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. 2023 Jan 23;23(3):1298.
doi: 10.3390/s23031298.

Smart Shoe Insole Based on Polydimethylsiloxane Composite Capacitive Sensors

Francisco Luna-Perejón  1 , Blas Salvador-Domínguez  2 , Fernando Perez-Peña  2 , José María Rodríguez Corral  3 , Elena Escobar-Linero  1 , Arturo Morgado-Estévez  2
Affiliations

Smart Shoe Insole Based on Polydimethylsiloxane Composite Capacitive Sensors

Francisco Luna-Perejón et al. Sensors (Basel). .

Erratum in

Abstract

Nowadays, the study of the gait by analyzing the distribution of plantar pressure is a well-established technique. The use of intelligent insoles allows real-time monitoring of the user. Thus, collecting and analyzing information is a more accurate process than consultations in so-called gait laboratories. Most of the previous published studies consider the composition and operation of these insoles based on resistive sensors. However, the use of capacitive sensors could provide better results, in terms of linear behavior under the pressure exerted. This behavior depends on the properties of the dielectric used. In this work, the design and implementation of an intelligent plantar insole composed of capacitive sensors is proposed. The dielectric used is a polydimethylsiloxane (PDMS)-based composition. The sensorized plantar insole developed achieves its purpose as a tool for collecting pressure in different areas of the sole of the foot. The fundamentals and details of the composition, manufacture, and implementation of the insole and the system used to collect data, as well as the data samples, are shown. Finally, a comparison of the behavior of both insoles, resistive and capacitive sensor-equipped, is made. The prototype presented lays the foundation for the development of a tool to support the diagnosis of gait abnormalities.

Keywords: PDMS; capacitive sensor; deep learning; smart insole.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Scheme of main layers that make up the proposed plantar insole.
Figure 2
Figure 2
(a) Location of the sensors in the proposed capacitive insole. (b) Layout of the layer with the electrodes on the capacitive plantar insole.
Figure 3
Figure 3
Block diagram of the main components of the plantar insole system.
Figure 4
Figure 4
Prototype components: (a) PDM-based dielectric layer; (b) flexible PCB with remaining photoresist ink, prior to copper-dissolution step; (c) the insole with three layers finished, prior to fixing them with Kapton; (d) ACShield built to house the CDC Controller Ad7147-1 and to connect both plantar insole, batteries, bluetooth and MCU to the whole system; (e) ACShield with MCU and batteries connected.
Figure 5
Figure 5
Capacitive plantar insole, size 38 (24 cm). Behavior of sensors against weight in the area they occupy. (a) show the average results for each repetition performed. (b) shows the combined average of all repetitions.
Figure 6
Figure 6
Capacitive plantar insole, size 43 (27 cm). Behavior of sensors against weight in the area they occupy. (a) show the average results for each repetition performed. (b) shows the combined average of all repetitions.
Figure 7
Figure 7
Resistive plantar insole. Behavior of sensors against weight in the area they occupy. (a) show the average results for each repetition performed. (b) shows the combined average of all repetitions.
Figure 8
Figure 8
Behavior of sensors against weight in the area they occupy, Using higher loads. (a) show the average results for each repetition performed. (b) shows the combined average of all repetitions.
Figure 9
Figure 9
Behaviour during user gait—capacitive insoles. (a) EU43 size, left insole. (b) EU38 size, right insole.
Figure 10
Figure 10
Map distribution samples obtained during different gait stages. For size EU 43 insole: (a) the forefoot is resting on the ground; (b) the whole foot is resting; (c) the hindfoot is resting. (d–f) reflects the same stages as (a–c), respectively, but with the size EU 38 insole.
Figure 11
Figure 11
Behaviour during user gait—resistive insole.
See this image and copyright information in PMC

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