Hello and welcome to another polymer materials selection example using the Polymer Funnel methodology. In this post we discuss the selection of radar transparent plastics for e-mobility applications such as Radar and Lidar. Figure 1 presents the four different stages of the material selection funnel and this overview serves us as a guideline.
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| Figure 1: Polymer Selection Funnel with its four stages. |
Global e-Mobility market 2030
Battery electric vehicles (BEVs) are on the rise in Europe and research found out that in Europe around 16% of all new car sales will be BEVs by 2025. This number has the potential to rise to almost 50% by 2023. Looking at a global level, BEV sales will grow from 12 to 25% in the same time period.
What are the top 5+ plastics used in the automotive industry?
In the past 40 years plastic materials incrementally found their way into automobiles and will continue to support the e-mobility revolution. Currently, the average global plastic amount used in cars is 100 kg. I made an infographic on this topic which can be found here.
The top three plastics used in Automotive by volume are PP, PVC, and PU, Followed by engineering polymers such as Polyamides, Polyesters (PBT), POM, ABS, PMMA, and PC. On the high performance side, polymers such as PEEK, PPS, PPA, fluoropolymers and fluorelastomers are used.
Polymer material selection for radar transparent applications - selecting the optimal plastic material
Apart from the rise of e-mobility, we see a rise in autonomous driving applications in cars to improve safety and in the long run have a new way of mobility. Part of the autonomous and safety equipment (Advanced Driver Assistance Systems = ADAS) are radar and lidar systems to analyze the surroundings of the car.
Figure 2 shows as an example the Porsche Macan Distronic Radar made by Automotive Tier-1 Bosch. Main components are the front cover which is often referred to as radome, the back cover, together with the RF absorber and circuit boards. In this material selection example we focus on the radome element.
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| Figure 2: Porsche Macan Distronic Radar made by Automotive Tier-1 Bosch. |
Funnel stage 1: Material selection factors
In Funnel stage 1 we assess the requirements which need to be fulfilled by the radome material:
- Environment including temperature rating: exposure to UV-light and resistance towards weatherability conditions is needed;
- Radar transparency: low dielectric constant (Dk) and low dissipation factor (Df) since low values mean better dielectric materials with less dielectric heating which is needed for high-frequency applications such as radar equipment. Estimated according to the ASTM D2520, ASTM D150 (estimated at @Frequency 1.00e+6 Hz) or IEC 60250. Df should be between 10 and 200; loss tangent of 0,01 in the ultra-wide 79-GHz millimeter wave band. The dielectric constant should in the range of 3 @76 GHz (rule of thumb).
- Temperature rating (HDT @ 1.82 MPa): min 200 °C
- Mechanical requirements: resistance towards stones; impact modified materials;
- Chemicals and chemical compatibility: salt and salt water;
- Space layout: limited; dimensions of radom are given; integration into car bumper;
- Lasting: 5.000 hours
- Costs: medium to higher cost range possible;
- Recyclability: must be given at end of life;
- Laser welding: is optional;
Table 1 summarizes the important requirement information (requirement worksheet).
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| Table 1: Requirement worksheet of Funnel stage 1. |
Funnel stage 2: Decision on thermoplastic or thermoset
In Funnel stage 2 we assess whether a thermoplastic or thermoset material is able to fulfil the described requirements from step 1. Thermoset polymer matrix as Radar dome materials are used in aircraft and airspace, however in Automotive production lot numbers are ranging in the million parts per year. Since we need longer cycle times in thermoset moulding compared to thermoplastic moulding, together with better impact performance of thermoplastics, selection is made for the thermoplastic route.
Since we selected the thermoplastic root, we can choose between semi-crystalline and amorphous polymers. In our case we continue on the semi-crystalline route which allows for better chemical resistance compared to certain amorphous grades.
Among the semi-crystalline engineering polymers we have Polyamides (aliphatic short- and long chain), Polyester (PBT), and POM.
For further decision making on the base polymer type, it helps to check the Dielectric Constant (ε) of different materials (Figure 3).
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| Figure 3: Dielectric Constant (ε) of different materials. |
Next, let us check the polarity of base polymers. Polar polymers such as PMMA, PVC, Polyamide, and PC absorb moisture from the environment and this in turn will raise the dielectric constant and lower the resistivity. Temperature (
10-degree rule) accelerates the chain movement and enables dipole polarization which further decreases the insulation properties of such polymers. On the other hand, non-polar polymers such as PE, PP, PS, PTFE, and PPS are not affected by changing the electrical properties when exposed by moisture and temperature increase.
PBT absorbs much less water compared to aliphatic Polyamides and it keeps its dimensional stability in dry and wet environments. Dielectric constant (Dk) and low dissipation factor (Df) are in a good range too and this leads to a search in PBT grades from different material suppliers on databases such as
CAMPUS or Omnexus.
We found the following four PBT grades suitable for Radar domes, which have laser weldability, hydrolysis resistance, strength, toughness, and low Warpage (Table 2):
- TORAYCON™ 1101G-30H
- TORAYCON™ 4158G-30H (laser welding)
- Pocan B1205XHR
- Sabic LNP™ THERMOCOMP 6F006
Other options in the high performance polymer segment for radomes would be
PPS or PEI.
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| Table 2: Overview pre-selected thermoplastics. |
Funnel stage 3: Selection discussion with worksheet (qualitative matrix analysis)
Now we have reached the heart of the Polymer Selection Funnel method: the qualitative matrix analysis. First we rank how good each of the materials can fulfil the requirements from step 1 (0 to 5=best), followed by secondly, assigning priorities to each of the requirements (0 to 5 = highest priority). Finally a multiplication of the requirement fulfilment with the priority is done and the values are added up for each material. Table 3 summarises the outcome of this process.
The grades 1101G-30H, 4158G-30H, and THERMOCOMP 6F006 are close together in result points followed by B1205XHR.
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| Table 3: Result of the qualitative matrix analysis. |
Funnel stage 4: Testing, selection of material and vendor
In the final stage of the funnel we test and validate the pre-selected grades from the outcome of Funnel step 3. If laser weldability, together with excellent Radar transparency is the focus, then 4158G-30H and THERMOCOMP 6F006 will be in the validation focus. Otherwise, 1101G-30H and B1205XHR can be evaluated too. After ordering sample materials and designing a prototype tool or 3D printing parts, evaluation on part level can start. Depending on the OEM testing standard, several investigations need to be performed, especially Radar transparency at different frequencies needs to be evaluated. In our case, 1101G-30H, THERMOCOMP 6F006, and B1205XHR are good material choices. If assembling with the base house of the Radar using laser welding is needed, then further tests need to be conducted.
Conclusions
There are several advantages in the use of engineering polymers such as PBT for Radar radomes and ADAS applications in general:
- Low dielectric constant
- Low dissipation factor
- Excellent mechanical properties (high strength and modulus; high impact resistance)
- Weatherability and UV resistance
- Processing via injection moulding in high numbers
- Low water absorption
By using the four step
Polymer Funnel method we could systematically find the optimum material for our radome application.
More polymer material selection examples can be found in my "
start here" section.
Thanks for reading and #findoutaboutplastics!
Greetings,
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[2] https://www.curbellplastics.com/materials/industries/radomes/
[3] https://www.rohde-schwarz.com/cz/applications/characterizing-the-material-properties-of-polymers-for-radomes-and-bumpers-to-optimize-radar-transparency-application-card_56279-1233408.html
[5] https://www.diva-portal.org/smash/get/diva2:1136102/FULLTEXT01.pdf
[6] https://radar-blog.innosent.de/en/design-of-a-radome/ SG
[7] https://www.generalplastics.com/technical-papers/dielectric-materials-use-radomes#:~:text=POLYURETHANE%20FOAMS%20IN%20RADOMES%3A,performance%20of%20the%20antenna%20inside. SG
[8] https://www.ti.com/lit/an/swra705/swra705.pdf?ts=1683015383043 SG
[8] https://solutions.covestro.com/-/media/covestro/solution-center/brochures/pdf/ep_sensor-brochure_en_final.pdf
[9] https://www.accenture.com/us-en/insights/automotive/electric-vehicles-on-the-rise
[10] https://www.ebay.de/itm/125432456436?var=0&mkevt=1&mkcid=1&mkrid=707-53477-19255-0&campid=5338765354&toolid=20006&_trkparms=ispr%3D1&amdata=enc%3A1jh97u_e2TWSBwLjLmt1fJg69&customid=DE_131090_125432456436.153165883401~2079861677694-g_CjwKCAjwyqWkBhBMEiwAp2yUFlS_64OthQZ9tiDysgItcO7RHcRvbMZDNISXMnUsyV5HxayPttmmRhoCa28QAvD_BwE
[11] https://www.generalplastics.com/technical-papers/dielectric-materials-use-radomes
[12] https://www.plasticstoday.com/automotive-and-mobility/new-pbt-slashes-dielectric-loss-without-compromising-dimensional-stability
[13] https://passive-components.eu/what-is-dielectric-constant-of-plastic-materials/
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