Concentration Measurement of Uniform Particles Based on Backscatter Sensing of Optical Fibers

Round 1

Reviewer 1 Report

The manuscript describes the design, fabrication and evaluation of an optical fiber setup used to measure sediments concentration on water. The optical fiber measurement concept is based on the well-known “Fotonic” sensors. Results are presented and fitting on curves allows to get the calibration parameters that can be used to perform direct measurement with other particle sizes that have not been previously calibrated. Some discussions are presented all along the manuscript and the influence of the light intensity closes the experiments realized and presented here.

 

I think that authors have a bit neglected the “Fotonic” measurement principle (I give some information later in my response) and they could have found very valuable information to better understand some behaviours observed in the experiments. Finally the conclusion giving some ways to explore in order to improve the measurement is bringing an overall quality of the manuscript that I believe can be published. Nevertheless, some points have been highlighted and must be corrected/adapted in order to publish this work.

 

Abstract

 

Author doesn't mention on which fluid these concentrations are measured. Even if it sounds obvious, abstract must highlight this information.

 

Chapter 1

 

Introduction is fine and orientates well the reader to the work performed by the authors. Nevertheless, in lines 51-52, authors write scattering method and backscatter method. It sounds obvious that these are the same but for sake of clarity one term must be used for this method.

 

Chapter 2

 

Line n°96 : Optical fibers have a numerical aperture that generates a light divergence at its output. So, here, authors claim that the optical fibers emit parallel light. This claim is basically false and could only be achieved if they have specially lensed the output fibers. If it is this last case, authors must mention how they did the lensing, otherwise they have to change the "parallel light" statement.

 

Lines 110 to 118 : This paragraph is not well written and explained. One may know that light scattered by farther particles will have less power on the receiving fiber, but it is also not quickly understood that particles very close to the emitting fibers couldn't generate a detectable scatter. Especially if we take into account that an optical fiber doesn't produce a parallel light at its output. An analogy of this measurement problem can be understood from the well-known "Fotonic sensors" (see chapter 2.1 of https://doi.org/10.1364/AOP.4.000441). This fact can also be observed in the Figure 3 of your reference n°36 (distance 0 to 7-8 mm). This paragraph needs to be improved in that sense.

 

Line 136 : It is dangerous to talk about "good bending" as the fiber can be probably mechanically bent but the optical losses generated by the bend will strictly depends on the fiber design and could seriously change the received light intensity if the fibers bend dynamically during the measurement.

 

Authors must change this explanation.

 

Line 141 : In figure 3 we can clearly see that there are 5 probes but there are 7 cables going out from the box. Could you please give some explanation about this difference ?

 

Chapter 3

 

Lines 187-188 : The sentence is not clear and must be rewritten. Do the authors claim that saturation is achieved quicker with the concentration increasing ? Based on the graphic curves, it is quite difficult and hazardous to claim such behaviour.

 

Lines 194-195 : Explanation of the parameter V is a bit confused and it must be improved.

 

Lines 225-227 : Authors must link the concentration measurement errors, with a higher concentration, with the saturation observed on measurements that are shown of Figure 5 and adapt the comments consequently. It is obvious that this saturation induces such behaviour in both cases and a link between them must be performed in order to improve the quality of the results.

 

Chapter 4

 

Lines 262-266 : Multiple reflections must always occur, no matter the light intensity. That means that if light intensity increases, the back scattering level must increase with a linear response. Consequently, this can't explain the response of the blue curve compared to the others. A better explanation has to be found or, if not, a statement giving further ways to explore in order to better understand what is happening.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper by Huang et al. present the concentration measurement of SiC particles based on the backscatter sensing of optical fibres. The design and idea work fine. But there remains many issues below to be addressed before the acceptance for the publication:

-Based on the reference 25 and the description in line 91, there seems to have other reports addressed the particle concentration measurement based on the backscatter sensing of optical fibre. So what is the main difference from your design? Why you initiate this work? Any advance/consideration about it?

-Both the literature and figure citations are messed. Please correct them all.

-As the scattering is often relied upon the wavelength of the light, so please give out the specification for your LED source.

-What is the physical meaning for the fitting parameters a, t and b? Please add the error bar for Figure 6 and Figure 7;

-The English is casual at some places, like ‘high light intensity’, ‘kg/m3’, ‘VA and VR’, etc.

-Please unify the reference format, like 1, 5, 6 and 7.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

All my concern have well responded and I recommend the acceptance as it is.