Electronics Weekly Electronics Design & Components Tech News
Old-fashioned light bulbs may retake the lead in the efficiency race after a marriage with photonic crystals.
Invented at Sandia Labs in the US, tungsten photonic lattice filaments cut energy wasted as heat from 95 to 40 per cent, claimed the organisation.
Photonic crystals are 3D arrays of objects, commonly cylinders or spheres spaced at optical wavelengths, which can filter or diffract light in a similar way to prisms and lenses.
The filament structure acts as a band-pass filter at visible frequencies. Infra-redradiation, normally wasted heat, cannot escape and remains in the structure contributing to the generation of higher energy photons – which can escape.
“Energy at the edge of the photonic band was observed to undergo an order-of-magnitude absorption increase, or enhancement. This meant that energy was being preferentially absorbed into a selected frequency band. Meanwhile periodic metallic-air boundaries led to an extraordinarily large transmission enhancement,” said the lab.
Exactly what is happening is not clear. “It’s not theoretically predicted. Possible explanations may involve variations in the speed of light as it propagates through such structures.”
Although the work points to better visible sources, effort so far has been with all-infra-red sources which emit more than their fair share of high-frequency radiation.
“The work was performed with a photonic crystal operating in the mid-infra-red range, but no theoretical or practical difficulties are known to exist to downsizing the structure into the visible light range,” said the lab.
Experimental results show that a large photonic bandgap for wavelengths from 8 to 20um proved “ideally suited” for suppressing broadband black-body radiation in the infrared and has the potential “to redirect thermal excitation energy into the visible spectrum”.
Sandia’s tungsten photonic crystals are made by micromachining silicon to form a mould, then casting tungsten into it using chemical vapour deposition.
The picture shows lattices with 1.2um rod width and 4.2um pitch with (a) and without(b) oxide. The filling fraction of tungsten material is 28 per cent, said Sandia.
Sorry dear reader, yet again, the images have been lost during ‘improvements’ to the platform on which Electronics Weekly runs, said the technology editor bitterly…..
