BEAMFORMING WITH DENSE RANDOM ARRAYS - THE DEVELOPMENT OF SPATIALLY SHADED POLYVINYLIDENE FLUORIDE ACOUSTIC TRANSDUCER

This article describes an approach to array design that results in the construction of transducers producing precisely controlled radiation patterns. The method of dense random arrays employs an array of equall y weighted elements, randomly distributed with a density distribution that matches a desired shading. As the spatial density of elements inc reases, the theoretical radiation pattern approaches that of the ideal shading. If the ideal shading is real (e.g., for a symmetric beam), a ll elements in the random array will be either in phase or in phase op position, and the array will require a single amplifier coupled with a phase inverter. If the ideal shading is both real and positive (e.g., Gaussian or Blackman-Harris shading), all elements will be in phase a nd will require only one amplifier. This approach was used to design a linear array to generate a 2-degrees wide Gaussian beam. The elements had a minimum spacing of one-quarter of a wavelength and were placed using a Monte Carlo approach. A theoretical sidelobe level of -21.8 dB was achieved, with good agreement in the central beam (2.4-degrees be amwidth predicted). A 500-kHz acoustic transducer with this element di stribution was built using 110-mum-thick polyvinylidene fluoride (PVDF ). Experiments reveal a radiation pattern very close to the predicted pattern, with -20.8-dB sidelobes.