In Japanese you do not generally write western names in kanji. You can try, but nobody would recognise that as "Michael". It would be katakana: マイケル or ミカエル (depending how you pronounce it).
Writing foreign names with kanji/hanzi is done in Chinese, and 迈克尔 seems to be used in Chinese to represent Michael (source: wikipedia)
I would suggest you don't trust random tattoo websites, generally. I've seen some right howlers. (best: "Diva in Japanese" written as literally "female opera singer").