Massachusetts Institute of Technology

David J Warkentin

Stephen D Senturia

Mehran Mehregany

Joseph H Haritonidis

A micromachined diaphragm is positioned across a gap from an end of an optic fiber. The optic fiber and the diaphragm are integrally mounted. The end of the optic fiber provides a local reference plane which splits light carried through the fiber toward the diaphragm. The light is split into a transmitted part which is subsequently reflected from the diaphragm, and a locally reflected part which interferes with the subsequently diaphragm reflected part. The interference of the two reflective parts forms an interference light pattern carried back through the fiber to a light detector. The interference pattern provides an indication of diaphragm deflection as a function of applied pressure across the exposed side of the diaphragm. A detection of magnitude and direction of diaphragm deflection is provided by use of a second fiber positioned across the gap from the diaphragm. The second fiber provides an interference pattern in the same manner as the first fiber but with a phase shift. An opening allowing communication between ambient and the gap enables use of the interferometer sensor as a shear stress measuring device.

Pressure transducer apparatus

A thin diaphragm receives pressure across one side and faces a beam splitter on the other side. The beam splitter is integrally attached to the diaphragm and serves as a local optical reference plane for the entire assembly. Coherent light from a light source is partially reflected at the beam splitter. The remainder of the light is reflected from the diaphragm. The reflected beams recombine at a detection point and have a phase difference which is a function of the amount of deflection of the diaphragm. The detected recombined beams are indicative of the deflection of the diaphragm. Optical calibration of the aseembly is a function of the distance between the diaphragm and beam splitter which remains as predefined because the beam splitter is integral with the diaphragm. A vent in the small cavity formed between the diaphragm and beam splitter enables the diaphragm to sense small pressures with increased sensitivity. Through micro-fabrication techniques, the diaphragm is made sensitive to dynamic and static pressure. Detection of the thermal expansion of the assembly as well as deflection of the diaphragm enables a sensed pressure measurement as a differential between the detected thermal expansion and deflection.

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Cambridge, MA, United States of America

David J Warkentin