Highly Efficient Omnidirectional Integrated Multiband Wireless Energy Harvesters for Compact Sensor Nodes of Internet-of-Things

A novel highly efficient radio-frequency (RF) energy harvester (rectenna) array with multifrequency coverages (1.7-1.8 GHz and 2.1-2.7 GHz) as well as an omnidirectional 3-D radiation pattern is presented. The harvester array is very compact and of low-profile, which strategically combines 12 single Vivaldi slot rectenna elements. More importantly, the proposed rectenna array is significantly simplified through a codesigned effective impedance tuning and array combination method to reduce the overall circuit complexity whilst maintaining high energy conversion efficiency (up to 67%) over the desired frequency band under different input powers (-25-5 dBm) and circuit loads (0.2-8 kΩ). Having utilized the proposed wireless energy harvester array, a complete system-level demonstration of ambient RF energy-powered, a self-sustainable IoT sensor node is demonstrated for reliably operating in a typical indoor environment. Such a demonstration has never been reported before. In addition, the proposed rectenna array has novel features in terms of simplified Vivaldi rectenna matching, compact array combination and optimal beam shaping, which has proven to be an effective energy harvester in most domestic environments; therefore, having significant implications in powering small electronics for real-world Internet-of-Things (IoT) and industrial Internet-of-Things (IIoT) applications.