An apparatus for providing improved gray mapping may include a processor. The gate tunable diode includes a gate dielectric formed on a gate electrode and a graphene electrode formed on the gate dielectric. The first conductor is fixed to a first inner surface of the first frame facing the second frame. The elongated shaft and the elongated ablating surface of each probe are configured to ablate a portion of the heart. This frictional relationship maintains the position of the louvers when rotated by the tilt rod.