1. Field of the Invention
This invention concerns a micropulverization device of a type including an ultrasound wave generator, a means for focusing ultrasound waves at one point at least in the liquid for micropulverization near its surface, a chamber for the formation of microdroplets and a means for diffusing the microdroplets thus formed.
2. Description of Prior Art
Conventional therapy makes considerable use of pulverization devices when it is necessary to apply microdroplets to the part of the body to be treated, usually an internal part, such as the nose, throat or bronchi.
Conventional pulverization devices based on mechanical pulverization, such as vaporizers with a nozzle under pressure or piezoelectric sprays using a cone do not make it possible to obtain microdroplets of sufficiently small diameter to be effective for some therapy. Thus, for pneumological applications, it is necessary to generate aerosols in microdroplets.
For several years, the ultrasound pulverizing technique has been used to generate a mist of microdroplets. In this technique, ultrasound waves are generated using electromechanical transducers in a liquid bath. The ultrasound wave beam is directed towards the surface of the bath where the water-air impedance interruption creates a liquid jet called `acoustic fountain`. This phenomenon is accompanied by a mist of microdroplets between 3 and 6 .mu.m in size, created by cavitation or by resonance of the jet's capillary waves.
The above technique is applied in patent FR-89/16.424 describing a process and device for micropulverization of a liquid solution using ultrasound to obtain microdroplets to form a mist of disinfectant products for asepsis on medical premises. But devices of the type described in the above patent have the disadvantage of requiring a large amount of liquid for micropulverization, since the ultrasound waves are transmitted inside the liquid. Because of the considerable amount of liquid for micropulverization, it is necessary to foresee a system for preheating the liquid. Devices of this type are thus generally bulky, wasteful and require a great deal of care in their use (assay, sterilization, cleaning, heating temperature . . . ).
This disadvantage has been partially reduced by focusing ultrasound waves in a propagation medium different from the liquid for micropulverization. Thus, in patent DE-B-1.003.147, focusing is performed by concentrating the waves using a circular wave generator, in which the centre coincides with the point where micropulverization is to take place.
Another type of focusing involves using a system for concentrating ultrasound waves using a Fresnel-type lens as described in U.S. Pat. No. A-3.433.461.
All these systems use the non-linearity of the ultrasound wave field to obtain good pulverization at the focusing point. The distribution of energy between the fundamental frequency (generator exciting frequency), upper harmonics and subharmonics varies with propagation distance in the propagation medium. There should thus be a minimum propagation distance for ultrasound waves to obtain the greatest possible efficacy at the focusing point.
Consequently, the systems described in the abovementioned patents have the disadvantage of being bulky and are not intended for use as portable equipment.
Moreover, a great amount of energy is required for generating ultrasound waves since there must be a relatively powerful source of ultrasound waves to obtain sufficient energy at the wave focusing point after considerable attenuation, either by the propagation liquid as in patent DE-B-1,003.147, or through the Fresnel lens as in U.S. Pat. No. A-3,433,461. This is why the devices described are connected to an outside source and no autonomous energy source is foreseen to make them portable.