Consider solving the Dirichlet problem of Helmholtz equation on unbounded region
R2\Г with Г a smooth open curve in the plane. We use simple-layer potential to construct
a solution. This leads to the solution of a logarithmic integral equation of the first kind for
the Helmholtz equation. This equation is reformulated using a special change of variable,
leading to a new first kind equation with a smooth solution function. This new equation
is split into three parts. Then a quadrature method that takes special advantage of the
splitting of the integral equation is used to solve the equation numerically. An error analysis
in a Sobolev space setting is given. And numerical results show that fast convergence is
clearly exhibited.