Electrodless light sources and applications
The purpose of this research activity is the development of a microwave (MW) electrodeless UV/Vis source based on patented CNR technology.
Usually electrodeless MW sorurces are excited by introducing a glass bulb in a MW oven, or in a MW cavity or in a monomode MW waveguide applicator. In our research work the excitation of plasma discharges in atomic gas/vapors and the construction of a spectral lamp with CW or pulsed UV-Vis emission, is obtained by introducing a dipole coaxial antenna in a glass recess of the bulb. Light pulses with 300 ns rise time and 20 kHz repetition frequency are obtained. The sealed-off glass bulb is fed with microwave power, typically at 2450 MHz, without resorting to a metal cavity. MW power up to 700 W in continuous wave regime or 8 kW (in pulsed regime) is applied to an Ar–Hg filled cylindrical bulb, and 160 W to a XeBr<sub>2</sub> filled spherical bulb at 2.45 GHz.
The advantages of the new method of excitation in terms of luminous efficiency in UV emission from a 6 W Ar–Hg lamp results from direct comparison between a commercial lamp (with arc plasma discharge emission). When the cavity-less lamp is excited at high MW levels, the coaxial antenna can be cooled using forced air or water flowing into the glass recess. The physical modeling of the electromagnetic field distribution in the near-field region of the antenna and its interaction with the gaseous discharge are in good agreement with experimental results.
The new excitation method is characterized by extreme simplicity, low cost, flexibility and versatility in a number of applications, due to the absence of resonant metal enclosures. Thus the technology enables easy scale–up applications, being available for industrial production. A not exhaustive list of potential industrial needs applications of this technology, can be the following:
i) microwave+UV advanced oxidation methods;
ii) microwave heating in conjunction with UV irradiation;
iii) UV treatment of microorganism contaminated materials; MW and UV water disinfection;
iv) environmental remediation by an integrated MW/UV illumination technique;
v) MW activation of processes in photochemistry and photo catalysis;
vi) nanoparticles preparation by photo-reduction;
vii) MW driven UV photo-decomposition of organic species;
viii) lighting technologies.
It is possible to define a series of advantages that could result from the use of the new cavity-less MW/UV source. Noteworthy:
– It is a system that can easily provide UV/Vis light in situ, in any kind of vessels or material without the need and restrictions of having a defined cavity.
– The technology can be useful to apply a number of microwave activated light sources to very large batch reactors (pilot plants) as well as continuous flow systems (production scale).
– There should be no more problems of maximum workable volume of material.
– No other instruments on the market can provide a so large application versatility, being this one adaptable to most of the process technologies already available.
– Having no cavity, this MW electrodeless light source will be apart from the conventional definition and differentiation between multi-mode and mono-mode MW driven device.
The new method of activation is a winner in lamp technology, starting from the construction modalities. It can be used in industrial and multi-disciplinary applications, especially when the controlled treatment of materials, (also in vivo), with microwave activated luminous power and simultaneously with other physical agents (electric and/or magnetic fields, X-rays, nuclear particles, mechanical actions, etc.), in specific conditions of biological, medical, environmental, industrial or laboratory interest, is at a premium. Relevant advantages are attainable in comparison with the technology of the multimode or mono-mode resonant applicators. The CNR lamp is currently utilized in experiments of photocatalysis and in laboratory procedures of advanced analytical chemistry. At present our research work is dedicated to the development of a light bulb with solar-like spectral emission for industrial and civil large scale applications.