>> “Experimental implementation of a hybrid nonlinear control design for magnetostrictive actuators” appeared in ASME Journal of Dynamic Systems, Measurement, and Control

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A hybrid nonlinear optimal control design is experimentally implemented on a magnetostrictive Terfenol-D actuator to illustrate enhanced tracking control at relatively high speed. The control design employs a homogenized energy model to quantify rate-dependent nonlinear and hysteretic ferromagnetic switching behavior. The homogenized energy model is incorporated into a finite-dimensional nonlinear optimal control design to directly compensate for the nonlinear and hysteretic magnetostrictive constitutive behavior of the Terfenol-D actuator. Additionally, robustness to operating uncertainties is addressed by incorporating proportional-integral (PI) perturbation feedback around the optimal open loop response. Experimental results illustrate significant improvements in tracking control in comparison to PI control. Accurate displacement tracking is achieved for sinusoidal reference displacements at frequencies up to 1 kHz using the hybrid nonlinear control design, whereas tracking errors become significant for the PI controller for frequencies equal to or greater than 500 Hz.

 

W.S. Oates, P.G. EVANS, R.C. Smith, and M.J. Dapino, “Experimental implementation of a hybrid nonlinear control design for magnetostrictive actuators,” ASME Journal of Dynamic Systems, Measurement, and Control, Vol. 131, Issue 4, 041004, July 2009.

>> “Microphone based on Polyvinylidene Fluoride (PVDF) micro-pillars and patterned electrodes” appeared in Sensors and Actuators A: Physical

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This article is focused on the development of an acoustic pressure sensor with extremely high sensitivity and small footprint. We propose a sensor design consisting of micron-sized Polyvinylidene Fluoride (PVDF) pillars which generate a charge when subjected to normal stresses associated with acoustic waves. A rigid membrane placed between the micro-pillars and the acoustic medium ensures high mechanical coupling. The electrode covering the micro-pillars is patterned to decrease the capacitance, and hence increase the sensitivity of the sensor. The key sensor parameters (diameter and height of the micro-pillars, gap between pillar edges, and number of pillars) are determined through a constrained optimization algorithm in which the penalty function is the sensor footprint. The algorithm incorporates the effects of mechanical and electrical properties of the sensor and conditioning amplifier. Details of the fabrication process are described. Nano-indentation tests demonstrate that the PVDF micro-pillar sensor exhibits piezoelectric responses under an applied voltage or strain, thus demonstrating the sensor concept.

 

J. XU, M.J. Dapino, D. Gallego, D. Hansford, “Microphone based on Polyvinylidene Fluoride (PVDF) micro-pillars and patterned electrodes,” Sensors and Actuators A: Physical, Vol. 153, Issue 1, pp. 24-32, 25 June 2009.