The antennas, at just 10 to 100 micrometres in size, could be used in mobile phones, radio frequency identification (RFID) tags and the so-called Internet of Things, in which everyday devices such as toasters are able to communicate wirelessly. The research is published in Physical Review Letters.
Antennas work by converting electrical energy into electromagnetic, or radio waves. These radio waves are then picked up and converted back into electrical energy by an antenna on the receiving device.
However, while the electronics used in mobile devices are constantly shrinking, the antennas have remained bulky in comparison, said Gehan Amaratunga, professor of engineering at Cambridge, who led the research team. “At the moment there is no prospect of integrating the antenna onto a chip because it’s just too big,” he said. “A typical antenna used in a mobile phone occupies around one quarter of the device’s cover.”
To tackle this problem, the researchers began investigating the use of piezoelectric thin film materials such as gallium nitride and gallium arsenide. These films, which vibrate when a voltage is applied to them, are a type of dielectric, or insulating material. Piezoelectric thin films are much more efficient at storing energy within a certain volume than the dielectric materials conventionally used for mobile phone antennas, according to Amaratunga.
But the researchers found that at a certain frequency, the materials also become efficient emitters of electromagnetic radiation, meaning they can act as effective antennas.
They attribute this to a process known as “symmetry breaking” of the device’s electric field. “This simply means that the energy of the electric field is changed in time or space,” said Amaratunga.
By exciting the material asymmetrically - by connecting only one end of it to an electric signal and leaving the other end free - the researchers were able to break the symmetry of the field, generating electromagnetic radiation.
“If you excite the material from one end and leave the other end floating, then as the energy builds up and cannot be returned to a supply through another contact, it is released as electromagnetic waves,” he said.
The work was carried out alongside researchers from the National Physical Laboratory and dielectric antenna developer Antenova, which is based in Cambridge.