A subspace phase inverter was an instrument used by Starfleet in the mid-24th century, known to emit Eichner radiation. In 2365, when attempting to trace the source of Eichner radiation causing uncontrolled growth of a sample of plasma plague on board the USS Enterprise-D, Data suggested that a subspace phase inverter might be the cause, but Geordi La Forge dismissed this idea, as the Enterprise was not carrying that specific piece of technology. (TNG: "The Child" )