Measuring soil temperature and moisture using wireless MEMS sensors

Soil moisture and temperature are important variables in controlling the exchange of water and heat energy between the land surface and the atmosphere through evaporation and plant transportation. As a result, soil temperature and moisture play a significant role in the development of weather patterns and the production of precipitation and irrigation. Current techniques for detecting soil moisture and temperature such as gamma attenuation, soil heat flux, and GPR are mostly surface measurements and these surface measurements cannot provide profound temperature and moisture profile. In addition the noisy environment can significantly alter their results thus requiring a complex and expensive signal processing. The objective of this paper is to study the feasibility of using inexpensive wireless nanotechnology based devices for the field measurement of soil temperature and moisture. The developed temperature and moisture MEMS sensors are composed of micromachined MEMS cantilever beams equipped with a water sensitive nano-polymer and an on-chip piezoresistive temperature sensor. The sensor is based on a shear stress principal, which the microsensor chip combines a proprietary polymer sensing element and Wheat stone Bridge piezoresistor circuit to deliver two DC output voltages that are linearly proportional to moisture and temperature. Preliminary results obtained from embedded wireless MEMS for soil temperature and moisture measurements are presented in this paper. (C) 2007 Elsevier Ltd. All rights reserved.