Textile Research Journal, 2014 vol. 84 no. 2 200-213.
Jinfeng Wang1, Hairu Long2 , Saeid Soltanian3, Peyman Servati3 and Frank Ko4
1 College of Materials and Textiles, Zhejiang Sci-Tech University, China and
2 College of Textiles, Donghua University, China and
3 Department of Materials Engineering, University of British Columbia, Canada and
4 Department of Electrical and Computer Engineering, University of British Columbia, Canada.
An optimization design about the relationship between the elastic resistance and the strain based on the fabric loop structure has been built to predict the deformation behavior and the related electric-mechanical properties of the fundamental elastic weft knitted structure. A computer program can give the fabric equivalent resistance, which is obtained by solving the circuit network equations. Besides the resistance of the fabric in one direction of elongation, the model is also used to simulate the electric knitted fabric resistance subjected to a planar deformation. The program can be used for all elastic plain knitted sensors with different conductive yarns and to simplify the computational process immensely. Experiments about the relationship between the electrical resistance and the strain have been done to validate the approach of the model and the computer program. Also, in order to simplify the calculation of the contacting forces on the overlapped yarns, two hooked yarns were used to represent the loop configurations. Compared to the existing models, the proposed model greatly simplifies the calculation of the equivalent resistance under the premise of a given material and knitted structure. The simulated results reasonably agree with the experimental data. From the theoretical analysis and experimental investigations, it is found that the resistance changing due to the yarn segment transfer is the key factor for the sensitivity of elastic fabric sensors. This makes the resistance linear increasing with the strain increasing. Analysis of the experimental results show that change in the resistance of a fabric sensor due to the contact resistance has a minor contribution to the sensitivity of the sensor in the large-strain regime. The contact resistance of the overlapped yarns follows a power law decrease trend with increasing of the tensile strain. Also, the fabric structure and the yarn elongating affect the characteristics of the fabric sensor. To design a wearable sensor, the width of a unit structure w and the loop length l are significant design parameters. Lower unit width and higher loop length will produce higher strain. This parameter study can instruct the design of wearable sensors.