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The electromagnetic environment inside a shielding enclosure is affected by the absorption characteristics of the contents, which should therefore be represented in shielding measurements and simulations. At frequencies up to a few gigahertz, lossy dielectric materials have previously been used as surrogates for printed circuit boards in enclosure shielding assessment, both experimentally and in simulations. However, no systematic methodology for the design of these surrogates and their calibration against real hardware at high frequencies has been elucidated. In this paper we show how both lossy dielectric material and microstrip transmission line based “representative contents” can be designed and calibrated against real printed circuit boards over the frequency range 2-20 GHz using power balance concepts. The calibration is made by matching the average absorption cross-section of the surrogate to an average value for a class of real contents measured in a reverberation chamber. The surrogates are designed using efficient power balance models for layered media and field-excited microstrip lines and verified using full-wave simulation. The fabricated surrogates are validated by shielding measurements. The methodology presented could form an important part of future standards for enclosure qualification measurements that more accurately represent the internal environment of real equipment.

Determination of the distribution of electromagnetic energy inside electrically large enclosed spaces is important in many electromagnetic compatibility applications, such as certification of aircraft and equipment shielding enclosures. The field inside such enclosed environments contains a dominant diffuse component due to multiple randomizing reflections from the enclosing surfaces. The power balance technique has been widely applied to the analysis of such problems; however, it is unable to account for the inhomogeneities in the field that arise when the absorption in the walls and contents of the enclosure is significant. In this paper we show how a diffusion equation approach can be applied to modeling diffuse electromagnetic fields and evaluate its potential for use in electromagnetic compatibility applications. Two canonical examples were investigated: A loaded cavity and two cavities coupled by a large aperture. The predictions of the diffusion model were compared to measurement data and found to be in good agreement. The diffusion model has a very low computational cost compared to other applicable techniques, such as full-wave simulation and ray-tracing, offering the potential for a radical increase in the efficiency of the solution high frequency electromagnetic shielding problems with complex topologies.

The inclusion of thin lossy, material layers, such as carbon based composites, is essential for many practical applications modeling the propagation of electromagnetic energy through composite structures such as those found in vehicles and electronic equipment enclosures. Many existing schemes suffer problems of late time instability, inaccuracy at low frequency, and/or large computational costs. This work presents a novel technique for the modeling of thin-layer lossy materials in FDTD schemes which overcomes the instability problem at low computational cost. For this, a 1D-subgrid is used for the spatial discretization of the thin layer material. To overcome the additional time-step constraint posed by the reduction in the spatial cell size, a Crank-Nicolson time-integration scheme is used locally in the subgridded zone, and hybridized with the usual 3D Yee-FDTD method, which is used for the rest of the computational domain. Several numerical experiments demonstrating the accuracy of this approach are shown and discussed. Results comparing the proposed technique with classical alternatives based on impedance boundary condition approaches are also presented. The new technique is shown to have better accuracy at low frequencies, and late time stability than existing techniques with low computational cost.

Computational solvers are increasingly used to solve complex electromagnetic compatibility problems in research, product design and manufacturing. The reliability of these simulation tools must be demonstrated in order to give confidence in their results. Standards prescribe a range of techniques for the validation, verification and calibration of computational electromagnetics solvers including external references based on measurement or for cross-validation with other models. We have developed a modular test suite based on an enclosure to provide the EMC community with a complex external reference for model validation. We show how the test suite can be used to validate a range of electromagnetic solvers. The emphasis of the test suite is on features of interest for electromagnetic compatibility applications, such as apertures and coupling to cables. We have fabricated a hardware implementation of many of the test cases and measured them in an anechoic chamber over the frequency range to 1 – 6 GHz to provide a measurement reference for validation over this range. The test-suite has already been used extensively in two major aeronautical research programmes and is openly available for use and future development by the community.

Body composition measurements play an important role in nutritional studies, renal medicine and sports science, while human exposure to electromagnetic fields (EMF) is an area of growing concern owing to the implementation of Directive 2013/35/EU on EMF. Resonant cavity techniques offer an attractive alternative to traditional methods in these fields, as they allow rapid, non-invasive measurements without using ionising radiation. At frequencies of a few tens of MHz, a large screened room can act as a cavity resonator. A human subject inside the room perturbs its low-order resonances, and the resulting shift in frequency depends on the tissue dielectric properties, which correlate strongly with water content. This approach has been well tested and shows good agreement with current methods of measuring total body water. The number of resonant modes increases rapidly with frequency, so if we instead use microwaves at 1GHz and above, many modes can be excited simultaneously. Adding a rotating paddle to the room creates a ‘stirred mode’ environment, where the body is effectively illuminated by microwave radiation from all directions. For EMF exposure studies this a more realistic scenario than considering only a single direction and polarisation. The average absorption cross section (ACS), which is closely related to specific absorption rate (SAR), can be rapidly obtained over a very broad band (1GHz to 15GHz and beyond), whereas the alternative is detailed computer simulations that take many hours for just a single frequency. At these microwave frequencies, the field penetration into tissues is a few cm, so the ACS gives useful information about the composition of tissues near the body surface. Normalising the ACS to body surface area gives us an ‘absorption efficiency’ that is independent of body size. Results will be presented of the relationship between this parameter and the thickness of subcutaneous body fat. Both techniques are comfortable for the subject, use safe levels (around 1mW) of non-ionising radiation, and allow measurements to be made in less than 10min.

Average ACS can be measured in a reverberation chamber; however, the existing technique determines a value that includes the effects of the radiation efficiencies of the antennas used in the measurement. Correcting for these necessitates further complex measurements. Here we present the theory of an alternative measurement methodology using two nested or contiguous reverberation chambers which is free from errors caused by the radiation efficiencies of the antennas. The new method is based on the theoretical average transmission cross sections (TCSs) of circular holes in a metal plate between the two chambers. In fact the method can be viewed as an accurate transfer calibration measurement between TCS and ACS that is independent of both the chamber and antenna characteristics. Further, since the existing method of measuring ACS includes the effects of the radiation efficiencies of the antennas, a comparison of the ACS of a reference object, measured using both the existing and new methods, also provides an alternative method of determining radiation antenna efficiency. Measurement uncertainties for both alternative measurement methods – ACS and antenna radiation efficiency – are also derived.

The contents of an equipment enclosure, particularly printed circuit boards (PCBs), affect the enclosure’s shielding performance. At high frequencies this absorption can be quantified using the angle of arrival and polarization averaged absorption cross-section (ACS). However, there is no available data on the high-frequency absorption characteristics of modern PCBs. In this study we apply a reverberation chamber to the determination of the average ACS of a large number of printed circuit boards taken from contemporary information and communication technology (ICT) equipment to provide a unique and comprehensive data-set. The ACS was found to range from 4×10-4 –10-2 m2 from 2-20 GHz and different classes of PCB could be identified according to their surface characteristics. The "shadowing effect" of densely packed PCBs was also quantified for a subset of the PCBs. It was found that the ACS of a PCB in the stack was reduced by 20% - 40% compared to its value when isolated. By way of a review of the general power balance analysis of an electrically large populated equipment enclosure in an external environment we show how the acquired data will be useful for future qualification methodologies for ICT enclosures and PCBs.

This paper reports the results of two experimental campaigns aimed at studying the high-frequency response of a raceway containing low voltage power, telephone, and Ethernet cables, to external electromagnetic field illumination. The raceway was tested against HPEM transients inside a GTEM cell and low power fields inside a reverberation chamber (RC). The HPEM tests revealed that the low voltage power cables have the greatest coupling under a hyperband illumination, compared to telephone and Ethernet cables. The RC tests allowed the determination of statistical transfer functions from random incident field configurations into DM voltage in cable loads. The responses were found to be governed by the raceway under test at the lower frequencies (below 1 GHz). Between 0.2-1 GHz, the raceway gives about 10 dB higher coupling than a short patch cable. The difference is even greater at lower frequencies and for shielded cables. In the frequency band 1-3 GHz, little difference was observed between short patch cables and the full raceway, but both were still significantly higher than direct coupling to the measurement card. Beyond 3 GHz, the coupling is clearly dominated by the terminal equipment. The experiments performed in this work provide a better understanding of the expected induced voltages and currents in commercial cable systems when exposed to IEMI-like signals.

Average absorption cross section can be measured in a reverberation chamber with an uncertainty estimated from the number of independent samples of the chamber transfer function taken during the measurement. However, the current uncertainty model does not account the loading effect of the object being measured or the presence of nonstochastic energy in the chamber, as characterized by the Rician K-factor. Here, the uncertainty model for the absorption cross-section measurements has been extended to include both of these effects for the case of stepped mechanical tuning with a paddle and frequency tuning. The extended uncertainty formula has been applied to predict the range over which absorption cross-section measurements can be made with a defined relative uncertainty in a chamber of given geometry, using both simple models for the reverberation chamber and the measured quality-factor and K -factor. The model has been validated using measurements on a set of absorbing cubes of different sizes compared to Mie Series calculation on sphere of equivalent surface area. The extended error model is particularly utile for the design of reverberation chambers and experiments for absorption cross-section measurements across a wide range of application areas.

A measurement methodology for polarization and angle of incidence averaged electromagnetic absorption cross-section using a reverberation chamber is presented. The method is optimized for simultaneous rapid and accurate determination of average absorption cross-section over the frequency range 1–15 GHz, making it suitable for use in human absorption and exposure studies. The typical measurement time of the subject is about 8 min with a corresponding statistical uncertainty of about 3% in the measured absorption cross-section. The method is validated by comparing measurements on a spherical phantom with Mie series calculations. The efficacy of the method is demonstrated with measurements of the posture dependence of the absorption cross-section of a human subject and an investigation of the effects of clothing on the measured absorption which are important considerations for the practical design of experiments for studies on human subjects.

We present broadband reverberation chamber measurements of the absorption cross section (ACS) of the hu- man body averaged over all directions of incidence and angles of polarization. This frequency-dependent parameter characterizes the interactions between the body and the enclosures of rever- berant environments such as aircraft cabins, and is therefore important for the determination of the overall Q-factor and hence the field strength illuminating equipment inside such en- closures. It also correlates directly with the electromagnetic expo- sure of occupants of reverberant environments. The average absorption cross section of nine subjects was measured at fre- quencies over the range 1-8.5 GHz. For a 75 kg male the ACS varied between 0.18 and 0.45 square meters over this range. ACS also correlated with body surface area for the subjects tested. The results agree well with computational electromagnetic simu- lations, but are obtained much more rapidly. We have used the obtained values of absorption cross section to estimate the effect of passengers on the Q-factor of a typical airliner cabin. Index Terms—reverberation chamber, absorption cross

A method is presented for the measurement of shielding effectiveness of planar materials with nonconducting surfaces such as carbon fiber composites. The method overcomes edge termination problems with such materials by absorbing edge-diffracted energy. A dynamic range of up to 100 dB has been demonstrated over a frequency range of 1-8.5 GHz, depending on the size of the sample under test. Comparison with ASTM D4935 and nested reverberation measurements of shielding effectiveness shows good agreement.

This paper presents some thoughts on how to compare the results from a numerical electromagnetic solver with measured data in a reverberant environment where a large number of resonant modes are present in the data.