An ultrasound probe array for a high-pressure, high-temperature solid medium deformation apparatus

Inelastic deformation of minerals and rocks is associated with activation of various defects such as fractures, twins, and dislocations. Active and passive ultrasound probes are potential tools to examine the nature of these defects under a broad range of pressure and temperature conditions. Here, we report on the development of an ultrasound probe array that allows us to monitor deforming samples in a high-pressure, high-temperature solid medium apparatus (a modified Griggs rig). We utilize several broadband miniature piezoelectric sensors that are placed above and below the sample to record acoustic emissions accompanying deformation and determine their locations in 1D. The emissions are recorded at 50 MS/s with a 12 bit resolution. Proper grounding and electric insulation of the sensors, together with optimized power delivery from the heating system, tremendously reduces electromagnetic interference and allows for a background noise level of ≈90 mV at a full range of ±2 V and 60 dB amplification. The system is capable of recording acoustic waves from 80 kHz to 2.5 MHz at sample temperatures up to 1100 °C and confining pressure up to 2.5 GPa.