Wei Bin

A cryogenic front end for CDMA and UMTS wireless base stations

The design and the laboratory performance of a cryogenic front end for CDMA and UMTS wireless base stations is described together with the results of a first field test at a CDMA base station in the region of Tangshan in China. The central elements of the cryogenic front ends are the cryocooler, the cryostat and the cryogenic platform mounted with up to 6 HTS pre-selection filters of high selectivity combined with the corresponding cryogenic low noise amplifiers of high dynamic range as well as the associated control electronics. Design and performance of the UMTS and CDMA filters are described and the characteristic parameters of the cryogenic low noise preamplifier are given. An analysis of the results of the first field test is discussed.

Simulation and experiment of viscous torque for disengaged wet clutches of tracked vehicle

In order to predict the viscous drag loss for tracked vehicles, the drag torque of the friction pair with different grooves was investigated in this paper. The traditional computation method is difficult to adapt for the new kinds of friction plates with complex grooves. A numerical method with the help of CFD models is adopted to simulate the fluid flow status in the grooves and the drag torque was obtained by the accumulation of the discrete viscous force. The simulation results implied that the plates with different kinds grooves were provided with various characteristics of viscous torque and these characteristics could be affected by the rotation direction for the plate with spiral grooves, which are proved in experiment. Meanwhile, it was also found that the two kinds of plates with double arc or spiral grooves, which have different sensitive parameters in drag dissipation, have to perform accurate flow control and clearance design respectively. The simulations and experiments showed that the ‘positive spiral grooves’ friction plates had minimum drag torque in regular heavy-duty conditions. It can be used in transmission system with requirements of limited space and high mobility, which can lead to better heat dissipation and less power loss.

Tangential motion mechanism and reverse hydrodynamic effects of acoustic platform with nonparallel squeeze film

In order to explain the reverse hydrodynamic effects on acoustic platform with nonparallel squeeze film, a theoretical model was proposed to evaluate the levitation and movement capacity in this paper. The mechanism of movement and levitation was revealed by the viscous fluid mechanics and dynamic lubrication theory. The transient pressure gradient and steady average velocity were calculated in different deflection angles of nonparallel squeeze film by means of numerical calculation of Reynolds equation. The theoretical results indicated that the platform of nonparallel squeeze film was provided with a bearing and pushing capacity in both normal and tangential directions and it was amazing that the reverse hydrodynamic effects made the levitated plate move into the opposite direction of gravitational tangential component. This proposed theoretical model for acoustic platform with nonparallel squeeze film was different with the original parallel one. Its driving mechanism was the reverse hydrodynamic effect instead of travelling waves. This reverse hydrodynamic effect was proved in the experiments, which could be used in levitation and transport field for precise component in future.

Influence of the surface gold thin film on HTS filter performance

A four-pole high temperature superconducting (HTS) filter was designed and fabricated to investigate the influence of gold (Au) thin film on the HTS filter performance, including the bandwidth, insertion loss and return loss. Due to the resistance of the Au, dissipative loss is an important issue. Simulation showed that the insertion loss was reduced with the Au film being gradually thinner. The experimental results of 0.2 dB insertion loss, -22 dB return loss were achieved and the bandwidth met the design need when the gold film was thinner than 90 nm. Furthermore, a thin Au layer is in favor of the stability for HTS material as well as for the HTS filter.