2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/212864The beam coupling impedances of small obstacles protruding inside the vacuum chamber of an accelerator are calculated analytically at frequencies for which the wavelength is large compared to a typical size of the obstacle. Simple formulas for a few important particular cases, including both essentially three-dimensional objects like a post or a mask and axisymmetric irises, are presented. The analytical results are compared and agree with three-dimensional computer simulations. These results allow simple practical estimates of the broad-band impedance contributions from such discontinuities.4 pages, LaTeX (REVTeX), 2 figures (eps); corrected and revised, comparison with simulations added; presented at PAC97 (Vancouver, May 97)Accelerator Physicstext