Nebulizer

#The present invention relates to a nebulizer and, particularly, but not exclusively, to an ultrasonic nebulizer suitable for nebulizing/atomizing liquid based medication for the purpose of inhalation by a patient.

#It is well known for liquid nebulizers to employ ultrasonic technology to provide a required degree of liquid atomization. Conventional ultrasonic nebulizers incorporate a piezo-oscillator element (i.e. a piezo-electric crystal) which is exposed to a liquid to be atomized and selectively excited by means of an electric oscillating circuit. Upon excitation, the piezo-oscillator element acts as a transducer and generates ultrasonic waves in the liquid, which are directed to the liquid surface. As a consequence, the surface of said liquid is atomized into a fine mist, which may be transported, as necessary, by suitable means such as an electric fan or simply by the inhalation of a patient.

#The characteristics of piezo-oscillator elements are well known and must be carefully considered when designing the oscillating circuit of a nebulizer if efficient liquid atomization is to be achieved. Both the electrical and mist generating characteristics of a typical piezo-oscillator element are schematically shown in FIGS. 1a, 1b and 1c of the accompanying drawings. It will be seen by reference to FIG. 1a that the effective reactance of a piezo-oscillator element is inductive (i.e. positive) at frequencies between a series (resonance) frequency fr and a parallel (anti-resonance) frequency fa of the transducer. At other frequencies, the effective reactance of the piezo-oscillator element is capacitive (i.e. negative). Also, it will be seen from FIG. 1b that the effective impedance of a piezo-oscillator element is minimized at the resonance frequency fr and maximized at the anti-resonance frequency fa.

#An embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

#FIGS. 1a, 1b and 1c respectively show the variation with frequency of reactance, impedance and quality of mist generation of a piezo-oscillator element;

#FIG. 2 shows a schematic perspective view of a nebulizer according to the present invention;

#A nebulizer 10 according to the present invention incorporates a reservoir 12 for retaining a liquid based medication 14 to be nebulized (see FIGS. 2 and 3). This liquid 14 may include a solution or suspension of solid compounds. As is known in the art, an ultrasonic transducer 16 (i.e. a piezo-oscillator element) is mounted relative to the reservoir 12 so as to be exposed to the liquid medication 14. The transducer 16 is itself connected to appropriate electrical control circuitry (not shown in FIGS. 2 and 3) for providing excitation energy at a required frequency. The control circuitry is powered by means of rechargeable batteries.

#A nebulizing chamber 18 is located above the surface 20 of the liquid medication 14 so as to receive liquid, which has been atomized. A mouthpiece 22 extends into the nebulizing chamber 18 to allow a user of the nebulizer 10 (i.e. a patient) to inhale any atomized medication produced following excitation of the transducer 16. The lower end of the mouthpiece 22 is located adjacent the transducer 16 so as to receive all (or a substantial proportion) of the atomized medication generated during excitation. Atomized mediation is generally ejected from the surface of the liquid 14 as a fountain of small particles. In order to prevent these particles from being undesirably ejected from the nebulizer 10 through the mouthpiece 22, a barrier member 21 is located in the mouthpiece 22. The barrier member 21 is in the form of a concave dome and completely blocks the passage of fluid through the mouthpiece 22. In use, atomized medication to be inhaled by a patient bypasses the barrier member 21 by flowing from a location in the mouthpiece 22 below said member 21 into the nebulizing chamber 18 via one of four elongate slots 23. The slots 23 are equi-spaced about the circumference of the mouthpiece 22. The atomized medication then flows through one of two apertures 25 to a location in the mouthpiece 22 above the barrier member 21. The two apertures 25 are located on opposite sides of the mouthpiece 22.

#An inlet port 24 (provided as necessary with an appropriate one way valve) ensures that fluid pressure within the nebulizer 10 is equalised with the atmospheric pressure external to the nebulizer 10 as atomized medication is inhaled.