Development of a high frequency underwater acoustic intensity probe

The development of an underwater acoustic intensity probe for high frequency applications (e.g., f ∼ 10 kHz) is presented. The probe measures the acoustic pressure along with two orthogonal components of the particle acceleration; hence, the probe relies on inertial sensing as opposed to a gradient technique. The acoustic pressure is measured with a ring hydrophone that is capped at both ends. The accelerometers are positioned within the internal cavity created by the hydrophone and are oriented to measure sound in the horizontal plane. The probe is negatively buoyant, contains a viscoelastic suspension system, and is positioned within a free-flooding stainless steel cage that contains extensional damping treatments and exhibits a low scattering cross-section. Negative buoyancy results from making the probe small so that it does not scatter the acoustic field over the frequency range of interest nor exhibit any in-band structural modes. The consequence of this action translates into an in-water acceleration sensitivity that is reduced by a factor of two relative to the intrinsic value. The hydrophone has an omni-directional beam pattern and the accelerometers have dipole directivity. Lumped parameter circuit models will be presented along with performance data.