Research & development - Eindhoven | More than two weeks ago
Conductivity is one of the most often determined fluid parameters and is a measure for the total amount of dissolved ions. To determine conductivity, the resistance of a fluid sample located in the area between at least two electrodes is determined by impedance spectroscopy. The conductivity is then given by multiplying the measured conductance with, the so-called cell constant of the sensor (Kcell).
The conductivity range that can be determined with a sensor depends on the chosen Kcell. This implies that a correct conductivity sensor must be chosen, fitting with the expected concentration range in the targeted application.
Commercially available conductivity sensors utilize two parallel planar electrodes (with a certain area and distance that define the Kcell). Such a geometry is difficult to miniaturize. However, Timmer et al  describe how planar interdigitated 2-electrode sensors on chip can be designed and how the Kcell value can be derived. A disadvantage of the 2-electrode conductivity sensor is the large electrode-electrolyte interface resistance which limits its application for a wide range of conductivity solutions.
To minimize this, a 4-electrode sensor can be used, in which one pair of electrodes are injecting the current, while the other pair are sensing the voltage. We have extended this concept to microfabricated 4-electrodes conductivity sensor . These geometries are tested and the Kcell must be determined analytically. For optimizing the sensor design, new designs and sensors must be made and tested, this process needs to be repeated several times to achieve the desired Kcell. Designing in such way is a time consuming and expensive process. Therefore, a theoretical and/or a simulation model is desired which can determine the Kcell of a 4-electrode conductivity sensor.
The student will develop and verify a new model that predicts the Kcell of a 4-electrode conductivity sensor.
 B. Timmer, W.
Sparreboom, W. Olthuis, P. Bergveld and A. van den Berg, “Optimization of an
electrolyte conductivity detector for measuring low ion concentrations,” Lab
Chip, vol. 2, pp 121-124, 2002
 Brom-Verheijden, Greja JAM, Martijn H. Goedbloed, and Marcel AG Zevenbergen. "A Microfabricated 4-Electrode Conductivity Sensor with Enhanced Range." Multidisciplinary Digital Publishing Institute Proceedings. Vol. 2. No. 13. 2018.
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