WO1996000132A2 - A method of creating an effect - Google Patents

Abstract

In creating an effect in which small droplets are suspended in the air, such as a visual effect, one or more transducers (3, 50) are used to excite a fluid (2) to expel small droplets. The fluid (2) may comprise a weak solution of glycol and may incorporate an electrically conducting additive. Each transducer (3, 50) may be driven in the anti-resonance mode. Each transducer may be associated with a tube (51), there being a flow passage (52) to provide access for fluid from the exterior of the tube (51) to a position immediately above the transducer (50). The apparatus may incorporate means to terminate operation of the apparatus if the temperature and resistivity of the fluid (2) are not within predetermined parameters. A first air stream may flow through a chamber in which the transducers are located, to be subsequently admixed with a second, more swiftly flowing air stream.

Description

A METHOD OF CREATING AN EFFECT"

THE PRESENT INVENTION relates to a method of creating an effect such as a visual effect, or an airborne aroma effect, or a treatment effect, or a humidification effect.

In this Specification the term "visual effect" is used in a very broad context, to include a visual effect of a type which might be used in a theatre, but which might also be used in a television studio, a film studio, a nightclub, or in connection with any other form of entertainment. The visual effect may also be used when training service personnel such as firemen, ambulance men, or military personnel.

It has been proposed previously to create a visual effect of "fog" or "smoke".

In creating this effect a large number of small particles or droplets of liquid which are suspended in air are directed to the region where the effect is to be achieved.

In one conventional way of creating an effect of this type, a solution of glycol and water, having a very high concentration of glycol, is heated to a temperature in excess of 290°C. Typically, the glycol content of the solution is greater than 90%. The solution evaporates to give a white smoke.

It is believed that the inhalation of the smoke produced in this manner many be detrimental to health. It is considered that the glycol, or at least part of the glycol, may be chemically degraded due to the high temperature to which the glycol is exposed, and the resultant mixture of a high concentration of glycol and glycol degradation products may trigger various diseases.

Another technique of creating a "fog" effect involves the use of a device termed "an oil cracker". In such a device air compressors are utilised to compress air, which is directed, as very fast moving jets of air, toward the surface of mineral or vegetable oil in an appropriate reservoir. The air-stream leaving the oil cracker has droplets of oil entrained in it. Even though an oil cracker operates at ambient temperature, thus leading to a minimum of chemical degradation of the oil, nevertheless, it is believed that the inhalation of mineral or vegetable oil droplets may be injurious.

The present invention, in one aspect, seeks to provide a method of creating a visual effect in which the problems of the prior proposed arrangements as outlined above are obviated or reduced. A preferred embodiment of the invention seeks to provide a visual effect comprising a translucent haze. If the haze is present light beams passing through the haze are clearly visible.

This invention also relates to an airborne aroma effect. Such an effect may be termed an olfactory effect. At the present time there is a growing interest in the use of perfume, scent or aroma to control or influence the actions of people. It has been known for some time that if certain scents are present in the air the behaviour of people can be modified. For example, it is known that if certain aromas are present in the atmosphere in a supermarket, the level of sales may rise significantly. As a very simple example of this, it is not at all unusual for air extracted from the bakery region of the supermarket to be injected into the area of the supermarket immediately adjacent the main entrance so that people entering the supermarket are immediately greeted with the smell of freshly baked bread. This may make many of the people entering the supermarket feel hungry, leading to enhanced levels of sales.

It has been proposed to introduce droplets of scent or aroma into air which is directed to certain areas of a supermarket to provide an equivalent effect.

The use of scents and perfumes is not restricted to supermarkets. It has, for example, been found that certain scents injected into a casino will initially excite people and enhance the levels of gambling and sales of drink. This will increase the profits of the casino. It is envisaged that a specific scent may be used for other purposes, such as calming a crowd in a football stadium.

Various techniques have been proposed for creating an air-stream carrying an appropriate perfume or scent, but most of the techniques utilised are very crude. Many techniques involve the use of a spray to create droplets of scent which are entrained in a stream of air. This uses an excessive amount of scent. Generally speaking scent is a very expensive commodity. Alternative techniques utilise heat to vapourise the scent or a solution of the scent. This may lead to a chemical degradation ofthe chemicals forming the scent. The degradation produts may be toxic. The present invention seeks to provide a method for injecting scent or perfume into an air-stream to provide safely a maximum effect for a minimum amount of perfume. This invention also relates to a treatment effect.

According to one aspect of this invention there is provided a method of creating an effect comprising the steps of taking a solution, introducing the solution to a reservoir, subjecting the solution to ultra-sonic energy from one or more transducers, without heating to a high temperature, and passing an air-stream across the surface of the solution in the reservoir to obtain a moving outflowing air-stream carrying a plurality of droplets of the solution.

Preferably the temperature is less than 50°C, most preferably less than 30°C and in the preferred embodiment, less than 25°C.

The method may be a method of creating a visual effect and the solution may be a solution of glycol and/or glycerine and preferably comprises at least 80% water. Most preferably the solution comprises at least 90%, advantageously at least 92% water and up to 8% glycol. The glycol may comprise triethylene glycol or monopropylene glycol, dipropylene glycol, butylene glycol, or polyethylene glycol.

The method may comprise the additional step of determining the temperature and electrical resistivity of the solution, and terminating the steps of subjecting the solution to ultra-sonic energy and passing an air stream across the surface of the solution if predetermined parameters are exceeded.

Preferably the method comprises the step of generating a second air stream and admixing the second air stream with the said moving outflowing air stream carrying said plurality of droplets of the solution.

Conveniently the second air stream has a higher flow rate and a higher flow speed than the said moving outflowing air stream.

The transducers are preferably operated at the anti-resonance frequency thereof.

In one embodiment each transducer is tuned to the anti-resonance frequency by applying, to the transducer, an increasing frequency starting at a frequency higher than the natural resonant frequency, determining the number of bubbles created in the solution in the reservoir by the transducer and adjusting the frequency until the maximum number of bubbles is determined.

The frequency may be continually or frequently adjusted, so that the frequency continually "hunts" the maximum alue, but it is preferred to determine the optimum frequency, and to store that frequency ina memory, adjusting the oscillation driving the transducer so that the transducer runs at that frequency.

Advantageously a notch filter is connected to the transducer, the notch filter providing a signal related to the number of bubbles, the amplitude of the signal being monitored to determine the optimum of bubbles.

Preferably a plurality of transducers are tuned sequentially, each transducer commencing its tuning cycle after a randomly determined period of time of non-tuning of any transducers has passed. Alternatively a plurality of transducers are provided, the method comprising the steps of successively activating selected transducers or selected groups of transducers with ultra-sonic energy for a brief period of time.

Preferably each transducer or group of transducers is activated for a period of time substantially equal to one-quarter of a second, the transducer or group of transducers subsequently being un-activated for a period of time of at least substantially one-quarter of a second.

In a further alternative arrangement the or each transducer is driven at substantially the natural resonance frequency thereof.

The method may be used to create a visual effect comprising a translucent light-reflecting haze and the invention relates to such a haze.

The invention also relates to use of an aqueous solution of glycol and/or glycerine comprising at least 80% water in the creation of a visual effect. The soilution may contain ammonium chloride.

The invention also relates to an aqueous solution of glycol and/or glycerine comprising at least 80% water for use in the creation of a visual effect. The solution may contain ammonium chloride.

In an alternative embodiment of the invention, the solution is a solution of scent or perfume. In another alternative embodiment of the invention the solution may be a solution of an active ingredient. The method may thus create a fine mist or haze of droplets containing the active ingredient. The method may be used for example in a hospital to create an atmosphere containing the active ingredient. The active ingredient may be a sterilising or antiseptic agent, or even a therapeutic agent which is breathed in by persons in the hospital. The therapeutic agent may have a curative or prophylactic effect. Alternatively again the active ingredient may be a herbicide fungicide or pesticide or a fumigating agent and the mist or haze containing the active ingredient may be applied to plants - both in greenhouses and out-of-doors, or may be used in other locations.

The invention also relates to an apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultra-sonic energy, and means to direct a stream of air across the top of the solution, each transducer being located at a predetermined position relative to one end of a tube which extends into the solution, there being a flow path for fluid from the exterior of the tube to a position immediately above the transducer. The flow path may be formed by an aperture or slot formed in the tube extending through the side wall of the tube at a position just above the upper surface of the transducer. Alternatively there may be a space between the end of the tube and the transducer.

Preferably the or each tube and the or each transducer is inclined at an angle to the vertical.

Conveniently said angle is approximately 15°.

According to another aspect of this invention there is provided an apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultrasonic energy, and means to direct a stream of air across the top of the solution, means being provided to operate each transducer at the anti-resonance frequency thereof.

Preferably tuning means are provided to tune the frequency of operation of each transducer, the tuning means comprising a filter connected to an output of the transducer adapted to pass signals generated by bubbles bursting within the solution, means being provided to determine the amplitude of the signal passed by the filter, means to adjustably control the frequency of the signal generator which activates the transducer and to control the frequency so that an optimum signal is passed through the filter.

The apparatus may incorporate circuit means adapted to drive the transducers, the circuit means being such that selected transducers or groups of transducers are activated successively for predetermined brief periods of time.

Conveniently the circuit mens are adapted to drive the transducer or selected transducers for successive periods of approximately one-quarter second.

Alternatively there are two groups of transducers, the circuit means incorporating switching means adapted to activate one group of transducers for the said predetermined brief period of time and subsequently to deactivate the said group of transducers and to activate another group of transducers for the said brief period of time. The invention also relates to an apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultrasonic energy, and means to direct a stream of air across the top of the solution, each transducer being mounted in a side wall of the receptacle and being adapted to direct a beam of ultrasonic energy substantially horizontally, there being an element located in front of each transducer presenting an inclined face.

Preferably the angle of inclination of the face is approximately 45°.

The invention also relates to an apparatus for creating an effect comprising a receptacle to contain a solution and one or more transducers to excite the solution with ultra-sonic energy, and means to direct a stream of air across the solution, there being means to determine the temperature and resistivity of the solution and means to disable the apparatus if predetermined parameters are exceeded.

Preferably the determining means comprise a wheatstone bridge, one arm of which comprises electrodes exposed to the solution, and another arm of which comprises one or more elements submerged in the solution, which elements have a temperature characteristic which matches the anticipated resistivity/temperature characteristic of the solution.

The apparatus may contain a solution which has a predetermined non-uniform resistivity/temperature characteristic. The apparatus may contain a solution which comprises ammonim chloride.

The invention also relates to an apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultra-sonic energy, and means to direct a stream of air across the top of the solution, to entrain droplets of solution in the stream of air, and means to lead the said stream of air, with the entrained droplets, to an outlet, the apparatus comprising additional means to generate a second stream of air, and means to lead t e second stream of air to the said outlet, so that, in use, the second stream of air is admixed with the first stream of air.

Preferably the means to generate the second stream of air are adapted to generate a stream of air of a higher flow rate and a higher flow speed than the first stream of air.

Preferably a plurality of transducers are provided, an element of open cell structure being provided defining a plurality of apertures therein, each transducer being received within a respective one of the said apertures.

Conveniently the element of open cell structure comprises an element of polyurethane foam.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a part-diagrammatic, part block diagrammatic illustration of one embodiment of the invention,

FIGURE 2 illustrates a circuit for use in driving a transducer of the apparatus of Figure 1,

FIGURE 3 illustrates part of a fog generating apparatus showing a transducer and an associated de- terbulator tube,

FIGURE 4 illustrates a resistivity sensing circuit,

FIGURE 5 is a block circuit diagram for an apparatus as illustrated in Figure 1.

FIGURE 6 is a frequency spectrum graph illustrating resonance and anti-resonance modes of a typical transducer,

FIGURE 7 is a block diagram of part of a control arrangement in accordance with the invention,

FIGURE 8 is an enlarged block diagram corresponding to Figure 7,

FIGURE 9 is a circuit diagram of one part of an embodiment of the arrangemet shown in Figure 8, and

FIGURE 10 is a diagrammatic sectional view of a further embodiment of the invention.

In a preferred embodiment of the invention there is a reservoir containing a solution that is eventually to be present in the form of very small droplets in a stream of air. The reservoir is provided with one or more high frequency transducers that inject ultra-sonic energy into the solution in the reservoir. This causes small droplets of liquid to emerge from the upper surface of the solution in the reservoir. Air is caused to flow across the surface of the liquid in the reservoir thus entraining the droplets.

Whilst not wishing to be bound by the following explanation the applicant believes that the ultra-sonic energy produces small lens shaped bubbles or cavities in the fluid with strong oppositely signed static electric charges on the opposite sides of each cavity. As each bubble or cavity collapses a minute hot spot is created by the adiabatic compression of gas or vapour within the bubble or cavity. The temperature within each cavity or bubble as it collapses can be very high. Thus, each bubble or cavity as it collapses effectively creates a miniature implosion which creates shock waves which can eject micron sized particles from the surface of the solution in the reservoir, especially if the bubble is close to the surface of the reservoir. The number of bubbles created can depend upon the viscosity of the solution.

Referring to Figure l, a reservoir 1 is shown illustrated schematically which contains a fluid 2. The base of the reservoir is provided with a plurality of ultra-sonic transducers 3 which may be Piezo electric transducers driven by one or more high frequency oscillators. A level sensor and control arrangement 4 is provided in order to maintain the level of liquid 2 within the reservoir 1. This may comprise any appropriate type of level sensor such as a ball cock or an optical sensor. The sensor will control the supply of fresh liquid to the reservoir 1. An air supply 5 is provided which is connected to the reservoir 1 to supply a stream of moving air which passes across the surface of the liquid within the reservoir. The air supply may thus comprise an air compressor or a fan. Droplets of the liquid become entrained in the moving stream of air which is carrying the droplets.

An outlet conduit from the reservoir 1 is connected to a droplet separator 6 adapted to separate from the air- stream leaving the reservoir any large droplets. The droplet separator may comprise, for example, an arrangement of baffles or some other convoluted pipework which causes the air-stream flowing through the droplet separator to impinge upon a successive plurality of surfaces. Large droplets adhere to such surfaces and eventually coalesce to flow back into the reservoir.

An adjustable second air-supply 7 is provided adapted to supply a somewhat larger volume of air than that provided by the air supply 5, and at a higher speed. Thus, the total flow rate and the flow speed of air from the second air supply may be greater than the flow rate and/or flow speed of air from the first air supply as it leaves the reservoir, depending upon the adjustment of the second air supply 7. An outlet duct 8 leads from the second air supply 7 to an outlet port 9 for the illustrated apparatus. A further duct leads to the outlet 9 from the droplet separator 6.

In operation of the device the transducers 3 are activated (in a manner that will be described hereinafter) , and air from the air supply 5 moves across the surface of the liquid 2 within the reservoir 1. Small droplets of the fluid to the container in the reservoir 1 emerge from the surface of the liquid and the droplets of liquid become entrained in the moving stream of air. The stream of air moves relatively slowly. As the stream of air passes through the droplet separator, droplets that are relatively large impinge on the baffles or convoluted pipework and become retained. If the stream of air moved quickly this would not happen, and the large droplets would be entrained with the flow of air leaving the described apparatus.

After passing the droplet separator 6 the moving stream of air, with the small droplets, passes to the outlet port 9 where the stream of air comes admixed with a relatively large volume, relatively high velocity stream of air provided by the second air supply 7. The outlet duct 8 from the second air supply 7 may terminate immediately adjacent the end of the conduit emerging from the droplet separator 6. Thus, the air carrying the suspended droplets will be entrained with the air from the second air supply 7.

It has been found preferable to utilise two separate air supplies. The first air supply moves relatively slowly through the reservoir to entrain with it the droplets of fluid driven from the surface of the fluid 2 within the reservoir 1 by the transducers 3. The first air suply does create a certain degree of turbulence within the reservoir which tends to cause the heavy droplets to drop back into the fluid 2 within the reservoir, while the lighter drops s are entrained by the first air supply. Any larger droplets entrained with the first air supply are trapped in the droplet separator. The second air supply can be used to cause the resultant "smoke" or "haze" to fill completely, and rapidly, a space where an effect is to be provided. Reference will now be made to Figure 2 of the accompanying drawings which is a circuit diagram of a circuit adapted to drive one of the transducers of the apparatus shown in Figure 1.

Referring to Figure 2, an earth supply 10 is connected by means of a ballast resistor 11 to an earth rail 12. The earth rail 12 is connected by means of a smoothing capacitor 12 to a positive rail 13, the positive rail 13 being connected by means of a ripple suppressing inductance 14 to a positive terminal 15.

The positive rail 13 is connected to a node 16 which is connected to a centre tapping of a fly-back transformer comprising a first coil 17 and a second coil 18 wound on a common core 19. The opposed ends of the coils 17 and 18 are interconnected by a voltage centring inductance 20.

The free end of the coil 17 is connected via an impedance matching coil 21 to the node 16.

The coil 17 is connected to a node 22 which is connected by a switch mode inductance 23 through the controlled current path of a power MOSFET transistor 24 to the earth rail 12.

The coil 18 is connected through a feed-back capacitor 25 to a node 26. The node 26 is connected by a parallel connection comprising a phase correcting resistor 27 which is connected in parallel with a series connection of two current control capacitors 28,29 and a current limiting resistor 30 to a node 31 which is connected to the gate of the MOSFET transistor 24. A lead 32 which is connected to a point between the capacitors 28 and 29 is connected to a terminal 33 which is connected to the transducer.

The node 31, which is connected to the gate of the MOSFET transistor 24 is connected to the earth rail 12 by means of an anti-over voltage gate protecting zener diode 34 and is also connected by a symmetry ensuring coil 35 to a node 36. The node 36 is connected to the earth rail by means of a start fail/re-try resistor 37 in parallel with a voltage steadying capacitance 38. The node 36 is connected by a series connection comprising a resistance 39 and a starting zener diode 40 to the node 22. The node 36 is also connected by means of a power drop-out shut-off diode 41 to the node 16. The node 31 is connected by means of a "boot strap" diode 42 to the node 22. The node 22 is connected to a point between the switch mode inductor 23 and the controlled current path of the MOSFET transistor 24 by means of a back EMF diode 42. The node 22 is connected by means of an inductance 43 to a node 44. The node 44 is connected by means of a capacitance 45 to the earth rail 12 and the node 44 is also connected to a terminal 45 which is connected to the transducer.

The illustrated circuit operates to drive the transducer substantially at the resonance frequency of the transducer. A conventional Piezo electric transducer is such that the characteristics of the transducer change as the transducer passes through the resonant frequency. The impedance of the transducer is mainly capacitative on one side of the resonant frequency and inductive the other side of the resonant frequency. This feature of operation of the transducer is relied on in the described circuit to cause the transducer to be driven at the resonant frequency. Thus, the circuit incorporates means which are responsive to the change in the impedance of the transducer as it passes resonance to control the frequency of the signal applied to the transducer so that the transducer is driven at its resonance frequency. It is preferred that the resonant frequency is of the order of 1.9 MHz, although satisfactory results may be obtained within the range of 1.0 to 2.5 MHz. The resonance frequency of any specific transducer depends on the manufacturing tolerances and the design of that transducer.

When a positive potential is applied to the positive terminal 15, the positive potential passes through the ripple suppressing inductance 14 to the positive rail 13 and thus to the node 16. The positive potential is thus applied to the centre tap of the fly-back transformer constituted by the coils 17 and 18 on the common core 19. The effect is that a positive voltage which is significantly greater than the positive voltage present on the rail 13 is generated at the end of the coil 18. This voltage passes through the feed-back capacitor 25 to the node 26 and thus through the parallel connection of the resistance 27 and the series connection of the current controlled capacitors 28 and 29 together with the current limiting resistor 30 to the node 31, thus rendering the power MOSFET transistor conductive. Current thus flows through the controlled current path. A potential is thus present on the node 22 which passes through the coil 43 to the node 44 and thus to the terminal 45.

The coil 43 and the capacitance 45 act as a radio frequency reduction circuit, thus preventing any undesired emissions of RF energy.

Current flows through the start zener diode 40 from the node 22, and the associated resistance 39 to the node 36, thus charging the voltage steady capacitance 38. The presence of a steady voltage on this capacitance maintains the MOSFET transistor 24 conductive, unless the MOSFET is switched off. If an over-large potential is applied to the gate 31 the anti over-voltage gate protecting zener diode 34 reverse conducts, thus protecting the MOSFET.

The boot strap diode 42 can act to turn the MOSFET off.

The power drop-out and shut-off diode 41 operates to discharge the capacitance 38, and also other capacitances present in the described circuit, in the event that there is an interruption in the power supply. This ensures proper circuit re-start when the power is re- applied.

While the MOSFET 24 is effectively rendered conductive by a potential from the capacitance 38, it can be turned off by a low potential applied to the node 31 from the circuit comprising the resistor 27, and the parallel connection of the capacitances 28,29 and the resistor 30 applied to the node through the inductance 35. The circuit is connected to the terminal 33 of the transducer and has a resonance frequency which is responsive to changes in impedance of the transducer. The MOSFET 24 is thus turned on and off at a frequency which is controlled to be the frequency of oscillation of the transducer. The arrangement thus operates as an oscillator which is brought to oscillate at a frequency which is equivalent to the oscillation frequency of the transducer.

Figure 3 shows a disc-shaped transducer 50 which is received within the lower end of a tube 51. The tube has an outer diameter of approximately 18 millimetres and a wall thickness of approximately 1 millimetre. The tube is approximately 9 millimetres high. The transducer and the tube are to be submerged in the liquid in the reservoir.

Formed within the side wall of the tube at a position just above the top of the transducer 50 is an aperture or slot 52 having a diameter or width of approximately 2 millimetres. The aperture or slot forms a flow path for fluid from the exterior of the tube to a position immediately above the transducer. In alternative embodiments other means of admitting fluid to the transducer, such as a gap between the transducer and the tube base, may be utilised.

The tube 51 may be made of any appropriate material such as stainless steel, nylon or any other corrosion- resistant material.

The tube, it is believed, acts to reduce the velocity of fluid flowing to the region immediately above the transducer to replace fluid ejected from that region upwardly by operation of the transducer.

It is believed that when the transducer operates, fluid immediately above the transducer is moved upwardly as a consequence of upward movement of the top surface of the transducer, but when the upper surface of the transducer moves downwardly, a vacuum is created between the liquid which is moving upwardly and the upper surface of the transducer which is, at that point in time, moving downwardly. This is filled by more fluid which is sucked in from the sides. The provision of the tube 51 and the aperture 52 operates, it is believed, to reduce the velocity of fluid flowing to the point immediately above the upper surface of the transducer. Thus the same fluid remains over the transducer for a longer period of time resulting in a greater intensity of standing wave in the fluid column over the transducer at any one time, thus improving efficiency.

It is also believed that the tube acts to "focus" the energy dissipated into the fluid by the transducer, causing a large number of the bubbles mentioned above to be generated just below the surface of the fluid.

It is to be observed that the transducer 50 is set at an angle, so that the axis of the transducer is not vertical but is inclined. Similarly, the tube 51 is inclined at a corresponding angle. It is believed that this may lead to the reduction of standing waves, extending across the width of the tank, by reducing energy losses.

As can be seen in Figure 3, a plurality of tubes 51 are provided each with their respective transducer 50. The tubes 51 form a regular "square" array of tubes.

The tubes extend above the base 53 of the reservoir. Provided within the reservoir, surrounding the tubes 51, resting on the base 53 of the reservoir, is a sheet of open cell foam material 54. The foam material may be polyurethane foam material or other synthetic sponge. The sheet of foam material has an area which is substantially equivalent to the area of the interior of the reservoir and is provided with a plurality of apertures 55 positioned so that the sheet may be lowered into position resting on the base 53 of the reservoir with each tube 51 passing through a respective aperture 55. The sheet 54 of open cell material may have a height which is less than the height of each tube or may have a height which is substantially equal to the height of each tube or, alternatively, may extend just slightly above the top of each tube.

It is preferred that the foam material extends slightly above the top of each tube, as shown, thus forming, above the top of each tube, a discrete "well".

The level of liquid within the reservoir may be maintained such that the level of liquid is above the top of the tubes 51 but is below the top of the open cell sponge material. The upper surface of the liquid is thus only present within isolated wells located above each tube 51, thus preventing the formation of standing waves in the surface of the liquid extending across the interior of the reservoir.

The open cell foam material also serves to absorb liquid present within the reservoir if the machine is tilted, for example, during transportation of the machine, thus reducing the risk of spillage.

Referring now to Figure 4, the apparatus is provided with means incorporated in the apparatus to ensure that the apparatus is only used with appropriate solution.

There are various conventional types of fluid which have been utilised previously in the creation of "fog" or "smoke" effects and a person using the machine of the present invention for creating a "fog" or "haze" effect may be tempted to use conventional fluid diluted with tap water. However, it has been found that tap water, at least in many parts of the world, contains impurities which tend to scale up the reservoir of the described apparatus. This leads to inefficient operation of the apparatus. Also, it is not unknown for people to use all manner of different chemicals as fluid in a "smoke" machine, and if fluids other than the appropriate fluid are used in the machine of the present invention, as described above, it is possible that many various harmful side effects may arise, both to any humans who breath in the "fog" or "haze" emitted by the machine, and to the machine itself.

Thus, in a preferred machine in accordance with the present invention, an arrangement as illustrated schematically in Figure 4 is provided.

Referring now to Figure 4, there is illustrated a wheatstone bridge circuit 60 which is intended to be at least partly submerged in the solution comprising two arms, each formed of a single reference resistor 61,62 and two other arms, one of which, 63, comprises two electrodes 64/65 adapted to be submerged in the solution within the reservoir, thus forming a conductive path between the two electrodes. The resistance of the arm 63 thus depends upon the resistivity of the solution within the reservoir. The final arm 66 comprises one or more elements, also intended to be submerged in the solution, with a predetermined resistance/temperature characteristic. Such elements are known but the arrangement may comprise a "step ladder" series of diodes and resistors.

Two leads 67,68 supply current to opposed corners of the wheatstone bridge and the remaining two opposed corners are interconnected by a cut-out device 69. The cut-out device is activated whenever current flows through the cut-out device which exceeds a predetermined level, the cut-out device serving to disable the apparatus. The apparatus may be disabled either by terminating operation of the transducers and/or by terminating operation of the means which create the air stream flowing across the surface of the solution within the reservoir.

It is envisaged that the circuit shown in Figure 4 will be utilised when the solution present in the reservoir has a predetermined resistivity/temperature characteristic. This may be accomplished by incorporating in the solution a specific chemical, such as a salt, which has a predetermined solubility/temperature characteristic, this characteristic being non-uniform. There are many chemicals which possess such a non-uniform resistivity/temperature characteristic, but the preferred material is ammonium chloride. This material has a very pronounced resistivity/temperature characteristic, since ammonium chloride is such that at 0°C only 29.4 grams of ammonium chloride can be dissolved in 100 grams of water, whereas at 40°C 45.8 grams of ammonium chloride can be dissolved in 100 grams of water.

The arm 66 is so designed that the resistivity/temperature characteristic of the arm matches the resistivity/temperature characteristic of the solution to be used in the apparatus, bearing in mind the initial concentration of the solution.

When the solution is used in the machine, due to the design of the wheatstone bridge, the wheatstone bridge remains "in balance" since if the temperature rises, the decrease in resistance between the electrode 64 and 65 is matched by decrease in the resistance of the arm 66. Thus, since the wheatstone bridge is in balance, no current flows through the cut-out device 69. However, should a person use the described apparatus with a fluid other than the intended fluid, whilst the fluid may have the correct resistivity at one predetermined temperature, thus causing the wheatstone bridge to be in balance, should the temperature change (and it is almost inevitable that the temperature of the fluid will change during operation of the machine) then the wheatstone bridge will move out of balance causing a current to flow through the cut-out device 69. When this current exceeds a predetermined limit the cut-out device 69 will be actuated.

Ammonium chloride is preferred not only because it has a desirable solubility/temperature characteristic, but also is a salt which is capable of subliming. The ammonium chloride will, it has been found, not become concentrated within the solution in the reservoir as that solution is driven off in the form of droplets which form the described "haze". The ammonium chloride will be driven off at the same rate as the solution is driven off, thus meaning that the concentration of ammonium chloride will not increase. When the water droplets finally evaporate, the ammonium chloride will simply sublime and thus be dispersed without final trace.

Referring now to Figure 5, it has been found that if a transducer submerged in liquid, of the type described above with reference to Figure 3, is activated with an oscillating signal of an appropriate frequency, small droplets of fluid will be caused to emerge from the surface of the liquid above the transducer. However, it has been found that the number of droplets produced by the transducer are at an optimum during a very brief period of time after initial activation of the transducer. It is now believed that this is because, when the transducer is initially turned on, it enters an "anti-resonance" mode (as will be described in more detail below) for a brief period of time. When in this "anti-resonance" mode energy is coupled very efficiently from the transducer into the fluid, causing the creation of a large number of the "bubble" mentioned above. After this initial period, the transducer enters a "steady state" where a lesser number of droplets of liquid are provided.

Consequently, in preferred embodiments of the invention, switching means are provided adapted to switch individual transducers or groups of transducers on and off rapidly, so that at any instant transducers within the reservoir are in a condition where they have just been activated and are providing the maximum number of droplets.

Referring to Figure 5, a power supply 70 is connected to a two-way switch which is controlled by a timer 72. The switch 71 has two outputs 73,74. A first output is fed to a plurality of oscillators, 75, each of which is associated with a respective transducer 76. The second output 74 is also connected to a plurality of oscillators 77, each of these oscillators also being connected to a respective transducer 78.

The transducers thus effectively form two distinguishable groups 79,80 of transducers. The two groups 79,80 of transducers are preferably inter-mingled so that each alternate transducer in each row, and each alternate transducer in each column, (of the square array of transducers in the reservoir) is in a different group of transducers.

In operation of the arrangement as illustrated in Figure 5, the timer causes the switch to switch power from the power supply between the two groups of oscillators and thus the two groups of transducers at a frequency of approximately 2 Hz. Each group of transducers is activated for the same period of time, which is thus approximately one-quarter of a second, this being an optimum time for the generation of a substantial number of droplets. After having been activated for one-quarter of a second, each group of transducers is de-activated for a quarter of a second whilst the other group of transducers is activated. This enables the liquid above the transducer to return to a quiescent state, so that when the transducer is re¬ activated, again the optimum quantity of liquid droplets is generated.

Referring now to Figure 6, which is a graphical figure illustrating the resonance characteristics of a typical transducer, it can be seen that a typical transducer illustrates various peaks in the amplitude of the oscillations of the transducer as compared with the frequency supplied to the transducer.

In a typical transducer, the primary resonance or "natural resonance" exhibits a peak 81 at approximately 1.6 MHz. During this type of resonance the current flowing through the transducer is substantially in phase with the voltage across the transducer meaning that the transducer provides a substantially resistive effect.

Two relatively smaller side peaks 82,83 are associated with the principal peak, and in these regions the transducer operates respectively in a capacitative and an inductive mode. This can lead, therefore, to high voltage across and/or a current flowing through the transducer. At a higher frequency, three further resonance peaks 84,85,86 are present. The centre of these three peaks, peak 85, is a relatively high peak, but is usually a substantially inductive peak meaning that a very high voltage is created across the transducer when in this mode, which can lead to damage of the transducer. The smaller, slightly lower frequency peak 84 is a resistive peak and is known as the "anti-resonance" peak. Often this peak merges with the peak 85 to form a plateau where the transducer is operating in a "resistive" mode. Somewhat surprisingly it has been found that when in this particular "anti- resonance" mode, the transducer couples power to the solution in a very effective manner, creating a large number of bubbles adjacent the surface of the liquid, and consequently it has been found desirable to operate the transducers in this particular mode.

It has been found that the transducers automatically enter this mode briefly for an initial period after they are first activated. However, a method has been devised to "tune" the transducers to be in this particular mode during prolonged operation.

Whilst reference has been made, in Figure 6, to specific frequencies being the resonance frequency and the anti-resonance frequency, it is to be understood that these frequencies are given for a particular model of transducer. Other models of transducer will have different resonance and anti-resonance frequencies. However, the resonance frequency will always be lower than the anti-resonance frequency and the anti-resonance frequency will always be at a slightly lower frequency than an immediately adjacent inductive resonance frequency. Referring now to Figure 7, a transducer 90 is driven by a high frequency signal generator 91. However, the transducer 90 is also connected to a notch filter 92. The notch filter is adapted to pass all frequencies except the frequency of the signal generator 91. Both the high frequency signal generator and the notch filter are connected to a micro-processor 93.

A transducer, in addition to being driven by a signal generator to transfer energy to a fluid in which it is submerged may also receive acoustic waves from the liquid in which it is submerged and transform those waves into electrical energy.

Thus, a transducer 90, when provided with a high frequency signal from the signal generator 91, which causes bubbles and cavitation to appear in the liquid in which the transducer is submerged, will also receive shock waves from the bubble or cavities as they collapse. The shock waves are effectively "Enoise" which has frequency components below and above the frequency of the signal from the signal generator 91.

Consequently, a notch filter, such as the filter 92, can be provided, which can provide an output which is proportional to the number of bubbles being generated. The micro-processor can analyse the signal coming through the notch filter and can control the high frequency signal generator to provide an optimum number of "bubbles".

Referring to Figure 8 which illustrates the situation in more detail, it can be seen that the output of the notch filter is fed to an amplitude discriminator 94. A random number generator 95 is provided adapted, whenever the apparatus is initially activated, to generate a random number. The random number is supplied to a timer 96 which times the time period equivalent to the random number. If, during the time period measured, the amplitude discriminator does not detect any substantial signal from the notch filter 92, the timer activates a tuning process as will be described. However, if, during the time period, the timer does detect a signal passing through the notch filter 92, which would most probably be occasioned by another transducer present within the liquid undergoing the tuning process, the timer resets to zero and commences the timing process again.

This means that if a plurality of transducers are present within a single tank, when the apparatus is initially switched on, each of the random number generators associated with each of the transducers will generate a random number and the timers will be activated to measure periods of time determined by the random numbers. As soon as the shortest period of time has elapsed, the timer that measures the shortest period of time will initiate the tuning cycle for the associated transducer. All the other transducers will immediately detect the bubbles generated by the transducer being tuned, thus re-setting the timers of all the other transducers.

The amplitude discriminator 94 is connected to a second timer 97 which measures a period of time which is much longer than the period of time that can be measured by the timer 96 in response to the generation of the random numbers. If, during the period of time measured by the timer 97, there is no signal from the notch filter 92, it is assumed that all of the transducers have effectively been "tuned" or are deficient in some way. The timer 97 then passes an appropriate signal to the high frequency signal generator 91 enabling the signal generator to generate an appropriate signal when the appropriate switch or control on the apparatus is actuated.

When the timer 96 actuates the tuning of the transducer, initially a control 98 gradually increases the frequency of the signal generated by the high frequency signal generator. The lowest frequency generated by the high frequency signal generator is selected to be a frequency higher than the three relatively low frequency resonance peaks 81, 82 and 83 as illustrated in Figure 6. The signal gradually increases in frequency on a step-by- step basis.

An appropriate detection and monitoring arrangement 99 monitors the amplitude of the signal passing the notch filter 92, in conjunction with the frequency, and the appropriate data is stored in a memory 100.

The frequency is increased until either a clear maximum has been encountered or until the voltage across the transducer, measured by a monitor voltage arrangement 101 exceeds a predetermined threshold, which tends to suggest that the frequency has been raised to such a degree that the resonance peak 85, as illustrated in Figure 6 has been encountered. When this occurs, there are no further increases in frequency.

The memory 100 thus contains an indication of the optimum frequency for the transducer determined during the tuning step. The transducer is then subsequently driven at that frequency. It is thus to be appreciated that a plurality of transducers will each wait until no other transducer is being "tuned" and will then tune to the optimum frequency. The transducers will then effectively wait until all the transducers have been tuned, and the transducers will then be ready for operation.

During operation of the transducers from time-to- time, as determined by the timer 97, for example, the amplitude passing the notch filter 92 will be determined, and if it is below a certain threshold, then operation of the transducer will be terminated. The amplitude will only be below a predetermined threshold if the level of liquid does not submerge the respective transducer. It will be understood that if the transducer is submerged, it will be able to "hear" the bubbles, thus providing an output throught he notch filter 92. If the transducer operates without being submerged in liquid the transducer may become damaged or "burn out". Once operation of a transducer has been terminated in this way, from time-to-time, again as determined by an appropriate timer, the output of the notch filter 92 will be monitored, because if further liquid has been added to the tank, the transducer will then again be receiving a signal generated by bursting bubbles, and can safely be re-activated.

In an embodiment of the invention adapted to operation in the "anti-resonance" mode as described above, it may well be unnecessary for the "tubes", such as the tubes 51 (as shown in Figure 3) to be provided for each transducer. The primary function of the "tubes" (it is believed) is to "focus" the ultra-sonic energy generated by the transducer. When operating in the "anti-resonance" mode, there is no need for such a focusing effect to be present. Nevertheless, it may well be advantageous to operate the transducers with the "foam" material, with a separate aperture being formed in the "foam" material for each transducer.

Referring now to Figure 9 it will be appreciated that a substantial part of the control function described above will be effected by a microprocessor. The various timers and discriminators will be present within the microprocessor.

Figure 9 illustrates one embodiment of circuitry that can be connected to the microprocessor.

The high frequency signal generator 91, in the embodiment illustrated in Figure 9, is constituted by a "4046" integrated circuit 110, which incorporates a voltage controlled oscillator.

The voltage controlled oscillator 110 is provided with power from a 12 volt rail through input pins 16, 3 and 14. The initial range of operating frequencies of the voltage controlled oscillator are determined by resistors R8 and R9 connected to pins 11 and 12 and a capacitance C9 connected across pins 6 and 7. The voltage controlled oscillator is provided with a controlling voltage on pin 9. Pin 9 is connected to one plate of a capacitance 111, the other plate of which is connected to earth. The said one plate of the capacitance is connected by means of a first resistor to a terminal that can be supplied with a signal which is either 0 volts or +12 volts under the control of the microprocessor. The said one plate of the capacitor is connected by a second resistor 113 to a second terminal which can be supplied with a signal of 0 volts or -12 volts under the control of the microprocessor.

At this stage it should be mentioned that the capacitance 111 has a low leakage rate to earth. When the microprocessor determines that the frequency generated by the voltage controlled oscillator should rise, a potential of +12 volts is applied to the terminal connected to the resistance 112, causing the capacitance 111 to charge up. As the capacitance charges up, the voltage applied to the pin 9 rises meaning that the output frequency rises. On the other hand, if the frequency generated by the voltage controlled oscillator is too high, the microprocessor causes a potential of -12 volts to be applied .to the terminal connected to the resistance 113, meaning that the potential on the capacitance 111 will reduce, leading to a reduction in the frequency of the signal generated by the voltage controlled oscillator. The microprocessor will determine the frequency generated by the transducer 90 at regular and frequent intervals, comparing that frequency with the frequency stored in the memory 108, and will adjust the frequency of the signal generated by the voltage controlled oscillator appropriately.

The output of the voltage controlled oscillator 110 is present on pin 4 and is connected to one buffer element 114 of a hex buffer constituted by an integrated circuit of the "4069" type. The buffer 114 inverts the signal. The inverted signal is fed to the parallel connection of the remaining five buffers 115 of the inverting buffer. The parallel connection re-inverts the signal, so the signal has its original polarity, but provide a substantial current flow. The output of the parallel connection of the buffers 115 is connected through a resistance R17 to a complementary pair of emitter followers Q2,Q3. The complementary pair are connected between earth and a node 116. The node 116 is connected to a 30 volt rail by reistance R6, and is also connected to a 20 volt rail. The node 116 is also connected to plates of two capacitances C6 and C7, the other plates of which are connected to earth.

The output of the complementary pair is fed by resistors R2 and R3, and a capacitance C3 to a node 117. The node 117 is connected to earth by back-to-back zener diodes Dl and D2. The zener diode Dl has a break-down voltage of 4 volts and the zener diode D2 has a break-down voltage of 10 volts. The zener diodes serve to clamp the wave form present at node 117. If the wave form exceeds +6 volts by a substantial amount it will be clamped by the zener diode D2, which will break down conducting any excess voltage to earth. Similarly, if the wave form has a voltage which is lower than approximately 5.4 volts (which is a combination of the break-down voltage of the diode Dl and the reverse bias of the diode D2) then the negative excursion will be clamped.

The back-to-back diodes, in combination with the capacitance C3, act as a level shifting arrangement. The node 17 is connected to the gate of a power FET Ql. The gate of transistor Ql is AC coupled so that drive failure cannot destroy the transistor Ql. The transistor Ql is operated at substantially a zero voltage switch so that the Miller effect between drain and guage is not a problem during gate transitions.

The source-drain path of the transistor Ql, that is to say the current controlled path is connected in series between earth and a 30 volt rail, a first winding of a transformer Trl being included in the series connection. A node between the primary winding of the transformer Trl and the current controlled path of transistor Ql is connected to earth by means of a capacitance C2, thus forming a "tank" circuit.

The secondary winding of the transformer Trl is centre tapped, the centre tap being connected to earth. One part of the winding is connected by means of the series connection of two diodes D3,D4 to the 20 volt rail and supplies power to the 20 volt rail when the circuit is fully operational. The second part of the secondary winding of the transformer Trl is connected to a node 118 which is connected, to one input of the transducer 90.

At this stage it should be explained that when the circuit is initially activated, a 30 volt power supply is connected to the 30 volt rail, which is connected to resistor R6 and a 12 volt power supply, as connected, for example, to the voltage controlled oscillator is generated from the 30 volt signal by a conventional 12 volt power supply. The voltage controlled oscillator will start to oscillate. The signal from the 30 volt rail will charge up the capacitors C6 and C7 to such a level that, as the oscillator oscillates, current will flow through the controlled current paths of the complementary pair of transistors Ql and Q2. This will enable the power transistor Ql to be switched on and off, causing current from the 30 volt rail to flow through the primary winding of the transformer. The effect of this current flowing through the primary winding of the transformer will be to generate, in the secondary winding of the transformer, a current which, through the connection of the diodes D3 and D4 is fed to the 20 volt rail. Thus the 20 volt rail is now supplied with power, that power being sufficient to supply the current to flow through the complementary transistor pair Q2,Q3. It is to be noted that the complementary pair cannot be driven at 30 volts, but is ideally driven at 20 volts. An arrangement of this type is known as a "boot strap" arrangement.

The circuit incorporates means for inhibiting the operation of the voltage controlled oscillator if the voltage generated across the transducer exceeds a predetermined limit. The node 118 is connected by means of a series connection of resistors R4 and R5 to earth. The central node between the resistors R4 and R5 is connected, by means of a diode D5, a capacitance C5 and a resistance R16 which rectify and smooth the voltage present on the node, to one input of a comparator U3B. The present circuit incorporates two comparators U3A,U3B which are embodied on an integrated circuit of the "LM393" type.

The other input of the comparator U3B is connected to a node which is at the centre of a voltage dividing bridge constituted by resistors R13,R14 and capacitance CIO connected between the 12 volt rail and earth. If the voltage supplied to the comparator U3B, which is scaled voltage representative of the voltage existing across the transducer 90, exceeds a predetermined limit, the output of the comparator U3B, which is initially a "floating" output, goes low. The output of the comparator U3B is fed to one input of a second comparator which also receives an input control voltage from the centre part of a resistive bridge consituted by the resistors R12 and R15 extending between the 12 volt rail and earth. If the voltage on the output of the first comparator U3B goes low, the output of the second comparator U3A goes high. The output of the first comparator U3A is connected to a node 118 which is connected to inhibit the pin 5 of the voltage controlled oscillator. The node 118 is connected by resistance R7, in association with a capacitance C6 which has one plate connected to earth, to the 12 volt rail which serves to provide an initial "pull up" on the pin 5.

The inhibiting output of the second comparator U3A is connected to a capacitance Cll, the other terminal of which is connected to a centre node of the resistive bridge constituted by the resistances R12 and R15, that node also being connected to earth by means of a diode D7. When the output of the second comparator U3A goes high, the immediate effect is to terminate operation of the voltage controlled oscillator, which terminates the opertion of the drive circuit for the transducer 90, meaning that the voltage generated across the transducer 90 falls, which means that the input signal provided to the first comparator changes, meaning that the output of the first comparator will also change. However, the capacitance Cll initally charges to have a voltage of approximately 12 volts across it since it is connected in a series connection between the 12 volt rail, the resistance R7 and earth. When the comparator U3A provides an output signal, the voltage present on the plate of the capacitance Cll which is connected to the output of the comparator U3A rises, meaning th't the voltage on the other plate also rises. The other ±iate of the capacitance Cll is connected to the centre node of the series connection of the resistors R12 and R15, meaning that the voltage of that centre node also rises. This provides a "latching" effect for the comparator U3A. Over a following brief period of time, the relatively high potential present at the node between the resistors R12 and R15 leaks away, meaning that the voltage controlled oscillator is then no longer inhibited. It is necessary to provide means to enable the voltage controlled oscillator to commence oscillation when the arrangement is first turned on. When the device is first turned on, the 20 volt rail will carry some potential, as stored on the capacitance C6 and C7 described above. When the potential on the 20 volt rail reaches approximately 15 volts, a current is flowing through a zener diode D6 which is connected between the 20 volt rail and earth in a series connection incorporating a resistance RIO. The current flow is sufficient to generate a voltage of approximately 5 volts at the node between the zener diode D6 and the resistance R10. This node is connected by a relatively high value resistance Rll to the line between the output of the first comparator U3B and the input of the second comparator U3A. Since this line is "floating", a voltage of 5 volts is applied to the line. This voltage is sufficient to ensure that the voltage controlled oscillator is not inhibited, allowing commencement of the operation of the device as described above.

Turning now to Figure 10, a further modified embodiment of the invention is illustrated. In this embodiment of the invention, a tank 120 is provided with a plurality of transducers, such as the transducer 121, the transducers being mounted in the side wall of the tank substantially at the level to which the tank is to be filled by the appropriate fluid.

The transducer thus directs a beam substantially horizontally.

An element 122 is provided located within the tank which presents a sloping face 113 directed towards the transducer. Preferably the sloping face slopes at an angle of approximately 45°, but the optimum angle is best determined on a trial-and-error basis.

It is believed that by utilising an apparatus as illustrated in Figure 10, a substantial number of small bubbles can be created just below the surface of the liquid, thus giving an improved degree of efficiency.

The arrangement of Figure 10 may incorporate a foam element with respective apertures for each trnsducer of the type described above.

In use of the various types of apparatus as described above to create a visual effect in the form of a light translucent haze that reflects light, the fluid introduced to the reservoir is preferably a weak solution of glycol or glycerine. Preferably the solution is at least 80% water, with the balance being glycol. The glycol may be triethylene glycol, monopropylene glycol, dipropylene glycol, butylene glycol or polyethylene glycol. Other glycols or glycerines may be utilised, or a number of glycols may be used in admixture. The solution may contain a salt with a predetermined solubility/temperature characteristic, such as ammonium chloride, as described above.

It is to be noted, however, that the total glycol content is less than 20%, conveniently less than 10% and is preferably less than 8%.

The apparatus is operated at ambient temperature, meaning that the temperature of the liquid within the reservoir 1 is no more than 50°C and usually less than 30°C, and most frequently less than 25°C. No heat is applied to the liquid in the reservoir. This means that the glycol solution is not heated and it has been found that with the use of a glycol solution as described above, with an apparatus incorporating a plurality of transducers, operating at ambient temperature, fine droplets are suspended in the air passing through the droplet separator which provide a translucent light-reflecting haze. The preferred solution is a very low concentration solution of glycol, and the haze that is provided by the technique described above, while providing a very desirable theatrical effect, does not have the density of the "fog" produced by the prior art techniques. The haze is particularly effective when used with light beams, since the passage of the light beams through the haze is clearly visible. The glycol or glycerine has not been heated to a temperature at which the glycol or glycerine may degredate, and consequently it is envisaged that the use of a technique described above will not present a health hazard. The haze dissipates relatively rapidly and leaves no detectable residue.

The apparatus of all the embodiments of Figures 1 to 10 may be used with an aqueous solution of a scent or perfume or an active ingredient present in the reservoir 1. The solution may comprise between 2 and 3% perfume or scent, the remaining part of the solution comprising water.The scent or perfume may be selected to provide a desired effect on a person, or on people, who are to breath air to which the air flow leaving the droplet separator is mixed. Thus the scent or perfume may have the effect of encouraging people breathing the scent to make purchases, or may present other effects. The active ingredient may be any appropriate chemically active ingredient. Thus the active ingredient may comprise a sterilizing or an antiseptic agent, a therapeutic agent or medicament, a pesticide, a fungicide, a herbicide, or a fumigant. If the active ingredient is a sterilizing or antiseptic agent, a therapeutic agent or a medicament, the apparatus may be used, for example, in a hospital creating a very fine air-borne mist comprising the active ingredient. A person present in the hospital will therefore breath in the active ingredient whenever drawing in a lung-full of breath. Thus, the active ingredient may be delivered on a regular basis to a site such as the surface of the lungs.

If the active ingredient is a fungicide or a herbicide, the apparatus could be used, for example, in a greenhouse, thus providing a fine mist that will pervade the greenhouse and which will be available within the greenhouse for a relatively long period of time, since a mist generated by an apparatus in accordance with the invention may tend to remain suspended in the air for many hours. The apparatus may also be used in other agricultural environments, such as for example, an orchard where the mist will deliver the active ingredient to the trees. The mist may serve the additional function of shading plants from direct sunlight. This may reduce the temperature of the environment directly experienced by the plants. This may enable plants to be grown in areas that would otherwise be too hot. The active ingredient may alternatively comprise an appropriate active ingredient for use in fumigating infested premises.

Thus the invention, in various aspects, provides a treatment effect for the treating of plants or the like.

Whilst not wishing to be bound by the following explanation, the applicant believes that when droplets of perfume are breathed in, it is the perfume at the very outer periphery of a droplet that provides the effect sensed by the olfactory organ. Thus, if large diameter droplets are produced effectively, any scent present within the centre of such a large droplet is never utilised. Thus the present invention insofar as it relates to an olfactory effect enables a minimum amount of perfume to provide the maximum effect by creating very small droplets of scent. Nonetheless the system works very well with scent whatever the precise mechanism.

Claims

CLAIMS :

1. A method of creating an effect comprising the steps of taking a solution, introducing the solution to a reservoir, subjecting the solution to ultra-sonic energy from one or more transducers, without heating to a high temperature, and passing an air-stream across the surface of the solution in the reservoir to obtain a moving outflowing air-stream carrying a plurality of droplets of the solution.

2. A method according to Claim 1 carried out at a temperature of less than 50°C.

3. A method according to Claim 2 carried out at a temperature of less than 30°C.

4. A method according to Claim 3 carried out at a temperature of less than 25°C.

5. A method according to any one of the preceding Claims wherein the method is a method of creating a visual effect and the solution is a solution of glycol and/or glycerine and comprises at least 80% water.

6. A method according to Claim 5 wherein the solution comprises at least 90% water.

7. A method according to Claim 5 wherein the solution comprises at least 92% water.

8. A method according to any one of the preceding Claims wherein the glycol comprises triethylene glycol.

9. A method according to any one of Claims 1 to 7 wherein the glycol comprises monopropylene or dipropylene glycol.

10. A method according to any one of Claims 1 to 7 wherein the glycol comprises butylene glycol.

11. A method according to any one of Claims 1 to 7 wherein the glycol comprises polyethylene glycol.

12. A method according to any one of Claims 1 to 11 wherein the method comprises the additional step of determining the temperature and electrical resistivity of the solution, and terminating the steps of subjecting the solution to ultra-sonic energy and passing an air stream across the surface of the solution if predetermined parameters are exceeded.

13. A method according to any one of the preceding Claims comprising the step of generating a second air stream and admixing the second air stream with the said moving outflowing air stream carrying said plurality of droplets of the solution.

14. A method according to Claim 13 wherein the second air stream has a higher flow rate and a higher flow speed than the said moving outflowing air stream.

15. A method according to any one of the preceding Claims wherein means are provided to operate the transducers at the anti-resonance frequency thereof.

16. A method according to Claim 15 wherein means are provided to tune each transducer to the anti-resonance frequency by applying, to the transducer, an increasing frequency starting at a frequency higher than the natural resonant frequency, determining the number of bubbles created in the solution in the reservoir by the transducer and adjusting the frequency until the maximum number of bubbles is determined.

17. A method according to Claim 16 wherein a filter is connected to the transducer, the filter providing a signal related to the number of bubbles, the amplitude of the signal being monitored to determine the optimum number of bubbles.

18. A method according to any one of Claim 16 or 17 wherein a plurality of transducers are tuned sequentially, each transducer commencing its tuning cycle after a randomly determined period of time of non-tuning of any transducers has passed.

19. A method according to Claim 15 wherein a plurality of transducers are provided, the method comprising the steps of successively activating selected transducers or selected groups of transducers with ultra-sonic energy for brief periods of time.

20. A method according to Claim 16 wherein each transducer or group of transducers is activated for a period of time substantially equal to one-quarter of a second, the transducer or group of transducers subsequently being un-activated for a period of time of at least substantially one-quarter of a second.

21. A method according to any one of Claims 1 to 14 wherein the or each transducer is driven at substantially the natural resonance frequency thereof.

22. A visual effect comprising a translucent light- reflecting haze whenever created by the method of any one of the preceding Claims.

23. Use of an aqueous solution of glycol and/or glycerine comprising at least 80% water in the creation of a visual effect.

24. Use of a solution according to Claim 23 wherein the solution contains ammonium chloride.

25. An aqueous solution of glycol and/or glycerine comprising at least 80% water for use in the creation of a visual effect.

26. A solution according to Claim 25 containing ammonium chloride.

27. An apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultra-sonic energy, and means to direct a stream of air across the top of the solution, each transducer being located at a predetermined position relative to one end of a tube which extends into the solution, there being a flow path for fluid from the exterior of the tube to a position immediately above the transducer.

28. An apparatus according to Claim 27 wherein the or each tube and the or each transducer is inclined at an angle to the vertical.

29. An apparatus according to Claim 28 wherein said angle is approximately 15°.

30. An apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultrasonic energy, and means to direct a stream of air across the top of the solution, means being provided to operate each transducer at the anti-resonance frequency thereof.

31. An apparatus according to Claim 30 wherein tuning means are provided to tune the frequency of operation of each transducer, the tuning means comprising a filter connected to an output of the transducer adapted to pass signals generated by bubbles bursting within the solution, means being provided to determine the amplitude of the signal passed by the filter, means to adjustably control the frequency of the signal generator which activates the transducer and to control the frequency so that an optimum signal is passed through the filter.

32. An apparatus for creating an effect according to Claim 30 incorporating circuit means adapted to drive the transducers, the circuit means being such that selected transducers or groups of transducers are activated successively for predetermined brief periods of time.

33. An apparatus according to Claim 32 wherein the circuit means are adapted to drive the transducer or selected transducers for successive periods of approximately one-quarter second.

34. An apparatus according to Claim 32 or 33 wherein there are two groups of transducers, the circuit means incorporating switching means adapted to activate one group of transducers for the said predetermined brief period of time and subsequently to deactivate the said group of transducers and to activate another group of transducers for the said brief period of time.

35. An apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultrasonic energy, and means to direct a stream of air across the top of the solution, each transducer being mounted in a side wall of the receptacle and being adapted to direct a beam of ultrasonic energy substantially horizontally, there being an element located in front of each transducer presenting an inclined face.

36. An apparatus according to Claim 35 wherein the angle of inclination of the face is approximately 45°.

37. An apparatus for creating an effect comprising a receptacle to contain a solution and one or more transducers to excite the solution with ultra-sonic energy, and means to direct a stream of air across the solution, there being means to determine the temperature and resistivity of the solution and means to disable the apparatus if predetermined parameters are exceeded.

38. An apparatus according to Claim 37 wherein the determining means comprise a wheatstone bridge, one arm of which comprises electrodes exposed to the solution, and another arm of which comprises one or more elements submerged in the solution, which elements have a temperature characteristic which matches the anticipated resistivity/temperature characteristic of the solution.

39. An apparatus according to Claim 37 or Claim 38 containing a solution which has a predetermined non-uniform resistivity/temperature characteristic.

40. An apparatus according to any one of Claims 37 to 39 containing a solution which comprises ammonium chloride.

41. An apparatus for creating an effect, the apparatus comprising a receptacle adapted to contain a solution, and one or more transducers adapted to excite the solution with ultra-sonic energy, and means to direct a stream of air across the top of the solution, to entrain droplets of solution in the stream of air, and means to lead the said stream of air, with the entrained droplets, to an outlet, the apparatus comprising additional means to generate a second stream of air, and means to lead the second stream of air to the said outlet, so that, in use, the second stream of air is admixed with the first stream of air.

42. An apparatus according to Claim 41 wherein the means to generate the second stream of air are adapted to generate a stream of air of a higher flow rate and a higher flow speed than the first stream of air.

43. An apparatus according to Claim 41 or 42 wherein the means adapted to generate the second stream of air are adjustable with regard to the flow rate and/or the flow speed of the second stream of air.

44. An apparatus according to any one of Claims 27 to 43 wherein a plurality of transducers are provided, an element of open cell structure being provided defining a plurality of apertures therein, each transducer being received within a respective one of the said apertures.

45. An apparatus according to Claims 44 wherein the element of open cell structure comprises an element of polyurethane foam.