Overview
Benchmarked Validated
The high-pass approximation (HPA) provides fast
broadband estimates for simple fluid-like canonical bodies by joining
low-frequency and reflection-controlled high-frequency behaviour.
Core idea
Use a rational form that recovers the Rayleigh-scale response at small acoustic size while limiting its high-frequency growth. The Johnson method is sphere-specific, while the Stanton method also covers prolate spheroids and cylinders (Johnson 1977; Stanton 1989).
Best for
- Rapid broadband trend calculations for spheres, prolate spheroids, and cylinders
- Screening shape, size, orientation, or material-contrast effects
- Comparison with a geometry-matched modal solution when fine resonances are not required
Supports
- The Johnson sphere and Stanton sphere, prolate-spheroid, and cylinder formulations
- Fluid-like density and sound-speed contrasts relative to the exterior medium
- Optional null-position and deviation controls
Main assumptions
- An interpolation formula rather than an exact boundary-value solution
- A supported canonical shape and the source formulation’s geometric prefactors
- No complete modal resonance structure
- Results are interpreted over the approximation’s acoustic-size regime
Validation status
- Benchmarked against the canonical spherical spectra stored in benchmark_ts.
- Validated against the spherical echoSMs implementation.
Family pages
- Implementation: method selection, supported shapes, output, and comparisons
- Theory: low-frequency term, reflection limit, and shape-specific forms
References
Johnson, Richard K. 1977. “Sound Scattering from a Fluid Sphere
Revisited.” The Journal of the Acoustical Society of
America 61 (2): 375–77. https://doi.org/10.1121/1.381326.
Stanton, Timothy K. 1989. “Simple Approximate Formulas for
Backscattering of Sound by Spherical and Elongated Objects.”
The Journal of the Acoustical Society of America 86 (4):
1499–510. https://doi.org/10.1121/1.398711.