Development of series SQUID array with on-chip filter for TES detector

A cold preamplifier based on superconducting quantum interference devices(SQUIDs)is currently the preferred readout technology for the low-noise transition edge sensor(TES).In this work,we have designed and fabricated a series SQUID array(SSA)amplifier for the TES detector readout circuit.In this SSA amplifier,each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers,and an on-chip low pass filter(LPF)as a radiofrequency(RF)choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells.In addition,a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation.The measured results show smooth V-Φcharacteristics and a swing voltage that increases linearly with increasing SQUID cell number N.A white flux noise level as low as 0.28μφ;/Hz;is achieved at 0.1 K,corresponding to a low current noise level of 7 pA/Hz;.We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.

Investigation of the aeroacoustic behavior and aerodynamic noise of a high-speed train pantograph

As one of the main aerodynamic noise sources of high-speed trains, the pantograph is a complex structure containing many components, and the flow around it is extremely dynamic, with high-level turbulence. This study analyzed the near-field unsteady flow around a pantograph using a large-eddy simulation(LES) with high-order finite difference schemes. The far-field aerodynamic noise from a pantograph was predicted using a computational fluid dynamics(CFD)/Ffowcs Williams-Hawkings(FW-H) acoustic analogy. The surface oscillating pressure data were also used in a boundary element method(BEM) acoustic analysis to predict the aerodynamic noise sources of a pantograph and the far-field sound radiation. The results indicated that the main aerodynamic noise sources of the pantograph were the panhead, base frame and knuckle. The panhead had the largest contribution to the far-field aerodynamic noise of the pantograph. The vortex shedding from the panhead generated tonal noise with the dominant peak corresponding to the vortex shedding frequency and the oscillating lift force exerted back on the fluid around the panhead.Additionally, the peak at the second harmonic frequency was associated with the oscillating drag force. The contribution of the knuckle-downstream direction to the pantograph aerodynamic noise was less than that of the knuckle-upstream direction of the pantograph, and the average sound pressure level(SPL) was 3.4 dBA. The directivity of the noise radiated exhibited a typical dipole pattern in which the noise directivity was obvious at the horizontal plane of θ=0°,the longitudinal plane of θ=120°,and the vertical plane of θ=90°.