Compact Rectennas for Ultra-Low-Power Wireless Transmission Applications

This paper addresses the design and characterization of compact rectennas for wireless power transmission application in the industrial, scientific, and medical 868-MHz/915-MHz band. These rectennas are designed for supplying power to a dcto-dc boost converter. The proposed low-profile rectenna exhibits a good tradeoff between compactness (0.06λ2at 900 MHz) and RF-to-dc conversion efficiency, which is higher than 25% for RF power densities of at least 0.25 μW/cm2and 37% for 2.1 μW/cm2. It is shown that this rectenna can activate the standard Bq25504 dc-to-dc boost converter for an RF power density higher than 0.6 μW/cm2. Moreover, through using a storage capacitor of 220 μF, a light emitting diode (LED) can be turned on for a duration of 60 ms with power consumption of 9.45 mW and a dc voltage of 3 V. The LED allows emulating the dc consumption of the QN908x ultra-lower-power Bluetooth 5 module which operates in the transmission mode with -4 dBm of output power.