E-Textile-Based Wavy Surface WPT Flexible Antenna With Frequency Self-Reconfiguration Function for Batteryless Sensor Platform

This article is a study on the center frequency reconfiguration of a flexible antenna. In the case of a flexible antenna, the center frequency shifts due to parasitic components generated when the antenna is bent. In previous studies, research has been conducted to reconfigure the center frequency through a reconfiguration circuit. When using a reconfiguration circuit, it is difficult to flexibly configure all systems due to increased complexity. Therefore, in this article, we propose a flexible antenna that does not change the center frequency even when the antenna is bent through a wavy surface structure without the aid of a frequency reconfiguration circuit. By studying the parasitic component that occurs when the antenna is bent, the cause of the change in the center frequency is identified, and a structure to solve it is proposed. In order to calculate the parasitic component, an approximate model divided by the vertical component of the bending surface of the flexible antenna was used. In this article, a gating air-gap structure was proposed to realize a wavy surface, and through this, the antenna gain was increased by 1.47 dBi. In addition, through the wavy surface structure using E-textile, it was possible to reduce the frequency shift by about 86% (70–10 MHz) and improve the gain reduction by about 86% (4.4–0.63 dBi). This allows the frequency to be reconfigured in real time without additional circuitry.