Atomisation apparatus using surface acoustic wave generation

Abstract

An apparatus for atomising liquid, including a piezoelectric substrate (1) having a working surface (3), and a peripheral edge (7) extending along a side of the working surface, an interdigital transducer (2) located on the working surface for generating surface acoustic waves (SAW) in the working surface, and a liquid delivery arrangement including a porous member (8) for supplying the liquid to be atomised, wherein the porous member is in contact with the peripheral edge of the piezoelectric substrate.

Claims

1. An apparatus for atomising liquid, including a piezoelectric substrate having a working surface, and a peripheral edge extending along a side of the working surface, an interdigital transducer located on the working surface for generating surface acoustic waves (SAW) in the working surface, and a liquid delivery arrangement including the liquid and a porous member for supplying the liquid to be atomised, wherein the porous member is in contact with the peripheral edge of the piezoelectric substrate and positioned relative to the peripheral edge such that an upper surface of the porous member is spaced a non-zero distance from the working surface equal to or less than a thickness of a boundary layer defined in a layer of the liquid formed over the working surface from the liquid drawn from the porous member by the SAW, the boundary layer being located immediately adjacent to the working surface.

2. The apparatus for atomising liquid according to claim 1, wherein the interdigital transducer is a DART-SPUDT.

3. The apparatus for atomising liquid according to claim 1, wherein the interdigital transducer has a thickness of at least 1% of the SAW wavelength.

4. The apparatus for atomising liquid according to claim 3, wherein the thickness of the interdigital transducer is between 1 to 5% of the SAW wavelength.

5. A method of pulmonary delivery of biological substances comprising: using the apparatus as claimed in claim 1 to deliver the biological substances.

6. The method of pulmonary delivery according to claim 5, wherein the biological substances include stem cells.

7. A method of delivery of pharmaceutical substances comprising: using the apparatus according to claim 1 to deliver the pharmaceutical substances.

8. A method of delivery of fragrant substances comprising: using the apparatus according to claim 1 to deliver the fragrant substances.

9. A method of delivering cosmetic substances comprising: using the apparatus according to claim 1 to deliver the cosmetic substances.

10. A method of generating sprays for a mouth and a throat of a person comprising: using the apparatus according to claim 1 to generate the sprays for the mouth and the throat of the person.

11. A method of generating sprays with cleaning, sterilizing and anti-allergy substances comprising: using the apparatus according to claim 1 to generate the sprays with the cleaning, sterilizing and anti-allergy substances.

12. A method of delivering agricultural chemicals including herbicides, fungicides, insecticides and fertilizers comprising: using the apparatus according to claim 1 to deliver the agricultural chemicals including the herbicides, fungicides, insecticides and fertilizers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) It will be convenient to further describe the invention with reference to the accompanying drawings which illustrate a preferred embodiment of the present invention. Other embodiments are possible and, consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

(2) In the drawings:

(3) FIG. 1 is a schematic top view of an atomisation apparatus according to the present invention;

(4) FIG. 2 respectively show a plan view and detailed cross-sectional view of an interdigital electrode of the atomisation apparatus of FIG. 1; and

(5) FIG. 3 is a detailed side view of the atomisation apparatus of FIG. 1 showing the liquid delivery arrangement of the apparatus of FIG. 1; and

(6) FIG. 4 is a detailed schematic view of the contact area of the peripheral edge of the piezoelectric substrate and the porous member of the atomisation apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring initially to FIG. 1, the SAW atomisation apparatus according to the present invention includes a piezoelectric substrate 1 which is typically formed from lithium niobate (LiNbO.sub.3). Unlike more commonly used piezoelectric material such as lead zironate titanate (PZT), LiNbO.sub.3 is lead free and therefore safe to use in medical applications. The piezoelectric substrate 1 has an upper working surface 3 through which an SAW can be generated. A peripheral edge 7 extends along the outer periphery of the piezoelectric substrate 1.

(8) An interdigital transducer, preferably of a DART-SPUDT type, is located on the working surface 3. The interdigital transducer 2 includes a positive electrode 5 and a negative electrode 4, with electrode fingers 6 respectively extending from the positive and negative electrodes. The electrode fingers 6 of each electrode 4,5 are located in an interlaced relationship. Application of an electrical signal to the transducer element 2 results in the generation of an SAW through the working surface 3 of the piezoelectric substrate 1.

(9) The liquid 10 to be atomised is accommodated within a liquid container 9. A porous member 8 extends from the liquid container 9, with one end of the porous member being in contact with the peripheral edge 7 of the piezoelectric substrate 1. The other end of the porous member 8 is supported by an absorbent support element 16 located within the liquid container 9. The support element 16 (as shown in FIG. 3), as well as supporting the porous member 8, also facilitates the transfer of the liquid 10 from the container 9 through into the porous member 8. The porous member may for example be made from a polymer cellulose such as biodegradable hydroxypropyl cellulose (HPC). The use of other hydrophilic materials for the porous member 8 is also envisaged.

(10) Referring now to FIG. 2 which provides a detailed view of the interdigital transducer 2, the electrode fingers 6 may have a elliptical or circular curved configuration. This arrangement allows the energy of the generated SAW to be directed to a predetermined area on the peripheral edge 7. In the SAW atomisation apparatus according to the present invention, the SAW can be directed to an area immediately adjacent to where the porous member 8 contacts the peripheral edge 7. It is also envisaged that the electrode fingers 6 be straight, in which case the generated SAW may be directed along a line extending parallel to the peripheral edge 7 contacting the porous member 8.

(11) Extending from the negative electrode 4 are reflector fingers 13 that are wider than the other electrode fingers 12, 14. The purpose of the reflector fingers 13 is to prevent the reflections of the SAW in a reverse direction to the SAW propagating from the DART-SPUDT transducer 2, thereby minimising the loss of energy from the generated SAW. A DART-SPUDT transducer 2 differs from other SPUDT transducers, for example an EWC-SPUDT or Hanma-SPUDT type, in that the reflector fingers 13 have a width of as shown in FIG. 2, being the wavelength of the generated SAW. By comparison, an EWC-SPUDT has reflector fingers with a width of , and a Hanma-SPUDT has reflector fingers with a width of 3/16. DART-SPUDT transducers therefore have the widest reflector fingers of these SPUDT types. The use of larger SPUDTs has the benefit of reducing the effects of electrode resistance and Joule heating. Another advantage of having larger sized interdigital transducers is that it is easier to deposit the transducer 2 on the piezoelectric substrate 1 using photolithographic techniques. The transducer 2 can therefore be deposited with greater accuracy leading to a lower defect rate for these transducers.

(12) FIG. 2 shows in more detail the configuration of a DART-SPUDT transducer. The positive electrode 5 has an electrode finger 14 with a width of , the positive electrode finger 14 being located and aligned with a negative electrode finger 12, and a reflector finger 13 extending from the negative electrode 4. The positive and negative electrode fingers 12, 14 and the reflector finger 13 are respectively spaced apart a distance of .

(13) As also shown in FIG. 2, the thickness of the interdigital transducer 2 may be greater than 1% , being the SAW wavelength. It is preferred that the thickness of the interdigital transducer 2 be between 1 to 5% . The transducer 2 therefore has a thickness that is greater than the thickness of traditional interdigital transducers. The greater thickness of the electrode fingers 6 results in lower relative impedance through the transducer 2 thereby improving the efficiency of the SAW atomisation apparatus. The improved efficiency means that a relatively lower amount of power need be applied to the transducer 2 to operate correctly. This furthermore reduces the local temperature of the aerosols that leave the apparatus to around 50 C.

(14) The SAW generated within the working surface 3 moves in a general direction towards the peripheral edge 7 in contact with the porous member 8. When the SAW reaches the peripheral edge of the working surface 3, a physical phenomenon known as Schlichting streaming acts to draw liquid 10 from the porous member 8. The result of this Schlichting streaming phenomenon is that the liquid will try to move towards the source of the SAW. This results in an accumulation of liquid, in a thin liquid layer 11 adjacent the peripheral edge 7. This thin liquid layer 11 can extend across the working surface 3 from the peripheral edge 7. The thin liquid layer 11 may also extend over onto the upper surface 8a of the porous member 8 as shown in FIG. 3. This liquid volume forms a liquid meniscus 11a from which is generated the atomised liquid droplets.

(15) FIG. 4 shows in more detail the configuration of the atomisation apparatus where the porous member 8 contacts the peripheral edge 7 of the piezoelectric substrate 1. The peripheral edge 7 is located where the working surface 3 meets a side surface 3a of the piezoelectric substrate 1. FIG. 4, only shows the porous member 8 contacting the piezoelectric substrate 1 at the peripheral edge 7. It is however also possible for the porous member 8 to contact the side surface 3a of the piezoelectric substrate 1. The porous member 8 is located relative to the peripheral edge 7 such that the upper surface 8a of the porous member 8 is spaced a fixed distance 19 from the working surface 3. This distance 19 is preferably equal to or less than the boundary layer thickness which is generally equal to the wavelength of the SAW propagating though the working surface 3. This helps to ensure that the maximum thickness of the liquid layer 11 extending from the peripheral edge 7 is similar to the boundary layer thickness. This will help to ensure that Schlichting streaming dominates the liquid motion so that the liquid can be drawn from the porous member 8 to form the liquid layer 11, and that the liquid can subsequently be atomised to an optimal size from the meniscus 11a of that liquid layer 11.

(16) As only a relatively small amount of liquid is drawn at any one time over the working surface, there is little involvement of that liquid volume with the SAW vibration generated in the working surface 3 leading to a reduced loss of energy from the atomisation apparatus when compared with other known apparatus. Furthermore, the limited contact of the porous member with the piezoelectric substrate limits any loss of SAW energy through being absorbed by the porous member. This results in improved operational energy efficiency for the atomisation apparatus according to the present invention. In addition, the reduced temperature of the aerosols/droplets produced by the atomisation apparatus according to the present invention allows for the delivery of more temperature sensitive biological substances, chemicals or pharmaceuticals.

(17) Modifications and variations as would be deemed obvious to the person skilled in the art are included within the ambit of the present invention as claimed in the appended claims.