Cloak­ing de­vices


Cosmos - - Contents - — AN­DREW MASTER­SON

Too many to list

IN SCIENCE FIC­TION, cloak­ing de­vices are very handy bits of kit that al­low an enor­mous and heav­ily armed space­craft – pi­loted by Klin­gons, for in­stance – to ap­proach an­other craft in cir­cum­stances where hos­tile in­tent is not re­vealed un­til the last mo­ment.

Such shields are thus the Trekky, techy equiv­a­lent of Harry Pot­ter’s in­vis­i­bil­ity cloak, and while no one is sug­gest­ing that large-scale in­duced van­ish­ing is an ac­tual prac­ti­cal idea – at least yet – cloak­ing of an­other type was demon­strated in proof-of-con­cept ear­lier this year.

Not ev­ery­thing has to be about the vi­su­als. Sub­marines, for in­stance, prowl about un­der­wa­ter look­ing for en­e­mies us­ing other senses – es­pe­cially sound. It would be tac­ti­cally ad­van­ta­geous, thus, if the search­ing sonar beamed out from a hos­tile craft could be pre­vented from re­veal­ing the pres­ence of one’s own sub, mak­ing it, to all in­tents and pur­poses, in­vis­i­ble.

And that, in minia­ture, is what Amanda Han­ford, an acous­ti­cal en­gi­neer from Penn­syl­va­nia State Univer­sity, re­cently un­veiled in the US city of Minneapolis, at a meet­ing of the Acous­ti­cal So­ci­ety of Amer­ica.

Han­ford’s in­ven­tion looked rather like a me­tre-high cheese grater. The de­vice gen­er­ates a com­plex ar­ray of acous­tic phases which com­bine to ef­fec­tively can­cel out the give­away reflections of prob­ing sonar beams. To all in­tents and pur­poses, thus, the grater be­comes in­vis­i­ble – or, at least, in­audi­ble.

The ma­chine uses “meta­ma­te­ri­als”, which are com­plex struc­tures com­posed of ar­rays of in­di­vid­ual com­po­nents sig­nif­i­cantly smaller than the wave­length of the sound waves they are in­tended to hide from.

At present, the pro­to­type can squish only a nar­row range of fre­quen­cies and is thus a long way from be­ing able to hide a sub­ma­rine in plain sight. Still, it’s a be­gin­ning. Even the Klin­gons had to start some­where.

Chris Polk / Getty Images

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