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. 2020 Jul 31;10:12980. doi: 10.1038/s41598-020-69547-1

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Conceptual representation of the operation of the proposed glucose monitoring system. (a) Fabricated sensor system including the reader and the tag, (b) sensing tag flexibility (c) electromagnetic simulation of the sensor over the external tissues from skin to muscle. It could be seen that the electromagnetic field concentration is much higher at skin region and into the fat with decay of the field at deeper levels such as muscle in muscles. That is the main reason behind using ISF as it is an ideal fluid for glucose monitoring because the higher field concentration results in the higher sensitivity of the system to the variation in the permittivity (this image is obtained from HFSS simulation and edited in MS Word). (d) Detailed illustration depicting the proposed application of this technology. Note that the field concentration decays with increased distance from the sensor. The immediate layer in contact with the sensor, Stratum Corneum, contains no ISF and hence doesn’t contribute to the glucose monitoring response (i.e. frequency variation). The next epidermal layer, basal layers, contains around 40% of ISF and according to its low distance from the sensor, it is the dominant layer determining the sensor response. id. Considering the cells as static variables, which is a reasonable assumption because of their very slow dynamics, the most important variables in this layer that could interfere with the response of the propose sensor are dehydration and saline variation. These topics are experimentally studied throughout the paper to have negligible impact on the sensor response. The overall epidermal thickness is about 100 µm varies depending to the location. The next layer is dermis containing around 40% of ISF, less cells, very small percentage of lymph fluid and about 8% of blood plasma. Again, the main possible interfering parameters in this layer are the same as epidermis. Since the average dermal thickness is about 2 mm, the layers after dermis have negligible impact on the sensor response because the field strength at those layers is very low. In addition, this figure conceptually presents the communication between the tag sensor and the reader which is mostly accomplished through fringing fields (the biological part of this part is from an open source document available at https://commons.wikimedia.org/wiki/File:3D_medical_animation_skin_layers.jpg and edited in MS Visio).