In het vakgebied van Elektromagnetische Compatibiliteit (EMC) kunnen globaal twee fenomenen beschouwd worden: de emissie en de immuniteit van elektronische producten.
Emissiemetingen van elektronische producten worden uitgevoerd voor de bescherming van radio systemen. We spreken van een emissiemeting via geleiding als er een stroom wordt gemeten en van een meting van emissie via straling als een elektromagnetische veldgrootheid gemeten wordt. Immuniteitstesten worden uitgevoerd om elektronische producten te testen op de bestendigheid tegen elektromagnetische stoorsignalen.

New concepts for EMC standards applicable to multimedia products

Correction factors between test sites are conventionally based on the antenna pattern of a tuned 1/2 /spl lambda/ dipole. Actual devices show diverse antenna patterns and correlation between results obtained at different test sites fails. This is shown in this paper using an Open Area Test Site, a Semi-Anechoic Chamber, a Full Anechoic Chamber and a Reverberating Intrinsic Reverberation Chamber for emission measurements between 20 MHz and 1 GHz. Differences between the sites of more than 40 dB can be observed.

Radiated electromagnetic fields of actual devices measured in different test environments

Correlating measurement data is a task many EMC engineers face when performing precompliance testing. Correlation, creating a point-for-point similarity between two measurement systems, is often the approach taken to determine if product modifications are needed before performing an, often costly, compliance scan. However, correlation methodologies rely on calibration methods which are inadequate in determining point-for-point measurement similarity for devices with non-rigid structures. This inadequacy has been quantified as measurement uncertainty in various standards. The inability to correlate measurements absolutely is further exacerbated by alternate test environments and a lack of industry agreement on standard test procedures. The authors have developed a novel approach for determining the pass/fail status of an EUT from precompliance data taken from uncorrelated measurement systems. This simple and effective approach evaluates past compliance data and applies it to the current precompliance data set. The EMC engineer is thereby enabled accurately to predict if a unit will pass or fail the forthcoming compliance scan, regardless of site-to-site correlation.

EMC precompliance testing - prediction not correlation

The goal of the COST IC1407 Action is to investigate the radiated emission characteristics in densely integrated technologies. One of the promising techniques for this application is the Near Field Scanning (NFS), as it allows to measure the near field intensity with a very high resolution, which is especially useful for tracking down critical components, even on a board level. The results can additionally be translated to the far field equivalents, comparable with the conventional emissions measurement standards. In this study, we investigate this technique with respect to another, commonly recognized emission measurement techniques, such as semi-anechoic chamber (SAC), fully anechoic room (FAR), gigahertz transverse-electromagnetic (GTEM) cell, and reverberation chamber (RC). As opposed to classical round-robin tests, where a simple reference radiator is measured, in order to increase the harshness of our tests, we used as a test sample with very complex, unpredictable and unstable behavior, an Intel Galileo board- a perfect example of real equipment.

Different Test Site Analysis of Radiated Field Measurements of a Complex EUT

Electro-magnetic compatibility (EMC) is the important parameter to guarantee that electronic and electrical products are electronically compatible with their environments. Radiated immunity (RI) testing, also called radiated susceptibility (RS) testing, requires a high field strength to illuminate the equipment under test (EUT). The crucial and important components of a susceptibility test system are the indispensable and high-cost power amplifier, an anechoic chamber (AC) and a proper antenna. The challenge and topic of this thesis is to make the RS test more effective to lower the cost of equipment, and more efficient by saving test time, while maintaining or improving the quality of the test results. There are three major techniques for creating high field strength for RS testing: an antenna inside the AC, an enclosed coaxial structure like the transverse electromagnetic (TEM) cell, or the reverberation chamber (RC). This thesis studies two methods: the antenna structure as a transmitting transducer inside the AC and the RC structure for creating high field strength for EMI testing. First, the antenna technique has been investigated by exploring and improving our understanding of the power required by the antennas and resulting field obtained in the uniform field area (UFA). By means of measurements (empirical) and numerical simulation it is shown that a double-ridged guide horn (DRGH) is comparable to a double log-periodic dipole array (LPDA) antenna in terms of power-to-field-strength and is slightly better in creating good field uniformity. Additionally, two different RS test methods have been studied showing that the size of the EUT affects the field strength. This research result supported the change in some standards where pre-calibration (or substitution) is now preferred above closed-loop-levelling when testing large EUT. Radiated electromagnetic (EM) field measurements in different environments, using the AC antenna technique, the TEM method, and the RC method have been investigated to analyze the relationship between the receive- radiation-pattern of an EUT and the test technique. Focusing on RS, this research could have been using an EUT with indication of the perceived field strength. In this work, such a fictitious EUT was replaced by a field strength sensor. By adding a box with different holes and hole patterns, a real-life EUT could be replicated. Although using this validation approach is very valid, it is cumbersome and costly, as high-power amplifiers are needed for all test environments. By using the reciprocity concept, the validity of comparing test environments is performed using radiated emission measurements where a broadband emitter was used as source. One major issue in applying the RC technique is the slow readout of electric field strength probes, and a key limiting factor in a widespread use of RCs. Furthermore, the number of sensors is often limited. In some standards, the field strength is monitored and/or measured using a single antenna (polarization). In various measurements described in this thesis fast three-dimensional (3D) sensors which allows time-efficient RS testing. Moreover, the fast and very sensitive field probe are best suited for vibrating intrinsic reverberation chamber (VIRC) measurements, which have rapid and time-varying electric field (E-field) behavior inside the chamber. To prove these advantages, a major automotive company has applied the VIRC and the fast multi-probe system that allows closed-loop EMC evaluation of large and complex systems. Finally, the RS test inside AC and VIRC with the box with field probe inside to represent EUTs were investigated to analyze the EUTs behavior and its susceptibility to the high E-field coming from various directions. The results showed that at higher frequencies, with thirty-six points in rotation increments, the probe inside the box received higher E-field strength than the target field. This implies that there is a high probability that in this frequency range the worst-case interference is coupled into the box and hitting the most susceptible part of the EUT. In the VIRC, with lower power and faster measurement time, the same results are also obtained. In conclusion, the classic antenna technique in the AC method is expensive mainly due to the necessary EM absorbers and expensive power amplifiers. Furthermore, the current AC method has limited robustness, since a few incident directions and field polarizations are tested, and thus does not resemble actual living and working environments. The (VI)RC has much lower costs for equipment, and illuminates an EUT from all directions, thus resembling actual living and working environments. Further research is suggested and could be focused on the behavior of EUT for directivity and in time-varying fields. The directivity becomes important at higher frequencies. Time-varying fields play a role in the dwell time, which is the time an EUT is illuminated.

/pdf/high-strength-electromagnetic-field-generation-for-radiated-a5yx0auxok.pdf

G. Hilverda

Papers

Radiated electromagnetic fields of actual devices measured in different test environments

Correlation between Simulated and Measured Radiated Electromagnetic Fields in Different Test Environments