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Sensors 2010, 10(6), 5845-5858; doi:10.3390/s100605847

Microfabricated Thin Film Impedance Sensor & AC Impedance Measurements

1,*  and 2
1 Purdue University Calumet, Hammond, IN 46323, USA 2 Case Western Reserve University, Cleveland, OH 44106, USA
* Author to whom correspondence should be addressed.
Received: 30 April 2010 / Revised: 26 May 2010 / Accepted: 1 June 2010 / Published: 9 June 2010
(This article belongs to the Section Physical Sensors)
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Thin film microfabrication technique was employed to fabricate a platinum based parallel-electrode structured impedance sensor. Electrochemical impedance spectroscopy (EIS) and equivalent circuit analysis of the small amplitude (±5 mV) AC impedance measurements (frequency range: 1 MHz to 0.1 Hz) at ambient temperature were carried out. Testing media include 0.001 M, 0.01 M, 0.1 M NaCl and KCl solutions, and alumina (~3 μm) and sand (~300 μm) particulate layers saturated with NaCl solutions with the thicknesses ranging from 0.6 mm to 8 mm in a testing cell, and the results were used to assess the effect of the thickness of the particulate layer on the conductivity of the testing solution. The calculated resistances were approximately around 20 MΩ, 4 MΩ, and 0.5 MΩ for 0.001 M, 0.01 M, and 0.1 M NaCl solutions, respectively. The presence of the sand particulates increased the impedance dramatically (6 times and 3 times for 0.001 M and 0.1 M NaCl solutions, respectively). A cell constant methodology was also developed to assess the measurement of the bulk conductivity of the electrolyte solution. The cell constant ranged from 1.2 to 0.8 and it decreased with the increase of the solution thickness.
Keywords: microfabrication; thin film; impedance sensor; AC impedance; Electrochemical Impedance Spectroscopy (EIS); bulk conductivity microfabrication; thin film; impedance sensor; AC impedance; Electrochemical Impedance Spectroscopy (EIS); bulk conductivity
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Yu, J.; Liu, C.-C. Microfabricated Thin Film Impedance Sensor & AC Impedance Measurements. Sensors 2010, 10, 5845-5858.

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