Abstract
Magnetic near-field probes (NFP) represent a suitable tool to measure the magnetic field level from a small electromagnetic interference (EMI) source. This kind of antenna is useful as a magnetic field probe for pre-compliance EMC measurements or debugging tasks since the user can scan a printed circuit board (PCB) looking for locations with strong magnetic fields. When a strong H-field point is found, the designer should check the PCB layout and components placement in that area to detect if this could result in an EMI source. This contribution focuses on analyzing the performance of an easy to build and low-cost H-field NFP designed and manufactured using a standard PCB stack-up. Thereby, the frequency range and sensitivity of the NFP-PCB are analyzed through a Finite Element Method (FEM) simulation model that makes it possible to evaluate its sensibility and effective frequency range. The numerical results obtained with the FEM models are validated against measurements to verify the design and performance of our NFP. The FEM model reproduces the experimental procedure, which is used to evaluate the performance of the NFP in terms of sensitivity by means of the simulated near-field distribution. The NFP-PCB has almost a flat response from 180 MHz to 6 GHz, with an almost perfect concordance between numerical and experimental S21 results. The numerical results show an average transmission loss of −27.9 dB by considering the flat response bandwidth, whereas the experimental one is −29.7 dB. Finally, the designed NFP is compared to two high-quality commercial probes in order to analyze its performance.
Highlights
A non-symmetrical shielded loop would not cancel out the flowing currents associated to tangential E-field and would be sensitive to this tangential E-field. These unbalanced currents would induce a secondary magnetic field which would induce secondary extra signal in the central conductor, masking the first one associated to the intended Hfield measurement [23,34]. When this narrow aperture on the shielding layers is located at the middle of the loop, and the common-mode currents on the external surface of the shield from the E-field can be cancelled based on the symmetric distribution, the near-field probes (NFP) is placed perpendicular to the source of emissions [39]
Bution of the magnetic field strength. This microstrip line (MSL) fixture is powered by a sweep frequency signal with a fixed power that generates a specific field that is acquired by the NFP by means of the S parameters. This measurement setup was numerically modeled with a Finite Element Method (FEM) simulator to determine the S21 of the NFP-printed circuit board (PCB) in order to make comparison with the experimental measurements obtained from the experimental setup
The knowledge of the gain is not torted by the spurious radiation of theoffeed of the gain is not relevant for the NFP-PCB operation because it is used in the near field region; it14isofnuElectronics 2021, 10, x FOR PEER REVIEW
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The continuous implementation of new advanced functionalities and the miniaturization of electronic devices for embedded systems has become a serious difficulty in terms of electromagnetic compatibility (EMC), especially in those than integrates communication modules [10,11,12] This evolution usually involves a higher component integration, printed circuit board (PCB) size and thickness reduction, and the miniaturization of the device housing [13,14]. It is essential to perform EMI measurements using different instrumentation, measuring probes and antennas to detect the electromagnetic fields that can provide information to the designer from undesired signals [7]. Radiated emissions are measured in far-field following the compliance testing They are regulated by standards to verify our system does not interfere with other equipment [26].
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