Implantable medical leads and methods of forming such leads are disclosed. The housing includes a stator arranged opposite to the magnet; a rotor accommodating portion arranged to accommodate the rotor portion; and an inlet and an outlet each of which is arranged to pass through a portion of the rotor accommodating portion. A transport system moves the workpiece positioned in a batch carrier plate through the controlled atmospheric region. Borehole environs are irradiated with neutrons, and induced gamma radiation is measured using a YAP scintillation detector. The cooling flow traverses the motor and the drive unit. A second design methodology uses a deterministic method to establish the parameters for the filler and shell materials.