Abstract:Terahertz(THz) pulses can be generated by pumping photoconductive antennas, magnetic heterostructures, electro-optic crystals, and air, etc. with femtosecond lasers, which are mainly based on non-thermal effects such as transient changes in carriers and electric polarization under femtosecond excitation. Meanwhile, the laser heating effects inevitably occur during the interactions of femtosecond lasers with matter, and the ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have gained increasing attention in recent years for the ability to generate terahertz waves. In this paper, the research progresses of THz emission induced by two ultrafast thermoelectric effects including the Seebeck effect and the Nernst effect, and two ultrafast spin caloritronics effects including the spin Seebeck effect and the anomalous Nernst effect, are introduced in detail. The ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have exhibited great potential in terahertz generation, which could promote the development and the applications of THz sources and related technologies.

Abstract:Broadband terahertz radiation sources have an urgent practical application demand in terahertz science and technology, and are the core components for constructing terahertz application systems represented by spectroscopy and imaging. Compared with commonly used commercial terahertz sources, spin-optoelectronics-based terahertz radiation sources have a series of advantages such as ultra-wide frequency spectrum, solid-state stability, and low cost. Currently, the research on the theory, materials, and device technology of spin-optoelectronics-based terahertz radiation sources is still in its infancy. This paper mainly summarizes the terahertz generation mechanism of single-layer ferromagnetic layers in recent years, and the relationship between the polarity of terahertz radiation signals and the excitation configuration. By changing the direction of the magnetic field, the direction of the incident laser, and the direction of sample incidence, the contributions of ultrafast demagnetization, Anomalous Hall Effect(AHE), and Anomalous Nernst Effect(ANE) to the terahertz radiation characteristics can be effectively distinguished, providing a reference for the research in the field of terahertz spin-optoelectronics.

Abstract:Due to the strong absorption of terahertz(THz) by water, the detection of terahertz spectroscopy for aqueous samples faces significant challenges. To address the issue of high-sensitivity detection of aqueous samples using terahertz spectroscopy, this paper proposes and experimentally verifies a high-resolution frequency-domain spectroscopy system based on terahertz Attenuated Total Reflection(ATR). The system employs an innovative optical heterodyne coherent detection technique, achieving excellent dynamic range and resolution performance. Within the range of 0.3 to 1.2 THz, the peak dynamic range exceeds 100 dB, and the frequency resolution reaches up to 100 MHz. The innovative ATR architecture effectively enhances sensitivity, and in experimental measurements of aqueous solutions with different concentrations of α-lactose, the system has realized direct and accurate quantitative detection of the aqueous samples.

Abstract:Terahertz communication with high information transmission rate and large bandwidth capacity is considered as a key technology to achieve 6G communication, which requires efficient, stable and compact terahertz sources and detectors. In order to improve the detection performance, the quasi-optical terahertz detector based on integration of Resonant Tunneling Diode(RTD) and on-chip slot antenna is studied. Aiming at the problems of increased loss and parasitic effects of the circuit at high frequencies, a design criterion that jointly considers impedance match factor and antenna radiation efficiency is proposed, and a RTD detector at a small bias voltage is designed at 0.67 THz. The detection performance is characterized by co-simulating of High Frequency Structure Simulator(HFSS) and Advanced Design System(ADS). The current sensitivity of the detector at 0.67 THz is about 2.349 A/W at the input power of -30 dBm. Compared with the design scheme of maximizing impedance match factor at microwave frequencies, the sensitivity is increased by 28.01%.

Abstract:Gyrotron Traveling Wave Tubes(Gyrotron-TWT) have both high power and broadband characteristics, which have broad application prospects in important military fields such as millimeter wave detection and imaging radar, electronic countermeasures, etc. The gyrotron traveling wave amplifier with large orbit electron beams can operate in high-order harmonic state, greatly reducing the operating magnetic field and even achieving superconducting free operation. It can improve the flexibility and maneuverability of Gyrotron-TWT. This paper optimizes and designs a Ka band second harmonic Gyrotron-TWT with large orbit electron beams, which adopts a longitudinal slot interaction high-frequency structure with dielectric loading to effectively suppress backwave oscillation and improve the stability of device operation. The process of beam wave interaction in the Gyrotron-TWT was simulated by using three-dimensional particle simulation software. The results show that at the condition of the electron beam voltage of 70 kV, the current of 6.5 A, the magnetic field can be reduced to 0.642 T, the corresponding output power can reach 106.5 kW, the bandwidth is 2.1 GHz, and the maximum gain is 35 dB.

Abstract:The terahertz frequency band, as an important alternative for the next generation of communication technologies, faces the challenge of rapid signal attenuation with increasing carrier frequency. Terahertz wired transmission technology is an effective means to address this issue, and precise control and optimization of material dielectric properties is the key to developing high-performance wired transmission materials in the terahertz frequency range. This paper modifies polymer materials and uses a terahertz time-domain spectroscopy system to test the dielectric properties of composite materials, studying the application of traditional dielectric constant equivalent models in the development of terahertz band materials. Based on the polarization characteristics and response mechanisms of terahertz band materials, a model and method for estimating the dielectric constant and loss tangent of composite materials in the terahertz frequency range is proposed, providing a scientific model guidance for the development of new terahertz wired transmission materials and their performance regulation.

Abstract:Beam hopping technology improves the resource utilization of the communication system by means of time slicing. However, the existing beam positions are relatively fixed and cannot change with the change of service requirements, and the more beams the beam hopping serves, the greater the queuing delay of the system. When multiple beams work at the same time, the same frequency interference can not be ignored. To solve the above problems, on the basis of beam position optimization, this paper further proposes a resource allocation algorithm that jointly optimizes the slot allocation and the hop beam pattern design. In order to maximize the system throughput, firstly, the phased array antenna can be beam shaped, and the appropriate size of beam position is configured according to the service requirements. Secondly, genetic algorithm is employed to design the hop pattern to avoid co-channel interference. By comparing the system performance parameters before and after the joint optimization, the simulation results show that the method can improve the system throughput and traffic satisfaction, and reduce the system queuing delay.

Abstract:Under large pitch angles, in the coarse alignment of the Strapdown Inertial Navigation System(SINS) using dual-vector attitude determination, the accuracy of the attitude angles, especially the azimuth angle, varies greatly under different vector combinations, and must be carefully selected. To address this, two of the most commonly used coarse alignment vector combination error equations are presented, and the main error-affecting factors are analyzed. Considering sensor errors, the accuracy of coarse alignment under full attitude angles is simulated using the Monte Carlo method, and a static coarse alignment experiment was conducted on a turntable at a pitch angle of 80°. In the turntable experiment, with SINS gyro error of about 1°/h and accelerometer error of about 0.1mg, the maximum azimuth angle coarse alignment errors for the first and second combination modes were 20° and 7.5°, respectively, with the second combination mode being about one-third of the first. In the simulation test, with SINS gyro error of about 0.1°/h and accelerometer error of about 1mg, at a pitch angle of 80°, the maximum azimuth angle coarse alignment errors for the first and second combination modes were 11° and 2.2°, respectively, with the former being about five times that of the latter. The results of the simulation and experiment show that the vector combination mode under large pitch angles is the most important factor affecting the accuracy of the coarse alignment of the SINS attitude angles and attitude matrix.

Abstract:Aiming at the baseline optimization of phase interferometer direction finding antenna array, the construction of virtual baseline and the optimization of real baseline are presented. Within the physical constraints of the phase interferometer, by reasonably designing the number of virtual baseline and optimizing the ratio of real baseline, the shortcoming of long real baseline caused by non-optimal real baseline ratio in traditional method is overcome, the optimal method of the length of direction finding antenna array baseline under any condition is realized. Finally, the presented method is employed to give the baseline optimization in 0.35~18 GHz, the ambiguity resolution and the angle measurement accuracy are analyzed and verified. Simulation experiment shows that, under the condition of satisfying angle measurement accuracy, the proposed algorithm can optimize the baseline of direction finding antenna array under any condition by optimizing the real baseline ratio.

Abstract:According to the application requirements of multi-beam in multi-functional phased array system, a two-dimensional multi-beam forming method based on the combination of optical Blass matrix and a two-stage cascade structure is proposed, in which coherent beam forming method in optical domain is employed to form the first-stage beam in horizontal direction, and the incoherent beam forming method in optical domain is employed to form the second-stage beam in vertical direction, such that the two-dimensional beams can be realized. This architecture bears several advantages:on the one hand, the scale of optical phased array system can be increased from dozens to more than several hundreds units, and this can break the limitation on the scale of the optical array beamforming due to the small quantities of optical wavelengths. On the other hand, it can significantly reduce the number of optical beam forming chips, and the number of beam chips can be reduced from M ² to (N+M) for the system with array number of N×N and beam number of M×M. Moreover, the structure of the multi-beam system can be drastically simplified by combining the photon integration technology, which is helpful to improve the integration degree and engineering realizability.

Abstract:Aiming at the problem of single frequency band and low integration of traditional RF receivers in multi-band and multi-mode wireless communication applications, a broadband blocker-tolerant RF receiver based on Complementary Metal Oxide Semiconductor(CMOS) with N-path filtering and receiver integration technology is proposed. The receiver integrates an N-path mixer and baseband filter. Layout testing under 65 nm CMOS process shows that the receiver provides more than 60 dB of out-of-band rejection outside of the 5 MHz baseband bandwidth and frequency tuning range of 0.25~2.5 GHz. The front balun's low-noise amplifier achieves a receiver conversion gain of 46 dB while reducing the overall Noise Figure(NF) to 3.1~4 dB. The receiver also achieves 24.5 dBm Out-of-Band Third-order Intercept Point(IIP3) and consumes only 26 mW.

Abstract:In response to the issue of performance degradation in signal detection bit error rate under spatially correlated channels, a method of multi-antenna diversity reception is proposed. This method reduces the impact of channel spatial correlation on signal detection by increasing the number of receiving antennas, and can flexibly configure the corresponding number of receiving antennas according to actual engineering needs. While avoiding the introduction of high-complexity detection algorithms, it offers superior performance in detection bit error rate. Simulation analysis is conducted on the proposed method using equal gain combining, and the simulation results confirm the effectiveness of the method.

Abstract:With the continuous advancement of the construction and development of urban rail transit networks, people's demand for transportation capacity is increasing day by day. Therefore, the shortage of on-board computing power has become one of the important issues, making it necessary to explore new solutions. In recent years, Edge Intelligence(EI) has emerged as a new field. Through edge intelligence, complex computing tasks can be offloaded to trackside computing servers, fundamentally liberating the computing power of onboard equipment. In this case, we can focus the onboard devices on performing simple, low energy computing tasks, while leaving most of the computing work to edge servers. Based on the above idea, this paper proposes a new train autonomous control system, which uses Google Kubernetes high reliability edge computing platform to realize the train autonomous control algorithm. In addition, we use the Linear Quadratic Gaussian(LQG) algorithm to model the train autonomous control process and utilize cloud security computing to ensure the high reliability of the entire system. At the same time, due to its ability to effectively avoid the impact of local faults, the system also exhibits excellent performance in terms of communication packet interval delay performance. After extensive experimental verification, we can conclude that the proposed train autonomous control system has high operational reliability and data security, as well as low communication packet delay performance. This result further proves that using the autonomous train operation control system can significantly improve the efficiency and safety of train operation, thereby improving the quality of train operation.

Abstract:To enhance the automatic detection and tracking capabilities of passive weak targets under low signal-to noise ratios and in the presence of multiple target interference, a novel algorithm with multi-line spectrum fusion and optimal line spectrum target automatic tracking is proposed. This algorithm is based on line spectrum detection and automatically tracks targets with fused multi-line spectrum features, establishing the criteria for the creation, deletion, fusion, and association of line spectrum targets. It employs a Multi-Hypothesis Tracking(MHT) algorithm tailored for trajectories to automatically track multiple targets, offering the advantages of low computational complexity and strong weak target tracking capability. Analysis of sea trial data indicates that even in the presence of strong target interference, this algorithm can still provide stable tracking for weak targets with line spectrum characteristics.

Abstract:Micro-Electro-Mechanical Systems(MEMS) inertial switches are passive electronic devices that integrate sensing and actuation. They have the advantages of small size, light weight, easy integration, good processing consistency, and no need for assembly. They have a broad application prospect in fields such as the automotive industry, aerospace, and military equipment. The application scenarios of low-g value MEMS inertial switches are mainly for triggering specific functions during the acceleration/deceleration process of aircraft. In the design, it is necessary to ensure low spring stiffness and a large mass block volume, which poses certain difficulties in structural design and processing technology. This paper introduces the basic physical model and working principle of low-g value MEMS inertial switches, discusses the current research status at home and abroad, summarizes the key issues that urgently need to be addressed at this stage, and proposes corresponding solutions, providing beneficial references for subsequent research.

Abstract:Theoretical and experimental research of the spatial resolution characteristics of magnetic focusing framing tubes with single magnetic lens, double magnetic lenses and triple magnetic lenses are simulated and studied by Monte Carlo method, finite difference method and finite element method. The relationship among the number of short magnetic lenses and the surface curvature of Micro-Channel Plate(MCP), imaging range and rotation angle is studied. The results show that the more the number of short magnetic lenses, the smaller the curvature of the imaging surface, the flatter the image surface. The imaging range increases with the increase of the number of short magnetic lenses; the electron rotation angle at the MCP point decreases with the increase of the number of short magnetic lenses. With triple magnetic lenses, the spatial resolution of the framing tube is 10 lp/mm within the diameter of 36 mm.