A new piezoelectric tube scanner for simultaneous sensing and actuation

Piezoelectric tubes with quartered external electrodes have been widely used as scanners in modern scanning probe microscopes. Various feedback control techniques have been developed to improve bandwidth and accuracy of these scanners. Non-contact displacement sensors, e.g. capacitive and inductive sensors, have been used for position feedback. However, their measurements contain a significant noise component if operated over large bandwidths. As an alternative measure of displacement, the piezoelectric voltage induced in a tube nanopositioner has been proposed recently. This technique provides a much improved noise figure, up to three orders of magnitude better than capacitive sensors. In this arrangement, an electrode is used to actuate the tube, while the opposite electrode is used as a sensor. Operating the tube in this mode has two drawbacks: i) the operating range of the tube is reduced to half, and ii) the tube is driven asymmetrically, thus the opposite sides of the tube are no longer stressed antisymmetrically, i.e. the tube cannot be considered as a perfectly collocated system. In this paper, a new electrode pattern for piezoelectric tube scanners is presented. This new approach addresses the aforementioned problems and allows simultaneous sensing and actuation of the tube in an efficient way.