Preliminary experimental results by the prototype of Sanya Incoherent Scatter Radar

In the past decades,the Incoherent Scatter Radar(ISR)has been demonstrated to be one of the most powerful instruments for ionosphere monitoring.The Institute of Geology and Geophysics at the Chinese Academy of Sciences was founded to build a state-ofthe-art phased-array ISR at Sanya(18.3°N,109.6°E),a low-latitude station on Hainan Island,named the Sanya ISR(SYISR).As a first step,a prototype radar system consisting of eight subarrays(SYISR-8)was built to reduce the technical risk of producing the entire large array.In this work,we have summarized the preliminary experimental results based on the SYISR-8.The amplitude and phase among 256 channels were first calibrated through an embedded internal monitoring network.The mean oscillation of the amplitude and phase after calibration were about 1 dB and 5°,respectively,which met the basic requirements.The beam directivity was confirmed by crossing screen of the International Space Station.The SYISR-8 was further used to detect the tropospheric wind profile and meteors.The derived winds were evaluated by comparison with independent radiosonde and balloon-based GPS measurements.The SYISR-8 was able to observe several typical meteor echoes,such as the meteor head echo,range-spread trail echo,and specular trail echo.These results confirmed the validity and reliability of the SYISR-8 system,thereby reducing the technical risk of producing the entire large array of the SYISR to some extent.

Nanosensitive Silicon Microprobes for Mechanical Detection and Measurements

Nanosensitive mechanical microprobes with CMOS transistors, inverters, inverters cascades and ring oscillators, integrated on the thin silicon cantilevers are presented. Mechanical stress shifts linear, steep switching fragment of the inverters’ electrical characteristics. Microprobes were fabricated with use of the standard CMOS technology (3.5 μm design rules, one level polysilicon gate and one level of the metal interconnections) and relief MEMS technique. Control of the silicon cantilever thickness was satisfactory in the range above the few micrometers. Several computer simulations were done to analyze and optimize transistors location on the cantilever, in respect to the mechanical stress distribution. Results of the microprobes electromechanical tests confirm high deflection sensitivity 1.2 - 1.8 mV/nm and force sensitivity 2.0 - 2.4 mV/nN, both in nano ranges. Microprobes, with the ring oscillators revealed sensitivities 5 - 8 Hz/nm. These microprobes seem to be appropriate for applications in precise chemical and biochemical sensing.

Zener Phenomena in InGaAs/InAlAs/InP Avalanche Photodiodes

Avalanche photodiodes are widely utilized in research, military and commercial applications which make them attractive for further development. In this paper the results of numerical simulations of uncooled InGaAs/InAlAs/InP based photodiodes are presented. The devices were optimized for 1.55 μm wavelength detection. For device modeling the APSYS Crosslight software was used. Simulated structure consists of separate absorption, charge and multiplication layers with undepleted absorption region and thin charge layer. Based on numerical calculations, the device characteristics like band diagram, dark current, photo current, gain, breakdown voltage and gain bandwidth product were evaluated. The simulation results highlight importance of Zener effect in avalanche photodiode operation.

Influence of processing on microstructure and electrical characteristics of multilayer varistors

The paper reports on the influence of processing on microstructure and electrical properties of multilayer varistors based on zinc oxide doped with Bi2O3,Sb2O3,Co2O3,MnO,Cr2O3,B2O3,and SiO2.0.5–1 wt%of AlF3–CaB4O7 was used as a new effective sintering aid.The behavior of green laminates during heating was characterized using differential thermal analysis and a heating microscope.As revealed by XRD,SEM,and EDS methods,the varistor layers are composed of ZnO grains of 1–5μm size,submicrometer spinel and pyrochlore grains situated at the ZnO grain boundaries,and nanometric Bi2O3-rich films surrounding ZnO grains.Complex impedance studies carried out in the frequency range of 0.01 Hz–2 MHz at temperatures changing from –30 to 150℃ imply the formation of semiconducting grains and insulating grain boundaries.Frequency dependence of dielectric permittivity shows a high plateau at lower frequencies,typical for barrier layer capacitance effect.The fabricated multilayer varistors show nonlinear current–voltage characteristics with a high nonlinear coefficient of 26–38.The breakdown voltage was found to decrease within the range of 66–130 V with sintering temperature increasing from 1000 to 1100℃.Good surge current capability of the varistors was confirmed by the tests using 8/20μs pulses.