Ambient RF-energy harvesting at 900 MHz

Abstract

In this thesis a RF-energy harvesting system able to harvest ambient power at 900MHz(GSM band) is simulated. Especially the efficiency at low power is of interest (-19 to -23 dBm rectifier input). A rectifier and a boost converter is simulated in Advanced Design System (ADS) to determine the efficiency and output voltage. A power managing circuit able to turn the load (nRF52 chip from Nordic Semiconductor) on when sufficient power is accumulated is also presented. Simulations show that a 3-stage rectifier is optimal to maximize efficiency. The efficiency is 32.4 % and 19.6 % at input powers of -19 dBm and -23 dBm. The output voltages are 435 mV and 184 mV respectively. The boost converter is simulated with input powers from -24 dBm to -30 dBm (output of rectifier). It is able to charge a capacitor to 2.5 V at all simulated input powers. The efficiency with 2 V output voltage is 61.7 % and 52.2 % with input powers of -24 dBm and -30 dBm. Since the loss in the oscillation network is not included these efficiencies are overestimated. The total efficiency is 20.0 % and 10.2 % at input powers of -19 dBm and -23 dBm. It is shown that the harvester can provide power to the nRF52 chip at input powers down to -21 dBm if the oscillation network consumes less than 733 nW. With this power consumption, estimates of the charge time reveal that the load can broadcast air temperatures at intervals of 84 seconds when the input power is -19 dBm. The interval is 188 seconds and 977 seconds (17 minutes) at input powers of -20 dBm and -21 dBmrespectively. If the oscillation loss is less than 367 nWthe harvester can operate down to -22 dBm.