US Patent 7271607 Electrical, high temperature test probe with conductive driven guard

A probe needle apparatus and method provides a drive guard having the same potential as a probe needle for reducing signal noise in low current measurements. The probe needle apparatus includes a conductive central core covered with alternating layers of dielectric and conductive materials, a first layer of dielectric material applied to maintain electrical access to the conductive central core while providing continuous isolation of the conductive central core elsewhere, and a conductive driven guard layer applied around the first layer of dielectric material in electrical isolation from the conductive central core.