2014 IR&D Annual Report

Development of a Wireless Power Transfer Technique for Quick-Charging Inaccessible Electronic Devices, 14-R8363

Principal Investigators
Monica Rivera Garcia
Richard D. Garcia
Joseph N. Mitchell
Grahm C. Roach
Jeffrey L. Boehme

Inclusive Dates: 01/01/13 – 07/01/14

Background — Many system- or mission-critical electronic devices are located off the electrical grid and, as a result, on-board energy storage units in the form of batteries are typically used to supply power to the devices. Due to finite energy storage limits, the energy storage units within these devices must be periodically replaced or replenished. Although the completion of this task is relatively straightforward for devices that are easily accessible, difficulties arise when the devices are located in areas that are inaccessible due to work force limitations, inhospitable terrain, adverse weather, hazardous environmental conditions, mission constraints, or the presence of hostile adversaries. While energy-harvesting systems are often incorporated into off-grid system-critical devices, the magnitude and consistency of the energy generated by these systems are still a concern. The primary objective of this research effort was to develop a wireless power transfer technique capable of quick-charging electronic devices located at inaccessible locations. To accomplish this goal, we developed a portable wireless power transfer technique, determined the appropriate design parameters to minimize charge time while maximizing power transfer efficiency, demonstrated the feasibility of quick-charging electronic devices from a mobile delivery platform, and generated credible data about the wireless transfer process and overall system performance.

Figure 1. Photos obtained during wireless power transfer flight tests.
Figure 1. Photos obtained during wireless power transfer flight tests: (a) this photo demonstrates payload functionality. The laser spot is clearly identifiable on the floor mats; (b) this photo demonstrates alignment capability. While the laser spot is visible, the properties and orientation of the photovoltaic (PV) panel make the spot less discernable in the video.

Approach — In this project, power was transferred wirelessly to an inaccessible electronic device via a narrow-band light source. The wireless power transfer process is unique from existing light-based wireless power transfer systems in that it can supply power to electronic devices in a recurrent, non-continuous fashion, store the delivered energy quickly in supercapacitors for abbreviated charge durations, and enable power transfer beyond the operator’s line-of-sight via the use of an unmanned aerial system (UAS).

Accomplishments — During the project, the team successfully transferred power via a laser-based system over a separation distance of one meter. In an effort to expedite the charging process, the team also designed and constructed a multi-phase supercapacitor charging circuit and investigated the parameters that influenced overall charge time. To facilitate power transfer beyond the operator’s line-of-sight, the research team designed and constructed a wireless power transfer payload compatible with a small commercial off-the-shelf UAS. The UAS and gimbaled payload were modified to increase the hovering and pointing stability of the platform and payload during autonomous flight modes. The program culminated with indoor flight tests of the complete wireless power transfer system.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.