Review Reports - Synergistic Integration of CIP and Graphene Within Honeycomb Architectures Toward High-Efficiency Electromagnetic Wave Absorption

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

A CIP / Graphene dual-mechanism absorbing material is proposed and analyzed in detail in the paper. This material uses carbonyl iron particles (CIP) and graphene particles as absorbing materials and aramid honeycomb as the substrate and epoxy resin as the filler. Due to the structure of the composite material, reflected waves are partially captured inside the cells of the structure. Furthermore, interface polarization gives rise to high microwave absorption. The structure under study introduces three types of interfaces into the composite material. By corresponding experiments, the excellent absorbing capability of the composite structure was verified. It was found that graphene significantly alleviated the agglomeration and sedimentation of CIP particles. Under the effect of interfacial phenomena, it formed an outer coating on the CIP spheres, thereby constructing an internal conductive network and enhancing the dielectric loss capability.

The paper is rather good structured. Preparation of CIP / Graphene absorbing honeycomb material is described. The morphology characterization and elemental analysis of honeycomb structure performed essentially help to understand the mechanisms of microwave absorption. The absorbing performance analysis is completed that is an indispensable part of the paper. Moreover, the magnetic loss analysis is performed based on the VSM measurements.

As a whole, the influence of graphene on the magnetic loss capability of the absorbing material was studied and the coupling mechanism between graphene and CIP was investigated. Introduction gives a good insight in the modern state of the problem. Conclusion of the paper is supported by the text. The list of references is appropriate. The paper falls into the scope of the journal, but cannot be published in the presented view because of many drawbacks.

It is necessary to explain the rules how the numerical values of graphene content were obtained in Table 1. Simple calculation gives, for example, the following result for No.2: 120g (CIP) + 0.3g (graphene) + 60g (epoxy resin) + 36g (curing agent) = 216.3g (total). The weight portion of graphene is 0.3g/216.3g = 0.14 wt.%, instead of 0.5 wt.% in Table 1. Analogously, for No.7 total weight is 217.8g and the graphene portion is 1.8g/217.8g = 0.83 wt.%, instead of 3.0 wt.%.
In p.1 the following statement is written: CIP has poor dielectric properties. Strictly speaking, dielectric properties cannot be referred to metallic CIP. The phrase has to be rewritten.
The authors established that influence of graphene on the permeability and magnetic loss capability of the samples is relatively small. Because of this result, the discussion about its influence in different frequency ranges in lines 248 – 251 seems to be excessive. In contrast, the comments in lines 252-256 about the influence of graphene on the agglomeration and sedimentation of CIP are quite worthy.
In discussion about the action of different sources on the reflection loss in lines 293 -295 it has been said nothing about multiple reflections inside the composite plate. Are the conditions of the quarter-wave plate essential or not?
The ray tracing in Figure 4. (a) does not correspond to the experimental scheme shown in Figure 7. (a), where irradiation falls normally to the absorbing plate. The diagram of the rays tracing in Figure 4. (a) is very schematic because it does not take diffraction into consideration. Diffraction is very substantial under the relation between the cell size and the wavelength. It is evident that diffraction is hardly to display in the figure. So, it is worthy to mention in the text that Figure 4. (a) is schematic. In Figure 7. (a) a metal back-reflector plate has to be shown.
Figure 9. presents the influence of electromagnetic fields on the composite structure. What component of applied electromagnetic field is shown? In any case, the lines of both electric and magnetic fields have to be curved in vicinity of a metallic ferromagnetic particle.

Author Response

It is necessary to explain the rules how the numerical values of graphene content were obtained in Table 1. Simple calculation gives, for example, the following result for No.2: 120g (CIP) + 0.3g (graphene) + 60g (epoxy resin) + 36g (curing agent) = 216.3g (total). The weight portion of graphene is 0.3g/216.3g = 0.14 wt.%, instead of 0.5 wt.% in Table 1. Analogously, for No.7 total weight is 217.8g and the graphene portion is 1.8g/217.8g = 0.83 wt.%, instead of 3.0 wt.%.

Author reply: Thank you for your correction. We added corresponding annotations below Table 1 to indicate that this is the proportion of graphene in the effective absorbing component.

In p.1 the following statement is written: CIP has poor dielectric properties. Strictly speaking, dielectric properties cannot be referred to metallic CIP. The phrase has to be rewritten.

Author reply: We gratefully appreciate for your valuable suggestion. We have corrected the description in the paper to describe the electromagnetic properties of carbonyl iron more accurately.

The authors established that influence of graphene on the permeability and magnetic loss capability of the samples is relatively small. Because of this result, the discussion about its influence in different frequency ranges in lines 248 – 251 seems to be excessive. In contrast, the comments in lines 252-256 about the influence of graphene on the agglomeration and sedimentation of CIP are quite worthy.

Author reply: Thank you for your comments. We deleted the relevant narration of the permeability of the materials in the corresponding paragraphs in the low frequency band, making the text more concise.

In discussion about the action of different sources on the reflection loss in lines 293 -295 it has been said nothing about multiple reflections inside the composite plate. Are the conditions of the quarter-wave plate essential or not?

Author reply: Thank you for pointing out the omissions in the article. We supplement the description of the optimization of the absorption performance of the honeycomb structure, and introduce a comparison with the flat plate structure to enhance the persuasiveness of the argument, which also refers to the proposal in another review opinion.

The ray tracing in Figure 4. (a) does not correspond to the experimental scheme shown in Figure 7. (a), where irradiation falls normally to the absorbing plate. The diagram of the rays tracing in Figure 4. (a) is very schematic because it does not take diffraction into consideration. Diffraction is very substantial under the relation between the cell size and the wavelength. It is evident that diffraction is hardly to display in the figure. So, it is worthy to mention in the text that Figure 4. (a) is schematic. In Figure 7. (a) a metal back-reflector plate has to be shown.

Author reply: Thank you for pointing out the contradictions. We add a description to the reference in Figure 4(a)(now Figure 6(a)) to make sure that this is a simplified diagram. In addition, for Figure 7(a)(now Figure 9(a)), we refer to the questions raised in another review opinion and replace it with a data graph of the flat sheet control group. For more relevant descriptions, please refer to the supplementary content in the “Experiments and simulations” section.

Figure 9. presents the influence of electromagnetic fields on the composite structure. What component of applied electromagnetic field is shown? In any case, the lines of both electric and magnetic fields have to be curved in vicinity of a metallic ferromagnetic particle.

Author reply: Thank you for the correction of the concept ambiguity in the text. We have clearly marked the outfield in Figure 9(now Figure 11) and corrected the figure. For the magnetic field lines in the figure, we understand it as the influence of the external field environment, and the role of the figure is more inclined to explain the internal changes of CIP under different graphene contents. In other words, the graphene content and the internal change of the structure are variables, not the external field.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

What is the degree of your graphene exfoliation?

For quantitative dispersion analysis, SEM alone is not enough. The authors will need to add on TEM mapping, Raman uniformity mapping, or conductivity measurements to determine whether graphene is uniformly distributed or agglomerated. This is necessary since the agglomeration could dominate both dielectric loss and magnetic coupling effects, invalidating the authors’ assumptions about “synergistic” enhancement.

No mention of how mass fraction affects density and impedance, which is critical for accurate reflection loss comparison.

The aramid honeycomb substrate affects EM reflection and absorption due to multiple reflections, air gaps, and geometry, but the authors seem to have treated it as neutral.

How much of the absorption is due to the honeycomb structure rather than the material itself?

Oversimplified electromagnetic characterization

Complex permittivity (ε′, ε″) and permeability (μ′, μ″) were measured, but no error analysis, frequency resolution, or thickness normalization is provided.

Dielectric loss must be deconvoluted into polarization and conduction contributions. No such analysis is presented, so “enhanced dielectric loss” could simply result from higher conductivity rather than genuine dipole relaxation.

Claims about “enhanced impedance matching” are qualitative. The authors should have plotted the normalized impedance |Zin/Z0| or the attenuation constant α vs. frequency to substantiate this.

VSM (hysteresis loops) gives static magnetization. How did the authors obtain frequency-dependent magnetic loss using VSM? Magnetic loss in the GHz range arises mainly from natural and exchange resonances, which require dynamic magnetic characterization (e.g., network analyzer ferrite measurements). So, linking VSM data directly to GHz-range absorption is physically weak.

The authors claim that graphene affects magnetic loss via a “synergistic mechanism”. Does graphene alter local magnetic anisotropy, eddy-current pathways, or interparticle exchange coupling? The authors will need direct microstructural or interfacial magnetic evidence, such as Mössbauer, XPS Fe–C bonding, or EELS mapping, to support the claim; otherwise, it is speculative.

Graphene and carbonyl iron can react or oxidize under heat or humidity, degrading performance. I don’t see any thermal stability or oxidation resistance analyses.

No comparison is done with pure CIP, pure graphene, or commercial absorbers (e.g., ferrite-based) to contextualize performance improvements. It is unclear whether the enhancement is meaningful or marginal.

Does the reported performance within 2–18 GHz translate to real stealth or EMI conditions (e.g., X-band focus)? If the optimal RL occurs only in narrow bands or at impractical thicknesses (> 3 mm), practical usefulness is limited.

Author Response

What is the degree of your graphene exfoliation?

Author reply: Thank you for your addition. We have modified and added a description of some parameters of the material in the “Experimental Materials” section.

For quantitative dispersion analysis, SEM alone is not enough. The authors will need to add on TEM mapping, Raman uniformity mapping, or conductivity measurements to determine whether graphene is uniformly distributed or agglomerated. This is necessary since the agglomeration could dominate both dielectric loss and magnetic coupling effects, invalidating the authors’ assumptions about “synergistic” enhancement.

Author reply: Thank you for your correction of the shortcomings of the experiment. We have added the corresponding Raman mapping results and analysis at the end of Section 3.1.1.

No mention of how mass fraction affects density and impedance, which is critical for accurate reflection loss comparison.

Author reply: Thank you for pointing out this important connection. We supplement the analysis of the relevant parameters at the end of Section 3.2.2, and add Table 2 to show the actual data. Through the analysis of the equivalent parameters, the influence between the electromagnetic parameters and the wave impedance is related.

The aramid honeycomb substrate affects EM reflection and absorption due to multiple reflections, air gaps, and geometry, but the authors seem to have treated it as neutral.

Author reply: Thank you for your reminder. We do find that the importance of honeycomb structure in materials cannot be fully demonstrated by the simplified schematic diagram of structural wave absorption principle. Therefore, we add a test of the wave absorption performance of the plane plate, and add a description of it in sections 2.2, 2.3 and 3.2.3. Through the comparison in 3.2.3 section, the influence of honeycomb structure on absorbing ability and its principle are elaborated in more detail.

How much of the absorption is due to the honeycomb structure rather than the material itself?

Author reply: Thank you for your reminder. As mentioned in the answer to the previous question, we compared the data with the plane plate structure to clarify the influence of the honeycomb structure on the absorbing performance, and the results are obviously. The honeycomb structure greatly broadens the absorbing frequency band of the material.

Oversimplified electromagnetic characterization

Author reply: Thank you for your advice. Due to the complexity of the honeycomb structure and the limitation of experimental conditions, we cannot carry out too many electromagnetic characterizations. However, we added an additional control group and other characterizations to assist in proving the relevant performance.

Complex permittivity (ε′, ε″) and permeability (μ′, μ″) were measured, but no error analysis, frequency resolution, or thickness normalization is provided.

Author reply: I 'm sorry to bring you a bad experience. Due to the limitation of experimental conditions, we were unable to collect more test data. However, based on the experimental exploration of the principle content, we are more concerned with the change trend between electromagnetic parameters than the accuracy of single-point data. During the experiment, we fully ensured the stability of the experimental environment and the reliability of the equipment to ensure the internal consistency and comparability of the experimental data.

Dielectric loss must be deconvoluted into polarization and conduction contributions. No such analysis is presented, so “enhanced dielectric loss” could simply result from higher conductivity rather than genuine dipole relaxation.

Author reply: Thank you for your correction. We would like to describe the contribution of graphene to dielectric loss through interface polarization and dipole relaxation process separately, so as to facilitate the description and understanding in this paper, but the original narrative method seems to lack strong proof. Therefore, we adjust the relevant narrative in the text to avoid ambiguity.

Claims about “enhanced impedance matching” are qualitative. The authors should have plotted the normalized impedance |Zin/Z0| or the attenuation constant α vs. frequency to substantiate this.

Author reply: Thank you for your valuable suggestions. We fully understand the importance of normalized impedance diagrams to confirm the impedance matching performance of materials. However, in the face of the honeycomb structure samples in this paper, its complex structured design limits the calculation of normalized impedance. Nevertheless, the wave absorption performance of the material is still affected by its impedance matching and internal loss ability. In the modified Figure 7(now figure 9), we have added the comparison of the absorbing ability of the planar plate samples, and the result is exactly the most powerful evidence for the enhancement of the impedance matching performance.

VSM (hysteresis loops) gives static magnetization. How did the authors obtain frequency-dependent magnetic loss using VSM? Magnetic loss in the GHz range arises mainly from natural and exchange resonances, which require dynamic magnetic characterization (e.g., network analyzer ferrite measurements). So, linking VSM data directly to GHz-range absorption is physically weak.

Author reply: I 'm very sorry to bring you confusion. VSM test is indeed a static test, and it is obviously not rigorous to use it to directly calculate the GHz magnetic loss. In this paper, we consider that VSM is almost the only technology that can characterize the overall state of the magnetic phase in the composite material macroscopically and quantitatively. Therefore, it is used to reveal the change of CIP magnetic microenvironment caused by the introduction of graphene, which is also the structural premise of high-frequency magnetic loss optimization. In this paper, we appropriately add some explanations to the VSM results to make the indirect argument more convincing.

The authors claim that graphene affects magnetic loss via a “synergistic mechanism”. Does graphene alter local magnetic anisotropy, eddy-current pathways, or interparticle exchange coupling? The authors will need direct microstructural or interfacial magnetic evidence, such as Mössbauer, XPS Fe–C bonding, or EELS mapping, to support the claim; otherwise, it is speculative.

Author reply: Thank you for your advice. In this paper, we have constructed a complete chain of proof from micro-scale to macro-scale through VSM, SEM / EDS, Raman mapping and other techniques, which can strongly support the conclusion that “graphene regulates CIP through interface interaction and produces synergistic effect”. The physical coating and electron interaction of graphene on CIP are the most suitable reasons for the change of its static magnetic properties.

Graphene and carbonyl iron can react or oxidize under heat or humidity, degrading performance. I don’t see any thermal stability or oxidation resistance analyses.

Author reply: Thank you for your addition. We added the content of TG test, and described the stability and oxidation resistance of the samples in the experimental part and Section 3.1.2.

No comparison is done with pure CIP, pure graphene, or commercial absorbers (e.g., ferrite-based) to contextualize performance improvements. It is unclear whether the enhancement is meaningful or marginal.

Author reply: Thank you for your proposal, which prompted us to clarify the core objectives and scientific positioning of this research work more clearly. Indeed, this paper does not directly compare the performance with pure components or commercial absorbers. However, this is not an omission, but is determined by the fundamental scientific purpose of this study. The primary goal of our work is not to develop an “optimal” absorbing material with performance beyond the existing standards, but to explore the intrinsic synergistic mechanism and law of “graphene” and “CIP”, which are mainly dielectric loss and magnetic loss, respectively, when they are compounded in a specific honeycomb structure, which has been described in the introduction and conclusion.

Does the reported performance within 2–18 GHz translate to real stealth or EMI conditions (e.g., X-band focus)? If the optimal RL occurs only in narrow bands or at impractical thicknesses (> 3 mm), practical usefulness is limited.

Author reply: Thank you for your attention to the practical application of the experimental product. According to the relevant test of the reflection loss in this paper, the material can indeed achieve stealth absorption in the whole X-band and most of the C-band and Ku-band. However, due to the estimation of honeycomb sample preparation, the actual sample thickness is about 5mm. Considering that there is still room for optimization of the actual impedance matching performance, in theory, it can produce an effective absorbing effect even on a smaller thickness, but this is obviously not within the scope of this study. As we answered in the previous question, we chose this thickness simply because it is more convenient to carry out research work, rather than to pursue the ultimate performance.