Low-Power Energy Harvesting Solutions for Wiegand Transducers

This paper proposes the use of Wiegand magnetic sensors as energy harvesters for low-power electronic equipments. When subject to an external, time-varying magnetic field, a Wiegand device releases a triangular voltage pulse several volts wide and of the duration of a few tens of microseconds. Due to the sharpness of the magnetic transition, pulse generation occurs regardless of how slowly the magnetic field variation occurs, an attractive feature which enables its use as an energy harvester even in the presence of low-frequency sources. In this paper, commercial Wiegand sensors are first experimentally characterized, with the purpose of devising a simple electrical model and derive the conditions for maximum energy extraction. Next, the use of Wiegand devices is discussed in the context of two modes of operation, namely, one-shot and battery-charging. In the former, the energy delivered by the Wiegand pulse is entirely utilized by the load circuitry in a one-shot fashion. In the latter, the Wiegand device is periodically excited so as to continuously deliver charge to an on-board rechargeable battery. Harvesting circuits are presented for both cases, and simulations and experimental results are provided supporting the developed theory and the effectiveness of the proposed implementations. With proof-of-concept harvesting prototypes based on discrete components, experimental figures of the extracted energy per pulse amount to $mathrm {24~ text {n} text {J} }$ /pulse in one-shot operation and $mathrm {30~ text {n} text {J} }$ /pulse in the battery-charging case.