音響レンズを用いた開口合成形イメージホログラフィ3次元水中撮像法

抄録

This paper proposes a three-dimensional underwater imaging method of “Synthetic Aperture Image Holography”. The method is based on techniques of computer synthetic aperture and sonar.
The imaging procedures are as follows: (1) A transmitter in the transmitting array projects burst sine ultrasound to a target. (2) The ultrasound reflected from the target is then focused on the receiving array by an acoustic lens. (3) A time series signal of focused ultrasound is detected by the receiving element and is converted to “Image Hologram”. It is the image which contains amplitude, phase and range information of the target. (4) Multiple image holograms are obtained while changing transmitters at different positions in the transmitting array by repeating procedures 1 though 3. (5) A final three-dimensional image is calculated by synthesizing all of these image holograms together.
A method analysis reveals that (1) the method can reduce the amount of calculation needed to obtain the image because the acoustic lens does part of the calculations physically. (2) Lateral resolution of the system is determined by the aperture of the transmitting array not by the lens diameter. It derives from the synthetic aperture calculation and enables us to utilize small diameter lens. (3) Aberration of small diameter lens can be negligible. (4) Since the received image hologram is band limited, intermediate pixels between receiving elements can be interpolated. This reduces the number of receiving ultrasound elements compare to that of image pixels.
“A” mode imaging experiment proved that (5) the experimental lateral and range resolutions are nearly equal to theoretical ones. Constructed imaging system proved that (6) it does not require the complex circuit like phased array, and can be constructed by rather simple circuitry. Three-dimansional images of a target is shown.