There is the "Industrial, Scientific, and Medicine" part of the rules. These may have higher limits if your device qualifies. The other problem you face is the safety laws about microwave power density near humans.
In general, if this is a short term academic type experiment the government will not bother what you do in the ISM band. It is when you make a product for the public that you have to get it certified. In many countries the ISM band can be used by hams with 1 kW+ rf power into antennas with unlimited gain.