Manipulation of Liquids by Use of Sound: Part II

Acoustic-radiation pressure can be used to improve performance in the dispensing of liquid drops into gases or vacuum and in dispensing gas bubbles into liquids. In a typical application involving dispensing a liquid, this is accomplished by use of a high-frequency, high-intensity acoustic transducer coupled with a conventional syringe and hollow dispensing needle (similar to a hypodermic needle). A small dose of liquid passes through the needle and forms a drop at the tip. The drop is held in place by surface tension. The acoustic transducer emits a premetered acoustic tone burst at high power. The bore of the needle conducts the acoustic waves to the drop, where acoustic-radiation pressure creates a force on the droplet. When the burst of force is sufficient to overcome surface tension, the drop separates from the tip.