TECHNOLOGY AREA(S): Air Platform, Electronics

ACQUISITION PROGRAM: USMC Expeditionary Energy Office

OBJECTIVE: Develop the means to recharge battery-operated micro and small unmanned aerial systems by harvesting energy from the battlefield, eliminating the need for the systems to return to base.

DESCRIPTION: The employment of micro (�-) and small unmanned aerial systems (sUAS) is expected to dramatically increase over the next decade. These �- and sUAS are anticipated to be battery-operated and capable of short-duration missions, for example up to 25 km distance and 30 minutes of flight, with operational capabilities increasing as battery technology improves. The infrastructure to manage a future fleet of sUAS in the field under austere conditions may be daunting considering the magnitude of battery recharging needs. It is also desirable to simultaneously increase mission duration and persistence; therefore, the ability to scavenge power directly from the battlefield would be an important military technology with other dual-use civilian applications. To that end, harvesting energy that would otherwise be wasted from the environment to power �- and sUAS is an attractive option because much of the fuel that is required for batteries, supercapacitors, and fuel-cells need not be always stored on the device. The types of energy harvesting that fall into this category are broad, and include vibrational energy, simple mechanical energy, and electromagnetic energy. Sources of electromagnetic energy that is abundant and available for harvesting and conversion include high-voltage substations, transformers, and alternating current transmission line (i.e., power lines). High-voltage (500 kV) substations generate AC electric field strengths that approach 18 kV m�1, and magnetic flux densities that can approach 10�Trms, which could produce a power density >100�W cm�3, which is comparable to solar panels operating on a cloudy day. Alternatively, allowing an unmanned aerial vehicle (UAV) to �dock� on a power line in an urban environment, scavenging magnetic energy as a means to trickle-charge its onboard batteries prior to mission continuation, could provide significant tactical benefits. If the energy scavenging source is collocated at the mission area, full mission persistence might be achieved and the �- and sUAS may never need to return to base. In addition to battery recharging is the increased demand of distributed sensing and communication. The same technological examples described above can be extended to the strategic placement and powering of wireless sensor nodes on the battlefield. Further, other energy modes are ripe for harvesting in the environment of, for example, an electrical transformer, including vibrational, thermal, and acoustic energy. Piezoelectric nanogenerators are one such technology that has been shown to convert small mechanical fluctuations and vibrations into electric energy, and can generate the magnitude of power (10�100s �W) required for these wireless sensor nodes [Refs 2, 4, 5].

PHASE I: Define and develop a concept/approach to recharge a �- or sUAS in the field without having to return to base. Conduct modeling and simulation and/or calculations to justify the feasibility of this energy harvesting concept in both pass and active mode. Preliminary environmental conditions to be considered include altitude, wind speed, humidity, and weather. Describe in detail the energy harvesting system design and proposed energy output and feasible battery size and recharge time, targeting a total recharge time =12 h. Develop a Phase II plan. The Phase I Option, if exercised, could include a sub-scale, lower fidelity, laboratory demonstration.

PHASE II: Develop, demonstrate, and validate the energy harvesting concepts in a laboratory or outdoor environment. The prototype should be delivered with a down-selected dimension and associated battery size; the prototype will be paired with an appropriately sized existing �- and/or sUAS for testing. The prototype should be delivered at the end of Phase II, ready to be flown by the Government once paired with a target �- and/or sUAS.� Document final prototype design and vendor test results.

PHASE III DUAL USE APPLICATIONS: Produce full-scale prototypes consistent with Program of Record needs and private sector transition of the technology. Successful demonstration of harvesting technology extends to the commercial sector in the fields of adaptable, wireless battery recharge and wireless sensor nodes.

REFERENCES:

1. Marshall, P. T. �Power Line Sentry Charging.� U.S. Patent 7,318,564 B1 (Issued 15 Jan 2008) https://patentimages.storage.googleapis.com/79/bc/ad/0029f206b3c875/US7318564.pdf

2. Hu, Youfan and Wang, Z. L. �Recent progress in piezoelectric nanogenerators as a sustainable power source in self-powered systems and active sensors.� Nano Energy, 14, 2015, 3�14. http://www.nanoscience.gatech.edu/paper/2014/14_NE_14.pdf

3. Roundy, S., Wright, P. K., and Rabaey, J. �A study of low level vibrations as a power source for wireless sensor nodes.� Computer Communications, 26, 2003, 1131�1144. https://www.sciencedirect.com/science/article/pii/S0140366402002487

4. Green, C., Moss, K. M., and Bryant, R. G. �Scavenging Energy From Piezoelectric Materials for Wireless Sensor Applications.� Proc. Of the IMECE2005, 2005, Orlando, Florida, USA. https://www.researchgate.net/profile/Christopher_Green7/publication/236274075_Scavenging_Energy_From_Piezoelectric_Materials_for_Wireless_Sensor_Applications/links/00b7d51788434d1b4f000000/Scavenging-Energy-From-Piezoelectric-Materials-for-Wireless-Sensor-Applications.pdf?origin=publication_detail

5. Yuan, S., Huang, Y., Xu, Q., Song, C., and Thompson, P. �Magnetic Field Energy Harvesting Under Overhead Powerlines.� IEEE Transactions on Power Electronics, November 2015.

KEYWORDS: Energy Harvesting; Energy Scavenging; UAS; Unmanned Aerial Systems; Battery Recharging