A well-conditioned combined field integral equation based on quasi-helmholtz projectors

We introduce a novel combined field integral equation that does not suffer from internal resonances and solves several drawbacks of existing resonance-free formulations. The new equation is obtained by combining a regularized electric type operator with a new magnetic type operator that exhibits uniform frequency scaling when acting on, or being tested within, the harmonic Helmholtz subspace for surface currents. With an appropriate use of quasi-Helmholtz projectors, the equation is stable for arbitrarily low-frequencies. Numerical results confirm the theoretical developments and show the effectiveness of the scheme.