FIGURE 1 - uploaded by Luis Polo-Parada
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a) Cross section of six finger interdigitated capacitor sensor with fringing electric fields and constant parameters used for 3D Finite Element Method simulations. b) Complete six finger interdigitated capacitor sensor used for 3D Finite Element Method simulations.
Source publication
We propose and analyze a high resolution capacitive sensor appropriate for monitoring physical or chemical processes in liquid films. The proposed sensor is based on a planar interdigitated capacitor with planar electrodes of dimensions in the milimeter scale. The electric field between electrodes extend above the plane of the electrodes up to a fe...
Contexts in source publication
Context 1
... capacitance C was calculated for different values of the dielectric constant k and thickness d of the MUT to obtain the performance parameters of the IDCS [20,21]. The charge on the driving electrodes was calculated with the following integrals over the entire surface of the driving electrodes, including the electrode connecting the fingers (see Fig. ...
Context 2
... expression (3) represents the ratio of changes in capacitance C to changes in dielectric constant k of the MUT for a thickness d min and larger. For instance, with d min = 2 mm and for k 1 = 6, k 2 = 8 we obtain their respec- tive capacitance values C 1 = 2.343 pF and C 2 = 2.797 pF, from curves of Fig. 1. With this data, the sensitivity S k,max for d min can be calculated form the slope S k,max ≈ 0.23 ...
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Citations
... We find in Fig. 6 that the variation introduced in the capacitance is important for a thickness of medium less than 1.2 mm and above that, this variation becomes almost constant; this is for any value of k. Due to confirmation of this observation, we calculated the sensitivity of this capacitance with respect to the thickness for a medium of the dielectric constant k = 20, Eq. (6): The Table 2 shows the sensitivity values of our results calculated from Fig. 6 and the results taken from [8]. The sensitivity is very high for a small electrode thickness. ...
We present in this work, a capacitive sensor used for the physicochemical control and diagnosis of a liquid medium. The sensor is composed of planar electrodes with interdigitated structures and dimensions on a millimeter scale. The polarization of the sensor introduces an electric field a few millimeters above the electrodes thus allowing the characterization of the liquid medium. We have simulated the electric field induced by planar electrodes by using the finite element method numerical analysis. On the one hand, a capacity study is proposed for the analysis of sensor geometry such as the width and spacing between electrodes to optimize geometrical parameters. And on the other hand, this capacity is calculated for variations of the physical properties of the liquid (dielectric constant which depends on the permittivity; thickness "Thm") thus making it possible to determine the optimum value of Thm for different values of the dielectric constant.
... Depending on the geometric configuration of the electrodes the electric field lines can penetrate deeper or less deep. The capacitance of an IDCS always depends on the dielectric properties of the MUT and the geometry of the electrodes (Guadarrama-Santana et al, 2014). When the sensitive layer (commonly a polymer) interacts with the chemicals present in the environment, the chemically sensitive layer changes its conductivity (σ), dielectric constant (ε) or its effective thickness (d). ...
... The latter formulas are for an ideal parallel-plate capacitor but using an effective value for the area A takes into account fringing field effects at and near the borders of the capacitor [39][40][41]. Typically, A is determined from experimental measurements. ...
We analyze the sensitivity of electrical measurements to lysis of biological cells in suspensions. We aim at discerning the electrical parameter and measuring conditions that are more convenient to monitor the kinetics of a lysis process. We consider single-frequency measurements of the capacitance and resistance of an electrical capacitor containing a suspension of biological cells at mid-radiofrequencies. We use well-established models to estimate the relative sensitivities to variations of the volume fraction of cells during a lysis process. Then we estimate values for the resolution in measuring the fraction of cells that have been lysed with commercially available LCR meters. Unexpectedly, our results indicate that, despite the total number of ions in solution remains constant during a lysis process, in general, the electrical resistance provides a more appropriate signal for sensing the evolution of cell lysis than the capacitance. This is contrary to the case when the cell's volume fraction without lysis is to be measured. We predict that, with single-frequency resistance measurements, a resolution better than 0.1% in volume fraction of lysed cells should be attainable without much difficulty.
This article presents a variable-capacitance sensor (VCS) for sessile droplet evaporation rate and lifetime measurements. The sensor consists of a plane-parallel-electrode capacitor with a commercial glass substrate inserted within. The glass substrate has a concave cavity at its center to deposit a liquid droplet for its measurement. An air gap is left between the substrate and the upper electrode to allow for the droplet’s evaporation. The main advantage of this configuration is that it fixes the position and geometric shape of the droplet. An analytical model based on the local-height approximation (LHA) is developed to calculate the capacitance of the device, with and without a liquid droplet. Its validity is initially tested comparing with finite element calculations. Then, using the analytical model, we simulate the capacitance signal during the evaporation of a sessile droplet and compare it with experimental results finding very good correspondence. The differential capacitance signal closely follows the volumetric changes of the droplet. The evaporation kinetics and lifetime of
${3}.{5}\pm {0}.{1} \mu \text{L}$
droplets of ethanol and methanol mixtures are presented. We also show that the evaporation kinetics and lifetime of a droplet can be used to reveal the presence of a surfactant at very low concentrations. The results presented demonstrate the ability of the sensor to monitor the evaporating droplet from start to end.
