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But this improvement is not unlimited. After exceeding a certain thickness, continue to thicken and the reading distance begins to decrease. Engineers sometimes observe this phenomenon during sample testing: from 0.1 mm to 0.2 mm, the reading distance increases significantly; From 0.2 mm to 0.3 mm, the increase in reading distance narrows; From 0.3 mm to 0.5 mm, the reading distance actually decreases. This is not a test error, but the result of the thickness's effect on system performance shifting from "positive dominance" to "negative dominance".
Before the turning point: magnetic flux capacity dominates, increasing thickness improves reading distance
The main benefit of increasing the thickness of the magnetic separator in the thin layer interval is the enhancement of magnetic flux capacity. The magnetic flux carrying capacity of a magnetic separator is proportional to its effective cross-sectional area, and an increase in thickness directly increases the cross-sectional area. Magnetic field lines have more "space" to bypass the metal through the magnetic separator.
Two positive returns of thin interval
Saturation margin improvement:For scenarios with insufficient saturation margin, increasing thickness leads to a decrease in saturation risk - the proportion of working magnetic flux density relative to Bs decreases, making it difficult for the magnetic separator to enter the nonlinear region.
Enhanced bypass effect:For scenarios with strong eddy currents on metal substrates, thicker magnetic separators provide stronger bypass effects, and the eddy currents in the metal are more thoroughly suppressed.
Within this range, the relationship between thickness and read distance recovery rate monotonically increases. Adding 0.1 mm to 0.2 mm may increase the read distance recovery rate from 60% to 85%; From 0.2 mm to 0.3 mm, it may increase from 85% to 90%. The increase is narrowing, but the direction is still positive.
After the turning point: Four negative effects begin to dominate
When the thickness exceeds the inflection point, four negative effects begin to compete with the positive benefits of magnetic flux capacity and gradually dominate.
The first one is the physical spacing effect
The thicker the magnetic separator, the greater the physical distance between the tag antenna and the metal surface. The influence of metal on the antenna will not completely disappear due to the presence of magnetic separators - magnetic separators only weaken the eddy currents of the metal, while the metal remains nearby. The farther away the distance, the "residual influence" of the metal "seeps back into the antenna through a longer spatial path, and the equivalent environment of the antenna transitions from" near metal "to" free space ", but this transition is not always conducive to reading distance. For some antenna designs, the matching that is tuned close to metal may actually become mismatched as the spacing increases.
The second one is the eddy current loss of the magnetic separator itself
Magnetic separators are not ideal insulators, as they not only guide magnetic flux but also generate eddy currents inside. The thicker the thickness, the larger the cross-sectional area of the eddy current circuit, and the higher the eddy current loss. In the low frequency range, this effect is not significant, but in the UHF frequency range, the eddy current loss of the magnetic separator itself may offset some of the benefits brought by the magnetic flux capacity.
The third one is the expansion of the edge leakage magnetic area
The edge of the magnetic separator is the location of magnetic flux leakage. The thicker the thickness, the larger the "side area" of the edge, and the wider the channel for magnetic field lines to leak from the edge side. An increase in edge leakage flux means a decrease in the proportion of effectively guided magnetic flux, and the effective magnetic permeability of the magnetic separator is' diluted '.
The fourth one is increased dielectric loading
Magnetic separators are not only magnetic conductors, but also dielectric layers. The increase in thickness leads to an increase in the dielectric volume occupied by the magnetic separator in the near-field of the antenna, an increase in the equivalent capacitance around the antenna, and a shift in the resonant frequency towards lower frequencies. For narrowband tag antennas, this offset may cause the antenna to deviate from the matching point of the chip.
What determines the inflection point position: the intersection of four variables
The thickness inflection point is not a fixed value. It depends on the combination of four variables.
Why does the intuition of 'thicker is better' mislead selection
The intuition of 'thicker is better' comes from the focus on the single variable of 'magnetic flux capacity'. In the thin layer interval, this variable is indeed dominant, and the improvement in reading distance caused by the increase in thickness is visible and measurable. Engineers conducting verification within this range can easily form the impression of a positive correlation between thickness and performance.
But this impression no longer holds true after crossing the turning point. If the thickness range after the inflection point is not covered during selection, engineers may consider 0.3 mm as the "optimal thickness", but in reality, a reading distance of 0.2 mm is better. Or consider 0.5 mm as a 'safer choice', when in fact it has already crossed the inflection point with a reading distance below 0.2 mm.
Selection and judgment of anti metal magnetic separators based on the "thickness inflection point"
Firstly, cover multiple thickness points during the sample stage, rather than measuring only one 'sufficient' thickness
Test at least three thickness points of 0.1 mm, 0.2 mm, and 0.3 mm, and observe the trend of read distance recovery rate with thickness. If the reading distance starts to decrease or remain stable between 0.2 mm and 0.3 mm, it indicates that a turning point has occurred and further thickening will not yield any benefits.
Secondly, distinguish between two different failure modes: "insufficient saturation margin" and "thickness has passed the inflection point"
If the reading distance improves with increasing thickness but the degree of improvement decreases, it may be approaching a turning point; If the reading distance decreases with increasing thickness, it may have crossed the inflection point. The response methods for the two situations are different: the former can be moderately thickened, while the latter requires thinning or adjusting the material system.
Thirdly, predict the approximate location of the inflection point based on the size of the tag antenna and the metal substrate material, rather than covering all scenes with a uniform thickness
Small size antenna, ferromagnetic substrate, UHF frequency band, nanocrystalline system, with the inflection point leaning towards the thinner side; Large size antenna, non ferromagnetic substrate, HF frequency band, ferrite system, with the inflection point leaning towards the thicker side. When selecting, estimate the inflection point interval based on these four variables, and then perform sample verification within the interval.
Fourth, use the "reading distance thickness curve" as the basis for selection, rather than an isolated "optimal thickness" number
The curve describes the relationship between thickness and performance, while the number only describes one point. If the antenna size or metal substrate of the application scenario changes, the position of the inflection point will also shift, and the curve can better guide reselection than numbers.
Advanced Institute (Shenzhen) Technology Co., LtdThe anti metal magnetic isolation sheet product line covers ferrite composite sheets and nanocrystalline composite sheets, providing read distance recovery rate data for multiple thickness points within the thickness range of 0.05-0.5 mm, as well as thickness inflection point evaluation under different tag antenna sizes and metal substrate conditions.
The product supports thickness matching based on the actual antenna size, substrate material, and operating frequency band of the application, helping engineers find the optimal point on the "thickness reading distance" curve, rather than default to "thicker is better". For more technical information, please visithttp://www.avanzado.cn/.