## Graduate College Dissertations and Theses

2020

Thesis

#### Degree Name

Master of Science (MS)

#### Department

Electrical Engineering

Jeff Frolik

#### Abstract

Passive wireless sensors provide an opportunity for long term monitoring of remote environments. Since these devices are not battery powered, they can be deployed for an indefinite amount of time. Such devices are energized by an interrogation signal that enables them to transmit information via a return signal. Some systems (e.g., RFID) utilize the same frequency for interrogation and the return, which causes unwanted interference, particularly in cluttered environments. This work considers an interrogation system for a different class of passive devices, i.e., passive harmonic transponders. Specifically, results are presented for a single-board software defined radio (SDR) interrogation system which transmits an interrogation signal at 1.3 GHz and receives a return at 2.6 GHz. The system is demonstrated with a passive, chip-less device known as a frequency doubling reflectenna (FDR). The SDR platform enables a compact, low-cost, and quickly operating design. The mean absolute error of the proposed interrogator was found to be 1.15 dB when compared with laboratory-grade instrumentation. Additionally, this system is capable of interrogating up to a distance of 70 cm with an EIRP of only 0 dBm.

This thesis presents an SDR system made with the open-source software package, GNURadio, capable of interrogating harmonic transponders with a single, full-duplex board. All signal processing is conducted on a laptop computer, eliminating the need for expensive laboratory instrumentation. The size of the system interrogator was also minimized, reducing the form factor of the whole interrogator to be only 25 $\times$ 15 cm. Furthermore, a new harmonic transponder was designed using transmission line matching methods, eliminating the need for discrete matching components. This harmonic transponder has a conversion loss of 31.04 dB at an input power of -28.21 dBm as demonstrated with the SDR interrogator.

en

82 p.

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