Alastair R. Ruddle

Application of a hybrid finite difference/finite volume method to solve an automotive EMC problem

In this paper, we present a hybrid finite difference/finite volume method and we apply it to solve an automotive electromagnetic compatibility (EMC) problem. The principles of the hybrid method and the numerical schemes are described. Simple examples are used to compare this method with the finite difference and finite volume methods alone in terms of accuracy and computing speed. The automotive EMC problem and its modeling are then presented. Finally, sample comparisons between measurements and calculations of both electric fields and S-parameters between an antenna and cables are given.

Investigation of electromagnetic emissions measurements practices for alternative powertrain road vehicles

Current automotive electromagnetic emissions measurements practices were developed for vehicles equipped with conventional internal combustion engines. However, alternative powertrain technologies based on electric and power cell power sources are not active under conventional (static) emissions test conditions. A program of measurements has therefore been conducted on a small set of representative alternative powertrain road vehicles in order to quantify their emissions and to investigate the associated practical measurement issues. This work also included investigation of emissions at frequencies from 9 kHz to 30 MHz. It is concluded that dynamic test conditions are needed to permit a more realistic assessment of the level of emissions generated by electric powertrain components.

Calibration of current transducers at high frequencies

The transfer impedances of current transducers are estimated using a special calibration fixture, which is often assumed to be perfectly matched at its coaxial ports. However, the errors inherent in this approximation increase with frequency, making the measurement of cable currents increasingly inaccurate at higher frequencies. A one-dimensional (1-D) transmission line model is proposed to account for such errors in a calibration fixture of simple design by using additional measurements to quantify the mismatches in the system. This technique is validated using a numerical model of such a calibration fixture as well against experimental data and numerical predictions for the current induced on a wire inside a rectangular cavity due to an external source that is coupled into the interior via an aperture. It is concluded that the proposed approach provides improved results with a calibration fixture of simple design for frequencies up to at least 600 MHz.

Numerical Investigation of the Impact of Dielectric Components on Electromagnetic Field Distributions in the Passenger Compartment of a Vehicle

Numerical methods have been used to investigate the possible impact of various dielectric components of vehicles on internal electromagnetic field distributions for frequencies up to 2 GHz. The electrical parameters used in the models were derived from measurements on samples obtained from vehicle components. It is found that the dielectrics investigated have a relatively small impact on the internal field populations due to sources located inside the passenger compartment. Under plane wave illumination from the front, however, the dielectric parts dampen the low frequency resonances, while the glass reduces the internal fields for horizontal polarization. Simulations of lossy materials in a vehicle-like cavity indicate that it may be possible to reduce field levels using readily available materials.

Computed SAR distributions for the occupants of a car with a 400 MHz transmitter on the rear seat

Numerical simulations have been used to investigate the impact of occupant distribution on the field exposure threat due to a transmitter operating at 400 MHz inside a car. Eight different occupancy configurations involving the driver and up to three passengers were considered, and both 10 g and 1 g SAR measures were determined. The models suggest that mean SAR limits are likely to be reached at lower power levels than would be needed to reach maximum SAR limits. The presence of the vehicle structures is found to result in higher mean SAR values for all occupant locations, although maximum SAR levels are lower with the vehicle for the driver position. It is concluded that evaluating the in-vehicle field exposure threat by comparing average fields over the interior of the empty vehicle with the reference levels recommended for assessing the exposure of the general public provides a safety factor approaching two for the source configuration under investigation.

Development of thin wire models in TLM

Numerical EMC models must cope with wide frequency ranges and complex structures. These requirements make differential time domain techniques such as transmission-line modeling (TLM) attractive. However, the structures of interest often contain elements with disparate dimensions. This can lead to enormous computing requirements, which can only be controlled by exploiting special models for features such as thin wires and slots. The performance of TLM thin wire modeling techniques, including a new multiconductor formalism, has been assessed by comparing predictions with theory, measurements and alternative numerical techniques. It is concluded that the performance of TLM models are comparable with the method of moments (MoM), and provide reasonable correlation with measurements.

Magnetic Field Exposure Assessment in Electric Vehicles

This article describes a study of magnetic field exposure in electric vehicles (EVs). The magnetic field inside eight different EVs (including battery, hybrid, plug-in hybrid, and fuel cell types) with different motor technologies (brushed direct current, permanent magnet synchronous, and induction) were measured at frequencies up to 10 MHz. Three vehicles with conventional powertrains were also investigated for comparison. The measurement protocol and the results of the measurement campaign are described, and various magnetic field sources are identified. As the measurements show a complex broadband frequency spectrum, an exposure calculation was performed using the ICNIRP “weighted peak” approach. Results for the measured EVs showed that the exposure reached 20% of the ICNIRP 2010 reference levels for general public exposure near to the battery and in the vicinity of the feet during vehicle start-up, but was less than 2% at head height for the front passenger position. Maximum exposures of the order of 10% of the ICNIRP 2010 reference levels were obtained for the cars with conventional powertrains.

An Automated System for Measuring Electric Field Distributions Within a Vehicle

An automated, low-field disturbance probe positioning system for measuring 3-D electric field distributions inside vehicles or similar resonant environments is described. Correlations between measured and simulated electric field distributions for a simple rectangular cavity demonstrate that the probe positioner has little impact on the measured field levels. Comparisons between measurements and simulations for a real vehicle indicate that the predicted field population distributions are within the estimated uncertainties of the measurements.

Calibration of current measurement transducers in oversized calibration fixtures

A simple one-dimensional (1D) transmission line model has previously been used to derive improved estimates for the transfer impedance of current transducers at high frequencies by taking account of the finite reflections that occur at the ports of the calibration fixture. This approach is further extended to take account of the additional reflections that occur in the system when an oversized calibration fixture is used. The success of this method is also assessed, for frequencies up to 600 MHz, using measured and computed results for the current induced on a wire inside a cavity backed aperture illuminated by a nearby antenna.

Numerical modeling of a stripline antenna in a large semi-anechoic chamber

Stripline antennas are used for automotive immunity testing in semi-anechoic chambers at low frequencies (<30 MHz). In order to investigate the behavior of such devices, a numerical model of the radiating elements of such a system has been developed using a 3D field modeling technique (TLM). The field distribution beneath this structure has also been measured for comparison with the computed results. At the operating frequencies of these antennas the absorbing lining of the chamber is too thin to provide significant absorption. Nonetheless, it is found that the presence of even an electrically thin layer of lossy material has a significant impact on the computed performance characteristics of the antenna. It is concluded that the absorbing lining must be represented in models that are used for the investigation and optimization of stripline antennas.