Acoustic Intensity Methods in Classical Scattering
Open Access
- Author:
- Rapids, Brian Richard
- Graduate Program:
- Acoustics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 28, 2004
- Committee Members:
- Gerald Clyde Lauchle, Committee Chair/Co-Chair
Thomas B Gabrielson, Committee Member
Russell Charles Burkhardt, Committee Member
Martin Wesley Trethewey, Committee Member - Keywords:
- acoustic intensity
vector sensors
underwater acoustics
scattering
prolate spheroid
detection - Abstract:
- Measurements made with scalar pressure sensors are only able to provide an estimate of the magnitude of the total intensity associated with an equivalent plane wave. This equivalence is an assumption that the relative phase between pressure and velocity is identically zero. True intensity sensors simultaneously measure the acoustic pressure and components of particle velocity (or related quantity such as acceleration, displacement, or pressure gradient) at a single coordinate in space. Numeric computations regarding the scattering of a steady-state acoustic field by a rigid spheroid indicate that the equivalent plane wave intensity field only varies by ±0.5dB rel. incident acoustic intensity many object lengths away in the forward direction at high frequencies. These computations also predict a phase difference of up to 5º between pressure and particle velocity at ranges exceeding 10 objects lengths away from the scattering body. The reactive intensity estimate, which is identically zero in the presence of a plane wave, also took on values as high as -25dB rel. incident acoustic intensity. The theoretical investigations concluded that the presence of a spheroid in a steady-state harmonic field would perturb the acoustic intensity field more significantly than the scalar pressure field. Experimental measurements involving a biaxial intensity sensor and a model prolate spheroid were conducted to determine if perturbations in the acoustic field due to a scattering body would be more readily observable with an intensity sensor than with a traditional pressure sensor. The experimental data also indicates that measurements of acoustic intensity may be more sensitive to the presence of the spheroid than measurements made solely with the pressure sensor.