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Nature paper about mechanical metamaterials violating Betti's theorem

Mike Ciavarella's picture

Maybe because I am proud of Betti's theorem being italian, I am curious about this big emphasys on systems violating it.  They may "open avenues for energy absorption, conversion and harvesting, soft robotics, prosthetics and optomechanics".... ?  I'd be curious to hear some comments.   Anyway, the last author Andrea Alu is anyway italian like Betti.   And he has been forgotten in the top italian engineers list, so I will add him.

Corentin Coulais, Dimitrios Sounas & Andrea Alù

Static non-reciprocity in mechanical metamaterials

Suitably engineered mechanical metamaterials show static non-reciprocity—that is, the transmission of motion from one side to the other depends on the direction of that motion.


Thanks for the link, Mike.

This is one of the more interesting developments in mechanics in recent years.  Now, all we need is for engineers to make some devices to show that this anomalous behavior can be harnessed.

-- Biswajit

Mike Ciavarella's picture

They first created a rubber-made, centimeter-scale metamaterial with a specifically tailored fishbone skeleton design. They tailored its design to meet the main conditions to break reciprocity, namely asymmetry and a response that is not linearly proportional to the exerted force. A second metamaterial, with unusually strong nonreciprocal properties with a more intricate architecture made of connected squares and diamonds. Are you saying these are not realistic and practical?

In my experience, a proof-of-concept prototype (such as the ones in the Nature paper) typically costs several $100,000 if you include the cost of the equipment, personnel, and time to create a prototype that is free of defects.  For the concept to be viable from an engineering point of view, that cost has to be decreased; particularly the cost of quick reproducibility and making large volumes.  

My experience with mechanical metamaterials suggests that making complex structures without defects in large volumes is nontrivial and that problem is not typically addressed by academics.  So we will have to wait until engineers get hold of the idea and try things out before we can claim that the idea is useful.  But the concept is definitely interesting from an academic point of view.

-- Biswajit

Mike Ciavarella's picture

I fully agree on this, and another Nature paper, explains the point.  Read patents, not just papers : Article : Nature Materials

So I searched in google patents, and I found 9000 patents using metamaterials. Of course I am not sure if Andrea's paper will lead to one, and even more importantly, to a true commercial revolution.  I have expressed before my concern about Nature papers...

Again from the Nature materials paper I extract the first lines.....

Like any true royal,a noble scientific finding has two kinds of offspring.There are the legitimate children,the groundbreaking papers,published in prestigious journals in glossy print and with beautiful graphics.And then there are the somehow illegitimate family members,the shadow-like patents:products of the dark,commercial side of a researcher’s brain.Made for profit,not for fame.No nice fonts here,and illustrations still done in the ancient, hand-drawn style. That is at least what most academic researchers still feel about patents.Patents are commercial instruments, hence not interesting from a scientific point of view. And realizing the commercial implications of research work requires a cultural change1,2— a change that occurred in the life sciences in the 1980s. Patent awareness among scientists working in materials research is generally less than of those in biotechnology (Fig.1),because examples of commercially successful spin-offs are still few and far between. Publications are what make reputations.But what is in a patent can be explosive,propelling not few but many careers.They may also be touchstones for the development of life-changing technologies:the ongoing controversies about the patenting of genes provide the most obvious example3

Mike Ciavarella's picture

If you search Andrea Alù in Google patents, you will find at least 10 of them.  Statistically, this may not be enough, if you beleive that

97 Percent of All Patents Never Make Any Money. |


Mike Ciavarella's picture

Perhaps Chiara's work is mostly on mechanical waves, whereas Andrea's work is quasi-static.

The Utility of Instability | Caltech 

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