Methods and apparatus for determining properties of a fluid

1. A method for determining a density of a fluid in a biosensing or chemical sensing application, the method comprising:

interacting the fluid with a standing wave having a first characteristic to establish a second characteristic;

measuring a frequency domain signal to determine a resonant frequency of the standing wave; and

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

2. A method for determining a property of a fluid, the method comprising:

providing an input signal to a resonant device to establish a standing wave in a surface of the resonant device, the standing wave having a first characteristic;

interacting the fluid with the standing wave to establish a second characteristic;

measuring an output signal of the resonant device in the frequency domain;

associating the output signal with the input signal or a reference signal to generate a second signal for selecting a signal value in the frequency domain, the signal value including a maximum phase slope, a phase slope at a resonant frequency, a maximum magnitude, or a magnitude at the resonant frequency of the second signal; and

determining the property of the fluid by comparing the signal value to a function that correlates a plurality of fluid properties with a corresponding plurality of signal values.

3. A method for determining a viscosity of a fluid in a biosensing or chemical sensing application, the method comprising:

interacting the fluid with a standing wave having a first characteristic to establish a second characteristic;

measuring a frequency domain signal associated with the first or second characteristic to determine a signal value based on a maximum phase slope, a phase slope at a resonant frequency of the signal, a maximum magnitude, or a magnitude at the resonant frequency of the signal; and

comparing the signal value to a function associating a plurality of viscosity values with a corresponding plurality of signal values to determine a viscosity value of the fluid.

4. The method of claim 3 , further comprising controlling a temperature of the fluid with a thermoelectric cooler.

5. The method of claim 3 , wherein the signal comprises a measured output compared to at least one of an input or a reference.

6. The method of claim 3 , wherein the first characteristic is associated with a first time and the second characteristic is associated with a second time.

7. The method of claim 3 , wherein the first characteristic is associated with the standing wave in the presence of a first fluid and the second characteristic is associated with the standing wave in the presence of a second fluid.

8. The method of claim 7 , wherein the viscosity value is associated with the first fluid or the second fluid.

9. The method of claim 3 , wherein the signal value comprises one or more phase values or phase slope values measured over a bandwidth of frequencies.

10. The method of claim 9 , wherein the bandwidth of frequencies includes one or more resonant frequencies.

11. The method of claim 10 , further comprising selecting the signal value from the phase slope at each of one or more resonant frequencies.

12. The method of claim 3 , wherein the signal value comprises one or more maximum magnitude values measured over a bandwidth of frequencies.

13. The method of claim 12 , wherein the bandwidth of frequencies includes one or more resonant frequencies.

14. The method of claim 13 , further comprising selecting the signal value from the maximum magnitude value at each of the one or more resonant frequencies.