The width of at least one felt out of a plurality of felts formed of ceramic fibers superposed between two wire nets for a heater is made to be narrower than the width w of said wire nets for heater, and the width of other felts is made to be the same as the width w of the wire nets for a heater. Therefore, the operating voltage is decreased and the efficiency of light extracting is improved. The particular amount of gain is adjusted based on the comparison to alter the power level of the amplified cellular signal by less than 1 dB. The precursor fusion condition is detected upon the peak RF current delivered to the tissue remaining below a threshold value for a threshold time. Also disclosed is a method and user interface device for discovering VPNs with extranet configurations.