Español
Français
Português
In the selection discussion of RFID absorbing materials, "peak reflection loss" is the most commonly compared number. A material that achieves -25 dB at 915 MHz looks "better" than a material that achieves -12 dB across the entire frequency range of 860-960 MHz. This judgment holds true under a single frequency point and ideal mounting conditions.
However, RFID systems rarely operate under the conditions of "single frequency point, ideal mounting". The UHF frequency band covers 860-960 MHz, with different frequency band allocations in different regions; 2.4 GHz RFID and UHF RFID coexist in the same device or storage environment; When labels are attached to metal surfaces, liquid packaging, or densely stacked shelves, the resonant frequency of the antenna will drift due to changes in the dielectric environment. Under these conditions, a high absorption peak does not equal stability, and the frequency selectivity of narrowband materials becomes the starting point for system level failure.
The Mechanism and Boundary of Narrowband Absorption: The Cost of "Frequency Accuracy" for Resonant Materials
The core mechanism of narrowband absorption is resonance. Tunable frequency absorbing materials (resonant frequency absorbing materials) have significant reflection losses at discrete frequencies, with a typical attenuation of up to 20 dB, covering a range from 1 GHz to 40 GHz. Metamaterial absorbers achieve near perfect absorption through periodic resonant elements, and the position of the absorption peak is determined by the geometric dimensions of the elements. In the UHF RFID frequency band, the grid patterned metamaterial absorber can achieve dual frequency absorption peaks of 880 MHz and 2.45 GHz, with a substrate thickness of only about 3.7 mm.
Advantage: Deep absorption within thin layers
The advantage of narrowband materials lies in their high absorption strength within thin layers. In thickness limited scenarios, the resonance mechanism can achieve deep absorption of the target frequency point with a thinner dielectric layer, which is difficult for magnetic loss materials to achieve at the same thickness. For metal tags or narrow slot fixtures with extremely limited space, narrowband schemes have irreplaceable performance at the target frequency point.
Boundary: Frequency selectivity is a double-edged sword
The frequency selectivity of narrowband materials is a double-edged sword. Once the center frequency of the absorption peak deviates from the target, the reflection loss will rapidly decay. If the resonant frequency of the tag antenna is shifted by tens of MHz due to metal reflection, liquid medium, or adjacent tag coupling, the narrowband absorption peak may fall outside the effective window, and the absorbing plate may degrade from a "performance component" to a "transparent layer". When multiple frequency bands coexist, a single narrowband material cannot simultaneously cover two separate frequency bands, requiring stacking or partitioning schemes, resulting in increased thickness and process complexity.
The Implementation Path of Broadband Absorption: Engineering Logic of Peak to Coverage Swap
The design philosophy of broadband absorption is opposite to narrowband: it does not pursue extremely deep reflection losses at a single frequency point, but maintains available absorption levels over a wide frequency range through frequency broadening of the loss mechanism and gradual impedance transition.
Frequency broadening of magnetic loss type
Magnetic loss broadband materials (carbonyl iron powder, FeSiAl, alloy powder composite system) rely on the frequency distribution of natural resonance and eddy current loss to achieve bandwidth. The loss of ferrite in the low frequency range mainly comes from hysteresis and eddy current effects, while in the high frequency range it turns to natural resonance and domain wall resonance. The frequency dependence of the loss mechanism itself provides a basis for broadening. Carbon loaded materials such as mesh foam have broadband reflection loss characteristics in the range of 1 – 20 GHz, at the cost that the peak absorption per unit thickness is usually lower than that of resonant materials.
Broadband path with impedance gradient
Impedance gradient is another broadband path. By constructing a gradient distribution of magnetic permeability and dielectric constant in the thickness direction, electromagnetic waves undergo a smooth impedance transition during the process of entering the material, reducing interface reflection and maintaining low reflection loss over a wide frequency range. Advanced Institute Technology adopts a magnetic dielectric gradient composite and multi-layer stacked structure in the design of UHF absorbing wave plates, covering 860-960 MHz at a thickness of 0.2-1.0 mm, with a reflection loss of ≤ -10 dB and an effective bandwidth of ≥ 100 MHz. The cost of broadband materials is' peak depth '. Under the same thickness and process complexity, the reflection loss of broadband materials at a single frequency point is usually not as good as that of narrowband resonant materials. But this "cost" will be offset by system level benefits in multi band coexistence and frequency drift scenarios: broadband coverage reduces the risk of mismatch caused by resonance offset and also reduces the dependence on precise tuning of tag antennas.
Selection boundary in multi band coexistence scenarios
The choice between narrowband and broadband is not a matter of "who is more advanced", but is determined by three system variables:
Firstly, the number of target frequency bands
If the system only needs to cover a single RFID frequency band (such as UHF 860-960 MHz), and the resonant drift of the tag antenna is controllable in the service environment, the deep absorption of narrowband materials at the target frequency point is valuable. If the system needs to cover both UHF and 2.4 GHz simultaneously, or needs to be compatible with frequency band allocations in different regions (865-868 MHz and 902-928 MHz), a single narrowband material cannot simultaneously match two separate frequency windows. At this point, broadband materials are needed to provide coverage, or dual frequency resonant structures (such as metamaterial dual frequency absorbers) are used, but the frequency gap between the two absorption peaks of the dual frequency structure still cannot be absorbed and covered.
Secondly, the amplitude of frequency drift
When the label is attached to a metal surface, the metal boundary will change the input impedance and resonant frequency of the antenna; Liquid packaging and dense stacking can also introduce frequency offset. If the drift amplitude approaches or exceeds the full width at half maximum of the narrowband absorption peak, the effective absorption window of the narrowband material will be "moved out" of the target frequency band. The larger the drift amplitude, the more obvious the relative advantage of broadband materials.
Thirdly, thickness budget
Narrowband materials have an advantage in peak absorption within thin layers, but this advantage only holds true in scenarios where thickness is extremely limited and frequency drift is controllable. If the thickness budget allows for 0.3-1.0 mm, broadband magnetic loss materials or gradient structures can provide sufficient absorption levels while covering the target frequency band. If the thickness is compressed to 0.1-0.2 mm, the narrowband resonant structure may be the only solution that can achieve usable absorption at the target frequency, but its sensitivity to frequency offset needs to be accepted.
Selection judgment based on "number of frequency bands x drift amplitude x thickness"
Firstly, confirm whether the target frequency band is single or multiple, and then discuss the height of the absorption peak
In scenarios with a single frequency band and controllable drift, the peak advantage of narrowband materials can be realized. In scenarios where multiple frequency bands coexist or there are gaps between frequency bands, broadband coverage or dual/multi frequency resonant structures are more realistic starting points, but it is necessary to confirm whether the absorption level of the gap frequency bands meets the system requirements.
Secondly, evaluate the applicability of narrowband materials using "frequency drift amplitude" instead of "static reflection loss"
Request the supplier to provide absorption peak half width data near the target frequency point and compare it with the frequency drift amplitude under actual assembly conditions. If the drift amplitude exceeds one-third of the half width, the robustness of the narrowband scheme needs to be re evaluated.
Thirdly, compare the product of "effective bandwidth x available absorption" within the thickness budget, rather than a single peak
A material that reaches -25 dB at 915 MHz but has a bandwidth of only 30 MHz, and a material that reaches -12 dB in the full frequency range of 860-960 MHz, the former has stronger performance at a single frequency point, while the latter has higher system level availability in multi band and drift scenarios. When selecting, the difference in the number of frequency points within the target frequency band that can reach the available absorption threshold between the two schemes should be compared based on the actual frequency coverage requirements of the system.
Fourthly, in multi band coexistence scenarios, priority should be given to evaluating the system complexity of layered or partitioned schemes, rather than forcibly covering all frequency bands with a single material
If UHF and 2.4 GHz need to be served simultaneously, a layer of UHF broadband magnetic sheet and a layer of 2.4 GHz thin resonant sheet can be stacked in the thickness direction, or the two materials can be arranged in a planar partition. The cost of layering/partitioning is thickness and process complexity, but it avoids the compromise of "wide but not strong" or "strong but not wide" caused by a single material between two frequency bands.
Advanced Institute (Shenzhen) Technology Co., LtdThe RFID absorbing material product line covers two technical routes: narrowband resonance type and broadband magnetic loss type, providing reflection loss curves, absorption peak full width at half maximum data, and performance retention data under frequency drift conditions within the target frequency band.
The UHF broadband series covers 860-960 MHz with a thickness of 0.2-1.0 mm and an effective bandwidth of ≥ 100 MHz; Narrowband series is designed for thin layer deep absorption scenarios with a single frequency point. The product supports customized design of layering and partitioning schemes, and can match material systems based on the number of target frequency bands, drift amplitude, and thickness constraints. For more technical information, please visithttp://www.avanzado.cn/.