A sensor, method and system, for measuring certain characteristics of a
fluid. The sensor utilizes a piezoelectric device having at least two
tightly coupled resonators providing a two pole electric transfer
function responsive to an electrical signal coupled to the input
resonator. The piezoelectric sensor has a textured entrapment layer,
constructed to entrap a known volume of fluid and impart motion to the
entrapped fluid as well as to surrounding non-trapped fluid. The common
mode frequency shift of the two resonant frequencies is related to mass
loading due to the entrapped fluid, while the energy absorbed by the
fluid, or a phase shift of one of the resonant frequencies, is related to
the viscosity/density product of the fluid. Extracting the viscosity is a
matter of mathematical manipulation. By controlling the energy level of
the input electrical signal, the viscosity measurement may be conducted
at a predetermined shear rate.