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When engineers choose electromagnetic wave absorbing materials, the first product parameters they usually see are the peak reflection loss and effective absorption bandwidth. But the underlying variable that determines these two values is the material's loss mechanism - it determines which frequency band of electromagnetic waves the material can absorb and how much it can absorb at a given thickness.
The loss mechanism was chosen incorrectly, and even the highest reflection loss peak cannot solve the actual noise problem. The antenna coupling interference of a 5G millimeter wave base station requires a completely different loss mechanism compared to the 30 MHz broadband noise of a new energy electric drive system.
Magnetic loss and dielectric loss: both mechanisms have boundaries
Electromagnetic wave absorbing materials attenuate incident electromagnetic wave energy through three main mechanisms: magnetic loss, dielectric loss, and conductive loss. The first two are the dominant mechanisms in near-field noise suppression in the GHz frequency band.
Magnetic lossThe interaction between the magnetic moment of the material and the magnetic field component of the incident electromagnetic wave includes processes such as hysteresis loss, eddy current loss, natural resonance, and exchange resonance. Soft magnetic powders (such as carbonyl iron, FeSiAl, ferrite) convert electromagnetic energy into thermal energy through domain wall resonance and natural resonance in an alternating magnetic field. The advantage of magnetic loss materials lies in their strong coupling ability of magnetic field components in near-field scenarios, with significant attenuation effects in the frequency range of tens of MHz to several GHz. However, magnetic loss materials face the constraint of Snoek limit - there is an upper limit to the product of the real part of the magnetic permeability and the resonance frequency. Increasing the low-frequency magnetic permeability will lead to a decrease in the resonance frequency, limiting the absorption capacity in the high-frequency range.
dielectric lossOriginating from the polarization response of materials in alternating electric fields, including mechanisms such as dipole polarization, interface polarization, and defect polarization. Carbon based materials (such as reduced graphene oxide, carbon nanotubes, MXene) and conductive polymers (such as polyaniline, polypyrrole) are typical dielectric loss absorbing materials. Dielectric loss materials exhibit good broadband absorption characteristics in higher frequency bands (X-band and above), but when used alone, they often face impedance mismatch problems - high dielectric constants cause electromagnetic waves to be heavily reflected on the surface of the material and unable to enter the interior to participate in loss.
The synergistic effect of composite systems: from "each managing one section" to "collaborative work"
The design concept of dielectric magnetic composite absorbing materials is to integrate two types of loss mechanisms into the same material system, and break through the bottleneck of a single mechanism through synergistic effects.
The first layer of synergy benefits is reflected in the improvement of impedance matching.When the contributions of magnetic loss and dielectric loss are close to matching, the input impedance of the material is closer to the free space wave impedance (about 377 Ω), and electromagnetic waves are more likely to enter the interior of the material rather than be reflected on the surface. This matching condition cannot be achieved by simply increasing magnetic loss or dielectric loss - the proportional relationship between the two is the key.
The second layer of synergy benefits come from the complementarity of loss paths.The dielectric phase attenuates the electric field component through dipole polarization and interface polarization, the magnetic loss phase attenuates the magnetic field component through natural resonance and eddy current loss, and the conductive network further dissipates energy through conduction loss. In a composite system, electromagnetic waves undergo a process of "entering multiple reflections gradually absorbing", extending their propagation path and significantly improving absorption efficiency.
At low filling levels, the performance of the dielectric magnetic composite system can already reach a high level. CeO₂/ Co@C The two-dimensional composite material achieved an effective absorption bandwidth of 6.08 GHz with a matching thickness of 2.55 mm at a filling ratio of 15 wt.%. Some optimized composite systems have a minimum reflection loss of less than -60 dB and an effective absorption bandwidth exceeding 9 GHz.
Engineering boundary of three types of loss systems
The following table summarizes the applicable frequency bands, typical thicknesses, and scene characteristics of different types of absorbing materials from the perspective of loss mechanisms:
Magnetic loss materials dominate in the mid to low frequency range (1 MHz – 6 GHz). The near-field magnetic component in this frequency band is strong, and high permeability materials can effectively couple and attenuate magnetic field energy. However, in noise frequencies above 2-3 GHz (such as Wi Fi and 5G Sub-6 frequency bands), the marginal benefits of further increasing magnetic permeability decrease. At this point, it is necessary to introduce a dielectric loss mechanism to broaden the effective absorption bandwidth.
The advantageous frequency band of dielectric loss materials is 2-18 GHz, but when used alone, they usually require a larger thickness to achieve performance matching in the low frequency range. The lightweight properties of carbon based aerogels and conductive polymer foam make them have unique weight advantages in wearable devices and aerospace scenes.
The dielectric magnetic composite system can broaden the effective absorption bandwidth while maintaining impedance matching by integrating two types of loss mechanisms. As 5G/6G communication and AI computing devices evolve towards higher frequency bands, the engineering value of composite systems is continuously increasing.
Three engineering judgments in selection
Engineers suggest establishing judgment logic in the following order when facing specific application scenarios.
Firstly, determine the frequency band and near-field/far-field properties of the noise
Near field noise (such as radiation near chips, DCDC converters, and connectors) is mainly composed of magnetic field components, and magnetic loss type or magnetic loss dominated composite systems should be given priority consideration. The far-field radiation or antenna coupling problem requires a balance between impedance matching and broadband loss capability, and the dielectric magnetic composite system is a more robust choice. If the target frequency band covers multiple discontinuous intervals (such as the presence of hundreds of MHz switching noise and 2.4 GHz wireless interference), a single loss mechanism is difficult to match simultaneously, and a broadband composite system or segmented mounting scheme needs to be selected.
Secondly, confirm the hard constraint of available space on thickness
The principle of quarter wavelength matching determines the rigid thickness requirement for low-frequency absorption. In space constrained scenarios, materials with higher real parts of magnetic permeability should be prioritized to achieve target frequency matching at thinner thicknesses. For example, materials with a real part permeability of 200 can cover the frequency range of 100 MHz to 8 GHz at a thickness of 0.2 mm. But it needs to be verified at the same time whether the increase in magnetic permeability is accompanied by the degradation of impedance matching, which can be preliminarily judged by checking the μ/ε ratio of the material in the target frequency band.
Thirdly, evaluate the impact of temperature on the stability of the loss mechanism
The magnetic permeability of magnetic loss materials is temperature sensitive, and the temperature coefficient of magnetic permeability varies significantly among different material systems within the working range of -40 ° C to 125 ° C. For applications with large temperature fluctuations such as in vehicle electronics and base station RF units, attention should be paid to the stability data of materials within the working temperature range of μ 'and μ' '. The effect of temperature changes on dielectric loss is relatively small, but the dielectric constant may change at high temperatures due to increased polarization relaxation. The high-temperature resistant absorbent/polyimide composite material with oriented sheet-like structure exhibits excellent radar absorption performance in the 1-8 GHz frequency band. After high-temperature treatment at 450 ° C/1h, the electromagnetic parameters change little when the doping ratio is 50% -60%.
Advanced Institute (Shenzhen) Technology Co., LtdThe research platinum brand absorbing material series covers three main models: XJY-MH100, XJY-MH150, and XJY-MH200. The real part of the magnetic permeability covers ≥ 100 to ≥ 200, and the recommended frequency range covers 10 MHz to 18 GHz. The standard thickness can be as low as 0.2 mm, and the working temperature range is -40 ° C to 125 ° C. The flame retardant rating reaches UL94 V-0.
This series adopts the orientation dispersion technology of sheet-like nanocrystalline soft magnetic powder, combined with surface coating and dielectric constant control process, to improve the real and imaginary parts of magnetic permeability while maintaining a stable μ/ε impedance matching window. The product supports flexible mounting, precision die-cutting, and multi-layer composite, and can be customized according to specific frequency bands and spatial constraints. For more technical information, please visithttp://www.avanzado.cn/.