- Conference date: 25-30 July 2004
- Location: Golden, Colorado (USA)
This paper demonstrates that a planar fracture can behave as a lens and focus ultrasound waves when the fracture has a spatially varying stiffness with axial symmetry. The fracture is modeled as a purely two‐dimensional structure using the displacement‐discontinuity boundary condition. A quadratic group delay as a function of distance from the acoustic axis converts an incident plane wave into a converging spherical wave. Simultaneously, a strong radial dependence of the fracture stiffness mimics a Fresnel zone plate. Analytic expressions are given for the focal lengths in these two limits, and numerical simulations based on Kirchoff diffraction are presented. Experimental results on synthetic fractures using ultrasonic frequencies confirm the predictions, showing energy concentration along the axis of symmetry near the focal plane.
- Acoustic waves
- Acoustic wave diffraction
- Boundary value problems
- Focal points
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