Peer review of: Tunable photo-responsive elastic metamaterials (2020)

Reviewers' comments: 
Reviewer #1 (Remarks to the Author): 

This manuscript presents experimental results on thermal modification of acoustic band structure 
of a linear periodic chain of elastic scatterers. The scatterers are fabricated from a thermo-
sensitive polymer which becomes softer under laser heating. The authors demonstrated relatively 
fast and reversible response of the chain by measuring the transmissivity of the chain subjected to 
a wide spectrum of elastic vibrations. The experiments are carried out with high precision allowing 
detection of the amplitude of vibrations within a very small area of each scatterer. The obtained 
results can find applications in design of remote controlled acoustic filters. I consider the presented 
results as a high-quality research, which, however, does not fit the scope of Nature 
Communication. The authors do not propose a new mechanism of control of the band structure; 
they rather propose a useful modification of the already known methods. 
I do not agree with the authors’ interpretation of the obtained results. The authors claim that 
heating of a single scatterer leads to extension of the band gap. This is not true. If elastic 
properties of a single element in a periodic chain are different form the others, this element is 
considered as a point defect in a periodic system. It is known that presence of a point defect leads 
to a discrete level within the band gap (so-called impurity level). If the level appears close to one 
of the band edges and the level width (due to dissipation) is sufficiently broad, it can be 
mistakenly interpreted as broadening of the band gap. There is one more reason for the observed 
extension of the gap. The band edges are not sharp because the chain contains only 8 periods. If 
the last element in the chain is removed it becomes shorter that leads to further degradation of 
the band gap. If the element is not removed completely but replaced by a defect, a Tamm state 
may appear in the spectrum. Since the chain is short the level associated with this state may be 
sufficiently broad that, again, can be interpreted as gap broadening. Additional study is necessary 
in order to understand what is the real physical nature of the observed lowering of acoustic 
transmissivity. 
In conclusion, I do not recommend this paper for publication in Nature Communication since the 
presented results do not contain a new physical effect and the proposed explanation is confusing. 



Reviewer #2 (Remarks to the Author): 

Authors presents the first steps of stimuli responsive metamaterials. The paper is well written and 
consistant. From the physical point of view i do not see any mistake. I cannot judge on the 
chimsitry but the obtained results confirm the efficiency of the procedure. 

In overall this study is perfectly in time with the current state of art to reach time modulated 
active metamaterial. 

I do recommend the paper for publication. 

Minor: they should discuss more the maximum modulation time of such structures and fix the 
typos in references. 




Reviewer #3 (Remarks to the Author): 

Title: Tunable photo-responsive acoustic metamaterials 
by A. S. Gliozzi et al 

The authors describe a one-dimensional acoustic metastructure based on a 3D printed light-
responsive patterned waveguide. Evidence is given on how to tune the width of the frequency 
band gap. Undoubtedly the paper is interesting and well written, but some figures are unclear and 
needs to be revised. 
In Conclusion the manuscript can be considered for publication on Nature Communications but 
only after some mandatory major revisions according to the following critical points: 

Figure 2a: the authors should define what is the “spectral weight” on the z axis of the figure. 
Figure 2f: it is unclear. On the vertical axis two different quantities are mixed: Time [ms] and 
Array longitudinal axis [mm]. This may confuse the general reader. 
Figure 3b: Dotted red line is interrupted. Moreover the difference among the colour curves are not 
reported in the caption. The authors should clarify this point. 
Line 74: the authors should explain in the text the meaning of the quantity Tg