Proposal Of A Novel Heat Dissipation Soil Moisture Sensor

A novel heat dissipation soil moisture sensor with only one bipolar transistor performing as both heating and temperature sensing element is presented. Due to the fact that the power dissipated in the transistor is a function of both the voltage and the current in the transistor, it is possible to obtain the required levels of heating power with low currents, increasing the battery life of the sensor's interrogator. Experimental results measured in a fabricated sensor show that in soils with high moisture levels the proposed sensor presents a sensitivity that is almost 10 times higher than those found in conventional sensors with separated heating and sensing elements. Since the transistor is used as both the heating and sensing elements, for the same applied energy (80 mW during 45 s) the temperature increase in the proposed sensor is about 7:5?C, while the conventional porous block probe presents a temperature increase of only 0:8°.124127Mori, Y., Hopmans, J.W., Mortensen, A.P., Kluitenberg, G.J., Multifunctional heat pulse probe for simultaneous measurement of soil water content, solute concentration, and heat transport parameters (2003) Vadoz.E Zone Journal, 2, pp. 561-571Bremer, D.J., Ham, J.M., (2003) Soil Moisture Sensors Can Help Regulate Irrigation, pp. 49-54. , Golfdom-JuneTan, K.H., Soil sampling preparation, and analysis (1996) Marcel Dekker, Inc, , New York, USAOuld Mohamed, S.P., Bertuzzi, S.P., Raison, L., Bruckler, L., Field evaluation and error analysis of soil water content measurement using the capacitance probe method (1997) Soil Sci. Am. J, 61, pp. 399-408Valente, A., Morais, R., Tulib, A., Hopmansb, J.W., Kluitenberg, G.J., Multi-functional probe for small-scale simultaneous measurements of soil thermal properties, water content, and electrical conductivity (2006) Sensors and Actuators A, 132, pp. 70-77Topp, C.G., Davis, J.L., Annan, A.P., Annan, Electromagnetic determination of soil water content using TDR: Measurements in coaxial transmission lines (1980) Water Resour. Res, 16, pp. 574-582Phene, C.J., Hoffman, G.J., Rawlins, S.L., Measuring soil matric potential in situ by sensing heat dissipation within a porous body: I. Theory and sensor construction (1971) Soil Sci. Soc. Am Proc, 35, pp. 27-33Flint, A.L., Campbell, G.S., Ellett, K.M., Calissendorff, C., Calibration and temperature correction of heat dissipation matric potential sensors (2002) Soil Sci. Soc. Am. J, 66, pp. 1439-1445Ham, J.M., Benson, E.J., On the construction and calibration of dual-probe heat capacity sensors (2004) Soil Sci. Soc. Am. J, 68, pp. 1185-1190(2006) Heat Dissipation Matric Water Potential Sensor Instruction Manual, 229. , Campbell Scientific, IncModel 220 current source manual model 230 voltage source manual (2001) Model 177 Microvolt DMM Manual, , Keithley Instruments Inc. USAMeijer, G.C.M., Vingerling, K., Measurement of the temperature dependence of the IC(VJ characteristic of integrated bipolar transistors (1980) IEEE J. Solid-State Circ SC, 15, pp. 237-24