CCD/SAW Sonar Beamforming

Charge-coupled devices (CCD's) have been used to scan convert sonar data rates to speeds where surface acoustic wave (SAW) technology is applicable. A discrete Fourier transform has been implemented with SAW's using the Chirp-Z Transform (CZT) algorithm. Beamforming techniques to focus in the nearfield for high resolution arrays are shown. The beam output rate is inversely proportional to the sample input rate. For a typical sonar application, input data rates of a few MHz reduce the beam output to a comparable rate. Experiments were conducted using a 40-kHz signal sampled at a 200-kHz rate. CCD's were then used to scan convert the 200-kHz sample rate up by a factor of 15 to the 3-MHz sample rate required for a comparable beam output rate. The CZT analyzer was implemented with experimental SAW's having 0.4MHz/
\mu
sec transfer characteristics. The technique is applicable to all sonars simply by using the CCD scan conversion speed up to match the sonar sampling rate to the desired CZT input rate.