A Silent Microwave Drill for Deep Holes in Concrete

This paper presents a mechanically assisted microwave drill (MWD) capable of drilling 26-cm-deep 12-mm-diameter holes in concrete. This record significantly extends the inherent λ/4-depth capability (~1.5 cm at 2.45 GHz) of the basic MWD scheme. Compared with conventional mechanical drills, this MWD is characterized by a relatively silent and vibration-free operation, but its drilling speed is yet slower than 1 cm/min. This paper reviews the fundamental MWD mechanism (utilizing localized microwave heating and thermal-runaway instability), and extends it for deeper holes by also using the coaxial applicator as a slowly rotating hollow reamer to remove the debris. The MWD prototype is introduced, including its adaptive impedance matching and remote-operation features, and its experimental results are presented. Theoretical and practical MWD aspects are discussed, and potential developments are indicated (e.g., for faster drilling and iron-rebar cutting). The present MWD performance can be useful for specific applications which critically require silent drilling operations in concrete.