Circuit Materials Improve ADAS Performance

 Passengers’, occupants’, and pedestrians’ safety is an important objective for car manufacturers and their suppliers, and there is a strong desire to further improve assisted driving performance and reliability. As adoption rates increase, the number of safety features and onboard electronic systems per vehicle increase every year, requiring engineers to look for lightweight material solutions and greater design flexibility.

SABIC is a global diversified chemical company that supports engineers in improving radar sensor technologies using materials that promote lightweight and metal replacement, overall system cost reductions, and greater design flexibility.

Radar systems are an integral part of the ADAS sensor suite that supports features such as Adaptive Cruise Control (ACC), Autonomous Emergency Braking (AEB), and Forward Collison Warning (FCW). Radar sensors require material solutions that provide effective electromagnetic interference (EMI) shielding of various system components and radar signal absorption properties to ensure that reflections and cross-interference do not disturb correct object detection, distance and velocity measurements in order to protect drivers, passengers, and pedestrians.

Speaking to EE Times, Dr. Martin Sas, lead scientist for SABIC’s Specialties business, highlighted how the materials must deliver high performance to help address the ever-changing ADAS landscape. In particular, SABIC’s specialty materials offer EMI shielding to protect circuitry components; eliminate cross-talk and radio frequency interference (RFI); enable radar absorption to attenuate impact of reflections on sensor readings; andprovide good thermal conductivity for heat dissipation, superior mechanical properties and resistance to automotive chemicals.

Advanced Driver Assistance Systems (ADAS) 

Future automotive electronic safety systems based on radar and wireless communications will rely heavily on antennas, efficient RFIC’s, and low loss compact electronic circuits, and materials will play a key role in order to help enable the expected performance. Improving road safety is a key motivation to expand the ADAS functions of vehicles. The implementation of these systems requires the manufacture of appropriate circuit materials.

SABIC’s Specialties business has highlighted two major segments of automotive radar sensors. One type is a small form factor with a high level of seamless integration and a focus on low power and short- to mid-range detection and ranging. The other type delivers high performance, accuracy and fidelity (high angular resolution) in mid- to long-distance detection and ranging.

SABIC has outlined how each category of radar sensor has a slightly different set of requirements. Solutions for radomes, including glass fiber-reinforced polybutylene terephthalate (PBT) compounds, polyetherimide (PEI) resins and foam sandwich panels, offer low dielectric performance, low warpage, high temperature resistance and laser welding capability.

He added that “Radio frequency (RF) absorbing materials such as LNP™ STAT-KON™ compounds can help to condition transmitted and received signals to mitigate reflections that can result in false detections. SABIC’s LNP™ KONDUIT™ thermal management materials for injection molded heatsinks can mitigate damaging heat buildup, while LNP™ FARADEX™ compounds provide inherent EMI shielding in radar sensor housings. SABIC’s specialties materials can be used as  substrates for radar antennas, where they support technologies like laser direct structuring (LDS) and selective electro or electroless plating.”

Automotive radar sensors are designed in two operating frequencies bands: 24 and 77 GHz. The first allocated band width will become too narrow to fulfil future needs by 2022 but will continue to be available. The 77-GHz band extends from 76 to 81 GHz. 24 GHz radar sensors are typically used for short- and medium-range functions. 77 GHz radar sensors can also be used for long-range target detection.

The importance of the material

Radar sensors rely on high-performance materials, focusing on their safety objectives. The properties that a designer should keep in mind are dielectric constant, dissipation factor, insertion loss, electrical-thermal-mechanical stability of the material, and homogeneity of the substrate.

“Several things should be considered when choosing materials for sensors, starting with the sensor’s location and how it will be integrated onto the vehicle: Is it visible? Will it be exposed to environmental impacts, including chemicals? Will it operate in high or low temperature conditions? For radar sensors, it is important to determine the acceptable level of signal distortion, which will guide material requirements for the radome and RF absorber. Another factor is overall power consumption, and thus the heat generated by each radar sensor electronics stage (RF unit, processing unit),” said Dr. Martin Sas.

 

Figure 1: Solutions for Radar Sensor System Applications (Source: SABIC)

 

The increasing integration of communication antennas within a vehicle poses many challenges, as space is limited and, above all, the RF noise must be processed and attenuated to avoid interference  in transmissions and measurements.

A major challenge is in the resolution of radar sensors and plans to incorporate a multiple-in, multiple-out (MIMO) antenna architecture to create the so-called “imaging radar”. SABIC stressed that this project will compete head-to-head with the LiDAR in resolution. Still, without the weaknesses of the optical sensors, it will probably increase demands on all aspects of material properties.

“For example, it is anticipated that the need for ultra-low dielectric materials for radomes with relative permittivity close to that of air can deliver significant benefits. Potential solutions include SABIC’s LNP™ THERMOCOMP™ compounds, LNP™ copolymers, and NORYL™ and ULTEM™ resins, depending on specific requirements such as dielectric properties and heat resistance,” said SABIC.

He added that “Requirements for materials used in RF signal conditioning and signal absorption will increase based on specific designs and scenarios. SABIC’s newest radar absorbing LNP™ STAT-KON™ compounds, based on polybutylene terephthalate (PBT), are intended for integration with radomes manufactured using PBT material. Other LNP™ STAT-KON™ compounds are based on polyetherimide (PEI) resin for withstanding higher processing temperatures, or on polycarbonate (PC) resin for general applications that require high durability and a balance of physical properties. A broad choice of radar absorbing materials can allow manufacturers to design sensors that are optimized for vehicle size, sensor location, function and other variables.”

Another challenge to consider is the expected increase in processing power required for longer range and higher resolution radar units, which will require significant thermal management to avoid overheating and EMI protection. Other short-range radar sensors will become seamlessly integrated into or onto other vehicle components and parts.

SABIC’s Specialties business has highlighted that other challenges are related to the future of electronic control units (ECUs). Today, a typical car can have more than two dozen distributed ECUs for specific functionality, which fall under two main architectures: decentralized and centralized. “In the future, most functionality can be centered on consolidated domain controllers. According to McKinsey, this consolidation is especially likely for stacks related to ADAS. The industry is moving towards a domain control ECU solution to manage multiple aspects of ADAS and other electronics-based actions taken by the car vehicle. SABIC’s current and future specialty thermoplastics offer attractive alternatives to traditional ADAS sensor materials such as metal and glass, in part because their key properties can be tuned to the specific needs of the customer and the application,” said SABIC’s Specialties business.

The performance requirements of the antenna and other electronic devices design needs in the automotive industry will guide the choice of materials that may also be affected by antenna positioning and coverage requirements. Radar-based solutions detect potential implementations for ADAS. Integration with artificial intelligence applications helps drivers make safe driving decisions and drive safely.