O. Bruno, C. Geuzaine, J. Monro, Jr., and F. Reitich. Prescribed error tolerances within fixed computational times for scattering problems of arbitrarily high frequency: the convex case. Phil. Trans. of the Royal Society Series A, 362(1816):629-645, 2004.
C. Geuzaine, O. Bruno, and F. Reitich. On the script O sign(1) solution of multiple-scattering problems. IEEE Trans. Magn., 41(5):1488-1491, 2005.