A Quasi-Isotropic and Uniformly Polarized Ultracompact Wireless Power Source for Energizing Battery-Free Internet of Things Devices

With the rapid development of wireless power transfer (WPT) technologies, battery-free Internet-of-Things (IoT) devices have become feasible and attractive. WPT enables single wireless power source to energize multiple IoT devices that are dispersed around it. This paper introduces a novel quasi-isotropic and uniformly polarized ultracompact wireless power source that is facilitated by a pattern reconfigurable electrically small Huygens dipole antenna (HDA). It consists of a reconfigurable capacitively loaded loop (CLL) with a PIN diode as the magnetic dipole, an Egyptian axe dipole (EAD) as the electric dipole, a reconfigurable short driven dipole with a PIN diode, and several switching components and circuits. By controlling the status of the two diodes, broadside and backfire Huygens patterns can be switched. This is realized as the phase of the electric dipole is altered by 180° by changing the coupling between the CLL and the EAD. The prototype was fabricated and measured. Throughout the entire space, the co-polarization gain variation is less than 6.9 dB. As an electrically small antenna with uniform polarization, it is an ideal candidate as a transmitting power source for WPT-enabled IoT applications.