Electronically Scanned and Focused Receiving Array
A ninety element electronically scanned and focused receiving array has been built and tested. The discrete transducer elements are formed by partial dicing of PZT-5 ceramic bars. Focused beamforming is accomplished by a hybrid analog-digital electronic system. Correct phasing of the transducer elements is achieved by multiplying the received 500 kHz acoustic signals by a low frequency FM sweep or “chirp” signal. The chirp, whose frequency range determines the focal distance, is generated by a VCO, digitized, and entered into a four-level digital delay line ninety units in length. An output tap on the delay line is provided for each hydrophone. Multiplication of the chirp and the acoustic carrier is accomplished by an integrated circuit digital-to-analog multiplier. The current outputs of the multipliers are added by a network of summing amplifiers. After high pass filtering, an amplitude modulated 500 kHz carrier remains. Single sideband demodulation is used to produce the scanning beam output. This signal is then rectified and low-pass filtered and can be used to intensity modulate a CRT display. The system can focus down to a range of less than one meter and produces a resolution of the order of one centimeter at that distance.
KeywordsDelay Line Instantaneous Frequency Voltage Control Oscillator Fresnel Zone Chirp Rate
Unable to display preview. Download preview PDF.
- 1.D. G. Tucker, V. G. Welsby, and R. Kendall, “Electronic Sector Scanning, Brit: Inst. Radio Eng., 26, 465 (1958).Google Scholar
- 2.V. G. Welsby and J. R. Dunn, “A High-Resolution `Electronic Sector Scanning Sonar,” J. Brit. Inst. Radio Eng. 26, 205 (1963).Google Scholar
- 3.U. Tucker, “Near-Field Effects in Elect-onic Scanning Sonar,” J. Sound Vibe 8, 355 (1968)Google Scholar
- 4.V. G. W;~elsby, “Electronic Scanning of Focused arrays,” J. Sound Vib. 8 390 (1968)Google Scholar
- 7.J. F. Haviice, G. S. Kino, J. S. Kofol, and C. F. Quate, “Pr Electronically Focused Acoustic Imaging Device,” Acoustical Holography, Vol. P. S. Green, Ed., New York: Plenum, 1974, pp 317–334.Google Scholar