Precision agriculture is a set of practices that seek to measure and understand different conditions in space and time across a field, in order to manage water and fertilizer efficiently. Precision agriculture requires high spatial and temporal resolution data, which comes from sensors. However, lack of simple, inexpensive, unobtrusive, low- maintenance sensors that can be widely distributed across a field is a challenge for precision agriculture producers. This thesis describes work towards a network of printed, biodegradable, wireless soil nitrate sensors to meet this need. Sensor nodes consist of potentiometric nitrate sensors, passive UHF-RFID antennas, and a silicon chip to manage power and data communication. Over 95% of the mass of the node is biodegradable.

The thesis includes a discussion of each part of the sensor stake. Fabrication techniques for biodegradable substrates, conductors, and encapsulants are discussed. A room-temperature process for printing highly conductive zinc on wood using beeswax encapsulants is a key enabling process. Nitrate sensor operation and development are described, and impacts of using biodegradable materials in nitrate sensors are explored. I show the design, fabrication, and testing of compact RF antennas, and discuss modifications which are required when using biodegradable materials. The printed antennas are integrated with silicon integrated circuits to form passive RFID tags. Requirements and challenges for integrating printed potentiometric sensors with these tags are also discussed. Finally, the impacts of field-deployment are explored. This includes materials lifetime characterization, measuring nitrate sensors in field soils, and validating passive RFID communication in growing crops.




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