an airway clearance combines a force multiplying percussor and a self - applicator assembly . the percussor has an anvil , a hammer , a coil , and a pulse generator . the anvil has a force receiving surface and a force delivering surface . the hammer also has a force - receiving surface and a force - delivering surface , and is attached to the anvil such that the hammer &# 39 ; s force delivering surface and the anvil &# 39 ; s force receiving surface are mechanically free to come together or move apart . when energized with an electrical current , the coil forces the hammer &# 39 ; s force delivering surface and the anvil &# 39 ; s force receiving surface to separate . the pulse generator supplies pulses of electrical current to the coil .