Geffrey K. Ottman

Damping as a result of piezoelectric energy harvesting

Abstract Systems that harvest or scavenge energy from their environments are of considerable interest for use in remote power supplies. A class of such systems exploits the motion or deformation associated with vibration, converting the mechanical energy to electrical, and storing it for later use; some of these systems use piezoelectric materials for the direct conversion of strain energy to electrical energy. The removal of mechanical energy from a vibrating structure necessarily results in damping. This research addresses the damping associated with a piezoelectric energy harvesting system that consists of a full-bridge rectifier, a filter capacitor, a switching DC–DC step-down converter, and a battery. Under conditions of harmonic forcing, the effective modal loss factor depends on: (1) the electromechanical coupling coefficient of the piezoelectric system; and (2) the ratio of the rectifier output voltage during operation to its maximum open-circuit value. When the DC–DC converter is maximizing power flow to the battery, this voltage ratio is very nearly 1/2, and the loss factor depends only on the coupling coefficient. Experiments on a base-driven piezoelectric cantilever, having a system coupling coefficient of 26%, yielded an effective loss factor for the fundamental vibration mode of 2.2%, in excellent agreement with theory.

The Pluto-New Horizons RTG and Power System Early Mission Performance

On January 19, 2006, the Pluto-New Horizons spacecraft was launched from Cape Canaveral Air Force Station (CCAFS) with a radioisotope thermoelectric generator (RTG) as the power source and a 30V power regulation and distribution system designed and built by the Johns Hopkins University Applied Physics Laboratory. Pluto-New Horizons is the flagship spacecraft of NASA’s New Frontiers program of medium-class interplanetary missions and targets the first reconnaissance of Pluto and its moon, Charon, and the Kuiper Belt. Arrival at Pluto is scheduled for July, 2015 at which time the spacecraft will have traveled 3 billion miles and be almost 32 AU from the sun. Due to the extended mission duration and extreme distance from the sun, a RTG was chosen as the spacecraft’s power source. RTG missions place complexity on the spacecraft power system design due to their unique power characteristics and limited opportunities for test prior to pre-launch field operations. The RTG integration and test with the spacecraft results are presented along with the spacecraft power system performance during launch and in the early mission phase. These in-flight operational results demonstrate a fully functioning power system that will supply the spacecraft with safe and reliable power during the exploration of the farthest reaches of the solar system.

Radiation-Induced Single-Event Effects on the Van Allen Probes Spacecraft

Electronic devices on the Van Allen Probes mission have experienced more than a thousand single-event effects (SEE) during the 4.5 years of transit through the inner and outer earth trapped radiation belts. The majority of these SEE have been due to trapped protons determined by the orbit timing and the dose rate response of the engineering radiation monitor. Fault tolerant systems engineering and spacecraft operation have enabled a successful mission to date without a safe mode or spacecraft emergency.

Structural damping as a result of piezoelectric energy harvesting

This paper describes an approach to harvesting electrical energy from a mechanically‐excited piezoelectric element. If the piezoelectric element is attached to a vibrating structure, this energy transfer also results in structural damping. The energy harvesting approach is loosely based on the fundamental electrical engineering concept of optimal loading. The harvesting circuit consists of an ac–dc rectifier with an output capacitor, an electrochemical battery, and a switch‐mode dc–dc converter that controls the energy flow into the battery. An adaptive control technique was initially used to vary the switching duty cycle so as to maximize power transfer into the battery. Experiments demonstrated that the adaptive dc–dc converter increased power transfer by over 400%, as compared to direct connection of the rectifier output to the battery. For persistent excitation above a certain level, the existence of a near‐optimum duty cycle was also observed. A standalone energy harvesting system that exploited this...