A Calibration Method for Spatial Resolution of Magnetic Probes Using a TEM Cell-Excited Slotted Rectangular Waveguide in Evanescent Mode

The spatial resolution of near-field magnetic probes is a crucial performance metric for conducting spatial field measurements in practical applications. However, the commonly adopted approaches for determining the spatial resolution of the probe face substantial ambiguity and limitations. Addressing this issue, a generalized definition of magnetic probe spatial resolution is proposed, which correlates directly with the effective size of the probe’s sensing front end. Following this definition, a novel calibration method is introduced, utilizing the evanescent field within a rectangular waveguide structure. This calibration method is implemented on the basis of a custom-designed transverse electromagnetic (TEM) cell, whose performance has been validated both in simulations and in experiments. The proposed method effectively mitigates uncertainties arising from the measurement position and field distribution, enabling a universal and accurate assessment of the spatial resolution of the probe. The efficacy of the calibration method is validated on a commercial magnetic probe. The comparative analysis demonstrates that the proposed calibration technique yields significantly improved accuracy compared to the existing method for determining the spatial resolution of the probe.

I. Introduction

Near-field measurement has been widely adopted in electromagnetic emission testing and diagnosis [1], [2], [3]. Near-field magnetic probes are measurement components suitable for conducting noncontact near-field measurements and are capable of capturing radiated field distributions of small structures, e.g., component pins, bypass capacitors, chip packages, etc. [4], [5], [6]. To accurately measure these microstructures, the spatial resolution of the probe is a critical parameter. If the probe’s spatial resolution exceeds the distance between two amplitude peaks of the spatial field, the probe could be insensitive to changes in the electromagnetic field within this range, resulting in inaccurate measurement results [7]. As the dimensions of structures within integrated circuits continue to shrink, magnetic probe design is evolving to achieve higher spatial resolution to distinguish electromagnetic radiation from miniature structures [8], [9]. Universal methods to accurately assess the spatial resolution of a given near-field magnetic probe, however, have not been investigated extensively.