Media Releases

Thin, active invisibility cloak demonstrated for first time

November 12, 2013

TORONTO, ON — Invis­i­bil­i­ty cloak­ing is no longer the stuff of sci­ence fic­tion: two researchers in The Edward S. Rogers Sr. Depart­ment of Elec­tri­cal & Com­put­er Engi­neer­ing have demon­strat­ed an effec­tive invis­i­bil­i­ty cloak that is thin, scal­able and adap­tive to dif­fer­ent types and sizes of objects.

Pro­fes­sor George Eleft­he­ri­ades and PhD stu­dent Michael Sel­vanayagam have designed and test­ed a new approach to cloaking—by sur­round­ing an object with small anten­nas that col­lec­tive­ly radi­ate an elec­tro­mag­net­ic field. The radi­at­ed field can­cels out any waves scat­ter­ing off the cloaked object. Their paper ‘Exper­i­men­tal demon­stra­tion of active elec­tro­mag­net­ic cloak­ing’ appears today in the jour­nal Phys­i­cal Review X.

“We’ve tak­en an elec­tri­cal engi­neer­ing approach, but that’s what we are excit­ed about,” says Eleft­he­ri­ades. “It’s very prac­ti­cal.”

Pic­ture a mail­box sit­ting on the street. When light hits the mail­box and bounces back into your eyes, you see the mail­box. When radio waves hit the mail­box and bounce back to your radar detec­tor, you detect the mail­box. Eleft­he­ri­ades and Selvanyagam’s sys­tem wraps the mail­box in a lay­er of tiny anten­nas that radi­ate a field away from the box, can­celling out any waves that would bounce back. In this way, the mail­box becomes unde­tectable to radar.

“We’ve demon­strat­ed a dif­fer­ent way of doing it,” says Eleft­he­ri­ades. “It’s very sim­ple: instead of sur­round­ing what you’re try­ing to cloak with a thick meta­ma­te­r­i­al shell, we sur­round it with one lay­er of tiny anten­nas, and this lay­er radi­ates back a field that can­cels the reflec­tions from the object.”

Their exper­i­men­tal demon­stra­tion effec­tive­ly cloaked a met­al cylin­der from radio waves using one lay­er of loop anten­nas. The sys­tem can be scaled up to cloak larg­er objects using more loops, and Eleft­he­ri­ades says the loops could become print­ed and flat, like a blan­ket or skin. Cur­rent­ly the anten­na loops must be man­u­al­ly attuned to the elec­tro­mag­net­ic fre­quen­cy they need to can­cel, but in future they could func­tion both as sen­sors and active anten­nas, adjust­ing to dif­fer­ent waves in real time, much like the tech­nol­o­gy behind noise-can­celling head­phones.

Work on devel­op­ing a func­tion­al invis­i­bil­i­ty cloak began around 2006, but ear­ly sys­tems were nec­es­sar­i­ly large and clunky—if you want­ed to cloak a car, for exam­ple, in prac­tice you would have to com­plete­ly envel­op the vehi­cle in many lay­ers of meta­ma­te­ri­als in order to effec­tive­ly “shield” it from elec­tro­mag­net­ic radi­a­tion. The sheer size and inflex­i­bil­i­ty of the approach makes it imprac­ti­cal for real-world uses.  Ear­li­er attempts to make thin cloaks were not adap­tive and active, and could work only for spe­cif­ic small objects.

Beyond obvi­ous appli­ca­tions, such as hid­ing mil­i­tary vehi­cles or con­duct­ing sur­veil­lance oper­a­tions, this cloak­ing tech­nol­o­gy could elim­i­nate obstacles—for exam­ple, struc­tures inter­rupt­ing sig­nals from cel­lu­lar base sta­tions could be cloaked to allow sig­nals to pass by freely. The sys­tem can also alter the sig­na­ture of a cloaked object, mak­ing it appear big­ger, small­er, or even shift­ing it in space. And though their tests showed the cloak­ing sys­tem works with radio waves, re-tun­ing it to work with Ter­a­hertz (T‑rays) or light waves could use the same prin­ci­ple as the nec­es­sary anten­na tech­nol­o­gy matures.

“There are more appli­ca­tions for radio than for light,” says Eleft­he­ri­ades. “It’s just a mat­ter of technology—you can use the same prin­ci­ple for light, and the cor­re­spond­ing anten­na tech­nol­o­gy is a very hot area of research.”


For more infor­ma­tion, con­tact:

Mar­it Mitchell
Senior Com­mu­ni­ca­tions Offi­cer
The Edward S. Rogers Sr. Depart­ment of Elec­tri­cal & Com­put­er Engi­neer­ing
Tel: 416–978-7997