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Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets
Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany
Biofluidix GmbH, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
* Author to whom correspondence should be addressed.
Received: 11 June 2012; in revised form: 17 July 2012 / Accepted: 25 July 2012 / Published: 3 August 2012
Abstract: In this paper a multi-disciplinary simulation of a capacitive droplet sensor based on an open plate capacitor as transducing element is presented. The numerical simulations are based on the finite volume method (FVM), including calculations of an electric field which changes according to the presence of a liquid droplet. The volume of fluid (VOF) method is applied for the simulation of the ejection process of a liquid droplet out of a dispenser nozzle. The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+. The investigated capacitive sensing principle enables to determine the volume of a micro droplet passing the sensor capacitor due to the induced change in capacity. It could be found that single droplets in the considered volume range of 5 nL < Vdrop < 100 nL lead to a linear change of the capacity up to ΔQ < 30 fC. The sensitivity of the focused capacitor geometry was evaluated to be Si = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.
Keywords: droplet sensor; CFD simulation; capacitive measurement; multi physics simulation; non-contact sensor; online process control
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Ernst, A.; Mutschler, K.; Tanguy, L.; Paust, N.; Zengerle, R.; Koltay, P. Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets. Sensors 2012, 12, 10550-10565.
Ernst A, Mutschler K, Tanguy L, Paust N, Zengerle R, Koltay P. Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets. Sensors. 2012; 12(8):10550-10565.
Ernst, Andreas; Mutschler, Klaus; Tanguy, Laurent; Paust, Nils; Zengerle, Roland; Koltay, Peter. 2012. "Numerical Investigations on Electric Field Characteristics with Respect to Capacitive Detection of Free-Flying Droplets." Sensors 12, no. 8: 10550-10565.