|Anechoic test chamber. University of Cambridge.|
|WiFi antenna etched on a printed circuit board.|
The phenomenon of radiation due to electron acceleration, first identified more than a century ago, has no counterpart in quantum mechanics, where electrons are assumed to jump from higher to lower energy states. These new observations of radiation resulting from broken symmetry of the electric field may provide some link between the two fields.
|Dipole antenna radiation pattern.|
"Antennas, or aerials, are one of the limiting factors when trying to make smaller and smaller systems, since below a certain size, the losses become too great," said Professor Gehan Amaratunga of Cambridge's Department of Engineering, who led the research. "An aerial's size is determined by the wavelength associated with the transmission frequency of the application, and in most cases it's a matter of finding a compromise between aerial size and the characteristics required for that application."
Another challenge with aerials is that certain physical variables associated with radiation of energy are not well understood. For example, there is still no well-defined mathematical model related to the operation of a practical aerial. Most of what we know about electromagnetic radiation comes from theories first proposed by James Clerk Maxwell in the 19th century, which state that electromagnetic radiation is generated by accelerating electrons.
|Dialectric patch antennas are already in use by GPS devices.|
Working with researchers from the National Physical Laboratory and Cambridge-based dielectric antenna company Antenova Ltd, the Cambridge team used thin films of piezoelectric materials, a type of insulator which is deformed or vibrated when voltage is applied. They found that at a certain frequency, these materials become not only efficient resonators, but efficient radiators as well, meaning that they can be used as aerials.
The researchers determined that the reason for this phenomenon is due to symmetry breaking of the electric field associated with the electron acceleration. In physics, symmetry is an indication of a constant feature of a particular aspect in a given system. When electronic charges are not in motion, there is symmetry of the electric field.
The researchers found that by subjecting the piezoelectric thin films to an asymmetric excitation, the symmetry of the system is similarly broken, resulting in a corresponding symmetry breaking of the electric field, and the generation of electromagnetic radiation.
The electromagnetic radiation emitted from dielectric materials is due to accelerating electrons on the metallic electrodes attached to them, as Maxwell predicted, coupled with explicit symmetry breaking of the electric field.
"If you want to use these materials to transmit energy, you have to break the symmetry as well as have accelerating electrons - this is the missing piece of the puzzle of electromagnetic theory," said Amaratunga. "I'm not suggesting we've come up with some grand unified theory, but these results will aid understanding of how electromagnetism and quantum mechanics cross over and join up. It opens up a whole set of possibilities to explore."
|Si doped 4 inch VGF-GaAs crystal grown in HMM|
Piezoelectric materials can be made in thin film forms using materials such as lithium niobate, gallium nitride and gallium arsenide. Gallium arsenide-based amplifiers and filters are already available on the market and this new discovery opens up new ways of integrating antennas on a chip along with other components.
"It's actually a very simple thing, when you boil it down," said Sinha. "We've achieved a real application breakthrough, having gained an understanding of how these devices work."