Abstract:Optoelectronic terahertz generation and detection play a key role in the applications of non-destructive testing, which involves different areas such as physics, biological, material science, imaging, explosions detection, astronomy applications, semiconductor technology and superconductiong electronics. In this article, we present a review of the principle and performance of typical terahertz sources, detectors and non-destructive testing applications. On this basis, the new development and trends of terahertz radiation detectors are also discussed.

Abstract:This paper investigates a fractional terminal sliding mode control for flexible spacecraft attitude tracking in the presence of inertia uncertainties and external disturbances. The controller is based on the fractional calculus and nonsingular terminal sliding mode control technique, and it guarantees the convergence of attitude tracking error in finite time rather than in the asymptotic sense. With respect to the controller, a fractional order sliding surface is given, the corresponding control scheme is proposed based on Lyapunov stability theory to guarantee the sliding condition, and the finite time stability of the whole close loop system is also proven. Finally, numerical simulations are presented to illustrate the performance of the proposed scheme.

Abstract:Stochastic resonance system is subject to the restriction of small frequency parameter in weak signal detection, in order to solve this problem, a frequency modulated weak signal detection method based on stochastic resonance and genetic algorithm is presented in this paper. The frequency limit of stochastic resonance is eliminated by introducing carrier signal, which is multiplied with the measured signal to be injected in the stochastic resonance system, meanwhile, using genetic algorithm to optimize the carrier signal frequency, which determine the generated difference-frequency signal in the low frequency range, so as to achieve the stochastic resonance weak signal detection. Results show that the proposed method is feasible and effective, which can significantly improve the output SNR of stochastic resonance, in addition, the system has the better self-adaptability, according to the operation result and output phenomenon, the unknown frequency of the signal to be measured can be obtained, so as to realize the weak signal detection of arbitrary frequency.

Abstract:The real-time retrieval of submicron aerosol size distributions is of major interest for applications. Based on the Mie theory, the spectral extinction method offers a simple measurement principle and a convenient optical arrangement. In contrast to the relative simplicity of the experimental measurement the retrieval of the particles size distribution and particle concentration from the spectral extinction method is difficult. Mie scattering Equation is a Fredholm Integral Equation of the First Kind. This paper develops a hybrid iterative model-dependent algorithm for on-line particle sizing from extinction spectra which is both computationally efficient and accurate. Applying the refined Mie diagnostic iterative procedures within some candidate solutions can identify the unique result accurately and rapidly enough for real time measurement. With the addition of added Gaussian noise, an average tolerance up to 5% of noise level is kept for particle size from submicron to micrometer under moderate polydispersity.

Abstract:Naxi Dongba hieroglyphs of China are the only living hieroglyphs world widely which still in use. There are thousands of manuscripts written in Dongba hieroglyphs scattering in different counties for history reason. For culture protection and inheritance, those manuscripts are in urgent need to be recognized and organized quickly. This paper focuses on the recognition of Naxi Dongba hieroglyphs by using coarse grid method to extract features and using support vector machine to classify. The designed Experiment shows that the method performs better than the commonly used clustering method in recognition accuracy in recognition of Naxi Dongba hieroglyphs. This method also provides some experience for recognition of other hieroglyphs.

Abstract:In order to improve work performance of Maglev vibration test systems, the relationships of operating parameters between different components and system were researched. The working principle of photoelectric displacement sensor was analyzed. The relationship between displacement of transducer and the infrared light area received by sensor was given. The method of expanding the dynamic range of vibrator was proposed, which makes dynamic range of Maglev vibrator doubled. By increasing the amplification of the amplifier, the sensitive photoelectric displacement sensor can be maintained. Two modes of operation of the controller were analyzed. Bilateral work of vibration test system designed can further improve the stability of the system. An object vibration was measured by Maglev vibration test system designed when different vibration exciter frequencies were loaded. Experiments show that the output frequency measured by Maglev vibration test system and loaded are the same. Finally, the errors of test system were analyzed. These errors of vibration test system designed can meet the requirements of application. The results laid the foundation for the practical application of magnetic levitation vibration test system.