Blake Marshall defended his PhD dissertation entitled, “STAGGERED PATTERN ENERGY HARVESTING AND RETRO-DIRECTIVE BACKSCATTER FOR PASSIVE RFID TAGS” on Thursday, 12 December 2017. This work invented a new class of antenna structures that exhibit retrodirectivity and optimal energy harvesting parameters. Such structures are crucial to building next-generation internet-of-things nodes, which can harvest energy and backscatter information with extraordinarily low power. Blake was a graduate of the Rose-Hulman Institute of Technology and received his MS and PhD with the GTPG. For the last several years, Blake has worked at Apple Computer in the bay area. Somehow, he found time to finish his PhD and have his first child.
This work introduces an optimal backscatter and energy harvesting solution for radio frequency identification (RFID) by using N antennas with N ports called a staggered patterned and retro-directive (SPAR) tag. By using the same physical area as a lower frequency single antenna tag, SPAR tags improve both the power-up and backscatter range of passive RFID tags without dramatically impacting coverage. By using multiple ports on the SPAR tag, the structure is able to create multiple radiation patterns. This is demonstrated by using a two-element patch antenna array fed by a unitary scattering matrix (implemented as a 90˚ hybrid) on a 5.8 GHz RFID tag. In addition to canonical designs, new SPAR structures are hypothesized with optimized size, bandwidth, etc. A co-simulator is developed capable of searching a vast space of possible feed networks with N-by-N ports that meet the requirements of a unitary scattering matrix. A new structure that meets the 2-by-2 SPAR scattering matrix requirements is presented to demonstrate the capabilities of the software. The software can also be generalized to discover new physical structures of larger N−by−N SPAR tags or other microwave devices such as circulators, power splitters, etc.