Impeham, I tried just the coil without the black backing, when stuck under the cover against the battery. The blue in-contact pad light did not come on and the phone didn't begin charging, the contact light comes on even if the receiver is not connected. Not 100% sure what the black layer does but it does keep the coil from receiving when it blocks the charge pad and possibly prevents some sort of interference from behind. Back during my Palm Touchstone charger days there was no black barrier layer just a coil.