Limits...
Numerical investigations on electric field characteristics with respect to capacitive detection of free-flying droplets.

Ernst A, Mutschler K, Tanguy L, Paust N, Zengerle R, Koltay P - Sensors (Basel) (2012)

Bottom Line: The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+.The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL.The simulation results are validated by experiments which exhibit good agreement.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany. andreas.ernst@imtek.de

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 < V(drop) < 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 S(i) = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.

No MeSH data available.


Comparison of the voltage signals obtained from the experiments and the results of the network simulation.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3472843&req=5

f11-sensors-12-10550: Comparison of the voltage signals obtained from the experiments and the results of the network simulation.

Mentions: Figure 11 shows the comparison of the experimentally determined sensor peak signals for various droplet volumes in comparison to the peak voltages predicted by the network simulation. It can be seen that the sensitivity, given by the slope of the linear regressions are similar for both, the simulation and the experiment. Obviously, there is a slight offset between the measurement and the simulation which might be caused by deviations of the real values of the electronic components (e.g., resistance, capacity etc.) from the ideal values used for the simulation, influencing the total amplification of the electronic circuit. This offset could be probably explained or compensated by carefully checking each electronic component in the network model as well as the experimental setup for consistency, which is not the objective of this work. Another reason for the off-set might be the limited accuracy of the CFD simulations predicting the change of charge for a given droplet volume used as input to the network simulation as discussed before. Therefore, also the simulation results have to be furnished with error bars. The error bars given for the simulation results are gained from the presented grid refinement study, whereas the error bars for the experiment are deduced by the standard error of repeated measurements for each of the presented data points. Each data point represents approximately 60 single droplet measurements. In summary the results allow for the conclusion that the accomplished CFD simulation leads to a realistic linear scaling behavior and values for the change of the charge which are actually in the region of ΔQ < 30 fC for pure water droplets in the range of V < 100 nL. In combination with the Saber network model a complete numerical description of the experimental setup has been accomplished with reasonable accuracy and consistency with experimental results.


Numerical investigations on electric field characteristics with respect to capacitive detection of free-flying droplets.

Ernst A, Mutschler K, Tanguy L, Paust N, Zengerle R, Koltay P - Sensors (Basel) (2012)

Comparison of the voltage signals obtained from the experiments and the results of the network simulation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472843&req=5

f11-sensors-12-10550: Comparison of the voltage signals obtained from the experiments and the results of the network simulation.
Mentions: Figure 11 shows the comparison of the experimentally determined sensor peak signals for various droplet volumes in comparison to the peak voltages predicted by the network simulation. It can be seen that the sensitivity, given by the slope of the linear regressions are similar for both, the simulation and the experiment. Obviously, there is a slight offset between the measurement and the simulation which might be caused by deviations of the real values of the electronic components (e.g., resistance, capacity etc.) from the ideal values used for the simulation, influencing the total amplification of the electronic circuit. This offset could be probably explained or compensated by carefully checking each electronic component in the network model as well as the experimental setup for consistency, which is not the objective of this work. Another reason for the off-set might be the limited accuracy of the CFD simulations predicting the change of charge for a given droplet volume used as input to the network simulation as discussed before. Therefore, also the simulation results have to be furnished with error bars. The error bars given for the simulation results are gained from the presented grid refinement study, whereas the error bars for the experiment are deduced by the standard error of repeated measurements for each of the presented data points. Each data point represents approximately 60 single droplet measurements. In summary the results allow for the conclusion that the accomplished CFD simulation leads to a realistic linear scaling behavior and values for the change of the charge which are actually in the region of ΔQ < 30 fC for pure water droplets in the range of V < 100 nL. In combination with the Saber network model a complete numerical description of the experimental setup has been accomplished with reasonable accuracy and consistency with experimental results.

Bottom Line: The simulations were realised using the computational fluid dynamic (CFD) software CFD ACE+.The sensitivity of the focused capacitor geometry was evaluated to be S(i) = 0.3 fC/nL.The simulation results are validated by experiments which exhibit good agreement.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for MEMS Applications, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany. andreas.ernst@imtek.de

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 < V(drop) < 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 S(i) = 0.3 fC/nL. The simulation results are validated by experiments which exhibit good agreement.

No MeSH data available.