Textile materials are the ideal substrate of the antenna of eco-friendly wireless radio frequency (RF) energy harvesting technology for sustainable battery-free operation of wearable electronic devices, while few of the work published have been focused on the effect of textile properties on the energy harvesting performance. This work will clarify the effect of typical fabric surface structures on the energy harvesting performance of Radio Frequency Identification (RFID) antenna. The antennas were screen-printed onto three different weave structures, and performance for the different fabric-based antennas were studied. The results showed that the antenna printed on plain fabric, which has the smallest porosity and lower surface roughness, was able to achieve a maximum transmission distance of 110 cm and output voltage of 3.003 mV at 69 cm. Consequently, in order to improve the energy harvesting performance of antenna, the smooth and compact fabric surface is more beneficial to highly efficient energy harvesting.

Radio frequency energy harvesting on textiles is seen as a method of enabling sustainable battery-free operation for wearable devices, while few works have clarified the influence of fabric properties on antenna performance. To prepare successfully a fabric-based circularly polarized antenna for radio frequency energy harvesting, this paper will clarify the effect of key fabric characteristics (such as dielectric properties and fabric thickness) on antenna performance by a finite element simulation. The simulated results showed the antenna resonant frequency is inversely proportional to the half square of the fabric’s dielectric constant, and the antenna radiation efficiency and gain are inversely proportional to the square of its dielectric loss tangent and thickness. Then, for the typical fabric substrates, the structure parameters of the existing circularly polarized antenna are optimized to work in the expected working frequency band, and the dominating structure parameter of the antenna in performance was identified. The optimized antenna prototype has excellent performance. The antenna has a bandwidth of 350 MHz and a maximum transmission distance of 190 cm. The received signal strength indication per unit area is 2.35 mW/cm2 and the output voltage is 1.19 mV/cm2 at a distance of 100 cm. It is concluded that the flexible size-minimized wide bandwidth circularly polarized radio frequency energy harvesting antenna screen-printed on fabric was derived from a commercial circularly polarized antenna with fiber-reinforced epoxy plate (FR4) substrate, and the critical geometrical and material parameters of the fabric substrate for this antenna performance as well as the affecting mechanism were identified.

An integrated solution providing a bi-stable antenna with reconfigurable performance and light-responsive behavior is presented in this paper for the first time. The proposed antenna includes a radiation layer with conductivity, which is integrated onto the bi-stable substrate. First, the effect of the radiation layer material and substrate layer parameters on antenna performance was studied. The experiment showed that an antenna with CNTF has a wider impedance bandwidth than one with CSP, namely 10.37% versus 3.29%, respectively. The resonance frequency increases gradually with the increase in fiber laying density and fiber linear density. Second, the influence of state change of the substrate layer on the antenna radiation pattern was studied. The measured results showed that the maximum radiation angle and gain of states I and II are at 90°, 1.21 dB and 225°, 1.53 dB, respectively. The gain non-circularities of the antenna at states I and II are 4.48 dB and 8.35 dB, respectively, which shows that the antenna has good omnidirectional radiation performance in state I. The display of the array antenna, which shows that the array antenna has good omnidirectional radiation performance in state A, with gain non-circularities of 4.20 dB, proves the feasibility of this bi-stable substrate in reconfigurable antennas. Finally, the antenna deforms from state I to state II when the illumination stimulus reaches 22 s, showing good light-responsive behavior. Moreover, the bi-stable composite antenna has the characteristics of small size, light weight, high flexibility, and excellent integration.