ATOMIZATION APPARATUS AND METHOD UTILIZING SURFACE ACOUSTIC WAVES

Abstract: The specification discloses an ultrasonic atomization apparatus utilizing surface acoustic waves. The atomization apparatus is provided with an oscillator (11) generating surface acoustic waves, and a thin porous sheet (12a) provided on an oscillating surface of the oscillator with a very narrow clearance left there between and having a plurality of through holes. A liquid (19) in a liquid vessel (18) is sucked into the very narrow clearance between the oscillator and thin porous sheet owing to the oscillation occuring due to the surface acoustic waves or owing to a capillary phenomenon. The oscillation of the surface acoustic waves is transmitted to the thin porous sheet (12a) via the liquid in the very narrow clearance, and a very small quantity of liquid permeated into the pores in this thin plate is atomized by the oscillatory force and sprayed to the outside. According to this atomization apparatus, the atomization of a liquid can be carried out by using a battery of a small electric power, and the balance between the feed rate and atomization rate of a liquid can be excellently maintained.

Description: Technical Field The present invention relates to an atomizer and an atomizing method utilizing surface acoustic waves, and more particularly, it relates to an ultrasonic atomizer used for cure of asthma or pulmonary diseases. Background Technique An atomizer employing surface acoustic waves is described in "Surface Acoustic Wave Atomizer with Pumping Effect" of Proceedings of 8 th IEEE International Workshop on Micro Electrictro Mechanical Systems 30 January - 2 February 1995 Amsterdam, The Netherlands, in detail. Fig. 1 illustrates the atomizer which has been described in this literature. The atomizer comprises an oscillator 3 having a pair of interdigital electrodes 5 and 5 on its surface for generating surface acoustic waves, a cover 4 arranged on the oscillating surface side of the oscillator 3, and a tube 1. A liquid 2 to be atomized passes through the tube 1 as shown by arrow A, to be supplied into a clearance between the oscillator 3 and the cover 4. The liquid 2 flowing out from the clearance between the oscillator 3 and the cover 4 is atomized and sprayed by surface acoustic wave vibration. In the atomizer shown in Fig. 1, various problems arise when the liquid supply quantity and the atomization quantity are unbalanced. If the liquid supply quantity is excessive, an overflow takes place and the atomization may stop. If the liquid supply quantity is insufficient, on the other hand, the atomization becomes so intermittent that continuous and smooth atomization cannot be attained. Further, high electric energy is required for atomizing and spraying the liquid with only vibration of surface acoustic waves, and it is difficult to perform a desired operation with driving by a battery of small power. Disclosure of the Invention An object of the present invention is to provide an atomizer and an atomizing method which can keep the balance between a liquid supply quantity and an atomization quantity excellent and perform stable atomization. Another object of the present invention is to make it possible to perform stable atomization with small power of a battery or the like. Still another object of the present invention is to make it possible to perform efficient atomization and spraying. The atomizer according to the present invention is as defined in claim 1. The liquid supply means for supplying the liquid into the small clearance part between the oscillator and the porous thin plate includes a liquid container storing the liquid to be atomized. The liquid in the liquid container is aspirated into the small clearance part by vibration by the surface acoustic waves, or by capillarity. The liquid is continuously automatically supplied into the small clearance part by the vibration by the surface acoustic waves and/or capillarity by surface tension also after the liquid in the small clearance part is atomized, whereby the balance between the supply quantity of the liquid and the atomization quantity can be kept excellent. Further, it requires no means for forcibly delivering the liquid into the small clearance in particular, whereby miniaturization of the atomizer can be implemented. In order to efficiently aspirate the liquid from the liquid container into the small clearance part by vibration by surface acoustic waves and/or capillarity by surface tension, the space between the oscillator and the porous thin plate is rendered to gradually enlarge towards the liquid container. The porous thin plate has a number of through holes. As the material for the porous thin plate, ceramics of a hard material with small damping of amplitude by absorption of vibration is preferable. The ceramics is excellent in corrosion resistance, and the safety for the human body is also confirmed. Therefore, in a nebulizer atomizing various types of chemical solutions employed for asthma cure, for example, a porous thin plate (mesh) of ceramics is optimum. In a preferred embodiment, the atomizer comprises a holder holding both of the oscillator and the porous thin plate with a small clearance. Due to provision of such a holder, the clearance between the oscillator and the porous thin plate is regularly maintained constant. The oscillator has a propagation part in which the surface acoustic waves are to be propagated, and a non-propagation part where no surface acoustic waves are propagated. In one preferred embodiment, the small clearance part between the oscillator and the porous thin plate extends over the propagation part and the non-propagation part. In order to aspirate the liquid in the liquid container into the small clearance part by vibration by surface acoustic waves and/or capillarity, the small clearance part on the non-propagation part is dipped in the liquid in the liquid container. In this structure, a region vibrating by the surface acoustic waves is not dipped in the liquid, whereby the load of the vibration does not enlarge and no remarkable reduction of the vibrational amplitude takes place. Therefore, the power of spraying and the atomization efficiency are maintained excellent. The atomizing method according to the present invention is as defined in claim 7. The aforementioned objects and other features as well as advantages of the present invention will become further obvious from the following detailed description made with reference to the drawings. Brief Description of the Drawings Fig. 1 is a perspective view showing a conventional atomizer employing an oscillator generating surface acoustic waves. Fig. 2 is an exploded perspective view of an embodiment according to the present invention. Fig. 3 is a perspective view of the embodiment of the present invention. Fig. 4 is a diagram for illustrating a used state of the embodiment of the present invention. Fig. 5 is a diagram showing an exemplary aspirator into which the atomizer is assembled. Fig. 6 is a perspective view showing an oscillator generating surface acoustic waves. Fig. 7 is a perspective view showing another embodiment according to the present invention. Fig. 8 is a diagram for illustrating a used state of the aforementioned another embodiment. Fig. 9 is a perspective view showing an oscillator having a projecting non-propagation part. Best Modes for Carrying Out the Invention With reference to Fig. 2, Fig. 3 and Fig. 4, an embodiment of the present invention is described. An atomizer comprises an oscillator 11 generating surface acoustic waves, a thin plate 12 having a mesh 12a substantially at its center, and a holder 13. The oscillator 11 includes a rectangular substrate 14 prepared from lithium niobate (LiNbO 3 ), for example, and a pair of interdigital electrodes 15 and 15 formed on a surface of this substrate 14. Comb-tooth parts 15a of the pair of interdigital electrodes 15 and 15 are arranged to be alternately positioned along the longitudinal direction of the substrate 14. Surface acoustic waves are generated when a high-frequency voltage is applied between the pair of interdigital electrodes 15 and 15. These surface acoustic waves propagate along the longitudinal direction of the oscillator 11. The substrate 14 of the oscillator 11 has positioning projections 14a and 14a on its side portions. The substantially quadrilateral thin plate 12 includes the mesh 12a forming a number of through holes. Each hole of the mesh 12a is set at a sufficiently larger diameter than the diameters of atomized grains generated by vibration. Ceramics is preferable as the material for the mesh 12a. The ceramics does not much absorb vibration, and hence damping of amplitude is small. Further, the ceramics is excellent in corrosion resistance, and the safety for the human body is also confirmed. As to the holder 13, the shape seen head-on is substantially U-shaped, and the shape seen from above is substantially rectangular, as illustrated. The holder 13 has a pair of side wall parts 13a and 13a, and grooves 16 and 17 are formed on inner wall surfaces thereof. The grooves 16, which are adapted to receive and hold the oscillator 11, extend substantially in parallel with respect to a bottom wall part 13b of the holder 13. The grooves 17 are adapted to receive and hold the thin plate 12 having the mesh. The grooves 17 are formed at an angle with respect to the bottom wall part 13b of the holder 13, and hence the spaces between the grooves 17 and the grooves 16 are not constant. The spaces between these grooves are rendered to gradually enlarge toward the forward ends. As dimensional illustration, the maximum spaces between the grooves 17 and the grooves 17 on the forward ends are rendered to be about 1 (1 mm), assuming that the lengths of the grooves 16 are 10 (10 mm), for example. In case of manufacturing the atomizer by assembling the oscillator 11, the thin plate 12 having the mesh and the holder 13 with each other, the forward end of the substrate 14 of the oscillator 11 is first moved in the direction shown by arrow A and fitted in the grooves 16 of the holder 13. The movement of the oscillator 11 is performed until the positioning projections 14a come into contact with the holder 13. Then, the thin plate 12 having the mesh is moved in the direction shown by arrow B and fitted in the grooves 17 of the holder 13. Thus, the atomizer shown in Fig. 3 is obtained. A small clearance is formed between the oscillating surface of the oscillator held by the holder 13 and the thin plate 12 having the mesh. The space between the oscillator 11 and the thin plate 12 is rendered to gradually enlarge toward the forward end. With reference to Fig. 4, an operation of the atomizer in use is described. A liquid 19 to be atomized is stored in a liquid container 18. The forward end of the oscillator 11 and/or the forward end of the thin plate 12 having the mesh is dipped in the liquid in the liquid container 18. Namely, the small clearance part between the oscillator 11 and the thin plate 12 is dipped in the liquid. When the oscillator 11 is driven in this state, surface acoustic waves are generated from the comb-tooth parts 15a of the oscillator 11, and these surface acoustic waves propagate on the oscillating surface of the oscillator 11 to reach the liquid surface of the liquid container 18. Due to vibration by these surface acoustic waves and capillarity by surface tension, the liquid 19 is aspirated into the small clearance part between the oscillator 11 and the thin plate 12. The quantity of the liquid in the small clearance part is small and proper, so that the liquid can be sufficiently atomized by the vibrational amplitude of surface waves driven with small power. The vibration on the oscillating surface of the oscillator 11 is transmitted to the mesh 12a of the thin plate 12 through the liquid in the small clearance part. Due to vibration of the mesh 12, the small quantity of liquid penetrating into the hole parts are atomized and sprayed. Fig. 5 is a sectional view of an aspirator into which the atomizer shown in Fig. 2 to Fig. 4 is assembled. The aspirator comprises a body case 21, and a chemical solution bottle 18. In the body case 21, a circuit board 23 carrying a circuit for driving the oscillator 11, a battery 24 and a power supply switch 25 are stored in addition to the atomizer consisting of the oscillator 11, the thin plate 12 having the mesh and the holder 13. The chemical solution bottle 18 stores a chemical solution 19 when in use, and is mounted on a lower portion of the body case 21. As illustrated, lower end portions of the oscillator 11 and the thin plate 12 having the mesh are dipped in the chemical solution 19. The small clearance part between the oscillator 11 and the thin plate 12 having the mesh is filled with the liquid, and hence the liquid in the small clearance part is atomized in the holes of the mesh 12a of the thin plate 12 and sprayed to the exterior by vibration of the surface acoustic waves when the power supply switch 25 is turned on. Reference numeral 20 denotes sprayed mist. According to the aforementioned embodiment, the small quantity of liquid penetrating into the holes of the mesh 12a of the thin plate 12 is atomized and sprayed by surface acoustic wave vibration, whereby stable atomization can be performed also by driving with the battery. Further, supply of the liquid into the small clearance part is automatically performed by vibration by surface acoustic waves and/or surface tension, whereby means for forcibly delivering the liquid is not required, and hence a miniature atomizer is obtained. Further, the liquid is supplied from the liquid container in response to atomization, whereby the balance between the supply quantity of the liquid and the atomization quantity can be kept excellent. While the thin plate 12 having the mesh has been employed as the porous thin plate having a number of through holes, the porous thin plate is not restricted to such a mesh, but a flat thin plate formed with a number of through holes may be employed. Fig. 6 illustrates an oscillator 30 having a pair of interdigital electrodes 31 and 31. Surface acoustic waves generated by application of a voltage between the pair of interdigital electrodes 31 and 31 are propagated in the longitudinal direction of the oscillator 30 in the width of a region where comb-tooth parts of the interdigital electrodes overlap with each other. Referring to Fig. 6, a region 32 shown by slant lines is a propagation part where the surface acoustic waves are propagated, and the remaining region 33 is a non-propagation part where no surface acoustic waves are propagated. In such a state that the forward end portion of the oscillator 30 is not dipped in a liquid, the surface acoustic waves are reflected by an end surface of the oscillator 30 and interfere with traveling waves, standing waves are generated and the vibrational amplitude increases. If the end surface of the oscillator 30 is dipped in the liquid similarly to the aforementioned embodiment, however, there is the possibility that the load of the vibration increases, the surface acoustic waves are diffused in the liquid, and increase of the vibrational amplitude by standing waves cannot be expected. In other words, there is the possibility that the power of atomization or atomization efficiency reduces, if the portion in the oscillator 30 dipped in the liquid is the surface acoustic wave propagation direction side. In an embodiment shown in Fig. 7 to Fig. 9, therefore, a non-propagation part where no surface acoustic waves are propagated in an oscillator 30 is dipped in a liquid. Concretely, a thin plate 34 having a mesh 34a faces both of a propagation part and the non-propagation part of the oscillator 30, to form a small clearance part. The space between the oscillator 30 and the thin plate 34 having the mesh 34a is rendered to gradually enlarge as approaching a liquid container. Fig. 8 shows such a state that the propagation part positioned on a side portion of the oscillator 30 and the forward end of the thin plate 34 having the mesh are dipped in the liquid in the liquid container 35. In this embodiment, the propagation part where the surface acoustic waves are propagated is not dipped in the liquid, whereby the vibrational load does not increase, and no reduction of the vibrational amplitude takes place either. Thus, improvement of the power of atomization or the atomization efficiency is expected. Fig. 9 illustrates another example of an oscillator 36 generating surface acoustic waves. The illustrated oscillator 36 has a projecting part 36a swelling its outer edge in a region where no surface acoustic waves are propagated. This projecting part 36a is dipped in a liquid in a liquid container. Industrial Availability The present invention can be advantageously applied to an aspirator for atomizing a chemical solution effective for asthma cure, pulmonary disease cure or the like.

Claims: An atomizer comprising: an oscillator (11, 30, 36), said oscillator having a forward end, a porous thin plate (12a, 34a, 48) having a number of through holes being arranged on the oscillating surface of said oscillator with a small clearance, said porous thin plate having a forward end, and means for supplying a liquid to be atomized into a small clearance part between said oscillator and said porous thin plate, said means comprising a liquid container (18, 35) for storing the liquid to be atomized, characterized in that said oscillator (11, 30, 36) is arranged to generate surface acoustic waves by means of interdigital electrodes (15, 31) formed on said oscillating surface, said forward ends of said oscillator (11, 30, 36) and of said porous thin plate (12a, 34a, 48) extending into said liquid container (18, 35) so as to be dipped into the liquid stored in said liquid container, the space between said oscillator and said porous thin plate is rendered to gradually enlarge as approaching said liquid container, and said liquid in said liquid container is aspirated into said small clearance part by vibration by the surface acoustic waves, or by capillarity for atomizing the liquid in said small clearance part by surface acoustic wave vibration propagated by said oscillator and spraying the liquid through the through holes of said porous thin plate. The atomizer in accordance with claim 1, wherein said porous thin plate (12a, 34a, 48) is a mesh. The atomizer in accordance with claim 1, wherein said porous thin plate (12a, 34a, 48) is made of ceramics. The atomizer in accordance with claim 1, further comprising a holder (13) holding both of said oscillator (11, 30, 36) and said porous thin plate (12a, 34a, 48) with said small clearance. The atomizer in accordance with claim 1, wherein said oscillator (30) has a propagation part (32) where the surface acoustic waves are propagated and a non-propagation part (33) where no surface acoustic waves are propagated, said small clearance part extends over said propagation part and said non-propagation part, and said non-propagation part is dipped in the liquid in said liquid container (35). The atomizer in accordance with claim 5, wherein said oscillator (30) has a projecting part (36a) swelling its outer edge in a region where no surface acoustic waves are propagated, said projecting part being dipped in the liquid in said liquid container (35). An atomizing method comprising: arranging a porous thin plate (12a, 34a, 48) having a number of through holes on the oscillating surface of an oscillator (11, 30, 34) with a small clearance, supplying a liquid into the small clearance part between said oscillator and said porous thin plate from a liquid container (18, 35) and atomizing the liquid in said small clearance part, characterized by aspirating said liquid into said small clearance part from said liquid container (18, 35) by vibration by surface acoustic waves or by capillarity, said small clearance part being dipped into the liquid in said liquid container (18,35) and being rendered to gradually enlarge towards said liquid container, said oscillator being arranged to generate surface acoustic waves by means of interdigital electrodes (15, 31) formed on said oscillating surface, and atomizing the liquid in said small clearance part by surface acoustic wave vibration propagated by the oscillator for spraying the liquid through the through holes of said porous thin plate.

Inventors: ASAI KEI, YAMAUCHI TAKANOBU, ASAI, KEI, YAMAUCHI, TAKANOBU, ASAI, Kei c/o Omron Healthcare Co., Ltd., YAMAUCHI, Takanobu c/o Omron Healthcare Co., Ltd.
Applicants: OMRON HEALTHCARE CO LTD, OMRON HEALTHCARE CO., LTD.
Application year: 1996
Main classification: B05B17
IPC codes: B05B17, A61M11, F24F6, A61M15