A new design for an energy harvesting device is proposed in this paper, which enables scavenging energy from radio frequency (RF) electromagnetic waves. Compared to common alternative energy sources like solar and wind, RF harvesting has the least energy density, and hence, the need of efficient design and optimization. The existing state-of-the-art solutions are effective only over narrow frequency ranges, are limited in efficiency response, and require higher levels of input power for successful operation. This paper has a twofold contribution: First, we propose a dual-stage energy harvesting circuit composed of a 7-stage and 10-stage design, the former being more receptive in the low input power regions, while the latter is more suitable for higher power range. Each stage here is a modified voltage multiplier, arranged in series and our design provides guidelines on component choice and precise selection of the crossover operational point for these two stages between the high (20 dBm) and low power (-20 dBm) extremities. We also show that the amount of harvested energy can be increased by implementing multiple input antennas. Second, we fabricate our design on a PCB to demonstrate how such a circuit can run a commercial Mica2 sensor mote, with accompanying simulations on both ideal and non-ideal conditions for identifying the upper bound on achievable efficiency. With a simple yet optimal dual-stage design, experiments and characterization plots reveal approximately 100% improvement over other existing commercialized designs in the power range of ?20 dBm to 7 dBm.