Infrasound microphones using microfabricated piezoresistive silicon diaphragms

Abstract

We report on the development of a new digital infrasound measurement system with integrated digitizing electronics. The system was designed to meet an input-referred noise floor specification of 95 μPa/√Hz over the frequency range of 0.01 Hz to 100 Hz. The infrasound sensor uses a microfabricated silicon diaphragm with four integrated piezoresistors connected in a full-bridge configuration. Fabricating the sensing element on a silicon wafer using conventional micro-electromechanical systems (MEMS) processing techniques is a convenient approach for realizing sensitive diaphragms with integrated piezoresistors, and, in turn, sensing elements that intrinsically respond to DC. This approach is thought to be suitable for large infrasound arrays. Integrating a secondary transducer into the package provides self-test capabilities, along with a geophone for correlating infrasound signals with seismic vibrations. Sensor self-noise and sensitivity measurements are presented, along with a discussion of system design considerations, including design of the electronics and packaging.