The sensing element can include {HEAD ~ a water permeable material} positioned in between {TAIL ~ two water impermeable material} 
positioned in between
The sensing element can include { HEAD ~ a water permeable material } positioned in between { TAIL ~ two water impermeable material }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL