Tim Claeys

Correlating the High-Frequency Shielding Performance of 'On-Board' Gaskets when Characterized using a Stripline or Reverberation Room Method

This paper compares the shielding performance or shielding effectiveness of gaskets for on-board applications when determined with either a stripline method or a reverberation room method. The shielding performance is considered in the frequency range from 1 up to 40 Ghz. Similar to PCB-level enclosures, gaskets for on-board applications differ significantly from other shielding products, therefore requiring an appropriate definition for their shielding effectiveness. It is shown by full-wave simulations that a 3rd order polynomial fit of the shielding effectiveness obtained with the stripline method correlates well with the shielding effectiveness obtained with a reverberation room method, in which case the shielding effectiveness is defined as the ratio between the radiated/received power with and without gasket.

Auxiliary Dipoles to Compensate for the Finite Size of the Planar Scanning Area in Near-to-Far-Field Transformations

A novel algorithm to obtain an accurate representation of the far-field emissions starting from a finite planar scan of the magnetic near-field is proposed. The algorithm introduces so-called auxiliary sources that compensate for the finite size of the scan area. While previous works typically introduce equivalent sources to represent the fields inside the scanning area, the auxiliary sources introduced in this paper approximate the fields outside of the scanning area. The auxiliary sources are located within the printed circuit board under the scanning area at the locations where the scanned field strengths are above a prechosen threshold. Their complex values are chosen such that they accurately represent the fields at the edge of the scanning area. Several numerical examples show that the application of these auxiliary sources considerably improves the accuracy of the obtained far-field.

Removing the Spectral Leakage in Time-Domain Based Near-Field Scanning Measurements

This paper describes the application of a new and easy to implement algorithm to EMI near-field scanning measurement results obtained with a time-domain-based measurement system. The algorithm aims to reduce the effect of spectral leakage on amplitude and phase of the measured field components. The proposed algorithm significantly increases the accuracy of the measured electromagnetic near field with a limited extra computational cost. The versatility and effectiveness of the proposed algorithm is shown on both simulated and measured data. It is shown that for situations with one single frequency component or with several well-separated frequency components, the algorithm is as performant as the application of a flat top window and outperforms other types of windows. However, as soon as the frequency components approach each other implying their spectral leakage patterns overlap, the proposed algorithm outperforms the application of a flat top window.

Towards a stripline setup to characterise the effects of corrosion and ageing on the shielding effectiveness of EMI gaskets

This paper introduces a novel measurement set-up dedicated to the characterization of the evolution of the high-frequency shielding-effectiveness of gaskets due to corrosion and ageing. The measurement set-up is based on the recently introduced stripline set-up which has been validated previously up to 40 GHz. Compared to the original stripline set-up, the adapted set-up has a removable “clamping module” which can be easily mounted and removed from the set-up. The clamping module allows to age the gasket inside e.g. a climate chamber while always keeping the gasket under the same compression rate. As the clamping module can be made out of different materials, it allows to study the influence of shielding-effectiveness of gaskets when applied to different materials. In order to avoid parallel leakage inside the measurement set-up, a high-performant gasket needs to be compressed below the module. Based on full-wave simulations, it is shown that the shielding-effectiveness given by this gasket underneath the clamping module is the main determining factor for the dynamic range of the set-up. In addition, a first set of measurements show the validity of the measurement set-up and approach.

Near-Field Edge Extrapolation Using Auxiliary Dipoles to Improve Probe Compensation

Probe compensation is an essential element in near-field measurements when accurate fields are required. However, the accuracy of probe compensation techniques heavily depends on the accuracy of the used probe factor. A major source of errors in the probe factors used in scalar and vector compensation is the truncation error. Increasing the size of the measuring plane offers a solution, but is not practical in most cases. First, not every near-field scanner allows to measure a large area. Second, increasing the size of the measuring plane also increases the measurement time. In this paper, a novel method to reduce the influence of truncation errors on probe compensation is presented. The method uses auxiliary dipoles to extrapolate the measured near-field values of the reference structure(s) outside the measuring plane. The accuracy and effectiveness of the method is evaluated for both scalar and vector compensation algorithms.

Automated line-based sequential sampling and modeling algorithm for EMC near-field scanning

In this paper, a novel algorithm that selects optimal paths for conducting automated near-field (NF) measurements is presented. The resulting dataset of measurements can then be used to model the complete NF electromagnetic emissions of an electronic device or predict the far-field emissions. The models obtained using the training sets generated with the aid of the proposed algorithm are substantially more accurate compared to existing point-based methods. The algorithm is validated by comparing it against an earlier adaptive sampling algorithm that optimizes point-based measurement datasets.

Shielding Effectiveness of anisotropic materials: How to measure?

In a number of applications, due to concerns such as weight and flexibility, shielding materials are used with anisotropic materials. Typically, in the case of some conductive textile materials, conductive yarns are only used in one direction (warp). Other materials will have different conductivity as a function of the direction, such as deployed metal grids. In this paper, measured Shielding Effectiveness SE results obtained by using different measuring setups are compared and discussed.

An Iterative Interpolated DFT to Remove Spectral Leakage in Time-Domain Near-Field Scanning

Time-domain near-field scanning is gaining more and more interest within EMC engineering to analyze electromagnetic near-fields of, e.g., quasi-stationar devices. When using a digital oscilloscope to scan the near-fields of an electronic device, the oscilloscope measures time-domain signals that comprise in most cases a large number of frequency components. For many of these components, noncoherent sampling occurs, resulting in spectral leakage when calculating the frequency spectrum of the time-domain signals with the discrete Fourier transform. This paper proposes an improved method to detect the presence of such noncoherently sampled signals as well as an iterative algorithm to obtain accurate approximations of all the frequency components with their accompanying amplitudes and phase angles. The algorithm excels over existing algorithms in obtaining these values especially in situations where several sinusoidal components are close to each other in the spectrum. This is achieved, thanks to an iterative process of removing the influence of the multiple sinusoidal components on each other. This paper contains the mathematical description of the algorithm and a numerical example evaluating the accuracy of the algorithm. The algorithm has a higher accuracy than the existing approaches, e.g., multipoint Interpolated Discrete Fourier Transform (IpDFTs), with only a slight increase of the computational cost.

Influence of sample shape and size on the shielding effectiveness of EMI when characterized with the stripline test method

This paper studies the influence of a gaskets shape and size on its high-frequency shielding-effectiveness as measured with the stripline test method. Based on full-wave simulations it is shown that the main influencing parameter for the shielding-effectiveness is the gaskets conductivity. Through a comparison with the reverberation room method, it is shown that differences due to shape and size of the gasket are not related to the stripline set-up, but are a reflection of the true shielding effectiveness of the gasket.