Systems and methods for driving nebulizers

1. A nebulizer system, the nebulizer system comprising:

a liquid reservoir that is adapted to hold a liquid that is to be atomized;

a nebulizer, comprising a nebulizer element having a plurality of apertures, wherein:

the nebulizer element is configured to vibrate to atomize the liquid drained from the liquid reservoir; and

the nebulizer element is driven by a drive signal;

a driver that outputs the drive signal, the driver comprising:

a frequency generator;

a phase shift detector configured to measure a phase offset of the drive signal, wherein

the phase offset indicates a phase difference between a voltage of the drive signal and a current of the drive signal;

a processor configured to:

determine a phase delta, wherein:

the phase delta indicates a difference between a target phase offset and the measured phase offset, and

the target phase offset indicates a non-zero target phase difference between the voltage of the drive signal and the current of the drive signal;

change a frequency of the drive signal that is output by the frequency generator to decrease the phase delta; and

adjust a voltage magnitude of the drive signal in response to the frequency of the drive signal being increased, the adjusted voltage magnitude compensating for an increased flow rate caused by a negative bias pressure developing within the liquid reservoir, wherein the driver outputs the drive signal to the nebulizer element, the drive signal having the changed frequency and the adjusted voltage magnitude.

2. The nebulizer system of claim 1 , wherein the processor being configured to change the frequency of the drive signal that is output by the frequency generator to decrease the phase delta comprises the processor being configured to:

change the frequency of the drive signal that is output by the frequency generator to decrease the phase delta to less than a threshold phase delta in a high gain mode;

determine the phase delta is less than the threshold phase delta; and

at least partially in response to determining the phase delta is less than the threshold phase delta, change the frequency of the drive signal that is output by the frequency generator to decrease the phase delta in a low gain mode, wherein

the low gain mode results in a smaller frequency change than the high gain mode.

3. The nebulizer system of claim 2 , wherein the processor is further configured to:

calculate an impedance of the nebulizer element, wherein

the processor changing the frequency of the drive signal that is output by the frequency generator in the low gain mode is conditioned on the impedance of the nebulizer element being below an impedance threshold.

4. The nebulizer system of claim 2 , wherein the processor is further configured to:

determine a slope of the phase offset, wherein

the processor changing the frequency of the drive signal that is output by the frequency generator in the low gain mode is conditioned on the slope of the phase offset being negative.

5. The nebulizer system of claim 2 , wherein the threshold phase delta is five degree or less.

6. The nebulizer system of claim 1 , wherein the target phase offset between the voltage of the drive signal and the current of the drive signal is between 25 degrees and 35 degrees.

7. The nebulizer system of claim 6 , wherein the target phase offset between the voltage of the drive signal and the current of the drive signal is 30 degrees.

8. The nebulizer system of claim 1 , wherein energizing the nebulizer element of the nebulizer with the drive signal causes the liquid to be atomized.

9. The nebulizer system of claim 8 , wherein the liquid is a medicine.

10. The nebulizer system of claim 1 , wherein the processor is further configured to limit adjustment of the voltage magnitude by a threshold rate such that the voltage magnitude is not decreased at a rate greater than the threshold rate.

11. The nebulizer system of claim 1 , wherein the processor is further configured to:

determine the phase delta has been less than a threshold value for at least a threshold period of time; and

in response to determining the amount of error has been less than the threshold value for at least the period of time, store a current frequency of the drive signal as output by the frequency generator as a lock-in frequency.

12. The nebulizer system of claim 1 , wherein the processor is further configured to:

determine that a present frequency of the drive signal is greater than the lock-in frequency; and

in response to determining that the present frequency of the drive signal is greater than the lock-in frequency, scale down the magnitude of the drive signal by a stored decay rate such that a rate of change of the drive signal is limited by a stored threshold rate.

13. A method for using a nebulizer system, the method comprising:

storing, in a liquid reservoir of the nebulizer system, a liquid to be atomized;

energizing, by a driver of the nebulizer system, a nebulizer element using a drive signal, wherein:

a frequency generator of the driver is used to create a frequency of the drive signal; and

the nebulizer element is configured to vibrate to atomize the liquid from the liquid reservoir and the nebulizer element comprises a plurality of apertures;

measuring, by a phase shift detector of the driver of the nebulizer system, a phase offset of the drive signal;

determining, by the driver, a phase delta of drive signal, wherein:

the phase delta indicates a difference between a target phase offset and the measured phase offset, and

the target phase offset indicates a non-zero target phase difference between the voltage of the drive signal and the current of the drive signal;

changing, by the driver of the nebulizer system, the frequency of the drive signal that is output by the frequency generator to decrease the phase delta; and

adjusting, by the driver of the nebulizer system, a voltage magnitude of the drive signal in response to the frequency of the drive signal being increased.

14. The method for using the nebulizer system of claim 13 , wherein changing the frequency of the drive signal that is output comprises:

changing the frequency of the drive signal that is output by the frequency generator to decrease the phase delta to less than a threshold phase delta in a high gain mode;

determining the phase delta is less than the threshold phase delta; and

at least partially in response to determining the phase delta is less than the threshold phase delta, changing the frequency of the drive signal that is output by the frequency generator to decrease the phase delta in a low gain mode, wherein

the low gain mode results in a smaller frequency change than the high gain mode.

15. The method for using the nebulizer system of claim 13 , wherein the processor is further configured to:

calculating, by the driver, an impedance of the nebulizer element, wherein

changing the frequency of the drive signal in the low gain mode is conditioned on the impedance of the nebulizer element being below an impedance threshold.

16. The method for using the nebulizer system of claim 13 , further comprising:

determining, by the driver, a slope of the phase offset, wherein

changing the frequency of the drive signal in the low gain mode is conditioned on the slope of the phase offset being negative.

17. The method for using the nebulizer system of claim 14 , wherein the threshold phase delta is five degree or less.

18. The method for using the nebulizer system of claim 13 , wherein the target phase offset between the voltage of the drive signal and the current of the drive signal is between 25 degrees and 35 degrees.

19. The method for using the nebulizer system of claim 18 , wherein the target phase offset between the voltage of the drive signal and the current of the drive signal is 30 degrees.

20. The method for using the nebulizer system of claim 13 , wherein energizing the nebulizer element of the nebulizer with the drive signal causes the liquid to be atomized.

21. The method for using the nebulizer system of claim 20 , wherein the liquid is a medicine.