Correction to: Scientific Reports https://doi.org/10.1038/s41598-017-15817-4, published online 13 November 2017

The original version of this Article contained a repeated typographical error in the ‘Design Procedures and Results’ section under the subheading ‘Array with bidirectional elements for use in tunnels’ where,

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now reads:

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This error has now been corrected in the HTML version of the Article; the PDF version was correct from the time of publication.