High Speed Model Implementation and Inversion Techniques for Ferroelectric and Ferromagnetic Transducers

Ferroelectric and ferromagnetic materials are employed as both actuators and sensors in a wide variety of applications including fluid pumps, nanopositioning stages, sonar transducers, vibration control, ultrasonic sources, and high-speed milling. They are attractive because the resulting transducers are solid-state and often very compact. However, the coupling of field to mechanical deformation, which makes these materials effective transducers, also introduces hysteresis and time-dependent behaviors that must be accommodated in device designs and models before the full potential of compounds can be realized. In this paper, we present highly efficient modeling techniques to characterize hysteresis and constitutive nonlinearities in ferroelectric and ferromagnetic compounds and model inversion techniques which permit subsequent linear control designs. 1 Ferroelectric and Ferromagnetic Transducer Materials Ferroelectric and ferromagnetic materials are increasingly considered as actuators and sensors for aerospace, aeronautic, and industrial automotive applications due to their unique transduction capabilities. Actuator capabilities are derived from the converse effect in which input fields produce deformations in the material whereas the direct effect, comprised of stress-induced fields, provides the materials with sensor capabilities. Ferroelectric materials are presently employed in microphones, accelerometers, fluid pumps, nanopositioning stages, sonar transducers, vibration sensors and actuators, ultrasonic sources, inkjet printers, and camera focusing mechanisms. Ferromagnetic transducers are typically bulkier than their ferroelectric counterparts, due to the circuitry and housing required to produce magnetic fields, but they generally provide greater input forces. They are also presently being considered for a wide variety of applications including torque sensors, high-speed milling, ultrasonic sources, sonar transduction, and vibration sensing and attenuation. Details regarding present and predicted applications can be found in [24]. However, the electromechanical and magnetomechanical coupling mechanisms that endow the compounds with unique transducer capabilities also produce hysteresis and constitutive nonlinearities that must be accommodated in designs before the multifunctional material attributes can be fully realized. For certain applications, these nonlinear effects can be minimized by restricting input field levels; however, this limits the applicability of the materials. For ferroelectric devices, hysteresis can be mitigated through the use of charge or current controlled amplifiers [11–14]. However, this is often significantly more expensive then using voltage controlled amplifiers and current control is ineffective if maintaining a DC bias as required for many positioning mechanisms. A third alternative is to linearize hysteretic devices using feedback control. Whereas effective at lower frequencies, this technique becomes less effective at higher frequencies if sampling rates are limited. Moreover, extensive linearization can limit control authority for prescribed tasks such as vibration attenuation or reference signal tracking. Email: [email protected]; Telephone: 919-854-2746 Email: [email protected]; Telephone: 919-515-7552