Magnetostatic field noise near metallic surfaces

TL;DR

This paper develops a low-frequency electromagnetic theory to accurately compute thermal magnetic noise spectra near metallic microstructures, addressing previous discrepancies in the field.

Contribution

It introduces a new theoretical approach that accounts for dielectric discontinuities at metal boundaries, improving the accuracy of magnetic noise predictions near microstructures.

Findings

Resolved discrepancies between previous methods

Provided a more accurate model for magnetic noise spectra

Highlighted the impact of dielectric jumps on magnetic field screening

Abstract

We develop an effective low-frequency theory of the electromagnetic field in equilibrium with thermal objects. The aim is to compute thermal magnetic noise spectra close to metallic microstructures. We focus on the limit where the material response is characterized by the electric conductivity. At the boundary between empty space and metallic microstructures, a large jump occurs in the dielectric function which leads to a partial screening of low-frequency magnetic fields generated by thermal current fluctuations. We resolve a discrepancy between two approaches used in the past to compute magnetic field noise spectra close to microstructured materials.