Performance regulation of high-precision wireless passive yarn sensor based on normal mode helical dipole antenna

Abstract

Stable and reliable sensing performance was required for high-precision wireless passive yarn sensor based on normal mode helical dipole antenna (NMHDA). The actual helical pitch of NMHDA was non-uniform due to manufacturing process, and the previous equivalent impedance model for uniform NMHDA, i.e., wire-loop model, was oversimplified, resulting in inaccurate predicted reactance and sensing performance of yarn sensor. This work combined the circular polarization principle and the asymmetric structure of non-uniform NMHDA to build the wire-loop-wire model. Based on the wire-loop-wire model, the parametric expression of NMHDA impedance and resonant frequency were obtained, and the results predicted by wire-loop model and wire-loop-wire model were compared with the measured one. Furthermore, to demonstrate the practicality of wire-loop-wire model and parametric resonant frequency expression, the impact of helical pitch uniformity on resonant frequency was discussed in terms of the statistical characteristics of prototype helical pitch, and also the parametric expression was applied to design wireless passive yarn sensors with expected working property. It was found that the wire-loop-wire model incorporating the asymmetric structure accurately described the impedance characteristics of the NMHDA with non-uniform helical pitches, and the maximum predicted deviation of resonant frequency was reduced to 1 MHz. The steady long reading range (19.42 ± 0.09 m) of wireless passive yarn sensors prototype demonstrated the capacity of wire-loop-wire model in designing high-precision sensor. Generally, this paper successfully built the wire-loop-wire model for NMHDA with non-uniform helical pitches, and provided a practical tool for designing e-textile devices with NMHDA.