A breakthrough in the understanding of electromagnetism may lead to antennas so small that they would fit on computer chips, which scientists from the University of Cambridge describe as the “last frontier of semiconductor design.”
Study leader, Professor Gehan Amaratunga, of Cambridge’s Department of Engineering, and colleagues believe their new understanding could help identify the points where the theories of quantum mechanics and classical electromagnetism overlap.
The research team claims to have unravelled one of the mysteries of electromagnetism, which they say will facilitate the design of antennas small enough to be integrated into an electronic chip.
The radiation pattern from a dipole antenna showing symmetry breaking of the electric field. (Credit: Generated using Mathematica from Wolfram Inc.)
A major milestone for wireless communications
These ultra-tiny antennas would be a mega leap forward for wireless communications.
Prof. Amaratunga and co-authors wrote in the academic journal Physical Review Letters (citation below) that electromagnetic waves are not only generated from the acceleration of electrons, but also from a phenomenon called symmetry breaking.
Radiation due to electron acceleration, a phenomenon first identified more than one hundred years ago, has no known equivalent in quantum mechanics, where electrons are believed to jump from higher to lower energy states.
The team’s new observations of radiation resulting from broken symmetry of the electric field may reveal some link between the two fields, the authors said.
The purpose of antennas, whether on a mobile phone or a communications tower, is to launch energy into free space in the form of radio or electromagnetic waves, and to collect energy from free space to feed into the device.
One of the main challenges in modern electronics, however, is that antennas are still fairly large and incompatible with electronic circuits – which are super-small and forever shrinking in size.
Antennas, the major obstacle in making systems smaller
“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.”
“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 problem with aerials is that some of the physical variables related to radiation of energy are poorly understood. For example, no well-defined mathematical model related to the operation of a practical aerial exists.
James Clerk Maxwell (1831-1879), a Scottish scientist in the field of mathematical physics, first proposed theories about electromagnetic radiation, which state that it is generated by accelerating electrons. Not much progress in our knowledge of electromagnetic radiation has been made since then.
However, his theory becomes tricky when dealing with radio wave emission from a dielectric solid, a material which generally acts as an insulator, meaning that electrons are not free to move about. In spite of this, dielectric resonators are already used as antennas in mobile phones.
Lead author, Dr. Dhiraj Sinha, said:
“In dielectric aerials, the medium has high permittivity, meaning that the velocity of the radio wave decreases as it enters the medium.”
“What hasn’t been known is how the dielectric medium results in emission of electromagnetic waves. This mystery has puzzled scientists and engineers for more than 60 years.”
Working with scientists from Antenova Ltd., a Cambridge-based dielectric antenna company, and the National Physical Laboratory, the Cambridge scientists used thin films of piezoelectric materials, a type of insulator which is vibrated or deformed when voltage is applied.
At a certain frequency, they found, these material become not only efficient resonators, but also efficient radiators, meaning they can be utilized as aerials.
The authors determined that this phenomenon happens due to symmetry breaking of the electric field linked to electron acceleration.
In physics, symmetry is an indication of a constant feature of a specific aspect in a given system. When electronic charges are not moving, there is symmetry in the electric field.
Symmetry breaking may also apply in such cases as a pair of parallel wires in which electrons are accelerated by applying an oscillating electric field.
Dr. Sinha said:
“In aerials, the symmetry of the electric field is broken ‘explicitly’ which leads to a pattern of electric field lines radiating out from a transmitter, such as a two wire system in which the parallel geometry is ‘broken’.”
The scientists found that when the piezoelectric thin films were subjected to an asymmetric excitation, the symmetry of the system was likewise broken, resulting in a corresponding symmetry breaking of the electric field, and the generation of electromagnetic radiation.
As Maxwell predicted more than a century ago, the electromagnetic radiation emitted from the dielectric materials is due to accelerating electrons on the metallic electrodes attached to them, plus the explicit symmetry breaking of the electric field.
Breaking the symmetry as well as having accelerating electrons
Prof. Amaratunga said:
“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.”
“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.”
This discovery will not only help in the advancement of mobile technology we use every day, but also in the development and implementation of the Internet of Things: where virtually everything in our offices and homes, from refrigerators, thermostats, to toasters will be connected to the Internet.
Billions of devices will be required for these devices, and being able to fit a microscopic aeriel on an electronic chip would be a major milestone.
Piezoelectric materials can be made in thin film forms using materials such as gallium arsenide, gallium nitride and lithium niobate.
Gallium arsenide-based filters and amplifiers are already available on the market. This new discovery opens up new ways of fitting antennas onto chips along with other components.
Dr. Sinha said:
“It’s actually a very simple thing, when you boil it down. We’ve achieved a real application breakthrough, having gained an understanding of how these devices work.”
The study was partly funded by the Cambridge Commonwealth Trust and the Wingate Foundation, the Nokia Research Centre, Cambridge Angels, Cambridge University Entrepreneurs, and the East of England Development Agency.
Citation: “Electromagnetic radiation under explicit symmetry breaking,” Dhiraj Sinha and Gehan A. J. Amaratunga. Physical Review Letters 114, 147701 (2015).