Chengjin Jin

THE FIVE-HUNDRED-METER APERTURE SPHERICAL RADIO TELESCOPE (FAST) PROJECT

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project funded by the National Development and Reform Commission (NDRC). The National Astronomical Observatories of China (NAOC) is in charge of its construction and the subsequent operation. Upon its expected completion in September of 2016, FAST will surpass the 300-meter Arecibo and the 100-meter GBT in terms of absolute sensitivity in the 70 MHz to 3 GHz bands. In this paper, we report the current status, the key science goals, and the aspiration of its early sciences. A special emphasis is paid to its innovative fatigue-resistant fibers, which are critical for the control and data acquisition under the unique FAST design.

A Wideband Superconducting Filter Using Strong Coupling Resonators for Radio Astronomy Observatory

A 12-pole wideband superconducting microstrip bandpass filter, which has a fractional bandwidth of 38% and a center frequency of 1455 MHz, is presented for the Miyun 50-m radio astronomy telescope, Beijing, China. A novel resonator, which can not only generate very large coupling, but also push its first spurious resonant peak away from the passband, is introduced. A new style interleaved coupling structure is proposed and successfully used in this study to realize the remarkably required strong coupling. To achieve high edge slope on the high side of the passband, as required, a single transmission zero was introduced. The filter was fabricated on a 36 mm times 30 mm times 0.5 mm double-sided YBa2Cu3O7 film deposited on an MgO substrate. The measured results showed that the filter had 0.05-dB minimum insertion loss, 0.08-dB passband ripple, and 23-dB return loss at a temperature of 40 K. The first spurious peak did not appear until 2632 MHz. The overall measured performance showed good agreement with the simulation.

Pulsar Observations with Radio Telescope FAST

FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star – black hole binary as the telescope is put into operation.

Preparatory Study for Constructing FAST, the World's Largest Single Dish

A 500-m aperture spherical telescope (FAST) was funded by the National Development and Reform Commission of China (NDRC) in July 2007 and will be located in the unique Karst region, a sinkhole-like landform, in Guizhou province. FAST can be seen as a modified ldquoArecibordquo type radio telescope using many innovative techniques, with as much as twice the collecting area and a wider sky coverage. FAST has, first, an active reflector, conforming to a paraboloid of revolution from a sphere in real time through actuated control, which enables the realization of wide bandwidth and full polarization capability by using standard feed design. Secondly, it has a light focus cabin suspension system, integrating optical, mechanical, and electronic technologies, reducing effectively the cost of the support structure and control system. With such a huge collecting area of more than 30 football fields, FAST will become the largest single dish ever built. Here we will summarize the FAST concept and the milestones achieved in experiments on its key technologies, i.e., site exploration, active reflector prototyping, focus cabin driving mechanism, measurement and control techniques, and the receiver layout. The Miyun FAST demonstrator also will be presented.

EELS studies of MgB2 superconductor obtained under high pressure

The MgB2 intermetallic superconductor obtained under high pressure, which has the transition temperature of above 39 K, has been studied by scanning electron microscopy (SEM), transmission electron microscopy and parallel electron energy-loss spectroscopy (EELS). From the SEM, it can be seen that the bulk compound is highly dense and the grains are connected compactly. The size of single crystal is at the magnitude of similar to mum. The high resolution transmission electron microscopy image of [001] zone axis clearly shows the hexagonal planes of the constituent atoms. The EELS spectrum of B shows the peaks of a and antibonding bonds. The EELS results show a good agreement with the theoretical band structure calculations and the hole doping in the B sigma (P-xy) bonding bands

Working space analysis and optimization of the main positioning system of FAST cabin suspension

This paper devotes to the working space analysis of the main positioning system of FAST cabin suspension, a flexible-cable-driven parallel manipulator. The problem formulation is deduced through equilibrium analysis of the cabin platform and suspension cables, which changes subsequently into a nonlinear constrained optimization intending a uniform allocation of the six cable tension force. The analysis verifies the accessibility of focus cabin to the whole focus surface. The optimization investigates the orientation of the focus cabin under equilibrium and the optimal cable forces, as well as elaborates their importance in the finite element modeling of the cable-cabin system and the respective layout designs of the rotator, Stewart stabilizer and capstan motors. In the end, the influences of the tower height and the position of mass center of the focus cabin on the optimization results are discussed.

Vivaldi antenna with balun feed for SKA feeding system in UWB

This paper represents a low cost printed Vivaldi antenna at 3-10 GHz bandwidth for Radio telescope Feed system. The idea of this design is to minimize the number of telescope receivers for Square Kilometre Array (SKA). A minimized tapered slot antenna with a balun feed for receiver systems is proposed. The Vivaldi antenna is design on a relatively low dielectric constant substrate which operates at Ultra-Wideband (UWB). A typical tapered slot antenna is a combination of a wideband balun and a radiator with different tapering shapes such as linear, constant width, exponential and dual exponential. Two feeding configurations are used such as coplanar waveguide (CPW) to slot line transition and microstrip line to slotline transition. The antenna modeling is analyzed using two different electromagnetic simulators such as HFSS and CST Microwave Studio. The results are shown that the antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 7.3 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below -20 dB. The realized antenna structure occupies a volume of 45 × 45 × 0.5 mm3, and possesses the essential time domain fidelity needed for UWB Radio telescope Feed system applications. A prototype Vivaldi antenna is constructed and measured for validation. The Voltage Standing Wave Ratio (VSWR) of the proposed antenna is verified against the simulated data results, the measured and simulated results are found to be in good agreement. In particular, a good impedance bandwidth matching and stable directional radiation patterns were achieved across the operating frequency range. The combination of design aims and outcomes described in the paper indicates that the proposed antenna can be a suitable candidate for portable RF systems, or possible sensor element in an UWB antenna array application.

Loop feed meander-line Antenna RFID tag design for UHF band

A loop feed meander-line Antenna (LFMLA) RFID tag on a relatively low dielectric constant substrate operates on the European UHF band 865-868 MHz is presented. The tag modeling is analyzed using two different electromagnetic simulator HFSS and CST. A prototype tag antenna is constructed and measured for validation. The input impedance of the proposed antenna is verified against the simulated data results, the measured and simulated results are found to be in good agreement. The compact size tag antenna shows excellent impedance matching to the typical input impedance of a RFID integrated circuit chip and a significant improvement in reading range up to 5 meters.

The structure and properties of the manganate with nominal composition La1.0Ca2.0Mn2O7

The manganate with nominal composition La1.0Ca2.0Mn2O7 was prepared using a standard solid-state reaction method under ambient pressure. The structure of the compound was investigated using powder X-ray diffraction, Rietveld analysis and TEM experiments. The results show that the compound forms multiphase mixtures comprising the layered perovskite manganate La1.0Ca2.0Mn2O7 with 91.3% weight fraction as majority phase, the perovskite manganate La0.5Ca0.5MnO3 with weight fraction 8.7% as the minority phase. The occurrence of weak magnetization at 250 K and the presence of weak magnetization in the lower temperature region of 5-135 K are linked to the perovskite manganate La0.5Ca0.5MnO3 and the layered perovskite manganate La1.0Ca2.0Mn2O7, respectively. The magnetoresistance (MR) occurred in the lower temperature range arises mainly from the layered perovskite manganate La1.0Ca2.0Mn2O7

Shielding effectiveness measurement for physically small enclosure in FAST telescope

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in Guizhou province, Southwest China. The construction of FAST will involve many kinds of analog and digital electrical equipments. The electrical equipments are potential threat to radio observation due to its ElectroMagnetic Interference (EMI) emission. The EMI should be safely shielded when FAST telescope operates. The shielding effectiveness of large shielding enclosures can be tested with two log periodic antennas, signal generator and spectrum analyzer. It is not suitable to test small shielding enclosure for that is not possible to put big antenna and signal generator inside. In this paper, an effective shielding effectiveness measurement system for the small shielding enclosure is introduced. This measurement system uses a frequency synthesizer of Valon Technology as signal generator which can measure the shielding effectiveness no more than 100dB in a frequency range of 23–6000MHz. Some of measurement results of shielding effectiveness are also presented.