Abstract
Magnetostrictive NiFeCo alloy films were investigated for use as sensors for ground fault current detection in photovoltaic systems. The magnetic field generated by a ground fault current applies a bias magnetic field to the magnetoelastic sensor, shifting the resonant frequency, and allowing for the detection of current in the microamp range. These are low-cost, passive sensors, that can be implemented to provide real time monitoring of PV systems and the early detection of failures in a system. Electrodepositing these films enables batch fabrication of thick (10-100µm) resonators with controlled resonant frequencies and optimization of material properties (magnetic, mechanical, and electrical) for increased sensitivity and signal amplitude.Dopants such as boron and holmium were used to increase electrical resistivity and magnetic permeability respectively. Controlling intrinsic stress was managed through additive selection and allowed for the release of planar resonators with a multistep microfabrication process. The composition and properties of the deposited films were controlled by temperature, agitation, concentrations in the electrodeposition chemistry, current density, and a post processing anneal step. The samples were analyzed with EDS to determine the composition and XRD to look at film texture. Magnetic testing was performed using a super conducting quantum interference device (SQUID) magnetometry and vibrating sample magnetometry (VSM). Magnetostriction was measured using an optical method and correlated to material properties. Acknowledgement Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Published Version
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