Electrical Resistivity Sensing Methods and Implications

This chapter discusses and explains the basic operating principles of various measuring methods of resistivity for materials in both liquid and solid phase. It provides explanations for two-, three-, and four-pole as well as toroidal resistivity cells. The van der Pauw technique is explored as a step-by-step procedure to estimate the resistivity of a material with no arbitrary shape. The special case of sheet material resistivity and resistance is explained in more detail, and equation for that special problem is simplified. It further provides information on common experimental errors and a short guideline to improve the reliability and accuracy of the measurements. The implications and challenges faced during resistivity measurements are explored and explained with ways to compensate for errors due to temperature and capacitance changes. In addition, the way to experimentally determine the cell constant of a cell is described and the necessity for calibration is clearly explained. It further provides information to overcome the standard problem of polarisation when the resistivity of solutions with high ionic content is investigated

A rainfall loading response recorded at 300 meters depth: implications for geological weighing lysimeters

Static pore water pressures in confined aquifers vary in response to ground surface loading changes, including precipitation and evaporation. Under certain hydrogeological conditions such aquifers can function as giant natural weighing lysimeters, referenced here as ‘geological weighing lysimeters’. The extent of the land area ‘weighed’ increases with aquifer depth and it is of interest to establish at what depth it is still possible to monitor surface water budgets. An 86 mm rainfall event produced a clear loading signal in a well in western Kansas at 300 m depth. The loading effect is quantitatively consistent with elastic deformation induced by the rainfall mass and suggests that geological weighing lysimeters could operate at considerably greater depths, thereby monitoring water budgets over a significant land area

A novel thick-film electrical conductivity sensor suitable for liquid and soil conductivity measurements

Results are reported from an initial evaluation of a novel conductivity sensor that could be incorporated onto a multi-element thick film (screen printed) sensor array designed for soil and water analysis. The new sensor exhibits a repeatable cell constant over a wide range of conductivities and is currently performing very well in an investigation of soil structural properties where its output is being correlated with soil water content in a study of different soil porosities.<br/

A novel thick-film screen printed electrical conductivity sensor for measurement of liquid and soil conductivity

Results are reported from an initial evaluation of a novel conductivity sensor that has been incorporated onto a multi-element thick film sensor array designed for soil and water analysis. The new sensor exhibits a more repeatable cell constant of approximately 0.15 cm-1 over a wider range of conductivities compared with conductivity sensor designs previously employed in the sensor array. The new sensor is currently performing very well in an investigation of soil structural properties where its output is being correlated with soil water content in a study of different soil porosities

Solution-processed, low voltage tantalum-based memristive switches

In this letter, preliminary results showing the memristive behavior of tantalum/tantalum oxide/platinum devices on glass substrates are reported. The ultra-thin (d &lt; 10 nm) tantalum oxide films were obtained using solution-based anodic oxidation (anodization) of Ta in citric acid. The devices were tested using standard ReRAM characterization tests from ±0.5 V to ±5 V and showed a promising memristive behavior. The memristive switches show an almost 80-times change in resistance between the ON and OFF states

Treated Wastewater and Nitrate Transport Beneath Irrigated Fields near Dodge City, Kansas

Use of secondary-treated municipal wastewater for crop irrigation south of Dodge City, Kansas, where the soils are mainly of silty clay loam texture, has raised a concern that it has resulted in high nitrate-nitrogen concentrations (10-50 mg/kg) in the soil and deeper vadose zone, and also in the underlying deep (20-45 m) ground water. The goal of this field-monitoring project was to assess how and under what circumstances nitrogen (N) nutrients under cultivated corn that is irrigated with this treated wastewater can reach the deep ground water of the underlying High Plains aquifer, and what can realistically be done to minimize this problem. We collected 15.2-m-deep cores for physical and chemical properties characterization; installed neutron moisture-probe access tubes and suction lysimeters for periodic measurements; sampled area monitoring, irrigation, and domestic wells; performed dye-tracer experiments to examine soil preferential-flow processes through macropores; and obtained climatic, crop, irrigation, and N-application rate records. These data and additional information were used in the comprehensive Root Zone Water Quality Model (RZWQM2) to identify key parameters and processes that influence N losses in the study area. We demonstrated that nitrate-N transport processes result in significant accumulations of N in the thick vadose zone. We also showed that nitrate-N in the underlying ground water is increasing with time and that the source of the nitrate is from the wastewater applications. RZWQM2 simulations indicated that macropore flow is generated particularly during heavy rainfall events, but during our 2005-06 simulations the total macropore flow was only about 3% of precipitation for one of two investigated sites, whereas it was more than 13% for the other site. Our calibrated model for the two wastewater-irrigated study sites indicated that reducing current levels of corn N fertilization by half or more to the level of 170 kg/ha substantially increases N-use efficiency and achieves near-maximum crop yield. Combining such measures with a crop rotation that includes alfalfa should further reduce the amounts of residual N in the soil, as indicated in one of the study sites that had alfalfa in past crop rotations

Engine oil acidity detection using solid state ion selective electrodes

Initial results from oil acidity measurements using thick film electrodes are presented. The results suggest that as the oil degrades, its pH/acidity follows a specific trend. Furthermore, an investigation into the feasibility of detecting changes in oil acidity (i.e. TAN value) using ion selective electrodes fabricated utilising thick film technology is presented. The thick-film (screen printing) technique is a decent means for the mass production of rugged, compact and disposable sensors as many such devices can be printed at the same time making them very cost effective to manufacture. Thick-Film ion selective and reference electrodes were fabricated, calibrated and tested in different oil samples varying its acidity. Ruthenium oxide (RuO2) pH sensitive electrodes were screen printed and were used against silver/silver chloride (Ag/AgCl) reference electrodes as well as a commercial glass Ag/AgCl reference electrode. The potentiometric sets of electrodes were calibrated in pH 4, 7 and 10 buffers in a cyclic manner and the voltage was recorded using a high input impedance voltmete

Seasonal groundwater contribution to crop-water use assessed with lysimeter observations and model simulations

Groundwater evaporation can play an important role in crop-water use where the water table is shallow. Lysimeters are often used to quantify the groundwater evaporation contribution influenced by a broad range of environmental factors. However, it is difficult for such field facilities, which are operated under limited conditions within limited time, to capture the whole spectrum of capillary upflow with regard to the inter-seasonal variability of climate, especially rainfall. Therefore, in this work, the method of combining lysimeter and numerical experiments was implemented to investigate seasonal groundwater contribution to crop-water use. Groundwater evaporation experiments were conducted through a weighing lysimeter at an agricultural experiment station located within an irrigation district in the lower Yellow River Basin for two winter wheat growth seasons. A HYDRUS-1D model was first calibrated and validated with weighing lysimeter data, and then was employed to perform scenario simulations of groundwater evaporation under different depths to water table (DTW) and water input (rainfall plus irrigation) driven by long term meteorological data. The scenario simulations revealed that the seasonally averaged groundwater evaporation amount was linearly correlated to water input for different values of DPW. The linear regression could explain more than 70% of the variability. The seasonally averaged ratio of the groundwater contribution to crop-water use varied with the seasonal water input and DTW. The ratio reached as high as 75% in the case of DTW = 1.0 m and no irrigation, and as low as 3% in the case of DTW = 3.0 m and three irrigation applications. The results also revealed that the ratio of seasonal groundwater evaporation to potential evapotranspiration could be fitted to an exponential function of the DTW that may be applied to estimate seasonal groundwater evaporation. In this case study of multilayered soil profile, the depth at which groundwater may evaporate at potential rate was 0.60-0.65 m, and the extinction depth of groundwater evaporation was approximately 3.8 m. (C) 2010 Elsevier B.V. All rights reserved

Electrical Modelling of In-Vivo Impedance Spectroscopy of Nicotiana tabacum Plants

Electrical impedance spectroscopy has been suggested as a sensing method for plants. Here, a theoretical approach for electrical conduction via the plant stem is presented and validated, linking its living electrical characteristics to its internal structure. An electrical model for the alternating current conduction and the associated impedance in a live plant stem is presented. The model accounts for biological and geometrical attributes. It uses the electrically prevalent coupled transmission line model approach for a simplified description of the complicated vessel structure. It considers the electrode coupling to the plant stem (either Galvanic or Faradic), and accounts for the different interactions of the setup. Then the model is simplified using the lumped element approach. The model is then validated using a four-point probe impedance spectroscopy method, where the probes are galvanically coupled to the stem of Nicotiana tabacum plants. The electrical impedance data was collected continuously and the results exhibit an excellent fitting to the theoretical model, with a fitting error of less than 1.5% for data collected on various days and plants. A parametric evaluation of the fitting corresponds to the proposed physically based model, therefore providing a baseline for future plant sensor design