During proposal and development of a new non-contact nano-probe based on tunneling effect, analysis of the bias electric field (BEF) distribution is a key step for modeling and characterization of the probe. However, the BEF between the spherical electrode serving as the probing ball and the surface to be measured has combined features of macro- and micro- dimensions, which makes the modeling of it a far tricky problem. In this paper, a modeling finite difference method (FDM) based on non-uniform grids generation according to the structural features of the BEF is proposed, and the field distribution is solved with high accuracy. The maximum relative calculation error is within 15% compared with calculation results for a bias electric field with regular boundary with analytical electric image method.
In order to solve the problem of noncontact, wireless and nonmagnetic displacement sensing with nanometer resolution within critical limited space for ultraprecision displacement monitoring in the Joule balance device, a novel wireless digital capacitive displacement sensor (WDCDS) is proposed. The WDCDS is fabricated with brass and other nonmagnetic material and powered with a small battery inside, a small integrated circuit is assembled inside for converting and processing of capacitive signal, and low power Bluetooth is used for wireless signal transmission and communication. Experimental results show that the WDCDS proposed has a resolution of better than 1nm and a nonlinearity of 0.077%, therefore it is a delicate design for ultraprecision noncontact displacement monitoring in the Joule balance device, meeting the demand for properties of wireless, nonmagnetic and miniaturized size.
In order to solve the problem of performance analysis and optimal design of flexible suspension structure for displacement measurement probing sensors, a novel theoretical model of stiffness with high accuracy is proposed. Both displacements constraint and angle constraint of elastic diaphragms are considered during modeling, and a stiffness equation including all dimensional parameters and material characteristics of elastic diaphragms is obtained. Thus the stiffness of the flexible suspension structure is modeled theoretically and accurately, and the influence on performance of probing sensors by each parameter can be analyzed. Simulations results show that the theoretical model of stiffness proposed is more accurate than existing models, and performance analysis and optimal design of probing sensors can be carried out based on it.