Mapping Technological Trajectories as Patent Citation Networks. A Study on the History of Fuel Cell Research

Technological change is argued to be taking place along ordered and selective pat-terns, shaped jointly by technological and scientific principles, and economic and other societal factors. Historical, descriptive analysis is often used to analyze these ''trajectories''. Recently, quantitative methods have been proposed to map these tra-jectories. It is argued that such methods have, so far, not been able to illuminate the engineering side of technological trajectories. In order to fill this gap, a methodology proposed by Hummon and Doreian (1989) is used and extended to undertake a cita-tion analysis of patents in the field of fuel cells.