THE IDEA: MULTIMEDIA DEVICES FOR THE CONNECTED CAR
Continental is a leading Original Equipment Manufacturer (OEM) supplier of automotive parts. One department of Continental is Interior Multimedia, which produces infotainment systems to provide navigation, communication and other multimedia services. These systems need to comply with a variety of different requirements, including performance, electromagnetic compatibility (EMC) and thermal specifications, while also satisfying the needs of the customer.
A modern car includes many systems at frequencies ranging from hertz to gigahertz for numerous functions, including radio reception, mobile communications, LTE, GPS and Bluetooth. This makes the EMC requirements stricter. In order to analyze devices and find potential EMC issues, Continental has used CST Studio Suite® for many years....
THE CHALLENGE: BALANCING COMPLIANCE AND CUSTOMER REQUIREMENTS
The sources of EMC issues may be small or in an inaccessible part of the device, and several rounds of prototyping may be needed to find and mitigate potential problems. EMC issues can have many different causes, and identifying these through measurement alone is difficult. Simulation using the time domain solver in CST Studio Suite offers more detail about the field and current distribution and the powerful CAD modeling and import tools make it easy to modify and re-simulate a design.
The device pictured in Figure 1 is one example where simulation was used to nip a potential EMC issue in the bud. For thermal reasons, the enclosure needs a fan, and the fan opening has a fixed area. However, when Continental simulated radiated emissions, they found that emissions were increased at GPS frequencies. A plot of the surface currents showed that this was due to a resonance in the vents of the enclosure. Changing the design of the vent significantly reduced these surface currents and solved the EMC issue.Figure 1: Surface currents around the fan on an enclosure, before (left) and after (right) modification.
For the board shown in Figure 2, a customer asked Continental whether it was possible to change the connection in order to decouple the USB cable shield from the PCB. A simulation showed that this change would both increase surface currents on the PCB and cause the USB cable to behave like an antenna. Simulation allowed this design modification to be ruled out without the use of prototyping.Figure 2: Shielded USB connector on a board, showing the connection to the ground plane.
Meanwhile, the system in Figure 3 showed unexpected behavior – the housing actually degraded the radiation behavior at certain frequencies, compared to an unshielded PCB (Figure 4). This was due to resonances within the enclosure. Using simulation, engineers were able to investigate mitigation strategies, and found that linking the RF connectors to the ground disrupted the resonance and improved the shielding effectiveness of the enclosure.Figure 3: Surface currents on the PCB, without (left) and with (right) the RF connected linked to ground.
Figure 4: The ratio (in dB) of farfield radiated emissions of the bare PCB versus the PCB in housing. The highlighted areas show where housing degrades the radiation behavior.
THE RESULT: HIGH-PERFORMANCE SYSTEMS FOR MODERN AUTOMOTIVE APPLICATIONS
In all of these cases, simulation was able to replace rounds of prototypes, allowing Continental engineers to investigate different potential designs faster and with reduced costs. This meant that they were able to deliver reliable products that met the customer’s needs and specifications.
The quick, reliable simulation results from CST STUDIO SUITE made it possible to anticipate and mitigate EMC problems before prototyping. This has reduced costs, shortened development time, increased customer confidence, and made it easier to develop patents.”