Cambridge engineer Gehan Amaratunga, was looking at Guglielmo Marconi’s British patent application from 1900, known as 7777 , and he spotted a little noticed detail.
A transmitter was linked to an antenna connected to a coil, which had one end dangling while the RF signal was fed to the middle of the coil.
This idea is pretty crazy, but the asymmetric coupling between the spark generator and the antenna allowed the transformation of the RF electric signal into electromagnetic radiation.
The researchers realized that it was this asymmetry, or “broken symmetry,” a concept borrowed from quantum theory, that explained the generation of electromagnetic waves in Marconi’s transmitter.
The UK team thought that symmetry breaking explained why dielectric matter can transmits electromagnetic waves.
Dhiraj Sinha said that until now this was not well understood. “Dielectric antennas are already in use, but they are too bulky for on-chip use. Instead of the dielectric materials in use today.
Sinha and his colleagues chose a piezoelectric film. “Normal dielectric antennas are limited by fabrication technologies because we cannot get dielectric materials in thin-film form. Piezoelectric materials can be in thin film form and their thickness can be in the order of 100 to 20 micrometers,” says Sinha.
The researchers used piezoelectric filters that consist of two interdigitated contacts deposited on a piezoelectric film, devices similar to crystal frequency filters now used in cell phones. When excited in a symmetric mode, they act as a simple L-C circuit.
When excited in an asymmetric mode, one of the two interdigital contacts was excited while the other interdigital contact was left floating, the piezoelectric filter acted as a monopole antenna, in fact, in a way comparable to the antenna described by Marconi in 1900.
The new antennas had an efficiency of up to 60 percent and could radiate one watt of power, which about what’s needed by most portable devices.
For their next experiments they will try to create dielectric antennae for longer wavelengths. “We are thinking of bands between 200 and 600 MHz, they are interesting, we could, for example, replace large television antennae by smaller ones,” says Sinha.