Antenna Characteristics of Helical Coil with 2.45 GHz Semiconductor Microwave for Microwave-Enhanced Laser-Induced Breakdown Spectroscopy (MW-LIBS)

Abstract

A copper helical coil antenna was developed, characterized, and optimized for 2.45 GHz operations supplied by a microwave semiconductor oscillator. The application field of interest is laser-induced breakdown spectroscopy enhanced by microwave. Simulations using the Ansys HFSS demonstrate the superior localized E-field strength of the helical coil antenna, compared with other antenna-type structures. Simulation results show that E-field strength at the tip of the antenna has a logarithmic trend for increasing the coil pitch. The optimum pitch is 5 mm for a coil diameter of 6.5 mm upon consideration of the system compactness. Despite the antenna’s open-circuit end, the presence of target samples does not interfere with the E-field and H-field distribution of the antenna and the surrounding environment. Applications in microwave-enhanced laser-induced breakdown spectroscopy (MWLIBS) confirm the importance of the antenna reflector. The electric field strength was over 100 times higher than the previous capacitor-like antenna. The antenna configuration angle was then experimentally optimized for maximum enhancement effects in the spectrochemical analysis of Al2O3. The antenna angle of 60° from the laser beam propagation achieved maximum enhancement in the emission signal of Al I.

Analysis of gadolinium oxide using microwave-enhanced fiber-coupled micro-laser-induced breakdown spectroscopy

“…The result is a high-volume nonequilibrium plasma with lifetimes that last longer than the microwave duration. In turn, the signal-to-noise ratio (SNR) increases several hundred times owing to the enhancement of the emission intensity, which was previously reported for various targets such as aluminum oxide (Al 2 O 3 ), lead (Pb) plates, copper (Cu) metal, and Zr metal 20 – 22 , 26 .…”

“…The development of a microwave source and helical coil antenna for MWE-LIBS applications on alumina has been reported previously 22 . The effects of microwaves on the laser-induced ablation of Gd 2 O 3 using standard LIBS in a reduced-pressure environment have been discussed in reference 15 .…”

“…Analysis of the surrogate nuclear debris was performed using another echelle-type spectrometer (Aryelle 400, Lasertechnik Berlin, Germany) with a very high spectral resolution of λ/50,000, which is capable of analyzing the surrogate nuclear debris. The microwave generator supplied the 2.45 GHz microwaves to the helical coil with cross-reflector plates 22 . The reflected power was minimized by an impedance tuner and monitored by power sensors.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…Novel methods of analysing alumina have featured in three research papers during this review period. [155][156][157] In the rst of these papers, Ikeda et al used microwave enhanced LIBS that employed a helical coil with a 2.45 GHz semiconductor microwave. 155 The theory is that the LIBS laser ablates the sample and then a microwave discharge operating at a frequency of 10 Hz excites the ablated matter causing it to emit light characteristic of its components which is then transmitted via a bre optic to a detector.…”

“…[155][156][157] In the rst of these papers, Ikeda et al used microwave enhanced LIBS that employed a helical coil with a 2.45 GHz semiconductor microwave. 155 The theory is that the LIBS laser ablates the sample and then a microwave discharge operating at a frequency of 10 Hz excites the ablated matter causing it to emit light characteristic of its components which is then transmitted via a bre optic to a detector. Several parameters were optimised including: the antenna angle from the laser beam (60 achieved maximum signal enhancement) and the microwave antenna type (the optimized version here gave an electric eld strength $100 times that of previous antenna designs).…”