Modern technologies experience time dependent processes and require measurements to improve the product, reduce cost, or extend lifetimes. Pressure is a key measurement that provides critical information on the changing conditions of a process or system, and microsecond response is crucial. Unlike static (unchanging) pressure which has a mature measurement infrastructure, dynamic (time-dependent) pressure lacks traceable standards. Currently, dynamic pressure sensors can only measure a relative pressure, with unknown errors. Within the Thermodynamic Metrology Group we have initiated a comprehensive research effort to establish the first traceable measurement infrastructure for dynamic pressure, including measurement standards, sensing technologies, and dissemination mechanisms. This infrastructure will utilize optical technologies that take advantage of advances in the telecommunications industry and frequency metrology.
|Scanning electron micrograph of fiber optic pressure sensor. Circular polymer membrane in center of fiber tip deflects with pressure, and deflection is detected with a Fabry-Perot interferometer.|
We are developing photonic-based dynamic pressure sensors using miniature Fabry-Perot interferometers placed on the tips of 150 μm optical fibers. This work is being performed in collaboration with experts at the University of Maryland Sensors and Actuators Laboratory, and has application to the early detection of traumatic brain injury (TBI). Battlefield explosions from IEDs produce dynamic pressure waves on the order of several hundred kPas, and the detection and modeling of these pressures will help better understand the response of brain tissue to an explosion and the resulting TBI.
|Dynamic pressure sensor using a graphene film on the tip of an optical fiber|
Photonic sensors will also have application to thermometry and static measurement applications, as well as sensor networks, which are being pursued in a closely related project in our group.
To characterize dynamic pressure sensors, we are developing a dynamic pressure source based on a shock tube. This shock tube will allow the evaluation of commercial sensors and our photonic sensors, initially at pressures up to 1 MPa and with expanded capability up to 7 MPa. The higher pressure range will cover the important application of gas turbine engine testing. Gas turbines are used for propulsion on aircraft and ships, as well as power generation for the electric grid.
The traceable measurement system for dynamic pressure will use the absorption properties of gas molecules to determine pressure and temperature. The new method will take advantage of the fact that atoms and molecules reach local thermodynamic equilibrium on a timescale much faster than the temporal changes of the pressure. Tunable lasers will generate light at the pressure-dependent absorption bands of molecules such as CO2 or H2O. Measurement of the time-varying transmitted light will yield the dynamic pressure and temperature.