Square Split-Ring Resonator as a Sensor for Detection of Nanoparticles in PVDF-Based Nanocomposites at Ultra-HighFrequencies: MXenes and MoS₂ Concentrations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study explores a square split-ring resonator (SRR) to sense concentrations of MXenes and MoS2 in PVDF nanocomposites at UHF bands. It reports frequency and S21 shifts with increasing concentration, with MXenes showing a stronger effect. The manuscript can be accepted after the authors have fully considered the following issues：
1.The authors' description of the sensor's performance in the abstract is not comprehensive. They do not provide any key quantitative indicators such as detection limits, but only describe the minor variation trends of frequency and S21 parameters.
2.In the introduction, although the authors mentioned the shortcomings of traditional detection methods, they failed to clearly expound the unique advantages and innovative points of this SRR sensing method compared with these traditional methods or existing microwave sensing technologies.
3.The title and abstract of the manuscript emphasize the detection of "nanoparticle concentration", but the initial particle size of the MXenes powder used is 40-60μm, and the particle size of the MoS2 powder is approximately 6μm. These belong to the micrometer scale and are not strictly nanoparticles. It is necessary to clarify the actual size of the nanosheets formed after the stripping treatment.
4.The authors derived and presented the lumped component model of SRR, but there was a significant deviation between the simulation results (fRL=505.96 MHz) and the measured no-load resonant frequency (fMR=500.4 MHz). I have not found any explanation or error analysis provided by the authors for this deviation.
5. The authors did not conduct any repetitive experiments or error analyses. Have multiple measurements been taken at each concentration point? What is the standard deviation of the measurement result? I'm not sure about the consistency and reliability of the sensors.
6. When discussing the more significant response of MXenes than MoS2, the authors merely attributed it to its inherent characteristics but did not provide any experimental evidence or cite any literature to directly support this causal relationship.
7. It is suggested that the author compare the performance indicators of this work with those of published sensors based on SRR or other microwave structures to highlight its advanced nature.
8. In the conclusion section, the authors merely repeated the results without summarizing the core findings and limitations of the study, nor did they propose clear and specific directions for future work.
9.The authors can reference 10.1016/j.snb.2023.135210, to enrich the research background.

Author Response

Answers are in word file

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript the authors propose a SRR-based sensor for the detection of NP concentrations in PVDF-based nanocomposites at ultra-high frequencies (UHF). The study investigates the relationship between the resonance of the transmission parameter S₂₁ of the SRRs and the NP-concentration within the nanocomposites located on the split of the SRR-sample. The influence of NP type, size, and distribution on the sensor is examined by SEM to elucidate the underlying sensing mechanisms. A numerical analysis based on Ansys electromagnetic software is employed to compare simulation against measurement results. The sensor presents an acceptable performance for detecting NP and the study shows that a broader range of concentrations of MoS2 and MXenes can be analyzed with MXenes being the concentrations that produce more noticeable shifts in the resonance frequency of S_21.

However, there are some issues that should be carefully addressed by the authors before a positive recommendation:

1) It would be useful for the readers if the authors present figure of merits of the designed sensor, like Q-factor and sensitivity for the NP concentrations under study.

2) In order to show that the current work is a significant advancement in both performance and practical utility, I suggest to provide a comparison against already reported SRR-sensors for detecting NP in this frequency range.

3) Please, correct the equation numbering of the manuscript.  

4) The appropriate references for the equations describing the equivalent circuit model should be given, i.e., in line 264 Eq. (2) as well as in lines 272-280, Eqns. (3)-(7). Otherwise, the derivation of these equations could be placed in an Appendix.   

5) In the title, I suggest to write ‘at ultra-high frequencies’ instead of ‘at UHF frequencies’

6) In the abbreviations section, please correct UHF instead of UFH. Please, note that References [22] and [41] are the same.

7) Figures (3) and (4) should be improved.

Author Response

Answers are in word file

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

A microstrip transmission line coupled square single ring split ring resonator (SRR) is proposed to measure the concentrations of MoS2 and MXenes based on Polyvinylidene fluoride (PVDF). However, the concept and equivalent circuit of the microstrip coupled SRR is well-known in the literature and not novel. In addition, the sensitivity for different MoS2 is very poor and very difficult to differentiate. A microwave sensor with higher sensitivity should be used. There exist lots of high-sensitivity planar microwave sensors in the literature using more sophisticated geometries. Comparison with other high-sensitivity microstrip filter-based microwave sensors should be added. The exact reason for the variations in the resonant frequency and magnitude level of the transmission coefficient characteristic should be clearly explained. Complex permittivity (relative permittivity and loss tangent) of PVDF, MoS2 and MXenes need to be provided. In this regard, the contribution and novelty of the paper are very limited and marginal.

Author Response

answers are in word file

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no other questions.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have responded adequately to my suggestions and concerns and have made the proposed changes in order to improve the manuscript. The manuscript has been improved a lot and it can be published in 'Sensors' in the present form.

Reviewer 3 Report

Comments and Suggestions for Authors

accept.