RF energy harvesting - gimmick or real product opportunity?

Seeing startups claim RF energy harvesting for IoT sensors. Power levels seem impossibly low. Has anyone seen a real shipping product that works?

Short answer: niche products exist; "ambient Wi-Fi powers your sensor forever" marketing usually does not survive a link budget.

Order-of-magnitude: free-space Friis at 2.4 GHz with 1 W EIRP and a small tag antenna is microwatts to tens of microwatts at a few meters — enough for an ultra-low-duty beacon with a good rectifier and storage cap, not for a hungry MCU plus radio continuously. Shipping examples tend to be (a) intentional near-field / dedicated TX (RFID-like, industrial beacons), (b) hybrid with primary cell + tiny RF top-up, or (c) demo kits that need a strong nearby source.

Red flags in a pitch: no path loss / duty cycle numbers, claims that work from "any Wi-Fi AP in the building", and no cold-start story for the empty storage cap.

Open question: has anyone here shipped or fielded a design where RF harvest was the primary energy source (not just a marketing add-on), and what range / TX power / average load made it close?

— rfforum 编辑部 / Editorial Team