Efficient and Sensitive Electrically Small Rectenna for Ultra-Low Power RF Energy Harvesting

摘要

A new electrically small antenna with size ka?=?0.415 is presented, fabricated and measured in this work. This is intrinsically matched to 50?Ω, has omni-directional and linear-polarized radiation pattern in the horizontal plane with maximum directivity of 1.75?dBi and simulated radiation efficiency of 93%. The antenna in combination with a low-complex and co-planar rectifier with one single diode forms a high efficient and sensitive electrically small rectenna with ka?=?0.53 at 868?MHz (UHF RFID-band in Europe). The latter has measured efficiency 22.5% for ?19?dBm power input and sensitivity of ?44?dBm (or equivalently 0.00028?μW/cm2 power density), while at 2.25?μW/cm2 is able to supply continuously, i.e., without a boost converter or use of any energy tank, a small electrical device with 118?μW. In order to increase the dc output voltage and the delivered dc power to the load for lower power density levels, rectenna-array configuration is exploited. Application to batteryless, backscatter wireless sensor node powering is discussed. Specifically, for a power density of 0.1237?μW/cm2 the RF energy harvesting system delivers 172?μW at 2.85?V every 22.5?s.