Determination of the humidity of soil by monitoring the conductivity with indium tin oxide glass electrodes

Abstract

A number of approaches to the determination of water content of soil use a dielectric permittivity measurement, which is accurate but involves expensive and complex devices. We explore the use of indium tin oxide, a wide-band gap semiconductor with high conductivity, long-term stability, and low cost, to build a cheap sensor of low humidity values for automatic irrigation systems. The electrical resistance determined by an ac impedance method discounts the effects of electrode contacts and provides a reliable measure of the water content, even when the chemical conditions of water vary widely. The reason for this is that, at low values of humidity, the conductivity is controlled by a surface conduction mechanism that is largely insensitive to the electrolytic properties of added water. The results appear promising for applications that require the detection of very low levels of humidity in soil.

An endothelial cell compatible biosensor fabricated using optically thin indium tin oxide silicon nitride electrodes

“…The combined electrical conductivity and optical transparency of indium tin oxide (ITO) makes it an attractive alternative to gold as a microimpedance biosensor (Ray et al, 1983;Bucher et al, 2001a,b;Fabregat-Santiago et al, 2002;Jun et al, 2005;Penza et al, 1999;Gritsch et al, 1998;Hillebrandt et al, 1999). Indium-tin-oxide is stable in electrolyte solutions, and the transparent properties of this electrode allow for the simultaneous optical investigation using phase contrast, interference reflection and fluorescence microscopy.…”

Strontium-Doped Hematite as a Possible Humidity Sensing Material for Soil Water Content Determination

“…Therefore, the devices used for measuring the atmospheric moisture have been also proposed for soil water content determination. These sensors are based on electrical resistance measurements of porous materials such as polymers and ceramics [6,7]. Ultrasonic waves have been also envisaged for this aim [8].…”

Development of ZrO₂-TiO₂ Porous Ceramic as Soil Humidity Sensor for Application in Environmental Monitoring

“…Both direct and indirect methods however, are very difficult to automatize due to their detection principles, which get difficult the fast environmental monitoring of the risk-areas in situ [11][12]. The selection of ZrO 2 -TiO 2 porous ceramic was adopted in order to assure the satisfactory operation of the soil humidity sensor, which includes good sensitivity, linearity over the range of application, fast response, low hysteresis and stability to the aggressiveness of impurities present in the environment, leading to a long useful life of the sensor ceramic material [3][4][5][6]. This is a matter of great originality in world-wide terms, mainly concerning to the influence of the pores form and pores size distribution on the capacity of chemical and physical interactions of water molecules with the surface of the sensor material.…”

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Due to the necessity of the automation and control of processes in agriculture, as well as to the crescent interest for the environmental monitoring, efforts have been demanded in the development of more versatile, reliable sensors and sensor systems with smaller cost [1][2]. In this sense, the search of new materials, the modeling study of sensor and the development of new measurement techniques and processing of signs have been orientating the progress in this area [3][4]. In this work, the results of the characterization analyses of sensor elements of ZrO 2 -TiO 2 porous ceramic for application as soil humidity sensor, are shown and discussed.

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