On the Capability of Measuring Actual Strain Values With Electrical Impedance Tomography Using Planar Silkscreen Printed Elastoresistive Sensors

A commonly used parameter in Structural Health Monitoring (SHM) to ensure the reliability and structural integrity of a lightweight structure is the mechanical strain. Usually, a strain gauge is the standard solution to measure local strain. The aim of this paper is to measure strain through two-dimensional Electrical Impedance Tomography (2D EIT) in combination with a planar elastoresistive sensor. Thereby, the quantitative value of the conductivity change as a function of strain is reconstructed. The advantage of this method compared to a conventional strain gauge is that the EIT allows simultaneous and spatial strain and damage monitoring by a single sensor. In the presented test setup, the sensor is bent uniformly over the sensor surface and the calculated EIT results are verified by using the Montgomery method. The article presents the main steps for strain measurement using 2D EIT, starting with an appropriate derivation of a Finite Element (FE) model of the sensor as well as the measurement data processing. Furthermore, the selection of the hyperparameter, which controls the EIT reconstruction algorithm, is presented. The selection of a suitable hyperparameter is essential for the reconstruction of actual conductivity values. The presented selection approach is based on the combinational use of the L-Curve (LC) method and the fixed Noise Figure (NF) method.