The authors developed a technique of generating periodical subwavelength light focusing array. In the technique, a proximity projection grating structure (PPGS) is employed. The size of focal spot obtained is dependent on the refractive index of film material used in the PPGS. When the film with the refractive index greater than 4 is used, focal spots with size of can be obtained. Additionally, the subwavelength light focusing will appear periodically along the propagation direction, which leads to the light focusing in both near field and far field. Both simulations and experiments verify the developed technique. The periodical subwavelegnth light focusing array has the potential in super resolution imaging applications.
With the development of military industry and intelligence, accelerometer with high-performance will be demanded imminently. The resonant graphene accelerometer combines excellent mechanics and mechanism properties of graphene with the technique of MEMS accelerometer, with the advantages of high-performance, low-energy consumption, lowcost and mass production. An optically driven resonant graphene accelerometer is resonated by a laser beam with periodically varying intensity. A single-layer graphene fixed on its substrate is heated by the laser beam to make the graphene film resonate. When there is external acceleration, a proof mass fixed on the single-layer graphene film can change the resonant frequency by adding a force on the film. The acceleration can be calculated through the variation of the resonant frequency. However, the deadly drawback of the optically driven resonant graphene accelerometer is its low quality factor, which is large dissipation. In this paper, the mechanism of the squeeze-film air damping of a resonant graphene accelerometer is theoretically modeled. The influential parameters are optimized to decrease the damping. The results show that the effect of squeezefilm damping on quality factor can be significant, while that on resonant frequency can be negligible. Meanwhile, the squeeze-film damping will increase as the pressure, free and fixed edges of the single-layer graphene grow. The influence on the quality factor by changing the size of the free edges is more remarkable, compared to that of fixed edges. Therefore, decreasing the pressure and geometrical size of the single-layer graphene, especially the free edges, is an effectively method to reduce the damping of the resonant graphene accelerometer.
Aiming at the deficiency of the traditional postgraduate education mode for professional degree, such as the conflict between work and study, restricted supply and demand and poor efficiency of course teaching, the emergence of Massive Open Online Course (MOOC) which has large scale, online and open features can make up for the shortage of traditional professional degree postgraduate education mode by introducing MOOC teaching mode. However, it is still a fangle to integrate MOOC into the traditional postgraduate education for professional degree and there are no standard methods for reference in the construction of MOOC courses as well as the corresponding evaluations. In this paper, the construction method and practical experience of MOOC courses for professional degree postgraduate education are discussed in details, based on the MOOC course of Introduction to Engineering Optics. Firstly, the principle of MOOC course contents for professional degree postgraduate education is introduced from the aspects of students’ demand, MOOC features and practical applications. Secondly, the optimization of MOOC teaching mode is discussed in order to improve the teaching quality and learning efficiency. Thirdly, in order to overcome the deficiency of current MOOC examination schemes, a novel MOOC evaluation scheme is proposed which is capable of assessing students’ learning attitude as well as their ability and performance differences. Finally, a practical summary is given about how to integrate the MOOC teaching mode into the postgraduate education for professional degree, including the constructions of teaching team, course system as well as other factors. From the paper, we can conclude that the integration of MOOC teaching mode into the postgraduate education for professional degree will improve the teaching quality and efficiency.
This paper is concerned with the acceleration sensing based on graphene resonator using finite-element software COMSOL Multiphysics. Based on the ordinary graphene resonator structure, a proof mass is attached to the surface of graphene sheet in order to sense acceleration and force more effectively. The rectangle-shaped gold proof mass is positioned at the center of the graphene sheet. Through COMSOL Multiphysics, the simulations about how the graphene sheet and mass’ dimension affect resonance frequency were performed and proper size parameters for the graphene resonator were chosen. By adopting these parameters, the analysis about the resonance frequency’s change responding to the acceleration or working force was carried out, which lays a foundation for further research of graphene resonator for acceleration sensing.
Lever arm effect has to be considered in transfer alignment technology. Between static lever arm and dynamic lever arm, the former has larger amplitude, and it is the major error source in transfer alignment. How to measure and solve it become an important problem. This paper takes vehicle as a rigid body. Assume that static lever arm does not change in a short time, based on two inertial measurement units(IMU), data are measured and constituted several matrixes properly. After that, by using least square method, static lever arm is solved finally. Simulation experiments are implemented, results show that static lever arm can be solved effectively. Further study shows that, the precision of the method can be improved by preprocessing low pass filter.
Ship deformation is the main error source of partial reference. Such deformation can be estimated by laser gyro units and Kalman filter technology. For Kalman filter, deformation was divide into two parts, dynamic deformation, and static deformation. Traditionally, dynamic deformation is treated as AR2 model .In this paper, dynamic deformation is taken as a kind of ARX model. Based on actual data measured by Yuanwang-3 Space Survey Ship, simulation experiments are studied. Results show that the novel model can improve the measurement precision.
In order to avoid the shortcoming of the passive gain control method in the 3D imaging lidar (light detection and ranging), we propose a new gain control method, which can adjust the gain of the amplifying circuit according to the target distance. This method complies with the principle that the laser echo amplitude is inversely proportional to the square of the target distance. In addition, to simplify the complexity of the gain control module, we propose a simple implementation method based on the charging process of a capacitor. Firstly, the theoretical waveform of the proposed gain control method and the gain control error are analyzed and simulated. The results indicates that when the gain ranged from 1 to 100, the maximum of gain error is less than 28% in the whole target distance range, and the gain error is less than 5% in the most target distance range. Based on this method, a new gain control and amplifying circuit has been developed, which is mainly composed of an amplifying module and a gain control module. The gain control module is used to generate a gain control voltage and apply the voltage to the gain control of the amplifying module. Finally, some experiments have been carried out to verify the entire circuit functions and performances. The experimental results show that the output signal amplitude keep constant on the whole when the target distance is changing. The pass band of the circuit ranges from 0.33 MHz to 150 MHz, and the maximum gain is 316.
Proc. SPIE. 8538, Earth Resources and Environmental Remote Sensing/GIS Applications III
KEYWORDS: Clocks, LIDAR, Laser range finders, Field programmable gate arrays, Time metrology, Precision measurement, Picosecond phenomena, Analog electronics, Defense technologies, Temperature metrology
In order to reduce the negative influence caused by the temperature and voltage variations of the FPGA (Field
Programmable Gate Array), we propose a new FPGA-based time-to-digital converter. The proposed converter adopts a
high-stability TCXO (Temperature Compensated Crystal Oscillator), a FPGA and a new algorithm, which can
significantly decrease the negative influence due to the FPGA temperature and voltage variations. This paper introduces
the principle of measurement, main framework, delayer chain structure and delay variation compensation method of the
proposed converter, and analyzes its measurement precision and the maximum measurement frequency. The proposed
converter is successfully implemented with a Cyclone I FPGA chip and a TCXO. And the implementation method is
discussed in detail. The measurement precision of the converter is also validated by experiments. The results show that
the mean measurement error is less than 260 ps, the standard deviation is less than 300 ps, and the maximum
measurement frequency is above 10 million times per second. The precision and frequency of measurement for the
proposed converter are adequate for the 3D imaging lidar (light detection and ranging). As well as the 3D imaging lidar,
the converter can be applied to the pulsed laser range finder and other time interval measuring areas.