-related resonance frequency band under strong interference.Secondly,motived by the Kurtogram,the CVRgram algorithm is developed for adaptively determining the optimal filtering parameters.Finally,the CVRgram-based bearing fault diagnosis method under strong gear meshing interference is proposed.The performance of the CVRgram-based method is verified by both the simulation signal and the experiment signal.The comparison analysis with the Kurtogram,Protrugram,and CVgram-based method shows that the proposed technique has a much better ability for bearing fault detection under strong noise interference.

Design of soil moisture distribution sensor based on high-frequency capacitance

In order to obtain accurate real-time soil moisture data and the spatial distribution of soil moisture,the soil moisture measurement methods based on high-frequency capacitance edge field effect were analyzed,the structure of probe was studied,and a multi-channel soil moisture sensor was designed.Moreover,with the established two-dimensional trace planar capacitance probe model and the method of the finite element analysis,relationship between the structure of sensor probe and electric field intensity was studied and capacitance of the probe trace amount planar capacitance model was analyzed,the most optimal structure of sensor probe was determined.Design parameters of the probe which can achieve optimal sensitivity and detection range are:outer diameter 40 mm and inner diameter 38.4 mm for the probe copper ring electrode,axial length 20 mm and axial spacing 10 mm.The sensor is suitable for measuring the moisture of different type of soil.Moreover,the features of the profile soil moisture sensor were experimentally explored.The measurement accuracy reached±1.31%with better stability and consistency.Sensor probes can be assembled according to the measurement depth and used to measure soil moisture of different crop root zone.

Weak RF signal detection with high resolution and no blind zone based on ultra-simple multi-mode optoelectronic oscillation

Weak RF signal detection with high resolution and no blind zone based on directly modulated multi-mode optoelectronic oscillation has been proposed.The high-sensitivity optical modulators and optical filters are avoided because multi-mode oscillation is obtained based on directly modulating the semiconductor laser at the relaxation oscillation frequency.For the directly modulated optoelectronic oscillator,the detection characteristics such as gain for the RF signal,resolution,noise floor,and sensitivity are firstly analyzed.The experimental results are consistent with the simulated results.For the RF signal of unknown frequency,it can be detected out and amplified by tuning the bias current and delay time of the loop.There is no blind zone within 1–4.5 GHz.The system provides a maximum gain of 17.88 dB for the low-power RF signal.The sensitivity of the system can reach as high as-95 dBm.The properties such as gain dynamic range and power stability are also investigated.The system has potential for weak RF signal detection,especially for the RF signal with unknown frequency.

Negative Selection of Written Language Using Character Multiset Statistics

We study the combination of symbol frequence analysis and negative selection for anomaly detection of discrete sequences where conventional negative selection algorithms are not practical due to data sparsity.Theoretical analysis on ergodic Markov chains is used to outline the properties of the presented anomaly detection algorithm and to predict the probability of successful detection.Simulations are used to evaluate the detection sensitivity and the resolution of the analysis on both generated artificial data and real-world language data including the English Wikipedia.Simulation results on large reference corpora are used to study the effects of the assumptions made in the theoretical model in comparison to real-world data.