Focus on OTA Testing, Aim at Internet of Everything
With the continuous improvement of the performance requirements of absorptive materials, polyurethane absorptive foam can no longer meet the requirements in some application areas of darkrooms. A type of absorptive material based on hard foam has been deeply researched. The substrates of this type of absorptive material include expanded polyethylene (EPE), expanded polystyrene (EPS), expanded polypropylene (EPP), etc. These materials have closed pores, better mechanical strength than polyurethane, and are not easy to absorb moisture or deform. The new type of absorptive material has added absorbing agent components in the raw material production stage, and then is molded into the desired shape and performance. The entire process of material preparation is mechanized, and the product properties are stable.
Selecting EPP as the Absorbing Matrix Material
- Excellent heat resistance: EPE can withstand temperatures of 70-80°C, while EPS can only withstand temperatures below 80°C. In contrast, EPP can withstand temperatures of up to 120°C and can shrink by less than 2% when placed at 120°C for 22 hours.
- Excellent mechanical properties: EPP with a density of 0.035g/cm³ has longitudinal and transverse tensile strengths of 0.56MPa and 0.38MPa respectively. Under high temperatures of 120°C, the bidirectional strengths are 0.07MPa and 0.035MPa.
- Excellent environmental performance: Compared with polyurethane (PU) foam, EPP does not produce harmful isocyanate residues to the human body, and the product can be recycled. During the foaming process, no fluorocarbon compounds or butane are used, which will not have a negative impact on the environment after degradation. Compared with polyethylene foam (EPE), the new foaming process reduces the use of chemical foaming agents, making it more environmentally friendly.
The adoption of full-wave simulation for optimized design
The traditional design method for absorbing materials is the “transmission line design method,” which uses transmission line theory to calculate only the normal incident performance without considering the influence of the cone shape.
Absorbing materials are simulated and optimized over the full frequency range to obtain the optimal absorbing structure, ensuring the electromagnetic wave absorption performance of the absorbing material.
Using spatial scanning method to measure absorption coefficient
The traditional “bowtie method” for measuring absorption rate is limited to a frequency range of only 2-18GHz, and cannot measure low and high frequencies, with low accuracy.
The absorption rate measurement of absorbing materials uses a self-designed “7”-shaped rocker arm structure for spatial scanning measurement, which can meet multi-degree-of-freedom scanning in an ultra-wideband of 0.5GHz~70GHz, greatly improving measurement accuracy.
- Electrical performance: EPP has a low dielectric constant, low surface reflection, and is a homogeneous material with sufficient attenuation in the interior. It has good absorption effects in the microwave frequency band.
- Flame retardant performance: Compliant with UL94 HF-1 standard.
- Oxygen index: >28%.
- Operating temperature: Long-term -50-100℃, short-term 120℃.
- Environmental performance: The raw materials are non-toxic and odorless, with no harmful gas release, ensuring peace of mind from the source.
- Finished product: Stable properties, in compliance with RoHS requirements.
- Physical performance: One-time molding, accurate dimensions; uniform appearance color, customizable; good stability and no deformation.
Wide range of applications
Electrical properties of the absorbing foam are measured using the RCS method in a compact range anechoic chamber with a quiet zone larger than 1.5 meters. The distance between the test piece and the antenna is greater than 10 meters, complying with the far-field condition. This can provide a low-noise, clean electromagnetic environment for various OTA measurement chambers, PIM chambers, etc.