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

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 AlO. The antenna angle of 60° from the laser beam propagation achieved maximum enhancement in the emission signal of Al I.