Cryogenic Behavior of Piezoelectric Bimorph Actuators

Abstract

In developing in Genoa a SQUID Scanning Magnetic Microscope working at LHe, we were faced with the problem of obtaining at cryogenic temperature a large and smooth movement of the sample relative to the SQUID sensor.

The scanning system was designed to examine a 2 by 2 mm² square region, using a lever mechanism to amplify the deflection generated by two piezoelectric actuators working at 4.2 K.

To obtain a large displacement with a small and simple object, we use piezoelectric bender actuators, of the bimorph type. The piezoelectric lamina is made by co-fired layers of PZT material, connected in parallel, working at a nominal voltage of 60 Volts maximum.

We report on the measurements that have been done to get the low temperature properties of these benders, and to develop a suitable type for the requirements of the microscope. We studied available commercial benders (P-803.50 manufactured by PI Ceramic GmbH) and new samples developed for this application, using thinner layers and higher electric field strength. A new material was also tested, which maintains good properties at low temperature.

The final product has a room temperature deflection of ± 1 mm, with a free length of 39 mm, and at LHe temperature this deflection is reduced only 6 to 7 times.