Motor vehicles represent one of the most demanding environments for electromagnetic compatibility (EMC). With the continual pressure to meet price/performance targets it is a particular challenge for automotive systems manufacturers to achieve the required EMC performance without compromising the financial budget. Continental – a global manufacturer of premium automotive multimedia systems for the OEM market – has applied state-of-the-art electromagnetic simulation techniques in the design of its latest car radio and multimedia systems (Figure 1), helping it to maintain its reputation for high quality, robust products.
Figure 1 Continental’s automotive multimedia systems have an enviable reputation for quality, reliability and robustness.
The use of EDA software for simulating PCBs and minimizing board-level interference in car radios was well-established, but the use of 3D simulation techniques for system-level field simulations and optimization of the housing was a new development to further improve quality....
Continental’s engineers had successfully used CST software on antenna and PCB applications, and this positive experience led them to place their trust in CST as a partner for the EMC/ EMI development of the antenna and housing for the new automotive multimedia system.
For an automotive system, electromagnetic interactions occur at various levels between the car and the system as well as within the system itself – as shown in Figure 2. The traditional design method, using PCB software alone, addresses only the board-level interference and ignores the effects of the housing and its interaction with the board and system components. Continental wished to obtain a deeper understanding of the fundamental electromagnetic design issues determining the EMC performance of a product, and to identify and characterize the design parameters that would allow it to control the EMC behavior.
Figure 2 EMC and EMI interactions in automotive multimedia environment.
Figure 3 Comparison of far-field EM radiation from PCB with and without housing present.
Product design is a complex process that involves hardware development, software development, and system integration. Each product is normally developed with a few variants, to support the different standards that may exist in specific geographic regions, and also the different vehicle product lines of Continental’s OEM customers. At the hardware development stage, the key tasks are electrical and mechanical engineering. The engineering phase is followed by production and testing, which typically involves a number of prototype phases before arriving at the final product – the target is to keep the number of iterations as small as possible to control development costs.
The aim of using EMC simulation is to introduce virtual prototyping in order to verify functional behavior before building a prototype, thus potentially saving on hardware iterations. This approach also allows an easy comparison of different implementation options, and provides the answers to “what if” questions such as:
Taking a concurrent approach to 2.5D board level simulation of the PCB and 3D simulation of the system means that a number of goals can be targeted at the same time, and the interactions between them can be accounted for. The goals of the PCB simulation are: to ensure signal and power integrity, coupling, and low electromagnetic emissions from the circuit; to verify the impedance-controlled characteristics of the PCB layout; and to optimize the signal routing and the properties of the drivers, and the effect of frequency variations on the PCB. The results achieved include S-parameters, voltages and currents, field levels, coupling coefficients and radiation levels.
The goals of the 3D simulation are: to understand and optimize overall EMC behavior; to compare and optimize different design alternatives; and to trade off these parameters against cost, weight and performance considerations. It also aims to ensure that the specified performance is achieved in the presence of electromagnetic interference. The properties of the mechanical assembly and the relevant signals need to be taken into consideration. The results produced demonstrate the electrical resonances of the housing, paths of coupling, electromagnetic fields, radiation parameters, and surface currents.
As an example, Figure 4 shows the E-fields and surface currents around a simple PCB, with and without its housing present.
Figure 4 Fields at 1.65GHz resonance, with and without housing.
EMC Verification Flow
Figure 5 shows the flow diagram of the EMC verification process. Additional aspects to be considered are the import of the mechanical design data into CST MICROWAVE STUDIO® (CST MWS®), then simplifying the model if necessary, and discretizing it for simulation in the numerical world. The materials and electrical contacts need to be modeled accurately, taking into account even fine details such as oxide layers.
Figure 5 EMC verification flow.
Essential for obtaining valuable results is an appropriate simulation test bench that is set up according to the simulation target. Finally, the results need to be interpreted correctly and fed back to the electrical and mechanical design teams for optimization of the system. The feedback from measurements is important for the model quality, as shown in figures 6 and 7.
Figure 6 Model setup for car radio housing.
Figure 7 Comparison of simulated and measured results.
Understanding EMC design parameters by using CST MWS has given a variety of benefits, including the reduction of hardware prototype loops due to the use of virtual prototyping, which both shortens development time and reduces NRE cost. It has also permitted the removal of some “safety components” such as shielding and filters, which reduces the Bill of Materials (BoM) and saves on PCB area. Considering EMC as a design parameter during development has allowed the adoption of leading-edge architecture, driving innovation as well as reducing costs and increasing quality.
Early presentation of EMC mechanisms to the customer creates confidence over the whole design cycle. As a result Continental has received some excellent feedback about EMC performance from its end customers.