Date of Degree
PhD (Doctor of Philosophy)
Electrical and Computer Engineering
One can use unlicensed and often very inexpensive radios for unconventional communication (underwater- and underground) links. However, one can go further, and use these radios as sensors rather than communication links. Such communication links and sensors can have important application in hydroscience. While the attenuation of RF signals is high in these mediums, by using the wireless sensor network (WSN) paradigm of multi-hop and retransmission, reliable networks can be formed underwater and underground. One no longer needs to think of RF modules as only a source of data transmission. This revelation lends itself to thinking of these modules as inexpensive RF wave generators at prescribed unlicensed frequencies. Analyzing the received signal strength indicator (RSSI) of a link over time, one can infer changes in the medium from the changes in RSSI. In this thesis, I develop a simple mathematical model to relate changes in RSSI to changes in the medium. Additionally, five experimentally validated examples demonstrate the possibility of non-traditional uses for RF modules. Demonstrated sensor possibilities include soil moisture estimation, leaf wetness measurement, and vegetation water content estimation. This thesis served to validate the use of inexpensive unlicensed RF modules as more than just communication links through air, but as links in unconventional media, and more importantly as measurement instruments.
Copyright 2010 James J. Niemeier