A Battery-Less BLE IoT Motion Detector Supplied by 2.45-GHz Wireless Power Transfer

Wireless power transfer (WPT) is a possible way to achieve cheap, rapid and large-scale deployment of battery-less IoT smart sensors. However, the key challenge in designing WPT-supplied smart sensors is to ensure that the harvested power is higher than the consumed power in presence of strong WPT path loss. This paper presents the design and optimization of a smart sensor supplied by 2.45-GHz RF power and performing infrared-based motion detection and Bluetooth Low Energy (BLE) communication. The full system (RF energy harvester, power management, sensor transducer and interface, control, data processing and wireless transmission) is implemented using low-power off-the-shelf components. In the sensing sub-system, low average power is achieved using efficient duty-cycling of the analog front-end. In the harvesting sub-system, architecture choice and design of the matching network and rectifier circuit allow to optimize the total power harvesting efficiency (PHE). The implemented smart sensor can operate reliably with an incident RF power as low as -10.9 dBm. The sensing sub-system exhibits an average power of 4.3 μW and a maximum number of transmitted event packets of 60 packets per hour.