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PotD: The Tunnel Diode that Started it All

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This Problem of the Day (PotD) post comes from a historically significant ECE test, from an RFID class that Manos Tentzeris and I developed 10 years ago.  The question asks how a biased tunnel diode increases reflected power and range from a backscatter antenna.  This idea of using an active, negative-resistance region device for backscatter has popped up in the patent literature from time to time, but Georgia Tech PhD  Francesco Amato performed some of the first microwave backscatter measurements with his custom-built Quantum Tunnel Modulator (QTM) tag.  This illustrated the feasibility of the idea, published in 2015.  The use of a tunnel diode modulator for backscatter has been investigated by researchers in UI Chicago, Sweden, and more Sweden.

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Cheng Qi Wins Best Student Paper at IEEE RFID-TA 2018

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Congratulations to Cheng Qi for his paper, “Low-power and Compact Microwave RFID Reader for Sensing Applications in Space”, which has been awarded the best student paper at the IEEE RFID-TA 2018 conference in Macau, SER China.  This work documents Cheng’s work on the RFsat mission with Northwest Nazarene University, which is taking a custom-built GTPG microwave backscatter reader and energy-harvesting tag into space as part of a novel science package.  His co-authors are Prof. Josh Griffin (GTPG alum) and Prof. Durgin.  Well done, Cheng!

Marshall’s PhD Dissertation on Energy-Harvesting Arrays Now on SmartTech

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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 multiple ports and a unitary scattering matrix on the SPAR tag, the structure is able to create multiple orthogonal radiation patterns to improve range of passive RFID tags. This is demonstrated on a 5.8 GHz RFID tag using a two-element patch antenna array fed by a 90˚ hybrid. 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.

PhD: Staggered Pattern Energy Harvesting and Retro-directive Backscatter Communications for Passive RFID Tags and Sensors

Varner’s IEEE SPAWC 2018 Paper on Perfect Pulse Ambient Modulation

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Michael Varner’s publication at IEEE SPAWC 2018 is now available for download in IEEExplore.  Entitled “Reflection of Modulated Radio (ReMoRa): Link Analysis of Ambient Scatter Radio Using Perfect Pulses“, the work explores the spectral properties for perfect pulse modulation of ambient backscatter. The impact on this modulation scheme and the link budget is explored. The ideas in this paper will allow long-range communications by embedding information on existing RF sources and reflecting them to collection nodes. There are numerous applications in machine-to-machine, internet-of-things, and sensor networks.