Electrical impedance spectroscopy for electro-mechanical characterization of conductive fabrics

Abstract

When we use a conductive fabric as a pressure sensor, it is necessary to quantitatively understand its electromechanical property related with the applied pressure. We investigated electromechanical properties of three different conductive fabrics using the electrical impedance spectroscopy (EIS). We found that their electrical impedance spectra depend not only on the electrical properties of the conductive yarns, but also on their weaving structures. When we apply a mechanical tension or compression, there occur structural deformations in the conductive fabrics altering their apparent electrical impedance spectra. For a stretchable conductive fabric, the impedance magnitude increased or decreased under tension or compression, respectively. For an almost non-stretchable conductive fabric, both tension and compression resulted in decreased impedance values since the applied tension failed to elongate the fabric. To measure both tension and compression separately, it is desirable to use a stretchable conductive fabric. For any conductive fabric chosen as a pressure-sensing material, its resistivity under no loading conditions must be carefully chosen since it determines a measurable range of the impedance values subject to different amounts of loadings. We suggest the EIS method to characterize the electromechanical property of a conductive fabric in designing a thin and flexible fabric pressure sensor.

Figure 1.

SEM images (×200) and EDS microanalyses of three conductive fabrics. Fabric A was plated with silver. Fabrics B and C were coated with carbon. Figures in the upper and lower rows are the SEM images and the EDS microanalysis results, respectively.

Figure 2.

Numerical models of a conductive fabric under tension and compression. The blue and grey regions denote the conductive yarns and air gaps, respectively. (a) Models of the conductive fabric subject to different amounts of tension at the edges. (b) Models of the conductive fabric subject to compressive forces at the middle.

Figure 3.

EIS measurements of conductive fabrics under tension and compression. (a) Four-electrode method for impedance measurements. (b) Measurement setup using the Solartron 1260 impedance analyzer. (c) EIS measurement setup for applied tension using acrylic supports. (d) EIS measurement setup for applied compression.

Figure 4.

Computed electric potential distributions and current streamlines inside the fabric under two different amounts of compression. The color bars denote the electric potential subject to the injected current from the right to left direction. The curved lines are current streamlines. (a) and (b) show the electric potential distributions and current streamlines, respectively, at 10, 500, and 1000 kHz subject to two different amounts of compression (1:0.6 and 1:0.51).

Figure 5.

Changes of the computed electric potentials along the middle horizontal line: (a) real and (b) imaginary parts.

Figure 6.

Simulation results of impedance spectra of conductive fabrics under tension and compression. (a) and (c) are the Argand diagrams. (b) and (d) show changes in the magnitude of the impedance for different amounts of loadings.

Figure 7.

Argand diagrams of the impedance spectra from three conductive fabrics without any applied loading. (a), (b), and (c) are from the fabrics A, B, and C. (d) shows the plots of the impedance magnitude changes at 10 kHz.

Figure 8.

Argand diagrams of the impedance spectra from three conductive fabrics under tension. (a), (b), and (c) are from the fabrics A, B, and C, respectively.

Figure 9.

Impedance magnitude spectra of three conductive fabrics under tension. (a), (b), and (c) are from the fabrics A, B, and C, respectively; (d) shows the plots of the impedance magnitude changes at 10 kHz.

Figure 10.

Argand diagrams of the impedance spectra from three conductive fabrics under compression. (a), (b), and (c) are from the fabrics A, B, and C, respectively.

Figure 11.

Impedance magnitude spectra of three conductive fabrics under compression. (a), (b), and (c) are from the fabrics A, B, and C, respectively; (d) shows the plots of the impedance magnitude changes at 10 kHz.

Figure 11.

Impedance magnitude spectra of three conductive fabrics under compression. (a), (b), and (c) are from the fabrics A, B, and C, respectively; (d) shows the plots of the impedance magnitude changes at 10 kHz.