Demonstration of energy-neutral operation on a WSN testbed using vibration energy harvesting

This study presents the design, implementation, and experimental validation of a wireless sensor network (WSN) testbed achieving energy-neutral operation through electromagnetic vibration energy harvesting. As part of the Chist-ERA E-CROPS project, the testbed employs MICAz motes equipped with MTS310CB sensor boards and TinyOS, operating over IEEE 802.15.4-compliant ZigBee communication protocols. Energy-neutral operation—defined as the condition where the energy harvested equals or exceeds the energy consumed—is demonstrated through comprehensive measurements and optimization of node duty cycles.

A custom-designed electromagnetic energy harvester (EMH) is developed to exploit low-frequency ambient vibrations (around 10 Hz) commonly found in human environments and industrial systems. The harvester consists of a cylindrical package with fixed and moving magnets, surrounded by a 650-turn coil and coupled with a two-stage Dickson rectifier to efficiently convert AC output to usable DC voltage. The compact energy harvesting module, comparable in size to a pair of AA batteries, is capable of charging 1800 mAh batteries over time and sustaining continuous sensor node operation when appropriately configured.

Extensive current consumption profiling is carried out across different hardware components, including the microcontroller, transceiver (in multiple TX power levels and RX mode), accelerometer, and LEDs. These empirical measurements form the basis of an energy consumption model that guides system-level optimization, including protocol selection, component scheduling, and duty cycle adjustment.

The experimental setup demonstrates that under optimized conditions—e.g., reduced RF power, low-frequency sampling, and deactivated non-essential peripherals—the energy provided by the harvester can fully offset the operational demand of the WSN nodes. This is validated through a comparative battery discharge analysis, where nodes powered by the energy harvester show significantly reduced or nearly flat discharge curves, especially when data transmission occurs at longer intervals (e.g., once per minute).

This work proves the feasibility of self-sustaining WSN nodes powered solely by ambient vibration energy. It highlights the synergy between hardware-level energy harvesting, low-power embedded design, and energy-aware software scheduling. Future developments will explore enhanced harvester designs at lower frequencies and alternative transduction mechanisms (e.g., piezoelectric), with the goal of enabling broader deployment of autonomous, maintenance-free WSNs in smart infrastructure, industrial monitoring, and IoT applications.

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