A silent mechanically-assisted microwave-drill for concrete with integrated adaptive impedance matching

This paper presents a prototype of a silent, remotely-operated microwave drill (MWD) for concrete. The MWD concept, based on the induced thermal-runaway instability and hotspot formation effects, is pushed here beyond the limit of quarter-wavelength drilling depth. This extension is achieved by a slow mechanical rotation (∼20-rpm) of the entire coaxial structure penetrating as a hollow reamer into the softened concrete. An adaptive impedance-matching tuner is incorporated in the microwavedrill system in order to enable its automatic operation remotely. The portable MWD prototype enables a silent drilling of deep holes in concrete (>20-cm depth). However, its present drilling speed (<1-cm per minute for 12-mm diameter holes) is too slow yet for most practical applications.