Powering-up Wireless Sensor Nodes Utilizing Rechargeable Batteries and an Electromagnetic Vibration Energy Harvesting System

This paper presents the design, development, and comprehensive evaluation of a self-sustaining wireless sensor network (WSN) powered by an electromagnetic (EM) vibration energy harvester. The proposed system integrates a compact EM energy harvesting module with MicaZ wireless sensor nodes, enabling continuous battery recharging during node operation and significantly extending the system’s operational lifetime without the need for manual battery replacement.

The custom-designed energy harvester is optimized for low-frequency environmental vibrations, particularly at 7.4 Hz and 0.4 g—frequencies typically observed in human activity, machinery, or structural vibrations. The harvested energy is rectified through a high-efficiency two-stage Dickson rectifier and stored in NiMH rechargeable batteries. This energy is then regulated to power the sensor node in real time. The total volume of the harvester and electronics is just 24.5 cm³, approximately the size of a C-type battery, making it highly suitable for embedded and portable applications.

Extensive power profiling and component-level current analysis were performed on the MicaZ mote, revealing that most of the energy is consumed during active transmission and sensor readout phases. By programming the node to operate with low RF power levels (e.g., −25 dBm) and enter standby modes between transmission events, the average power consumption was reduced to 186 µW under a 1-minute data transmission interval. In this configuration, the EM harvester was able to meet 90% of the power demand, resulting in more than a 10-fold increase in battery lifetime.

The study also investigates charging characteristics, battery discharge behavior, and the effectiveness of different task execution intervals (1 s, 20 s, 1 min). Results demonstrate that duty cycling and energy-aware scheduling are essential for maximizing the benefit of ambient energy harvesting. When properly tuned, the system operates near energy neutrality, where harvested power nearly matches or exceeds energy consumption, keeping batteries at a healthy charge level and further extending their lifespan by minimizing deep discharge cycles.

The developed system was tested under both laboratory and emulated real-world conditions, with detailed measurements of battery current, voltage, and load characteristics. The experimental platform demonstrated online charging capability—batteries were recharged while powering active sensor nodes—and achieved continuous autonomous operation without external intervention.

This energy harvesting framework represents a scalable, low-maintenance solution for WSN deployments in remote or hard-to-access environments, including structural health monitoring, offshore condition monitoring, bridge and tunnel diagnostics, and environmental sensing. By aligning hardware-level energy harvesting with software-level duty cycle optimization, the work paves the way for truly energy-autonomous sensing networks.

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