Mica plates act as a buffer for woods/incense/pellets/resins to get just enough heat to release the fragrance without getting too hot to produce a burnt scent. Mica plates are reusable and should last for a while.
(These are techincally replacement mica plates (without border) but will do the job just fine)
 
Click here for a demo on how to set up your burner with ash and a mica plate.
 
5x mica plates