Low-Cost, Miniature, Ocean Bottom Seisometer/Accelerometer

A six-month experimental program is proposed to demonstrate the critical technology and manufacturing methods to fabricate a micropower, low-frequency OBS/A having a projected thermal-noise limited sensitivity of one-half nano-G. The OBS/A will utilize a new capacitive sensing structure developed for silicon micromachined micrometers, pressure sensors, and microphones. OBS/A sensitivity is limited by the thermoelastic and mechanical coupling losses in the silicon suspension system. Micromachined capacitive micrometers have demonstrated the ability to detect inertial mass displacement of less than 0.5 nano-G. Ultra-low resonant frequency operation is made possible by using force-balancing feedback. A unique common-mode rejection technique reduces noise associated with low-voltage reference used to electrostatically balance the majority of the static 1-G field. Micropower, switched-bridge capacitive sensing electronics have been developed to detect capacitance changes corresponding to one-tenth of a nano-G. Design options include self-calibration and the use an ASIC chip. A Phase-I option is proposed to measure a technology verification unit at the UNC-Charlotte Metrology Laboratory. The OBS/A design has the capability to meet the storage, transport, vibration, and shock specifications for Navy air-launched weapons.