Acoustic liquid dispensing apparatus
A liquid dispensing apparatus for dispensing droplets of a liquid, and methods for measuring various fluid parameters of the liquid are described. The liquid dispensing apparatus comprises a container having a chamber for holding a liquid. An orifice is positioned at an end of the chamber for dispensing droplets of the liquid, the orifice being configured to retain the liquid in the container if the container is positioned with the orifice facing in a downward direction. An acoustic transducer means is at least partially positioned in the chamber for periodically propagating a focused acoustic beam toward the orifice and through at least some of the liquid while the liquid is contained in the chamber, with the focused acoustic beam being capable of causing a droplet of the liquid to be ejected from the orifice when a free surface of the liquid is within the depth of field of the acoustic transducer means. Fluid parameters that can be measured include the sound velocity in the liquid, liquid level and liquid concentration, liquid acoustic impedance, liquid density and ultrasonic viscosity.
1. A method for acoustically measuring one or more fluid parameters comprising:
propagating a test waveform from an acoustic transducer through a liquid contained in a container and towards a free surface of the liquid, the test waveform comprising a short burst of acoustic energy generated by a piezoelectric crystal positioned at a proximal end of the acoustic transducer that is focused by a lens positioned at a distal end of the acoustic transducer;
generating a step reflected wave by reflecting a portion of the test waveform off a calibration surface positioned between the acoustic transducer and the free surface, the calibration surface being positioned at a known distance from the lens;
determining a first period of time that corresponds to the time interval for the step reflected wave to travel from the lens to the calibration surface and back to the lens; and
calculating a sound velocity in the liquid by using twice the known distance of the calibration surface from the lens and the first period of time.
2. The method of claim 1 further comprising:
generating a lens reflected wave by reflecting a portion of the short burst of acoustic energy off the lens in the acoustic transducer;
detecting the lens reflected wave and the step reflected wave with the piezoelectric crystal; and
using the time interval between when the lens reflected wave is detected by the piezoelectric crystal and when the step reflected wave is detected by the piezoelectric crystal in determining the first period of time.
3. The method of claim 1 further comprising:
generating a liquid reflected wave by reflecting a portion of the test waveform off the free surface of the liquid;
detecting the liquid reflected wave with the piezoelectric crystal;
determining a second period of time that corresponds to the time interval for the liquid reflected wave to travel from the lens to the free surface and back to the lens; and
calculating the distance of the free surface from the lens by using the sound velocity in the liquid and the second period of time.
4. The method of claim 3 further comprising:
based on the distance of the free surface from the lens, changing an amount of energy applied to the acoustic transducer to control the size of a droplet of the liquid to be ejected from the free surface.
5. The method of claim 1 further comprising:
measuring the temperature of the liquid in the container; and
determining the concentration of a substance in the liquid by comparing the sound velocity in the liquid to a table that lists the sound velocity in the liquid versus concentration at the temperature of the liquid in the container.
6. The method of claim 5 further comprising:
based on the concentration of the substance in the liquid, changing an amount of energy applied to the acoustic transducer to control the size of a droplet of the liquid to be ejected from the free surface.
7. A method for acoustically measuring one or more fluid parameters comprising:
propagating a test waveform from an acoustic transducer through a liquid contained in a container and towards a free surface of the liquid, the test waveform comprising a short burst of acoustic energy generated by a piezoelectric crystal positioned at a proximal end of the acoustic transducer that is focused by a lens positioned at a distal end of the acoustic transducer;
generating a lens reflected wave by reflecting a portion of the short burst of acoustic energy off the lens in the acoustic transducer;
generating a step reflected wave by reflecting a portion of the test waveform off a calibration surface positioned between the acoustic transducer and the free surface, the calibration surface being positioned at a known distance from the lens;
generating a liquid reflected wave by reflecting a portion of the test waveform off the free surface of the liquid;
detecting the lens reflected wave, the step reflected wave and the liquid reflected wave with the piezoelectric crystal;
determining a first period of time that corresponds to the time interval between when the lens reflected wave is detected by the piezoelectric crystal and when the step reflected wave is detected by the piezoelectric crystal;
determining a second period of time that corresponds to the time interval for the liquid reflected wave to travel from the lens to the free surface and back to the lens;
calculating a sound velocity in the liquid by using the known distance of the calibration surface from the lens and the first period of time; and
calculating the distance of the free surface from the lens by using the sound velocity in the liquid and the second period of time.
8. The method of claim 7 further comprising:
based on the distance of the free surface from the lens, changing an amount of energy applied to the acoustic transducer to control the size of a droplet of the liquid to be ejected from the free surface.