Signal Integrity Considerations Applied to Automotive Grounding System's Design

Designing electric circuits which have the vehicle's body as a part of the current's path is a common practice in the automotive industry. In this case, the signal integrity is affected by many variables, e.g. the body's shape and its constituent materials. Nevertheless, the design of the vehicle's body is generally based only on esthetic and aerodynamic factors and signal integrity is not taken into account. This is not a great concern anyway, since this kind of signal usually comes from power supply and the electrical and electronic devices might work (at least partially) even with a voltage level decrease. However, although power supply signals are theoretically continuous, higher frequency components can be noticed through measurements. Besides that, the implementation of Power Line Communication system in vehicles is being studied lately, which means that the traditional power lines would also carry information signals, with associated high frequency content. These observations lead to a concern about the body's behavior when conducting higher frequency currents, since it is not considered for the design of the vehicle's grounding systems. In this case, it is desirable that these spurious frequency components have a minimum impedance path to the battery's negative pole. This goal can be achieved by calculating optimal points for the grounding points. However, this is not an easy task, since there are no analytical equations for the impedance in this case. Hence, this paper proposes the use of the Genetic Algorithm as a tool for numerically calculating the best grounding points in a vehicle, through the electromagnetic simulation software ANSYS HFSS®.