Abstract:A novel terahertz(THz) metasurface with multi-frequency narrow band resonance effect is constructed based on Single-Walled Carbon Nanotubes(SWCNTs) thin films. The influence of structural parameters of periodic microstructure unit on the resonance characteristics of the metasurface is analyzed. Furthermore, the resonance coupling mechanism of the device is studied, and the simulation and theoretical calculations have good consistency. In addition, the refractive index sensing characteristics of this THz metasurface device are analyzed by covering a dielectric layer with different refractive indexes on the metasurface. The function fitting results show that the metasurface device can achieve high sensitivity refractive index sensing up to 64 GHz/RIU.

Abstract:A new type of transmissive terahertz polarization conversion device is proposed based on the metamaterial structure of the combination of square open ring and metal rod. Specifically, the influence of different combinations of basic structural elements on the polarization conversion characteristics is first studied. The working bandwidth of the polarization conversion function is improved by optimizing the relevant parameters of the structural units. Finally, the efficient X-Y cross-polarization conversion is realized in the range of 0.45~1.30 THz, which is expected to be used in the research and application of integrated terahertz polarization conversion devices.

Abstract:Most existing special beams(focused beams, Airy beams, etc.) metasurfaces usually use metallic materials for a single wavefront modulation by changing the dimensions of the cell structure, the angle of rotation, etc. There are fewer researches on metasurfaces for special beams with dynamically tunable wavefronts. Therefore, breaking the barrier of traditional structures, special beam metasurfaces which utilize Fermi energy levels of graphene to dynamically modulate the wavefront are constructed. Stronger freedom in dynamically modulating the wavefront can be realized in order to achieve more and more complex phase requirements. Focusing metasurfaces with tunable wavefront and tunable Airy beam metasurfaces are designed, different phase distributions are obtained by tuning the Fermi energy levels of graphene. Utilizing the dynamic wavefront, the spatial position of the focal point, the switching of the focusing switch with the number of focal points, and the parameters affecting the Airy beam can be regulated.The proposed dynamic tunable wavefront special beam metasurfaces are helpful for terahertz applications in high-resolution imaging, focus-tunable planar lenses, optical micromanipulation, laser micromachining, and optical bullet molding.

Abstract:A novel one-dimensional graphene-Photonic Crystal(PhC) composite resonant structure is designed, and the strong coupling effect between the terahertz Tamm Plasmon Polaritons(TPP) and Cavity Modes(CM) supported by the Transmission Matrix Method(TMM) is theoretically studied. It is shown that the Rabi splitting energy employed to characterize the coupling strength increases with the decrease of the number of PhC periods. In addition, when changing the thickness of the spacer layer and the cavity, as well as the Fermi level of graphene, the Rabi splitting energy is also affected. Finally, the coupling mode can also be actively adjusted by changing the angle of incidence. When the angle of incidence is between 0° and 60°, the characteristics of the coupling mode are independent of polarization. This work provides a new idea for the study of strong coupling effect.

Abstract:Terahertz(THz) wave has great development potential in biomedical science due to its nonionizing, labelless and real-time characteristics. To distinguish biological tissues with similar permittivity, a metamaterial with Fano resonance is designed and fabricated for THz reflection imaging. The simulation and experimental results show that the reflection sensitivity of the metamaterial is 132 GHz/RIU at 0.82 THz. The metamaterial not only enhances the contrast of imaging resolution plate, but also improves the contrast between the muscle and the fat tissues by approximately 7.5%, therefore, it can improve the contrast of biological tissue slice images. This work has established an experimental and theoretical foundation for future terahertz applications in clinical tissue samples.

Abstract:Three artificial sweeteners, sucralose, erythritol and xylitol, are qualitatively and quantitatively studied based on Terahertz time-domain spectroscopy combined with machine learning algorithms and optimization algorithms.The results show that the Sparrow Search Algorithm-Support Vector Machines/Support Vector Regression(SSA-SVM/SVR) model is optimal for qualitative and quantitative analysis of the mixture. The accuracy of classification prediction is up to 95.56%, and the optimal regression coefficient for quantitative regression prediction is 0.999 8, so that a high-precision classification and quantitative analysis of three sweetener-flour mixtures is achieved. This provides an effective and reliable method for the rapid detection of artificial sweeteners.

Abstract:Radar waveform design is facing severe challenges with the development of electronic reconnaissance technology such as intra-pulse feature recognition and signal deinterleaving. Amplitude modulation can improve the anti-identification ability of the waveform by increasing the signal complexity in time domain, which is a newly developing modulation method. A novel radar waveform with joint amplitude-phase coding modulation is proposed in this paper. It improves the complexity of radar waveform through Amplitude-Phase Joint Modulation(APJM), which is promising in anti-reconnaissance. In addition, regarding the processing of this signal, an echo signal processing method combining matched filtering and Compressed Sensing(CS) is proposed, which uses the sparse sampling characteristics of amplitude. The proposed signal processing method effectively improves the detection probability under the condition of a low Signal-to-Noise Ratio(SNR). In the end, simulation results show the effectiveness of the proposed waveform design and processing method of the joint amplitude-phase modulation radar waveform.

Abstract:As an important part of space information network, low-orbit satellite Internet of Things (IoT) has the problem of high complexity of interference calculation in interference analysis and coordination with other communication systems due to its proliferation of constellation size, dynamic satellite platform and large number of terminals. In addition, the distribution of IoT terminals in practice is highly correlated with geography and population, but due to the large coverage area of a single satellite, it will face multiple densities and deployments of terminals, and the use of static traversal calculations will bring an explosion of computing power. Starting from the mechanism of co-channel interference generation, the regionalized transmit field strength is used as the core of modeling the uplink aggregate interference of dense IoT terminals, and the Poisson Point Process(PPP) distribution model is introduced to equivalently model the ground terminals, so that the regionalized uplink aggregate interference is only related to the distribution parameters and transmit parameters, but not to the exact location and number of terminals. The simulation results show that the proposed method has less error compared with traditional link analysis, and has better fitting performance for different number of terminals. It can effectively reduce the computational complexity in long-time analysis, and can be used for interference analysis and calculation with high efficiency.

Abstract:The existing transient magnetic field measurement in high power laser devices does not consider the shielding and signal reduction. A sensor is designed and developed for transient magnetic field measurement in high power laser devices according to the frequency range and characteristics of transient magnetic field. The brass is taken as the shielding material, and the leather is taken as the insulation material. The sensor is employed to measure the transient magnetic field, and the magnetic field response is up to 500 MHz. This work provides data support for the research on electromagnetic interference and electromagnetic compatibility for high power laser device.

Abstract:Transient response analysis of Transmission Line(TL) systems with frequency-dependent load is an important topic in the field of electromagnetic compatibility, especially for the situation where the frequency-dependent network is more complicated or the internal structure is not clear, the corresponding analysis of its transient response is more difficult. In this paper, firstly, the corresponding sampling values are obtained by measuring or calculating the admittances of the frequency-dependent loads at the sampling frequencies, and the equivalence of the admittances is performed by adopting the rational function approximation; then, the Piecewise Linear Recursive Convolution(PLRC) expression of the voltage at the connection point between the TL and frequency-dependent loads is obtained by bringing the poles and residues solved by Matrix Pencil Method(MPM) into the PLRC technique; finally, the transient response analysis of the TL system with frequency-dependent loads is obtained by combining the MPM, PLRC and TL equation, and the performance of the proposed method is verified by two numerical examples. The results illustrate that the proposed method has obvious advantages in calculation accuracy.

Abstract:Stochastic Testing(ST) method is an uncertainty quantification method. The existing ST methods are still unable to handle situations with arbitrarily distributed variables. This paper uses the Gram-Schmidt orthogonalization algorithm to construct a chaotic polynomial basis for arbitrarily distributed random variables to extend ST method. The extended ST method is applied to the field line coupling analysis of transmission lines. In the calculation of field line coupling, due to the uncertainty of the radiation field, there is uncertainty in the polarization angle, azimuth angle, and elevation angle of the incident wave, resulting in uncertainty in the response of the transmission line, leading to the problem of random field line coupling. For the case where the input parameters follow an arbitrary distribution, ST method is applied to quantify the uncertainty of the coupling response of the transmission line field. Performing polynomial chaos expansion on the output response of the model and solving the expansion coefficients, statistical information of the model response is obtained. Combining the field line coupling examples of single random variable and multi-random variable, the statistical information of transmission line voltage response is obtained. Compared with Monte Carlo Simulation(MCS) method, the correctness and efficiency of the ST method are verified.

Abstract:Hilbert-Huang Transform(HHT) is an efficient adaptive analysis method in nonlinear and nonstationary signal analysis, processing and feature extraction, which is widely used in engineering field. In this paper, Empirical Mode Decomposition(EMD) and Variational Mode Decomposition(VMD) are employed to compare and analyze the underwater acoustic signals of offshore motorboats. It is found that the energy of underwater acoustic signal is mainly concentrated in the low frequency band, and its amplitude is relatively large compared with that in the high frequency band. When analyzing this kind of signal, mode mixing is produced by EMD method, therefore using EMD cannot effectively decompose the signal and extract features. Nevertheless, using VMD method can effectively reduce the phenomenon of mode mixing and successfully extract its signal characteristics. The results show that VMD method is more effective in ship underwater acoustic signal processing and feature extraction.

Abstract:The fully polarized Radar Cross Section(RCS) sequences of two simulated ballistic targets are obtained from microwave anechoic static measurement inversion under typical combat conditions. In view of the nonsmoothness and proposed periodicity characteristics of this time series, it is not effective to estimate precession period directly by spectral analysis. Therefore, wavelet method is employed to reduce noise and enhance the details of the precession passband in the pre-processing process. The full polarization channel fusion process is carried out by Principal Component Analysis(PCA) and polarization invariant method respectively. The experiment results show that the extraction method using polarization information is significantly better than the single polarization channel extraction method, and the error is less than 0.002 Hz in noiseless observation environment.

Abstract:The attenuation characteristics of Acoustic Emission(AE) signals in liquid and gas pipelines with complex structures are studied. By collecting acoustic emission signals of pipe body under different flow pressures, the amplitude attenuation law is analyzed, and the composition changes of pipe acoustic emission signals are studied by DB8 wavelet packet and Fast Fourier Transform(FFT). Through collecting acoustic emission signals before and after valve, flange, flow meter and other six kinds of pipeline accessories and analyzing attenuation law, it is found that electromagnetic flow meter is the pipeline component that has the greatest influence on the attenuation of acoustic emission signals. Then, the effect of fastening degree of bolt connection on signal amplitude and frequency components is analyzed. The results show that the higher the fastening degree of bolt, the lower the signal attenuation. The relevant research conclusions of this paper have integrated reference value and guiding significance for the sensor layout decision of acoustic emission detection of oil or gas pipelines in engineering.

Abstract:The reliability of the device is very important in the complex space electromagnetic environment where the circuit is greatly affected by cosmic rays and single particles. Anti-fuse Field Programmable Gate Array(FPGA) is a one-time programmable device with anti-fuse as the basic programming structure. Since the state of anti-fuse FPGA cannot be reversed after programming, it has the advantages of non-volatility, high confidentiality, high reliability, and radiation resistance, which is very suitable for aerospace and other fields. A design scheme of anti-radiation wave control unit based on domestic anti-fuse FPGA is presented to solve the problem of radar array in space electromagnetic environment. The domestic anti-fuse FPGA chip is taken as the core in the proposed scheme. The working principle and realization block diagram of the system circuit are given, and relevant experiments are conducted. The experimental results show that the transmission delay of RS422 is less than the symbol period under the baud rate of 5 MHz, and the phase distribution time of the 144-unit phase-shifting component is less than 500 μs, which meets the design requirements.

Abstract:Micro-Electro-Mechanical System(MEMS) inertial switch has broad application prospects in the field of fuze, but there are few low-g MEMS inertial switches that can be used in the working environment of fuze. A design of MEMS inertial switch with low closing threshold is proposed for the fuse of ammunition with low launch overload, to meet the functional requirements of the fuze to identify the low-g value impact signal, and to realize the function of stable connecting the fuze power supply. At the same time, the designed MEMS inertial switch has the ability to resist high overload in the fuze's working environment and improve the reliability of the fuze. The design requirements are put forward according to the characteristics of the trigger signal and the working environment of the fuze. The oscillation model of the inertial switch is theoretically analyzed. The influence law of the structural size of the inertial switch on the switch performance is clarified. The overall design scheme of the switch is given, and the design results are simulated and verified by ANSYS finite element analysis software. The simulation results show that the designed inertial switch can monitor the impact signal with amplitude of 20g and pulse width of 1 ms, the response time is less than 1 ms, the electrode contact time is longer than 30 μs and anti-overload performance reaches 12 000g, meeting the proposed performance index requirements.