Traveling-Wave Induced Aerodynamic Propulsive Force using Active Control of the Dynamic Shape of Piezoelectrically-Deformed Plastic Substrates
Speaker: Noah T. Jafferis, Princeton University
Date: Monday, June 4 2012
Time: 1:30PM to 2:30PM
Location: 32-397
Host: Daniela Rus, MIT
Contact: Mieke Moran, 617-253-5817, mieke@csail.mit.edu
Relevant URL: Abstract:
We recently demonstrated the use of integrated piezoelectric actuators and sensors to produce traveling transverse waves in a thin plastic substrate in air above a flat surface, which created an aerodynamic propulsive force acting on the sheet. Experiments showed that the dependence of the propulsive force on the height above the ground and the amplitude of the traveling wave qualitatively confirm previous theoretical predictions.
In this talk, we discuss the fundamental and experimental conditions for realizing such a demonstration. We first present the theory motivating our work, and use it to determine the range of experimental conditions most likely to produce a forward propulsive force. We then present a detailed description of the experimental approach to produce the traveling waves and demonstrate propulsion, including integrated piezoelectric actuators and sensors to provide feedback control, artifact elimination, and power considerations.
Two sheets of PolyVinyliDene Fluoride (10cm x 4cm x 28μm) are glued together, and the metal coating on each sheet is patterned to form four actuators and four sensors. The sensors measure the actual time-varying shape of the sheet, allowing the actuator control signals to be adjusted to produce a traveling wave. The sensors are close to the actuators, so care must be taken to minimize capacitive pickup, and ensure that any remaining artifact is removed. Linear control matrices and feedback were used to correct for nonlinearities and cancel out undesired higher frequency modes. The propulsive force can be determined from the equilibrium displacement of the sheet, which is suspended either from elastic threads or above an “air-table”. With this approach, traveling waves have been produced with amplitudes up to ~500μm, and at 100Hz, measured propulsive forces exceed 100μN when the sheet is suspended ~1mm above the ground.
Theory also predicts that such forces should be able to accelerate a freely moving sheet up to a velocity of ~10cm/s (currently, the sheet is not free, so the observed velocity is ~1cm/s), sufficient for it to produce its own lift, resulting in the so-called “flying carpet” effect. To achieve this, work is ongoing to free the sheet from its tethers by providing on-board power or by having a cart follow it.
In summary, we have successfully produced controllable traveling waves in a thin sheet of material, and measured the aerodynamic propulsive force created by these waves, thus confirming the physical basis for a “flying” carpet near a horizontal surface. This work also demonstrates the advantages of using integrated sensors to control the dynamic shape of thin plastic sheets deformed by piezoelectric elements.
Bio:
Noah Jafferis is currently a PhD candidate in the Electrical Engineering Department at Princeton University, and will be finishing by the end of the summer. He was home-schooled before matriculating at Yale University at the age of 16, where he received his B.S. in Electrical Engineering in 2005.
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