Non-Contacting Borehole Sensor to Measure Stress Waves in Rock

A novel stress sensor is proposed that does not require mechanical or electrical contact to its surroundings, and is thus easy to deploy in almost all measurement scenarios. The sensor is based on a recent breakthrough in electric field sensing that hasalready demonstrated a sensitivity improvement of over an order of magnitude at the Nevada Test Site and other locations. In Phase I laboratory experiments will be done to relate peak stress and stress-time history in granite, quartzite, sandstone, andconcrete to the associated free-space E-field. Simple pressure and impact methods will be investigated to calibrate the stress to E-field coupling ratio while the sensor is emplaced. Based on these results, a design study will be carried out for compactsystems for use in a borehole and also a larger system for a tunnel. In Phase II several prototype systems will be built for evaluation by DTRA. The proposed sensor is a significant advance in stress measurement technology and could have widespread use inscience and engineering. Potential government and commercial applications include exploration, mining, seismology, geophysics, diagnostics for explosives testing, battle damage assessment, nuclear non-proliferation, and possibly planetary research.