In the design of 5G base stations, 77GHz automotive radar, and high-speed optical modules, electromagnetic interference suppression is an indispensable link. The traditional approach is to attach additional absorbing plates, spray absorbing coatings, or install independent absorbing brackets inside the metal shell.

The problem with this path is not the absorption performance, but the process - with one more part, there is one more incoming inspection, one more positioning and fitting, and one more layer of tolerance accumulation. For automotive radar or optical module products that produce hundreds of thousands of pieces per month, the proportion of these "additional costs" in the total cost cannot be ignored.

2、 How injection molding absorbing materials work: functionalization of absorbers in plastic matrix

Injection molded absorbing materials consist of two parts: a thermoplastic polymer matrix and an electromagnetic wave absorber.

matrixIt determines the mechanical properties, temperature resistance, and processing flowability of the material. Common substrates include polyamide (PA), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), and polypropylene (PP).absorbentIt is the functional source of electromagnetic wave loss, usually composed of micro powders of magnetic materials (ferrite, carbonyl iron powder) or dielectric materials (carbon based fillers) dispersed in a specific proportion in the matrix. When electromagnetic waves are incident on the surface of injection molded parts, the absorbent converts electromagnetic energy into thermal energy through hysteresis loss, eddy current loss, or dielectric loss, thereby attenuating reflected and transmitted signals.

3、 Material System: Performance Differences and Selection Logic of PA, PBT, PPS, PP

The significant differences in temperature resistance, mechanical strength, and density among different thermoplastic matrices directly determine the applicable scenarios of injection molded absorbing materials.

Data source: Laird, Guanxu New Materials, and industry public information

PA substrateIt is most widely used in millimeter wave radar because the processing fluidity and mechanical strength of polyamide can meet the injection molding requirements of thin-walled radar brackets, and the thermal deformation temperature of 245 ° C is sufficient to cope with the working temperature rise of radar modules.PBT substrateThe advantage lies in the co injection compatibility with the radar housing - when the bracket and housing use the same substrate system, the interface bonding and thermal expansion matching are more reliable.PPS substrateTargeting higher temperature resistance requirements, suitable for satellite communication and military electronic components that require reflow soldering.PP substrateThe density can be as low as 0.9 g/cm ³, and the attenuation rate at 77 GHz can reach 160 dB/cm, making it a lightweight choice for integrated radar absorbing structures in car bumpers.

4、 Key performance: Attenuation data from 24 GHz to 77 GHz

The core performance indicator of injection molded absorbing materials is attenuation rate, which represents the attenuation ability of electromagnetic waves per unit thickness of material in dB/cm.

In the 24 GHz frequency band, the attenuation rate of typical thermoplastic absorbing particles can reach over 80 dB/cm. In the 77 GHz automotive radar frequency band, the attenuation rate of some PA based injection molded absorbing materials exceeds 100 dB/cm. Taking Laird's Eccosorb JCP-PBT-252 as an example, based on PBT substrate and glass fiber reinforcement, the electromagnetic wave attenuation exceeds 100 dB/cm in 77 GHz millimeter wave radar applications, with good stability and enhanced mechanical properties. Eccosorb JCP-PP9 is based on polypropylene blend, with an attenuation rate of 160 dB/cm at 77 GHz, while maintaining physical properties close to the original polypropylene.

5、 Application Layout: From Automotive Radar to Satellite Communication

6、 Advanced Institute Technology's ability to customize injection molded absorbing materials

Advanced Institute (Shenzhen) Technology Co., Ltd. (referred to as "Advanced Institute Technology") was established in 2016 and is a national high-tech enterprise specializing in absorbing materials, shielding materials, flexible substrate coatings, and precious metal pastes. The company owns the independently registered trademark "Yanbo" and has passed ISO9001 quality management system certification.

7、 Selection considerations: engineering decisions from frequency, temperature to structure

When engineers choose injection molded absorbing materials, the following dimensions deserve special attention:

• Matching of target frequency with substrate system.Priority should be given to PA or PBT substrates for 24 GHz and 77 GHz automotive radar applications; Satellite communication and military electronics choose PPS substrates for higher temperature resistance requirements; PP substrate can be considered for scenarios that are extremely sensitive to weight.
• The trade-off between attenuation rate and structural thickness.The attenuation rate is measured in dB/cm, and the actual absorption depends on the wall thickness of the component. At 77 GHz, an attenuation rate of 100 dB/cm means that a wall thickness of 1 mm can provide approximately 10 dB of absorption. Radar brackets are typically designed with a wall thickness of 1.5-3 mm to achieve 15-30 dB attenuation.
• The influence of injection molding process on electromagnetic properties.The uniformity of wall thickness, flow direction, and filler orientation of the workpiece will affect the distribution of the absorbent in the matrix, thereby affecting the consistency of electromagnetic properties. During the mold design phase, it is necessary to consider the influence of channel layout and gate position on the uniformity of electromagnetic parameters of the workpiece.
• Temperature and environmental resistance.The car radar bracket needs to withstand temperature cycling from -40 ° C to 125 ° C; PPS based materials can meet the requirements of reflow soldering process. Outdoor applications also need to consider wet heat aging and UV stability.

8、 Conclusion

The essence of injection molded absorbing materials is to embed the electromagnetic wave absorption function into the structural components themselves as an engineering solution. It is not a replacement for structural components with absorbing materials, but rather a way for structural components to learn how to absorb waves - by blending absorbers with thermoplastic matrices, an injection molded part can simultaneously carry the tasks of "supporting and fixing" and "electromagnetic absorption".

From 77 GHz automotive radar brackets to phased array antenna phase shifters, from 5G optical module housings to satellite waveguide terminals - injection molded absorbing materials are pushing electromagnetic compatibility design from "post attachment" to "functional embedding". Understanding the temperature resistance boundaries of different substrate systems, attenuation data in millimeter wave frequency bands, and the impact of injection molding processes on electromagnetic performance consistency - these are the key to upgrading injection molding absorbing materials from "a modified plastic" to "engineering decisions".