Enhanced Performance of Spiral Co-planar Inter-Digital Capacitive Structures for Sensing Applications
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Enhanced Performance of Spiral Co‑planar Inter‑Digital Capacitive Structures for Sensing Applications Binu Ani Oommen1 · Jacob Philip1 Received: 25 July 2020 / Revised: 3 October 2020 / Accepted: 2 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work we consider a Spiral Inter-Digital Capacitive (SIDC) structure for its optimum design and performance analysis based on finite element simulation, for possible application as sensors. The effects of relevant geometrical parameters like sensor electrode width, inter-electrode gap, number of electrode pairs and electrode height on sensor output capacitance are evaluated and analyzed. In addition, influence of a test sample over the designed sensor for varying lift-off distances from the top of the sensor surface and for various material permittivity values are investigated. Results of the studies show that a spiral structure has about 25% higher sensitivity for its capacitance value compared to a corresponding Rectangular Inter-Digital Capacitive (RIDC) structure of comparable dimensions. The simulation results have been verified experimentally by fabricating and testing SIDC and RIDC structures for dielectric characterization of materials and proximity measurement applications. The results point to the possibility of designing and fabricating spiral interdigital capacitive sensors with higher sensitivity for a multitude of applications. Keywords Inter-digital capacitive sensor · Spiral inter-digital structures · Rectangular inter-digital structures · Finite element simulation · Proximity measurement
1 Introduction Inter-digital capacitive sensors are very promising for sensing applications, on account of several attributes like non- invasive sensing, speedy response, nonradiative nature, one-side access to measurand, ease of fabrication and low cost. The principle of operation of an inter-digital sensor is as follows. Consider a * Binu Ani Oommen [email protected] Jacob Philip [email protected] 1
Department of ECE, Amal Jyothi College of Engineering, Kanjirappally, Kerala 686518, India
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conventional parallel plate capacitor with uniform electric field across its driving and sensing electrodes, placed in close proximity to each other [1]. As the electrodes are expanded to co-planar geometry, the electric field is no longer confined to the region between the electrodes, but results in predominant fringing fields through the material under test (MUT) above the electrodes. The capacitance between two coplanar electrodes is usually comparable to the stray capacitance of the leads; hence the coplanar electrode pattern is repeated several times to build up the capacitance. Thus a basic inter-digital capacitive (IDC) structure comprises of a periodic digitlike pattern of electrodes on a substrate with the electric fields that penetrate into the material sample or sensitive coating above it. Inter-digital dielectrometry relies on dir
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