New Soil Water Tension Sensors: The Dihedral and Igstat Sensor.

Two new sensor concepts have been introduced for measuring soil water tension with a good potential for sensor technology development, named as dihedral (patent: PCT/BR2011/000001) and IGstat sensor (patent: PCT/BR2014/000128). The IGstat sensor is composed of non-sintered particles, with well-known size-distribution that retains or release water as the soil wets or dries. During the drying process, for instance, air permeates the medium and different systems can be used to detect changes in the hydraulic, optical or electrical properties of the medium. In this work we develop and test simple and low-cost IGstat sensors, using an optical transducer operating at the reflection mode. In the dihedral sensor two rectangular hydrophilic flat glass plates and/or fine porous flat plates are fixed in angle, defining the dihedral angle. The system is fixed in a porous element and the distance between the vertex and the water meniscus (L) formed after equilibration is proportional to the soil matric potential. Using different spacer thickness between the two flat plates allow constructing sensors for different matric potential ranges and applications. We present and discuss here the basic concepts of these two technologies and some results obtained with different manufactured devices.