Dr. Keith Gillis has major roles in three projects that exploit his expertise in physics and physical acoustics:
In earlier research at NIST, Gillis developed acoustic techniques for accurately measuring the thermodynamic and transport properties of gases over wide ranges of temperature and pressure. He developed an all-metal cylindrical acoustic resonator with remote transducers to measure the speed of sound, the ideal-gas heat capacity, and the equation of state of refrigerants that were candidate replacements for chlorofluorocarbons. This setup had acoustic transducers at room temperature and acoustic waveguides that transmitted sound to and from the resonator through metal diaphragms and was used between 240 K and 400 K and pressures up to 1 MPa. Gillis perfected the Greenspan acoustic viscometer for accurate measurements of the shear viscosity of gases. These instruments were also used to characterize hazardous gases used by the semiconductor industry. With NASA sponsorship, Gillis developed an acoustic resonator optimized to measure the bulk viscosity and speed-of-sound dispersion in xenon near its liquid-vapor critical point. This resonator spanned a factor of 50 in frequency from 100 Hz to 5000 Hz. Before joining NIST, Gillis studied third sound in thin superfluid helium films and the heat capacity anomaly at the superfluid transition in helium confined within porous glass.