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High permeability absorbing material · Magnetic loss type EMI suppression scheme
In the EMC design of electronic devices, engineers often encounter a dilemma: although metal shielding covers have been installed inside the devices, radiation emissions in certain frequency bands still exceed the standard. The problem lies in the reflection - although the metal shielding cover blocks the electromagnetic waves from radiating outward, inside the enclosed cavity, the electromagnetic waves reflect back and forth between the metal walls, forming standing waves and cavity resonance, generating abnormally high field strength at specific frequencies, which actually exacerbates the interference on sensitive circuits.
The solution to this problem is not to continue 'containment', but to 'diversion'. High permeability absorbing materials are born for this demand. Unlike metal shielding materials that rely on conductive reflection of electromagnetic waves, high permeability absorbing materials convert electromagnetic wave energy into thermal energy through magnetic loss mechanisms, eliminating interference from the source.
High permeability absorbing materials refer to electromagnetic wave absorbing materials with significantly higher real part permeability (μ ') in the target frequency band than conventional magnetic materials (usually μ'>5, and some systems can reach hundreds). Its complex magnetic permeability can be expressed as μ=μ '- j μ ", where μ' represents the material's ability to store magnetic field energy, and μ" represents the material's ability to dissipate electromagnetic wave energy.
High permeability materials can achieve stronger magnetic response at thinner thicknesses. When electromagnetic waves are incident on the surface of a material, the higher the μ ', the easier it is for magnetic field lines to be guided into the interior of the material; After entering the material, the magnetic loss mechanism converts electromagnetic energy into thermal energy. Magnetic losses mainly come from mechanisms such as domain wall resonance, natural resonance, and eddy current losses. High μ 'materials combined with appropriate dielectric properties and impedance matching design can efficiently convert incident electromagnetic wave energy into thermal energy, thereby achieving absorption attenuation.
The design core of high permeability absorbing materials is to find the optimal balance between the real part (μ ′) and imaginary part (μ ″) of the permeability, and between impedance matching and loss capability.
The 'μ' determines the ability of the material to 'gather' magnetic flux. The higher the μ ', the easier it is for electromagnetic waves to be introduced into the interior of the material. But the higher the μ ', the better - if the magnetic permeability is too high and causes impedance mismatch, electromagnetic waves will be reflected back on the surface of the material and cannot enter the interior for absorption.
The "μ" determines the efficiency of the material in converting electromagnetic energy into thermal energy. The magnetic loss tangent tan δ _m=μ "/μ 'is the core indicator for evaluating the magnetic loss ability of materials. In EMC/EMI suppression applications, materials require high μ 'and high μ' - high μ 'is used to gather the magnetic flux of the interference source, and high μ' is used to efficiently convert the gathered magnetic flux into thermal energy for consumption.
Advanced Institute of TechnologyBy using the orientation dispersion technology of sheet-like nanocrystalline soft magnetic powder, combined with surface coating and dielectric constant control process, the material maintains a stable impedance matching window of μ/ε while increasing the μ 'and μ' '. The result is that electromagnetic waves are more likely to enter the interior of materials and be efficiently attenuated through magnetic losses, rather than being reflected back into space or inside devices.
The performance of high permeability absorbing materials is rooted in their absorbent system. According to the mechanism of magnetic loss, the main systems include the following four categories:
| material system | Typical magnetic permeability μ ' | Main loss mechanism | Applicable frequency band | Core Features |
|---|---|---|---|---|
| Ferrites (Ni Zn/Mn Zn) | 20-500 (MHz frequency band) | Domain wall resonance, natural resonance, hysteresis loss | Mainly in MHz range, with some in GHz range | High magnetic permeability and controllable cost, but high brittleness and limited size |
| Magnetic metals and alloys (FeCo/FeNi/FeSiAl) | 5-50 (GHz band) | Eddy current loss, natural resonance, exchange resonance | GHz level dominant | High saturation magnetization and high current resistance, but high-frequency permeability attenuation |
| Magnetic composite materials (particles/polymers) | 5-80 (depending on filling amount) | Multiple resonance, interface polarization, eddy current loss | MHz – GHz broadband | Flexible and machinable, with adjustable performance |
| New two-dimensional magnetic materials (such as Fe ∝ O ₄ nanosheets) | 2-15 (high frequency band) | Interface polarization, natural resonance, dielectric magnetic synergy | 2–18 GHz | Thin layer broadband, at the forefront of research |
Data Source:Advanced Institute of TechnologyAnd industry public information
Ferrite based absorbing materials have the characteristics of high absorption frequency band, high absorption rate, and thin matching thickness, and are widely used in the field of electromagnetic radiation protection. At the same resonance frequency, the magnetic permeability of the sheet-like absorbent material is greatly increased, making it easy to break through the Snoek limit of the magnetic properties of isotropic absorbing materials. Magnetic metal micro powders (such as FeSiAl, FeNi) have the advantages of high saturation magnetization and low cost, but the loss mechanism is relatively single. When the magnetic permeability and dielectric constant do not match, it can lead to poor impedance matching and narrow absorption band. Material composite and structural design are two key approaches for developing high-performance electromagnetic wave absorbing materials.
Advanced Institute (Shenzhen) Technology Co., Ltd. has formed a complete series of high permeability absorbing material products for the MHz to GHz frequency band. The XJY-MH series includes three main models: XJY-MH100, XJY-MH150, and XJY-MH200, covering the low-frequency to microwave frequency range. The substrate is a flexible polymer composite system, and the surface can be covered with a conductive layer, insulation layer, or aluminum foil. It supports precision die-cutting and adhesive bonding.
| model | Magnetic permeability μ ′ @ 1MHz | Magnetic permeability μ ″ @ 1MHz | Recommended frequency band | Typical reflection loss | standard thickness | density | Operating Temperature | Flame retardant rating |
|---|---|---|---|---|---|---|---|---|
| XJY-MH100 | ≥100 | ≥55 | 10 MHz–3 GHz | ≤-18 dB@1GHz | 0.5–2.0 mm | 3.2 g/cm³ | -40~ 125℃ | UL94 V-0 |
| XJY-MH150 | ≥150 | ≥60 | 10 MHz–3 GHz | ≤-20 dB@1GHz | 0.3–1.5 mm | 3.0 g/cm³ | -40~ 125℃ | UL94 V-0 |
| XJY-MH200 | ≥200 | ≥65 | 10 MHz–3 GHz | ≤-22 dB@1GHz | 0.2–1.0 mm | 2.8 g/cm³ | -40~ 125℃ | UL94 V-0 |
Data Source:Advanced Institute of Technology
The research platinum brand high permeability absorbing material can achieve a reflection loss of over 20dB in the target frequency band, which means that at least 99% of the incident electromagnetic wave energy is absorbed by the material. The material has a wide absorption frequency band, a flat response curve, and stable absorption ability over a wide frequency range. In the multi-layer structure design, the reflection loss value of the research platinum brand multi-layer absorbing film reached -54.1dB at 14.08GHz, and the effective absorption bandwidth reached 6.3GHz (11.7-18GHz).
Product Extension:In addition, Advanced Institute Technology also provides XJY-F series flexible ferrite sheets/films (μ '@ 1MHz ≥ 150, suitable for 100kHz-1GHz, thickness 0.05-0.5mm, used for NFC/RFID, wireless charging) and XJY-M series sheet-like magnetic metal micro powder/polymer composite systems (μ' @ 3GHz ≥ 15, suitable for 0.5-8GHz, thickness 0.3-2.0mm, used for millimeter wave radar, 5G base stations, power amplifier modules).
When engineers choose high permeability absorbing materials, the following dimensions deserve special attention:
This is the most mature application field of high permeability absorbing materials. 13.56MHz high-frequency electronic tags are prone to distortion and reduced reading distance in metal and liquid environments. Advanced Institute Technology adopts a high permeability absorbing wave plate as the dielectric isolation layer to suppress the capacitive loading of liquid on the antenna, improve the antenna Q value, and maintain stable resonance of the label in scenarios such as liquid bottles, infusion bags, and reagent kits. In the metal asset management scenario, after redesigning the ferrite magnetic isolation antenna, the reading distance increased from 1.2cm to 5.8cm (383%), and the reading rate increased from 63% to 99.6%.
On mobile phones, tablets CPE、 In small base stations and RF front-end modules, high permeability absorbing materials are used to suppress 2.4GHz and 5.8GHz harmonic interference, reduce mutual coupling between antennas, and improve signal integrity.
In the 77GHz vehicle mounted millimeter wave radar, high permeability absorbing materials are used to absorb cavity resonance and sidelobe interference, improving radar detection accuracy. The XJY-M series products from Advanced Institute Technology are suitable for the 0.5-8GHz frequency band, covering the operating frequency range of millimeter wave radar.
In military aircraft, ships, and satellites, high magnetic permeability absorbing materials are applied to surface coatings and structural components, which significantly reduce the radar cross-section of targets by absorbing and attenuating incident radar waves and converting them into thermal energy.
The essence of high permeability absorbing materials is to use magnetic loss mechanisms to "absorb" electromagnetic wave energy rather than "reflect" it as a functional material. It introduces electromagnetic waves into the interior of the material through high μ ', converts them into thermal energy through high μ' ', and eliminates electromagnetic interference from the source.
The evolution of materials from ferrite to nanocrystals reflects the upgrading of EMI suppression demand from "medium high frequency applicability" to "wideband stability". Understanding the synergistic relationship between μ 'and μ' ', the decisive role of impedance matching in absorption efficiency, and the frequency response differences of different material systems - these are the key to upgrading high permeability absorbing materials from "functional materials" to "engineering decisions".
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