Accuracy Improvement of Magnetic Field Measurement in WPT Systems

In this paper, we present an electromagnetic field visualization system that integrates magnetic field measurement with augmented reality (AR) technology. A key aspect of this system is accurately converting the voltage measured by a shielded loop probe into magnetic field strength using a conversion coefficient derived from Faraday's law. Traditionally, this conversion requires frequent calibration due to inhomogeneous magnetic fields and probe dimensions. In this study, we validate that by designing a probe with sufficiently small electrical dimensions—a radius of approximately 9.7 mm at 13.56 MHz—the magnetic field within the probe area can be considered homogeneous. This allows for the direct application of the theoretical conversion coefficient without the need for calibration. Through full-wave simulations and experimental measurements using a two-loop coil as the device under test (DUT), we demonstrate that the theoretical CVH remains consistent in regions where the magnetic field is homogeneous. Our results confirm the validity of the proposed equation and enhance the practicality of electromagnetic field visualization systems.

I. Introduction

Recently, more and more WPT applications have emerged for electric vehicles (EVs) [1]. While roadway-powered EVs can lead to smaller batteries and eliminate charging wait times [2], the potential health effects caused by exposure to radiofrequency electromagnetic energy must also be considered [3]. To address these public concerns and facilitate more intuitive electromagnetic field measurements, we developed an electromagnetic field visualization system based on augmented reality (AR) technology [4]. In such system, the most important aspect is to measure the magnetic field accurately. Traditional magnetic field probes require calibration to account for factors like probe shape, device under test (DUT), relative positioning, and frequency, making the process time-consuming and inconvenient. In this paper, we will present and validate a method to calculate the magnetic field directly from the voltage measured by a shielded loop probe using a conversion coefficient derived from Faraday's law. This coefficient is typically valid under the assumption of a homogeneous magnetic field which can reduce the effort of frequent calibration to the probe.