A couple years ago, researchers intro­duced a new mate­rial that they said could make any object invis­ible to both radar and the human eye. Invis­i­bility cloaking would have a major impact on defense tech­nology, they explained, but there was only one problem: The cur­rent mate­rials used in this novel appli­ca­tion were only capable of hiding the object from a single fre­quency wave.

Some­body comes in with another fre­quency,” said Hos­sein Mos­al­laei, an asso­ciate pro­fessor of elec­trical and com­puter engi­neering, “they’ll get it like that.” He snapped his fingers.

It’s a problem of band­width, he said. But in a paper recently pub­lished in the journal IEEE Trans­ac­tions on Antennas and Prop­a­ga­tion, Mos­al­laei and his team over­come that problem.

New mate­rials like those that enable cloaking, as well as a host of other appli­ca­tions, are called meta­ma­te­rials: col­lec­tions of so-​​called “inclusions”—metal rings, for example, or wires—that are orga­nized so that the whole affords unique prop­er­ties not found in nature.

One of these properties—called per­me­ability, or the mag­netic polar­iza­tion of the atoms within—is only found in mate­rials with low exci­ta­tion fre­quen­cies. But the minia­ture devices that have come to define our tech­no­log­ical cul­ture operate at high fre­quen­cies. Meta­ma­te­rials devel­oped in labs like Mosallaei’s have been able to achieve the uncommon feat of per­me­ability at high exci­ta­tion frequencies.

But, still, a problem remained: The mate­rials only retained those prop­er­ties at a single fre­quency, just like the afore­men­tioned cloaking mate­rial. Researchers have the­o­rized dozens of new appli­ca­tions with novel com­bi­na­tions of per­me­ability and its sister prop­erty, per­mit­tivity (the elec­tric polar­iza­tion of the atoms in a mate­rial). From minia­tur­ized antennas to cloaking to extremely high-​​resolution imaging to con­cepts we can’t yet fathom, almost none of these will be of great use until meta­ma­te­rials become oper­able at a wide range of frequencies.

In the recent paper, Mosallaei’s team incor­po­rated active elec­tronic cir­cuits into the meta­ma­te­rials as yet another “inclu­sion.” Just like per­me­ability, the cir­cuit com­po­nents want to operate at spe­cific fre­quen­cies. Forcing them together into the con­fined space of the meta­ma­te­rials has the effect of can­celing out this fre­quency depen­dency. The band­width problem dis­ap­pears. This is achieved in the microwave spec­trum where work is cur­rently in progress to exploit the sim­ilar con­cept in higher fre­quen­cies and in the vis­ible band.

The new approach could have impli­ca­tions for a variety of appli­ca­tions. Invis­i­bility cloaking, Mos­al­laei said, is just the beginning.