Improved design of spherical multimode hydrophone

An earlier model for a spherical multimode hydrophone [S.H. Ko, G.A. Brigham, and J.L. Butler, J. Acoust. Soc. Am. 56, 1890–1898 (1974)] is able to predict the hydrophone response curves in which resonances are present. In order to eliminate these resonances, the surface area of a given hydrophone is divided into selected areas which are separated from one another and such that the sum of voltages from the elements of an area is zero for the resonant mode, while the sum of voltages due to the nonresonant modes still provides the essential information about the direction of the incoming acoustic wave. This method was used successfully to remove the lowest (n = 3) resonant mode [H.L. Pond, F.A. Alatalo, and S.H. Ko, J. Acoust. SOc. Am. 60, Suppl. (1976)]. However, the elimination of the n = 3 mode is not sufficient. For higher modes, the technique developed here is to keep only two zones instead of adding more zones and to select the position of the line of division between zones by using a weighting factor, so that the, n = 3 mode resonance is eliminated and the effect of the resonance for the other modes is greatly reduced. Experimental results are in agreement with the theoretical results. [Work supported by CNM.]