{HEAD ~ The diffuser elements} have {TAIL ~ an average space therebetween} of 50 to 300 micrometers 
have
{ HEAD ~ The diffuser elements } have { TAIL ~ an average space therebetween } of 50 to 300 micrometers
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH