Mathematical modelling and experimental validation of electrostatic sensors for rotational speed measurement

Recent research has demonstrated that electrostatic sensors can be applied to the measurement of rotational speed with excellent repeatability and accuracy under a range of conditions. However, the sensing mechanism and fundamental characteristics of the electrostatic sensors are still largely unknown and hence the design of the sensors is not optimised for rotational speed measurement. This paper presents the mathematical modelling of strip electrostatic sensors for rotational speed measurement and associated experimental studies for the validation of the modelling results. In the modelling, an ideal point charge on the surface of the rotating object is regarded as an impulse input to the sensing system. The fundamental characteristics of the sensor, including spatial sensitivity, spatial filtering length and signal bandwidth, are quantified from the developed model. The effects of the geometric dimensions of the electrode, the distance between the electrode and the rotor surface and the rotational speed being measured on the performance of the sensor are analyzed. A close agreement between the modelling results and experimental measurements has been observed under a range of conditions. Optimal design of the electrostatic sensor for a given rotor size is suggested and discussed in accordance with the modelling and experimental results

Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals

The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4} single crystals (0.178=<x=<0.290) has been measured. For the superconducting samples (0.178=<x=<0.238), the derived gap values (without any adjusting parameters) approach closely onto the theoretical prediction \Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity. In addition, the residual term \gamma(0) of SH at H=0 increases with x dramatically when beyond x~0.22, and finally evolves into the value of a complete normal metallic state at higher doping levels, indicating growing amount of unpaired electrons. We argue that this large \gamma(0) cannot be simply attributed to the pair breaking induced by the impurity scattering, instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys. Rev.

YBCO-buffered NdBCO film with higher thermal stability in seeding REBCO Growth

In this work, we report a strengthened superheating effect caused by a buffering YBa2Cu3Oy (Y123 or YBCO) layer in the Nd1+xBa2-xCu3O7-y (Nd123 or NdBCO) thin film with MgO substrate (i.e., NdBCO/YBCO/MgO thin film). In the cold-seeding melt-textured (MT) growth, the NdBCO/YBCO/MgO film presented an even higher superheating level, about 20 {\deg}C higher than that of non-buffered NdBCO film (i.e., NdBCO/MgO film). Using this NdBCO/YBCO/MgO film as seeds and undergoing a maximum processing temperature (Tmax) up to 1120 {\deg}C, we succeeded in growing various RE1+xBa2-xCu3O7-y (REBCO, RE=rare elements) bulk superconductors, including Gd1+xBa2-xCu3O7-y (GdBCO), Sm1+xBa2-xCu3O7-y (SmBCO) and NdBCO that have high peritectic temperatures (Tp). The pole figure (X-Ray \phi-scan) measurement reveals that the NdBCO/YBCO/MgO film has better in-plane alignment than the NdBCO/MgO film, indicating that the induced intermediate layer improves the crystallinity of the NdBCO film, which could be the main origin of the enhanced thermal stability. In short, possessing higher thermal stability and enduring a higher Tmax in the MT process, the NdBCO/YBCO/MgO film is beneficial to the growth of bulk superconductors in two aspects: (1) broad application for high-Tp REBCO materials; (2) effective suppression against heterogeneous nucleation, which is of great assistance in growing large and high-performance REBCO crystals.Comment: 9 pages, 4 figure