Methods and apparatus for determining properties of a fluid

1. A method for determining viscosity of a fluid comprising:

interacting the fluid with a standing wave in a first state to establish the standing wave in a second state;

analyzing an electric signal associated with the standing wave to determine a characteristic associated with the second state, wherein the characteristic comprises at least one of a maximum phase slope of at least a part of the electric signal, a phase slope associated with a resonant frequency, or both; and

determining the viscosity of the fluid by comparing the characteristic associated with the second state with a function that associates a plurality of viscosities with a corresponding plurality of characteristics.

2. The method of claim 1 , wherein a wave speed associated with the standing wave is less than the speed of sound in the fluid.

3. The method of claim 1 , wherein the function is a calibration function that associates a plurality of known viscosities with a corresponding plurality of known characteristics.

4. The method of claim 1 , wherein the function comprises a lookup table or a mathematical formula.

5. The method of claim 1 , wherein analyzing further comprises:

conducting at least a first sweep through a bandwidth of frequencies of the standing wave to determine at least two phase values associated with at least two corresponding frequency values of the second state; and

providing a phase function for relating each of the phase values to the at least two frequency values, wherein the maximum of the phase slope is defined as a phase value at which a derivative of the phase function is a relative extreme.

6. The method of claim 1 , wherein analyzing further comprises:

conducting at least a first sweep through a bandwidth of frequencies of the standing wave to locate the resonant frequency;

determining a phase value associated with the resonant frequency; and

defining the maximum of the phase slope as the phase value associated with the resonant frequency.

7. The method of claim 1 , wherein interacting further comprises providing one or more tone bursts to an acoustic wave device to generate the standing wave.

8. The method of claim 1 , wherein determining viscosity of the fluid comprises comparing the temperature of the fluid with a second function that associates a plurality of temperatures with a second corresponding plurality of viscosities.

9. The method of claim 1 , wherein the electric signal is produced by an acoustic wave device.

10. The method of claim 9 , wherein the acoustic wave device is a flexural plate wave device.

11. The method of claim 1 , further comprising:

determining density of the fluid by comparing the resonant frequency with a second function that associates a plurality of densities with a corresponding plurality of resonant frequencies.

12. The method of claim 11 , wherein the second function is a calibration function that associates a plurality of known densities with a corresponding plurality of known resonant frequencies.

13. The method of claim 11 , wherein the viscosity is the dynamic viscosity of the fluid, and further comprising:

determining the kinematic viscosity of the fluid by relating the density of the fluid and the dynamic viscosity of the fluid.

14. The method of claim 4 , wherein the viscosity is the kinematic viscosity of the fluid, and further comprising:

determining the dynamic viscosity of the fluid by relating the density of the fluid and the kinematic viscosity of the fluid.

15. A method for determining viscosity of a fluid comprising:

interacting the fluid with a standing wave in a first state to establish the standing wave in a second state, wherein a wave speed associated with the standing wave is less than the speed of sound in the fluid;

analyzing an electric signal associated with the standing wave to determine a characteristic associated with the second state, wherein the characteristic comprises a maximum magnitude of at least a part of the electric signal associated with a resonant frequency of the electric signal; and

determining viscosity of the fluid by comparing the characteristic associated with the second state with a function that associates a plurality of viscosities with a corresponding plurality of characteristics.

16. The method of claim 15 , wherein analyzing further comprises:

conducting at least a first sweep through a bandwidth of frequencies of the standing wave to determine at least two magnitude values associated with at least two corresponding frequency values of the second state; and

providing a magnitude function for relating each of the at least two corresponding frequency values to the at least two magnitude values, wherein the resonant frequency is defined as a frequency value at which a derivative with respect to frequency of the magnitude function is approximately zero.

17. The method of claim 15 , wherein determining the viscosity of the fluid comprises comparing the temperature of the fluid with a second function that associates a plurality of temperatures with a second corresponding plurality of viscosities.

18. A method for determining density of a fluid comprising:

interacting the fluid with a standing wave in a first state to establish the standing wave in a second state;

analyzing an electric signal associated with the standing wave to determine a resonant frequency associated with the second state; and

determining density of the fluid by comparing the resonant frequency with a function that associates a plurality of densities with a corresponding plurality of resonant frequencies.

19. The method of claim 18 , wherein analyzing further comprises:

conducting at least a first sweep through a bandwidth of frequencies of the standing wave to determine at least two magnitude values associated with at least two corresponding frequency values of the second state; and

providing a magnitude function for relating each of the at least two frequency values to the at least two magnitude values, wherein the resonant frequency is defined as a frequency value at which a derivative of the magnitude function is approximately zero.

20. The method of claim 18 , wherein analyzing further comprises:

conducting at least a first sweep through a bandwidth of frequencies of the standing wave to determine at least two phase values associated with at least two corresponding frequency values of the second state; and

providing a phase function for relating each of the at least two corresponding frequency values to the at least two phase values, wherein the resonant frequency is defined as a frequency value at which a derivative of the phase function is a relative extreme.

21. The method of claim 18 , wherein determining the density of the fluid comprises comparing the temperature of the fluid with a second function that associates a plurality of temperatures with a second corresponding plurality of densities.

22. An apparatus for determining viscosity of a fluid, the device comprising:

a means for interacting a fluid with a standing wave in a first state to establish the standing wave in a second state;

a means for analyzing an electric signal associated with the standing wave to determine a characteristic associated with the second state, wherein the characteristic comprises at least one of a maximum phase slope, a phase slope associated with a resonant frequency, or both;

a means for determining viscosity of the fluid by comparing the characteristic associated with the second state with a function that associates a plurality of viscosities with a corresponding plurality of characteristics.