Oil-free stress impedance pressure sensor for harsh environment

We report on the design, fabrication and demonstration of a pressure sensor using a magnetic material strain gauge. The gauge consists of a soft magnetic thin foil or ribbon patterned in various geometries. It is attached to machined stainless steel diaphragm by means of an adhesive layer. Upon application of pressure to the diaphragm, strain develops in the magnetic gauge leading to a change in its impedance phase and amplitude, which are measured and correlated to pressure. The sensor demonstrated high sensitivity (4 10(-5) degrees/Pa in phase angle and 5.4 10(-5) Ohm/Pa in amplitude) and low hysteresis (0.26% in phase angle, 0.03% in amplitude). Compared to piezoresistive strain gauges, the magnetic gauge provides approximately 5x to 9x improvement in strain gauge factor. In addition to higher performance, the magnetic pressure sensor is an attractive alternative to silicon-micromachined sensors for harsh environment high-pressure sensors.