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The temperature rise constraint of wireless charging receivers is becoming increasingly tight. The high-power charging time of flagship phones is strictly limited by temperature control strategies, and the surface temperature of the TWS earphone charging case directly affects the grip experience. The back shell temperature of smartwatches is directly related to skin safety. In these scenarios, the selection of magnetic separators is often simplified as "the lower the loss, the better", but in actual design, it is not just the loss value of the material itself that truly determines the temperature rise performance.
Magnetic separators play a dual role in the thermal management link at the receiving end. It is not only the location of eddy current loss and hysteresis loss, but also a part of the thermal conduction path from the coil to the metal shell. Focusing only on losses and neglecting thermal conductivity, or focusing only on thermal conductivity and neglecting thermal stability, may both expose issues of excessive temperature rise during overall testing.
Thermal confinement of ferrites: not just a first-order loss problem
The resistivity of ferrite magnetic separators is high, and eddy current losses can be ignored, occupying a dominant position in low and medium power scenarios for a long time. However, there is a structural shortcoming in the thermal stability of ferrite: its magnetic permeability, loss, and saturation magnetization all exhibit strong temperature dependence. When the temperature exceeds a certain threshold, the magnetic core loss increases with the temperature, and the increase in loss further pushes up the temperature, forming a positive feedback. In high-power scenarios such as wireless charging of electric vehicles, the risk of thermal runaway is one of the reasons why ferrite cores are referred to as "critical performance bottlenecks".
Even at the power level of consumer electronics, the temperature sensitivity of ferrite still constitutes a design constraint. When the ambient temperature is above 40 ℃ or below -20 ℃, the fluctuation amplitude of the magnetic permeability of ferrite significantly increases, which may lead to abnormal operation. This means that in high temperature environments or machine layouts near heat sources in summer, the actual magnetic properties of ferrite separators may deviate from the values specified in the room temperature specification sheet, and the temperature rise performance may also deteriorate accordingly.
Thermal stability of nanocrystals: expanding design margin from the material source
The thermal advantage of nanocrystalline magnetic separators first comes from the magnitude difference of Curie temperature. The Curie temperature of ferrite is usually below 200 ℃, while the Curie temperature of iron-based nanocrystals can reach 570-620 ℃. Within the operating temperature range of the wireless charging receiver (usually -40 ℃ to 125 ℃), the nanocrystalline material is far away from the Curie point, and the magnetic permeability will not experience a sharp decline due to the temperature approaching the Curie point.
The direct engineering implication of this difference is that nanocrystalline magnetic separators still maintain predictable magnetic properties near the upper limit of operating temperature, while ferrites may have entered the range of magnetic permeability fluctuations. For devices that need to maintain charging efficiency in high temperature environments, what nanocrystals provide is not "lower losses", but an expansion of thermal design margin - engineers do not need to reserve additional compensation space for temperature drift of ferrites.
The second thermal advantage of nanocrystals comes from their thermal conductivity. Nanocrystalline materials themselves have excellent thermal conductivity, and under the same wireless charging conditions, the temperature rise of nanocrystalline magnetic separators is 7-8 ℃ lower than that of ferrites. This temperature difference is not solely due to lower losses, but also to more effective thermal diffusion within the material. The oxide ceramic structure of ferrite has lower thermal conductivity, making it easier for heat to accumulate locally; The metal based structure of nanocrystals provides a better pathway for heat conduction from the loss area to the outside.
The linkage between thickness and temperature rise: why 0.11 mm has a thermal advantage over 0.27 mm
At the same charging efficiency, the typical thickness of nanocrystalline magnetic separators is 0.11 mm, while ferrite requires 0.27 mm, resulting in a charging efficiency increase of about 2.5% and a temperature rise decrease of 7-8 ℃. This set of data is often cited, but the correlation between thickness and temperature rise is often overlooked.
Thinner magnetic separators mean lower overall thermal resistance of the receiving module. After heat is generated from the coil and the magnetic separator, it needs to pass through the magnetic separator, adhesive layer, and metal shell to dissipate. The thinning of the magnetic separator itself shortens the length of the heat conduction path and reduces the thermal resistance of this section. Meanwhile, thinner magnetic layers allow for more effective temperature equalization or heat dissipation layers, such as graphite sheets or thermal conductive silicone grease layers, to be arranged within the same module height, without having to give up all space to magnetic materials. In other words, the temperature rise advantage of nanocrystalline magnetic separators is the result of the combined effect of "low loss" and "low thermal resistance brought by thinning", rather than the contribution of a single material parameter. In temperature sensitive designs, this combination has more engineering value than simply relying on loss values.
Thermal management collaboration: why adhesive backing and composite structures cannot be ignored
Magnetic separators rarely exist alone in the receiving stack. One side of it is attached to the coil, and the other side is connected to the metal frame, battery or temperature equalizing plate through adhesive backing. The thermal conductivity of the backing adhesive, the thickness of the adhesive layer, and the air gap at the bonding interface directly determine whether the heat generated by the magnetic separator can be effectively dissipated.
If the magnetic separator is attached with a low thermal conductivity pressure-sensitive adhesive, even if the intrinsic temperature rise of the material is low, heat will still accumulate between the magnetic separator and the metal shell, forming local hotspots. In temperature sensitive scenarios, choosing a thermal conductive backing adhesive or setting up a continuous thermal path between the magnetic separator and the heat dissipation layer is more engineering meaningful than simply pursuing lower material loss factors.
Multilayer composite structures also need to be examined from the perspective of thermal pathways. If the magnetic separator is composed of multiple layers of magnetic layers and adhesive layers alternately stacked, each layer of adhesive is a series thermal resistance for thermal conduction. The more layers there are, the higher the total thermal resistance. For high-power or long-term continuous operation scenarios, the accumulation of interlayer thermal resistance may offset the temperature rise advantage brought by the inherent low loss of nanocrystalline materials. When selecting, it is necessary to confirm the thermal conductivity and thickness of the adhesive layer in the supplier's composite structure, not just the total thickness of the magnetic layer.
Selection and judgment of nanocrystalline magnetic separators based on temperature rise constraints
For scenarios where temperature rise is sensitive or thermal management margins are limited, the selection of magnetic separators can be judged from the following three dimensions.
Firstly, confirm under what conditions the temperature rise data was measured
The temperature rise advantage of 7-8 ℃ is usually measured under specific coil, specific power, and specific bonding conditions. When selecting, the supplier should be required to provide testing conditions for temperature rise data, including input power, coil spacing, adhesive type, and heat dissipation boundary conditions. If the testing conditions differ significantly from the actual layout of the entire machine, the temperature rise data can only be used as a qualitative reference. A more reliable criterion is the magnetic permeability retention rate of the magnetic separator near the upper limit of the target operating temperature, which directly reflects the thermal stability of the material.
Secondly, distinguish between "material temperature rise" and "system temperature rise"
The low temperature rise of the magnetic separator itself does not necessarily mean that the temperature rise at the receiving end of the entire machine is low. The system temperature rise is also affected by coil losses, IC losses, and structural heat dissipation paths. The value of nanocrystalline magnetic separators lies in their ability to reduce the thermal resistance and heat source intensity of the magnetic layer, leaving room for system level thermal management. When selecting, it is necessary to combine the thermal simulation or actual measurement of the whole machine to confirm whether the improvement of the magnetic isolation sheet is masked by other heat sources.
Thirdly, evaluate the long-term stability under high temperature conditions, rather than just relying on room temperature data
For car or industrial scenarios, the receiving end may work for a long time at higher ambient temperatures. Suppliers should be required to provide data on the temperature coefficient of magnetic permeability and loss changes of the magnetic separator in the range of -40 ℃ to 125 ℃, as well as the performance retention rate after high-temperature storage. The high Curie temperature of nanocrystals provides the basis for thermal stability at the material level, but the temperature resistance of the adhesive layer and composite structure also needs to be verified. The temperature resistance range of conventional acrylic double-sided tape is about 90-120 ℃, which may become a weak link before the failure of magnetic materials in high temperature scenarios.
Advanced Institute (Shenzhen) Technology Co., LtdThe nanocrystalline magnetic separator uses iron-based nanocrystalline strips as the functional layer. The effective magnetic permeability of the finished product can be customized from 150-2000, with a saturation magnetic inductance of about 1.2 T. The Curie temperature is ≥ 500 ℃, and the typical thickness is 0.11 mm at the same efficiency, which is 7-8 ℃ lower than the temperature rise of the ferrite scheme.
The product supports thermal conductive adhesive options and multi-layer composite structures, allowing for thermal path design based on the overall thermal management boundary of the machine, and providing magnetic stability data in high-temperature environments. For more technical information, please visithttp://www.avanzado.cn/.