These are some notes on the nature of design research.
I wrote a paper in 2009 that identified 72 types of design research. These are not conventional definitions.
Based on the existing literature, there seem to be three main kinds of design research.
Research about design: This is the focus of my own work, and involves studying design as a phenomenon. It can be also thought of as design science - the science of design, a systematic, evidence- and theory-based explanation of how design happens.
Research in design: This is research carried out as part of a design process; it is part of design practise, where research is conducted to inform a design task.
Research through design: This is research that uses design as a tool. One example of this type of work is so-called design of experiments in which experiments are designed to fit into a larger research program.