A reflector is disclosed, suitable for use in an apparatus for sending and/or receiving ultrasonic energy through a propagating fluid. A thin layer of ultrasonically transmissive material is disposed on a supportive substrate having an optically rough surface. A single gaseous layer is trapped between...http://www.google.com/patents/US4207901?utm_source=gb-gplus-sharePatent US4207901 - Ultrasound reflector
