Designed by Greg Koo and Albert Lu, this microwave modulator demonstrated retrodirective backscatter with 4-ary Phase Shift Keying (PSK).

This would be the first of many low-powered, retrodirective designs that the group would develop.  Powered by a TI MSP 430 micro-controller, the device consisted of a dynamically switched Van Atta array in which 4 different phase lengths could be inserted into the electrical pathways.  The result was a QPSK backscatter signal with large retrodirective gains.

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2009: Development of the 5.8 GHz backscatter radio for high-voltage lines.  This was the first big technology transfer of our microwave backscatter radio work outside of the institute.  Southern states integrated this radio into their substation protection equipment and deployed these systems across 25 locations in North America.

Fun fact 1: During measurements, the group stumbled upon some unique and unexpected behavior of the high-voltage radio channel regarding radios operating in the presence of corona plasma.  The initial results were published, leading to a whole new tributary of channel modeling investigation.  Some of the most definitive characterization of this work lies in Marcin Morys’ dissertation, WIRELESS COMMUNICATION IMPACT OF HIGH-VOLTAGE CORONA FORMATION ON AN ANTENNA.

Fun fact 2:  This radio was based on the original prototype built by Josh Griffin for his PhD work, but had a massive group effort to improve the hardware.  Contributors included Patrick Graf, Greg Koo, Raj Bhattacharjea, Albert Lu, Chris Valenta, Ryan Pirkl, and Matt Trotter.

Here is another installment in the “Wireless Without Batteries Lecture” series. In this lecture, we cover the use of reflection amplifier and its applications in backscatter communications links.

WWB14:  Reflection Amplification
Reading:  F. Amato, C.W. Peterson, B.P. Degnan, M.B. Akbar, G.D. Durgin. “Long Range and Low-Powered RFID tags with Tunnel Diode”. IEEE RFID-TA 2015. Tokyo, Japan. 16-18 September 2015.

 

In this lecture, we discuss the origins of retrodirectivity, starting with the Van Atta array and its use as radar chaff.  We then demonstrate how to use these systems in communications links.  Part of the Shenzhen lecture series on wireless without batteries.

WWB13: Retrodirectivity
Paper:  C.R. Valenta, B. Marshall, M.S. Trotter, G.A. Koo, G.D. Durgin “Staggered Pattern Charge Collection and Retrodirective Active Phase Modulation: Two New Passive Sensing Technologies.” IEEE RFID Conference, Orlando, FL. April 2012.