(a) is the schematic of the LRDCT, and (b) is the equivalent circuit of this capacitive bridge. Each capacitance is determined by the coupling area discussed in the text. (c) is one unit of the schematic of the capacitive sensor used in this work, whose equivalent circuit is identical to (b). Part I is the mobile plate and II the stationary plate.
More realistic schematic of the sensor used in this work. The stationary plate is extended to an array, whose length determines the travel range. A fringe pattern is expected on the detection side due to the regularly repeated array on the stationary plate.
Schematics of the experimental setup.
Capacitive sensor read-out from a coarse motion test over a length of 1.6 cm. The fringes whose amplitudes are identical correspond to positions where the capacitive plates are completely coupled. When the mobile plate is entering/leaving the stationary one, the plates are only partially coupled, yielding smaller amplitudes on the right side of the graph.
Capacitive sensor read-out from a fine motion test over a length of . The read-out is calibrated by a low-resolution, educational grade Michelson interferometer. A resolution of is claimed through this test.
Schematic of a 2D nanopositioning capacitive sensor using the same principle as the 1D sensor, schematically demonstrated in Fig. 1(c) and tested in this work. The squares with the same color are electrically connected and essentially represent one electrode. Both - and -sensors can be made into arrays for better spatial resolutions. This schematic only shows how the - and -sensors shall be arranged. It should be noted that a second set of sensors with phase shifted from the first set is needed for truly unlimited displacement measurements. The proposed 2D sensor will also have the same advantage as the 1D version, i.e., unlimited travel range with subnanometer resolutions.
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