ACOUSTIC SYSTEM FOR USE IN PULSE ECHO RANGEFINDING

摘要

An acoustic system for use in pulse-echo ranging in air or other gaseous medium. The system includes a transmitter/receiver (24) which is arranged to transmit/receive acoustic energy from and/or at a curved working surface (20) in radial directions at an included angle between 20 and 180 DEG . The transmitter/receiver (24) is symmetrically located within a reflector having an outer parabolic part (25) and an inner curved part (26) which opposes the working surface (20) with an effective mutual spacing of n lambda /2 +/- lambda /10 where n = 0 or an integer, and lambda is the wavelength of acoustic energy in the medium at the frequency of the transmitter and/or receiver. The working surface (20) and inner reflective part (26) define a resonant cavity for the acoustic energy as it passes to or from the outer reflector part (25). The working surface (20) and inner reflector part (26) are so positioned relatively to the parabolic focus F of the outer reflector part (25) that the outer reflector part 25 converts acoustic energy transmitted/received from and/or at the working surface into and/or from a collimated beam.