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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.


Previously achieved experimental signal characteristics correlated to droplet positions while a droplet is passing the capacitor.
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f1-sensors-12-10550: Previously achieved experimental signal characteristics correlated to droplet positions while a droplet is passing the capacitor.

Mentions: The simulation study presented in this paper is based on measurement results achieved with a capacitive sensor prototype which was applied to detect single droplets in flight [8]. The used sensor provides an open plate capacitor forming the measurement electrodes, which are fabricated in PCB technology. A droplet which passes through the capacitor generates a specific time dependent capacity change which is amplified to a voltage signal like shown in Figure 1. The negative dip at the beginning of the signal describes unexpected signal characteristics which could not be explained in first instance. Even stroboscopic image analyses did not clarify the origin of this specific characteristic (see provided image sequence in Figure 1). The presented simulation study was initiated to investigate the characteristics of the electrical field causing the said specific signal. Furthermore, information about the effect of certain parameters influencing the electric field is aimed by this study.


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)

Previously achieved experimental signal characteristics correlated to droplet positions while a droplet is passing the capacitor.
© Copyright Policy
Related In: Results  -  Collection

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

f1-sensors-12-10550: Previously achieved experimental signal characteristics correlated to droplet positions while a droplet is passing the capacitor.
Mentions: The simulation study presented in this paper is based on measurement results achieved with a capacitive sensor prototype which was applied to detect single droplets in flight [8]. The used sensor provides an open plate capacitor forming the measurement electrodes, which are fabricated in PCB technology. A droplet which passes through the capacitor generates a specific time dependent capacity change which is amplified to a voltage signal like shown in Figure 1. The negative dip at the beginning of the signal describes unexpected signal characteristics which could not be explained in first instance. Even stroboscopic image analyses did not clarify the origin of this specific characteristic (see provided image sequence in Figure 1). The presented simulation study was initiated to investigate the characteristics of the electrical field causing the said specific signal. Furthermore, information about the effect of certain parameters influencing the electric field is aimed by this study.

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.