One embodiment includes an electromagnetic sensor which includes a header, an anode connected to a first terminal extending through the header, the anode in electrical isolation from the header, a cathode connected to a second terminal extending through the header, the cathode in electrical isolation from the header, a conductive case including a window transparent to electromagnetic energy, the conductive case enclosing the anode and the cathode and hermetically sealed to the header and an insulative sleeve disposed between the anode and the case and between the cathode and the conductive case.