Isotropic auxetic structure with fixed Poisson's ratio for piezo-resistive strain sensor to detect human body motion

Abstract

Auxetic materials have different types whose mechanical behaviors are different from each other, and these differences affect their sensitivity. However, in the piezo-resistive strain sensor field, less attention has been paid to this variety of structures. In this article, the isotropic auxetic structure with three axes of symmetry was used to construct the isotropic linear piezo-resistive strain sensor. Structures that have only three or six symmetry axes have isotropic mechanical behavior, and structures with many symmetry axes other than these two cases are not isotropic. Also, to obtain a sensor with a linear sensing performance, the Poisson's ratio of the sensor must be constant during the strain. Most of the structures presented in the previous works have a variable Poisson's ratio along the strain. When the Poisson’s ratio of the structure is constant during the strain, it causes the sensing elements to have the same increased space to separate from each other during the strain, and as a result, the sensor will have a linear performance. A computer numerical control device was utilized to manufacture the sensor mold. Silicon RTV2 as a substrate material, and graphite powder as a sensing element were mixed to provide the sensor constitutive material, and molded into the manufactured die. To evaluate the response of the sensor in different directions, the sensitivity tests were performed in the directions of 0°, 60°, and 120°, which are compatible with each other, and also the suggested sensor has linear sensitivity during the strain.

Nanocarbon-based sensors for the structural health monitoring of smart biocomposites

“…Reproduced with permission. 230 Copyright 2023 SAGE Publications (f ) Schematic structure of flexible piezoresistive sensors. (g) Photograph of an as-assembled PDMS/CB sensor and (h) schematic illustration of sensing mechanisms of piezoresistive sensor with vertical electrode design.…”

Novel Linear, Piezoresistive, Auxetic Sensors Coated by AAA Battery Active Carbons with Supreme Sensitivity for Human Body Movement Detection

“…However, using the auxetic structure to regulate the performance of strain sensor was reported by several papers in the past few years. [23][24][25]27,28,47,57,58,[61][62][63][64][65][66][67] In this article, the optimization was such that by changing the geometry of the sensor structure, its sensing performance was improved. It means that a connection was established between the mechanical properties and the sensory properties of the sensor, and this type of optimization had not been done in the literature review.…”

“…In the previous part, an important feature of the sensor (linearity) was discussed, and in this part, another feature (excellent sensory performance) will be discussed. Figure 13 shows the schematic comparison of the sensitivity of the presented sensor with the previous sensors including conventional sandwich, [7] auxetic sandwich, [24] auxetic mixed, [23] and isotropic linear auxetic mixed [28] sensors in terms of mean, median, and standard deviation. As shown in Figure 13, the presented sensor has a significantly better performance compared to the previous sensors.…”

“…Piezoresistive strain sensors, [1][2][3][4][5][6][7] which transform mechanical stimulation into readable optical or electrical signals, have a significant effect on the emerging fields of soft robotics, [8][9][10][11][12][13][14][15][16][17][18] healthcare monitoring, [19][20][21][22][23][24][25][26][27][28] electrical skins, [29][30][31][32][33] and wearable devices. [24,[34][35][36][37][38][39][40][41] For example, stretchable piezoresistive sensors on muscles of the neck profit throat cancer, respiratory disturbance, and diagnosis of defective vocal cords, [18] while those on the wrist of humans help with vibration identification in Parkinson's illness and epilepsy.…”

Novel Linear Piezo‐resistive Auxetic Meta‐Sensors with Low Young's Modulus by a Core–Shell Conceptual Design and Electromechanical Modelling

“…To explain the importance of changing the structure and the importance of using the core-shell idea, a comparison between the re-entrant, [8] constant Poisson's ratio (CPR), [17] and planar isotropic [31] auxetic sensors with the same condition (including materials and manufacturing methods) showed that the sensory performance of the sensor will change by changing the structure. Figure 1 shows the Poisson's ratio (PR) (a) and the sensitivity (b) in terms of the strain for the three mentioned sensors.…”