A Capacitive Ice-Sensor Based on Graphene Nano-Platelets Strips

Abstract

This paper investigates the possibility of realizing ice sensors based on the electrical response of thin strips made from pressed graphene nano-platelets. The novelty of this work resides in the use of the same graphene strips that can act as heating elements via the Joule effect, thus opening the route for a combined device able to both detect and remove ice. A planar capacitive sensor is designed and fabricated, in which the graphene strip acts as one of the armatures. The sensing principle is based on the high sensitivity of the planar capacitor to the change in electrical permittivity in the presence of ice, as shown in the experimental case study discussed here, can also be interpreted by means of a simple circuit and electromagnetic model. The properties of the sensor are analyzed, and the frequency range for its use as an ice detector has been established.

Keywords: electrical permittivity; graphene nano-platelets; ice sensors; nanomaterials.

Figure 1

A single GNP in a Scanning Electron Microscope picture (a); macroscopic strips (b).

Figure 2

Relative permittivity of water and ice compared to air, vs. frequency, according to the data provided in [49].

Figure 3

Cross-section of the designed ice sensor (planar capacitor).

Figure 4

Realization of the ice sensor with a PCB structure. The central gray strip is the graphene element. The amperometric cables (orange and brown cables) are separated from the voltmetric ones (black and red) to enable the 4-probe measurement technique.

Figure 5

Equivalent electrical circuit for the proposed ice sensor.

Figure 6

The 2D simplified model implemented in COMSOL to extract the bulk electrostatic capacitance.

Figure 7

Distribution of the electric displacement field (arrows) and of the electrical charge surface density (colored map) in the presence of air (a) and ice (b).

Figure 7

Distribution of the electric displacement field (arrows) and of the electrical charge surface density (colored map) in the presence of air (a) and ice (b).

Figure 8

The measurement set-up, where the electrical impedance of the sensor (placed inside a climatic chamber) is measured by an impedance analyzer, supervised by a PC via an RS232C interface: (a) schematic; (b) picture of the whole setup (top), with the detail of the sensor covered by ice (bottom).

Figure 9

Measured capacitance of the sensor versus frequency, in the absence and presence of different types of ice. Temperature −20 °C, coverage factor K = 1.

Figure 10

Measured capacitance of the sensor versus frequency, in the absence and presence of different types of ice. Temperature −20 °C, coverage factor K = 2.

Figure 11

Measured capacitance of the sensor versus frequency, in the absence and presence of different types of ice. Temperature −20 °C, coverage factor K = 3.

Figure 12

Measured capacitance (average value) of the sensor versus frequency, in the absence of ice, with varying temperature values and 0% humidity.

Figure 13

Measured capacitance (average value) of the sensor versus frequency, in the absence of ice, with varying humidity values, at 20 °C.

Figure 14

Sensor response in the presence and absence of ice with a coverage factor K = 1, corresponding to a confidence level of 68.4%.

Figure 15

Sensor response in the presence and absence of ice with a coverage factor K = 2, corresponding to a confidence level of 95.4%.

Figure 16

Sensor response in the presence and absence of ice with a coverage factor K = 3, corresponding to a confidence level of 99.7%.

Figure 17

Capacitance values estimated by means of the equivalent model in Figure 5.