氈 combines 毛 (hair, fur) with 亶, which likely contributes the sound. The character originally referred to a felt or woolen rug made from animal hair.
Meaning mnemonic
The right side 毛 means hair or fur, and the left side 亶 looks like a container or spread. Picture a thick rug made of pressed animal hair spread out on the floor.
Reading mnemonic
For セン, imagine a centipede crawling onto a woolen rug: cent -> セン, and the rug is made of hair.
