Attendance Tracking System using Many Battery-free Photovoltaic Bluetooth Beacon Badges

The concept of ambient IoT was introduced by 3GPP to describe low-cost, self-powered, or battery-free sensor nodes, which may reach up to 10 trillion units in the future. By replacing chemical batteries in many standalone IoT devices, we can achieve ubiquitous connectivity through environmentally friendly and maintenance-free solutions. This paper presents a systematic design of an attendance tracking system utilizing battery-free photovoltaic (PV) Bluetooth beacon badges, along with several stationary gateways. In particular, the experiences with real-world massive deployments of these battery-free Bluetooth badges are emphasized. Thanks to a customized power management design that experiences only nano-watt power leakage before activation, these beacon badges can operate in low-light environments by gradually accumulating energy from indoor lighting, functioning in conditions as low as 17 Lux. The design prioritizes cost-effectiveness, making these badges suitable for potential commercialization, with each compact badge measuring only 40 × 30 × 4 mm3 and a bill of materials (BOM) costing less than $1. In field tests, every attendee at an academic conference wore a souvenir battery-free PV badge, which broadcasted a packet once sufficient power was accumulated. Stationary gateways installed in various conference rooms collected attendance information, while a cloud-based program was developed to visualize the results.