Towards Chip-Based Salinity Measurements for Small Submersibles and Biologgers

Abstract

Water’s salinity plays an important role in the environment. It can be determined by measuring conductivity, temperature, and depth (CTD). The corresponding sensor systems are commonly large and cumbersome. Here, a 7.5 × 3.5 mm chip, containing microstructured CTD sensor elements, has been developed. On this, 1.5 mm2 gold finger electrodes are used to measure the impedance, and thereby the conductivity of water, in the MHz frequency range. Operation at these frequencies resulted in higher sensitivities than those at sub-MHz frequencies. Up to 14 kΩ per parts per thousand salt concentration was obtained repeatedly for freshwater concentrations. This was three orders of magnitude higher than that obtained for concentrations in and above the brackish range. A platinum electrode is used to determine a set ambient temperature with an accuracy of 0.005°C. Membranes with Nichrome strain gauges responded to a pressure change of 1 bar with a change in resistance of up to 0.21 Ω. A linear fit to data over 7 bars gave a sensitivity of 0.1185 Ω/bar with an R2 of 0.9964. This indicates that the described device can be used in size-limited applications, like miniaturized submersibles, or as a bio-logger on marine animals.

Spectroscopic Determination of Water Salinity in Brackish Surface Water in Nandoni Dam, at Vhembe District, Limpopo Province, South Africa

“…This is attributable to the low dilution effect of the total dissolved salts, which are presently deposited into the dam during the dry seasons. The salinity values seem to suggest that the water in the bulk of the Nandoni Dam was brackish [32,33]. A few exceptions were however noted; the water at the dam outlet and the treatment plant (the plant that sources the water from Nandoni Dam for treatment prior to distribution) indicate that this water falls within the freshwater category (i.e., salinity < 500 mg/L), although the water taste is unsatisfactory when drinking.…”

Graphite-Polyimide Sensor

“…The research work done (Bhat 2005;Gadani et al 2012;Huber et al 2000;Jonsson et al 2013;Le Vine et al 2010;Men et al 2008;Rahman et al 2011;Reul et al 2014;Scudiero et al 2012) based on the monitoring and evaluation of salinity involves certain demerits that deters them to be used on an industrial scale. Some sensors like that optical ones are used to measure the salinity (Huber et al 2000) for a concentration from 200 mM to 2M.…”

“…Thus, it is state of the art to fabricate a lowcost, efficient sensing system that can be used to determine the changes in the salinity level to apply immediate remedial measures. Some of the other impedance measurement systems that have been proposed earlier (Jonsson et al 2013) have certain demerits like low sensitivity and a complicated embedded system that need time and expertise to be operated. The sensors that are being developed with MEMS technology have a high fabrication cost.…”

Spectroscopic Determination of Water Salinity in Brackish Surface Water in Nandoni Dam, at Vhembe District, Limpopo Province, South Africa <strong>&nbsp;</strong><strong> </strong>

“…This is attributable to the low dilution effect of the total dissolved salts, which are presently deposited into the dam during the dry seasons. The salinity values seem to suggest that the water in the bulk of the Nandoni Dam was brackish [31,32]. A few exceptions were however noted; the water at the dam outlet and the treatment plant (the plant that sources the water from Nandoni dam for treatment prior to distribution) indicate that this water falls within the freshwater category (i.e.…”