How do I design an RF energy harvesting system for powering low power IoT devices?

Designing an RF energy harvesting system for powering low-power IoT devices captures ambient RF energy from the electromagnetic environment (cellular base stations, Wi-Fi access points, TV broadcast towers) and converts it to DC power for the IoT device. The system consists of: an antenna (a wideband or multi-band antenna that captures RF energy across the available spectrum; the antenna's effective area determines how much RF power is collected: P_received = P_density × A_effective, where P_density is the ambient power density (typically -20 to -40 dBm/m^2 in urban environments) and A_effective = G × lambda^2 / (4 × pi)), a matching network (an impedance matching circuit between the antenna and the rectifier; critical for maximizing power transfer; the matching must accommodate the rectifier's nonlinear, power-dependent input impedance), a rectifier (an RF-to-DC converter, typically using Schottky diodes (HSMS-2860, SMS7630) for low turn-on voltage; a voltage doubler or multi-stage Dickson charge pump topology multiplies the output voltage to a useful level (1.8-3.3V for powering electronics); the rectifier's efficiency depends strongly on the input power level: 40-70% at 0 dBm, 10-30% at -20 dBm, and drops rapidly below -20 dBm), and a power management IC (PMIC; a boost converter or charge pump that regulates the rectifier's output to the required voltage; includes energy storage (capacitor or thin-film battery) to buffer the intermittent harvested energy; specialized PMICs: TI BQ25570 (can cold-start from as little as 100 mV input)).