The Detection of Chemical Materials with a Metamaterial-Based Sensor Incorporating Oval Wing Resonators

Round 1

Reviewer 1 Report

This paper describes a metamaterial-based permittivity sensor to distinguish branded or unbranded diesels.  Experimental results show successful detection of these diesels from both resonant frequency and transmission/reflection coefficients. However, I, the reviewer cannot agree to accept this manuscript in the current form as there are several points to be clarified. They are listed as:

1. Image quality of illustrations are quite poor, in Figs. 1a, 2, 3, 10, 11, and 12. Please provide high-resolution images or vector graphics.
2. Why this work could achieve the highest sensitivity as shown in table 2? What is the key issue for design optimization to change measurement regime from resonant frequency shift to amplitude variation?
3. In the simulation section, parameters of w, epsilon, and mu were swept. However, metamaterial-related dimension parameters (oval diameters, curvatures, or something like that) are not changed. Why? These metamaterial parameters should be essential to determine and optimize resonant frequency and mode. In addition, how much were the fixed parameter for a sweep? (e.g. mu and eps values for w sweep) 
4. Related to 3., the adopted resonant modes shown in Fig. 10, electric field is confined not to sensor layer but to transmission line. In the metamaterial sensors, materials to be tested are often placed in the confined electromagnetic field. Why this mode was chosen in this paper?
5. Is fig. 5 calculated for air? Please confirm the condition.
6. Why permittivities are different between branded- and non-branded diesels? Is it reproducible? If there are any literature, please cite.
7. Why the authors calculate mu dependency in Fig. 9? Does diesel have magnetic response?
8. In Figs. 7 and 9, frequency-independent parameters of eps and mu were used. However, as shown in Fig. 4, eps has frequency dependence. In this frequency region, this dependency is due to polarization orientation. Why don't you use polarization orientation model with frequency dependence? It will provide much clarified information or parameter values to the interpretation of observed phenomena.
9. The order of figs. 12 and 13 should be swapped as described in the main text.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This work investigates a new design of metamaterials-based sensor integrated transmission line to be used for chemicals detection. The manuscript is well written and the technical Content has a high Quality. I can suggest the paper for publication after minor revisions:

1.) Please clarify the term "branded and unbranded diesel". What exactly did you measure (please provide chemical description of your diesel). As far as I know, the difference between branded and unbranded fuel is really rather minor. The fuel is the same, with the exception that branded fuel contains additives. These additives are intended to improve gas mileage, reduce carbon monoxide and increase performance, to name a few. Therefore, it is necessary to describe the properties of your diesel precisly.

2.) It is quite unusual to claim a sensitivity by using an Amplitude Variation. A sensitivity is typically defined as the Amplitude Variation per Variation of the dielectric constant. Please make clear why you decided to use only the Amplitude Variation.

3.) Please increase the quality of Figure 10 and 11 (About 300 dpi is better).

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The content of the paper is much improved through revision, and I recommend this paper to be published.