This paper presents an absolute capacitive angular-position sensor with a contactless rotor. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor, and a microcontroller. The electrically floating rotor can be either conductive or dielectric. For the dielectric material, we chose plastic, and for the conductive rotor, we chose aluminum. The sensing element has a redundant structure, which reduces mechanical nonidealities. The signal processor has a multicapacitance input and a single output, which is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. Theoretical analysis, supported by experimental results, show that the sensitivity to mechanical nonidealities of the sensing element is higher in the case of a conductive rotor. The resolution of the capacitive angular-position sensor over the full range (360 ) was better than 1". The measured nonlinearity was 100" and 300" for the dielectric and the conductive rotor, respectively.Index Terms-Absolute position encoder, angular position measurement, capacitance measurement, capacitive sensor, contactless angle encoder, rotary position.
Contrary to expectation, the electrostatic complexation of a rigid-rod anionic polyelectrolyte that exhibits nematic phase behaviour in aqueous solution with a flexible cationic polyelectrolyte forms homeotropically aligned films upon casting, i.e. the rigid molecules spontaneously align perpendicular to the substrate. Moreover, such alignment is retained upon the introduction of up to 10 mol% of a flexible cationic polyelectrolyte. The formation of a weak physical gel during film drying or in the precursor solution appears to be critical in facilitating homeotropic alignment in such films. Consequently, it can be envisaged that electrostatic complexation may be fine tuned in order to provide homeotropically aligned films of any rigid charged molecule.
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