The thermocouples/unicouples attached to the outer shell consist of a SiGe alloy n-leg doped with boron and a SiGe p-leg doped with phosphorus to provide thermoelectric polarity to the couple. The electrical and thermal currents of the system are separated by bonding the SiGe alloy thermocouple to a multifoil cold stack assembly of molybdenum, tungsten, stainless steel, copper, and alumina components. Several layers of [https://web.archive.org/web/20150219015544/http://jpsglass.com/aerospace.html Astroquartz] silica fiber yarn electrically insulate the legs of the SiGe thermocouples. In between the inner insulation system and the outer shell, copper connectors form the electrical circuit, which uses a two-string, series-parallel wiring design to connect the unicouples.  The circuit loop arrangement minimizes the net magnetic field of the generator.