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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.


Investigation of the influence of the capacitive coupling effect by variations of the liquid column height.
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f8-sensors-12-10550: Investigation of the influence of the capacitive coupling effect by variations of the liquid column height.

Mentions: The simulation of the full model as described in Section 3 results in different signal characteristics. Following the explanation given in Section 2, two separate situations can be distinguished, like depicted in Figure 7. The image shows a complete sequence of the simulated measurement process, given by 7 time discrete samples. It can be seen that the electric field gets increasingly attracted by the growing droplet from image 1 to 3 in Figure 7, leading to a declining charge on the measurement electrode (cf.Figure 8, line h = 5 mm which is the corresponding signal characteristics to this simulation). After the droplet's tear off (image 4 and following images.), the droplet acts as dielectric body, increasing the charge on the electrode due to its specific permittivity and volume. Some of the field lines still keep attracted by the liquid inside the nozzle, which is still connected to GND. This field however is constant over time, hence it does not influence the absolute value of the measurement. Movement of the liquid meniscus at the nozzle might entail additional fluctuations to the signal which could not be observed for the settings studied so far.


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)

Investigation of the influence of the capacitive coupling effect by variations of the liquid column height.
© Copyright Policy
Related In: Results  -  Collection

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

f8-sensors-12-10550: Investigation of the influence of the capacitive coupling effect by variations of the liquid column height.
Mentions: The simulation of the full model as described in Section 3 results in different signal characteristics. Following the explanation given in Section 2, two separate situations can be distinguished, like depicted in Figure 7. The image shows a complete sequence of the simulated measurement process, given by 7 time discrete samples. It can be seen that the electric field gets increasingly attracted by the growing droplet from image 1 to 3 in Figure 7, leading to a declining charge on the measurement electrode (cf.Figure 8, line h = 5 mm which is the corresponding signal characteristics to this simulation). After the droplet's tear off (image 4 and following images.), the droplet acts as dielectric body, increasing the charge on the electrode due to its specific permittivity and volume. Some of the field lines still keep attracted by the liquid inside the nozzle, which is still connected to GND. This field however is constant over time, hence it does not influence the absolute value of the measurement. Movement of the liquid meniscus at the nozzle might entail additional fluctuations to the signal which could not be observed for the settings studied so far.

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.