Adrian Robert Bowles

Self-optimising piezoelectric damping

Traditional solutions to vibration problems often employ viscoelastic materials which can be heavy, temperature-sensitive and bulky. Active solutions can provide useful damping but are often complex and expensive. This paper outlines a passive piezoelectric damping system with an adaptive controller capable of not only providing useful damping levels, but of modifying the components so as to change the circuit resonant frequency and thereby the damping effort. Experiments on simple beams and more realistic structures are described and the potential benefits and power requirements of such a system discussed. Increases in loss factor up to a factor of 10 and a high level of tuning repeatability were seen.

Characterisation of piezoelectric materials at high stress levels using electrical impedance analysis

Piezoelectrics are the active material of choice in a wide range of electromechanical applications including SONAR, medical ultrasound and non-destructive evaluation. However, designers of high power piezoelectric systems have suggested that a discrepancy exists between mathematical modelling predictions and measured transducer performance. In most high power applications piezoelectric materials are operated under large compressive stresses. Manufacturers of piezoelectric materials publish a wide range of performance data, however, the majority of the data is acquired under no bias stress. In this paper, a new technique that facilitates the characterisation of piezoelectric materials over a wide range of operating stresses (0-140MPa) at their resonant frequency is described. It builds upon the IEEE techniques for piezoelectric characterisation and utilises measurement equipment found in the majority of piezoelectric development laboratories. The technique therefore offers a low cost extension to existing facilities for the accurate determination of piezoelectric properties under high stress loading. Results gained using the new technique confirm that substantial variation in electromechanical properties of piezoelectric materials occurs under stress loading. Using this derived data, a more informed evaluation of transducer materials and more accurate predictions of transducer performance can be made.

A comparative study of ultrasonic micro-motors based on single crystal PMN-PT and polycrystalline PZT ceramics

A comparative study has been made to explore the potential benefits of newly available single-crystal ferroelectric materials when used in a practical device, in this case an ultrasonic micro-motor. This type of micro-motor exhibits exceptional power-to-weight characteristics, which could be exploited beneficially, for example, in unmanned air-vehicle (UAV) systems. The operating principles of a range of commercial and experimental motor designs were evaluated objectively in order to identify areas of performance that can potentially be enhanced using PMN-PT single-crystal piezoelectric ceramics. Based on this analysis a practical motor design was selected for construction and experimentation. Detailed numerical analysis indicated that a motor constructed from single crystal PMN-PT could be expected to provide an improvement in motor stall-torque by up to a factor of 2.8 and a no-load speed improvement by a factor of 1.5 when compared with motors based on standard polycrystalline lead-zirconate-titanate (PZT) ceramics. In practice single-crystal versions of the motor were found to produce double the power output of their polycrystalline counterparts. Overall efficiency was found to be improved two-fold. There were significant discrepancies between the numerical predictions for the single-crystal devices and their measured performance, whereas the polycrystalline devices were found to perform closely in line with predictions.