Gaofei Zhang

Hydrothermal synthesis of PbSe, PbTe semiconductor nanocrystals

Abstract Hydrothermal reaction of selenium or tellurium with lead acetate in sodium hydroxide solution in the presence of hydrazine hydrate as a reductive was investigated to prepare lead chalcogenides, PbE (E=Se, Te). Nanocrystals with different morphology could be obtained under mild conditions. Our experiment shows that source materials and reaction temperature play important roles in forming the objective products and controlling their morphologies. The formation of lead chalcogenides in our process is based on a direct elemental combination pathway. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).

A novel active pixels sensor (APS) based sun sensor based on a feature extraction and image correlation (FEIC) technique

A new feature extraction and image correlation (FEIC) algorithm is proposed and practised to improve the accuracy and reliability, the two key performances, of an APS sun sensor especially with multi-apertures and large field of view (FOV). A multi-aperture active pixel sensor (APS) based sun sensor, which is composed of a micro electromechanical system (MEMS) mask with 36 apertures and a detector plane placed below the mask at a certain distance, exactly matches this FEIC algorithm. When the sun illuminates the sensor, an image of apertures is formed on the APS detector. Then the sun angles can be derived by analyzing the precise aperture image location on the detector via the FEIC algorithm. With this system, the centroid accuracy of the sun image can be achieved to 0.01 pixels (3σ), even when some missing apertures and some bad pixels appear on the detector because of aging of the devices and a harsh space environment. With the aforementioned features, the working life and application of a sun sensor will be extended.

A Novel Multi-Aperture Based Sun Sensor Based on a Fast Multi-Point MEANSHIFT (FMMS) Algorithm

With the current increased widespread interest in the development and applications of micro/nanosatellites, it was found that we needed to design a small high accuracy satellite attitude determination system, because the star trackers widely used in large satellites are large and heavy, and therefore not suitable for installation on micro/nanosatellites. A Sun sensor + magnetometer is proven to be a better alternative, but the conventional sun sensor has low accuracy, and cannot meet the requirements of the attitude determination systems of micro/nanosatellites, so the development of a small high accuracy sun sensor with high reliability is very significant. This paper presents a multi-aperture based sun sensor, which is composed of a micro-electro-mechanical system (MEMS) mask with 36 apertures and an active pixels sensor (APS) CMOS placed below the mask at a certain distance. A novel fast multi-point MEANSHIFT (FMMS) algorithm is proposed to improve the accuracy and reliability, the two key performance features, of an APS sun sensor. When the sunlight illuminates the sensor, a sun spot array image is formed on the APS detector. Then the sun angles can be derived by analyzing the aperture image location on the detector via the FMMS algorithm. With this system, the centroid accuracy of the sun image can reach 0.01 pixels, without increasing the weight and power consumption, even when some missing apertures and bad pixels appear on the detector due to aging of the devices and operation in a harsh space environment, while the pointing accuracy of the single-aperture sun sensor using the conventional correlation algorithm is only 0.05 pixels.

Error Compensation for Area Digital Sun Sensor

Compared to the error factors of the Linear Array Digital Sun Sensor (DSS), those of the Area Array DSS are complicated and methods used for error compensation are not valid or simple enough. This paper presents the main error factors of the Area Array DSS and proposes an effective method to compensate them. The procedure of error compensation of Area Array DSS includes three steps. First, the geometric error of calibration is compensated; second, the coordinate map method is used to compensate the error caused by optical refraction; third, the high order polynomial-fitting method is applied to calculate the tangent of the sun angles; finally, the arc tangent method is used to calculate the sun angles. Experimental results of the product of the High Accuracy Sun Sensor indicate that the precision is better than 0.02° during the cone field of view (CFOV) of 10°, and the precision is better than 0.14° during the CFOV 10° to 64°. The proposed compensation method effectively compensates the major error factors and significantly improves the measure precision of the Area APS DSS.

Optical Flow Inversion for Remote Sensing Image Dense Registration and Sensor's Attitude Motion High-Accurate Measurement

It has been discovered that image motions and optical flows usually become much more nonlinear and anisotropic in space-borne cameras with large field of view, especially when perturbations or jitters exist. The phenomenon arises from the fact that the attitude motion greatly affects the image of the three-dimensional planet. In this paper, utilizing the characteristics, an optical flow inversion method is proposed to treat high-accurate remote sensor attitude motion measurement. The principle of the new method is that angular velocities can be measured precisely by means of rebuilding some nonuniform optical flows. Firstly, to determine the relative displacements and deformations between the overlapped images captured by different detectors is the primary process of the method. A novel dense subpixel image registration approach is developed towards this goal. Based on that, optical flow can be rebuilt and high-accurate attitude measurements are successfully fulfilled. In the experiment, a remote sensor and its original photographs are investigated, and the results validate that the method is highly reliable and highly accurate in a broad frequency band.

High-power mems relay array with improved reliability and consistency

This paper presents a power MEMS relay array with numerous improvements in current-carrying capacity, which adopts silicon-on-insulator (SOI) anodic bonding technology to significantly improve the reliability and consistency of the relay matrix. The relay array is designed as a matrix of microcantilevers connected in parallel to allocate high power to individual relays. This method allows the relay matrix to be configured according to different power requirements. The proposed novel hollow suspended springs ensure that the microcantilevers driven by electrostatic parallel-plate actuators have small driving voltage and high stability.