Patent Publication Number: US-7712249-B1

Title: Ultrasonic humidifier for repelling insects

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a device for repelling insects. More particularly, the present invention relates to an ultrasonic humidifier for dispersing insect repellant into the air. 
   Many types of insects and other nuisance bugs are considered pests, because they transmit diseases, damage structures or destroy agricultural products. Parasitic insects, such as mosquitoes, biting flies (black and greenhead), no-see-ums, lice, chiggers, ticks and bedbugs are notorious for decreasing the enjoyment of the out-of-doors for humans and pets alike. The options for pest control are generally limited to killing/capturing or repelling techniques. 
   Nuisance pests are typically killed through the application of a pesticide, such as by misting an area (see for example U.S. patent Ser. No. 11/524,073 to Modlin, et al. filed Sep. 20, 2006 and entitled “Automated Pest Misting System with Pump,” assigned to the assignee of the present invention, which is incorporated herein in its entirety), or through the use of bait and trap systems such as fly strips, CO 2 /octenol traps or electric bug zappers that attempt to attract pests with scent, heat, chemicals or light, or a combination of the above, and then either trap or kill pests that are lured to the bait. Each of these techniques has the unwanted detriment of killing beneficial insects, such as bees, butterflies, ladybugs and dragonflies, along with the nuisance insects. While there have been some advancements in biocontrol and in luring only nuisance insects to a trap, e.g., luring adult Japanese beetles into traps using beetle pheromones, generally it is difficult to attract unrelated types of nuisance insects to the exclusion of beneficial insects. 
   To date, one of the most effective method for repelling insects is by applying a coating of insect repellant containing synthesized DEET (n-n-diethylnetatoluamide) over exposed body parts and clothing which mosquitoes might penetrate. Currently DEET is the active ingredient in a wide range of repellants, such as creams, lotions, and aerosols. The disadvantages of using an insect repellant are many. For instance, the oily feel, they cause irritation to eyes, lips and other sensitive areas and can cause a skin reaction with some users, sometimes serious, and DEET is less effective in low concentrations, while higher concentrations may result in an increased risk of reaction. The product will often damage and/or stain certain plastics and fabrics and detractors often complain about the strong ‘chemical’ smell prevalent with DEET usage. Most people avoid using insect repellents around their home unless they intend to be outside for a prolonged period of time. Moreover, insect repellants are inconvenient and bothersome; they detract from the enjoyment with other people, such as on trips to the beach or camping, tailgating or picnicking. 
   Another, more convenient and environmentally friendly method for controlling nuisance pests in an area, is by application of a repellant throughout a control area. Although electronic repellants exist, such as by generating sound energy electronically at frequencies that repel insects, by far the most effective means is through the application of chemical repellants. Everyone has probably burned citronella to repel mosquitoes or heard of burning citronella in candles or torches or the like. Citronella candles and lamp fuel is relatively inexpensive, nontoxic and fairly easy to use. The active insect repelling ingredient in citronella, PMD (p-menthane 3,8-diol) has been demonstrated to repel mosquitoes, however, the recommended concentration of PMD is approximately ten percent and then citronella usually only repels mosquitoes for ten to twenty minutes. The reason that burning citronella is not always effective is that oftentimes the airborne concentration of PMD is very low, either because of the concentration being burned, or more probably because the dispersion pattern of the citronella fumes is not homogeneous in the control area. Insects do not breathe the way that mammals do and they do not have lungs, but instead they use tracheal respiration to transport air from spiracle openings on the surface of their bodies. Spiracles are located all along the insects&#39; abdomens. It follows that the more effectively a repellent is dispersed in a control area, the more spiracles on an insect&#39;s body will receive the repellent. Burning citronella has been reported to form long airborne ‘spider webs’ when burned rather than a homogeneous concentration within the control area. Light breezes that do not affect mosquitoes sometimes move the citronella fumes completely out of the control area. Furthermore, it is difficult to meter the amount of citronella in the air, at best the user lights more or less candles or torches and repositions them in the control area for effectiveness. 
   Handheld trigger sprayers for broadcasting repellents are well known and widely used, especially around farm animals and in kennels and stables. Certain mosquito repellents are also sprayed from trigger or larger pump sprayers. However, these repellants are generally not meant to remain airborne, but are often applied to ground cover, yards, gardens and campgrounds. Typically, these repellents have an aromatic ingredient, such as concentrated garlic solution, that has some repelling properties, but actually kills most insects that come in contact with it. Automated misting systems, such as those disclosed in the Modlin application identified above, may be altered for dispersing repellents rather than insecticides. It should be mentioned that the Modlin device utilizes misting nozzles rather than spray nozzles. Spraying systems are less effective for repelling flying pests because the particle size ejected from a spray head is relatively large, usually greater than 50 microns, and therefore they do not remain suspended in the air for longer than a very few seconds. A mist has fewer open spaces or gaps between particles than a spray, and is generally less dense and will remain airborne longer than spray particles. Mist infers that the diameter of the suspended liquid is generally between 30 microns and 50 microns. 
   While misting systems are much more effective for dispensing repellents, the repellent mist will eventually fall out of the air and lose its effectiveness. What is needed is a safe and effective repellant dispersion system for use out-of-doors. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to an ultrasonic repellent humidifier for dispersing insect repellant into the air as a micro fine repellent vapor. A repellent tank provides rhodinol and cedarwood oil based repellent to a repellent well. An ultrasonic transducer is positioned in the well beneath the level of the repellent. It vibrates, forming a repellant vapor that is drawn into a vapor duct by a forced air system and out of the unit, dispersing the repellent vapor into the surrounding air. The vibrating portion of the ultrasonic transducer that is exposed to the oil-based repellent is a ceramic material that inhibits residue from forming on the transducer that reduces its efficiency. The ceramic material may be formed on the metal case of the transducer or on the piezoelectric oscillation crystal, or it may be a separately replaceable disc. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings wherein: 
       FIGS. 1A and 1B  show the front and side views of a repellent humidifier for exterior use in accordance with an exemplary embodiment of the present invention; 
       FIG. 2  is a diagram depicting an exploded cross-sectional view of the sections of a repellent humidifier for exterior use in accordance with an exemplary embodiment of the present invention; 
       FIGS. 3A ,  3 B,  3 C and  3 D are diagrams depicting various views of the nebulizer section of a repellent humidifier for exterior use in accordance with an exemplary embodiment of the present invention; 
       FIGS. 4A ,  4 B and  4 C are diagrams depicting various views of the repellent tank section of a repellent humidifier for exterior use in accordance with an exemplary embodiment of the present invention; 
       FIGS. 5A ,  5 B and  5 C are diagrams depicting various views of the base section of a repellent humidifier for exterior use in accordance with an exemplary embodiment of the present invention; 
       FIGS. 6A and 6B  are diagrams depicting cross-sectional views of portions of the tank and nebulizer sections of a repellent humidifier showing the operation of the repellent tank valve in accordance with an exemplary embodiment of the present invention; 
       FIGS. 7A and 7B  are diagrams depicting cross-sectional views of portions of the tank and nebulizer sections of a repellent humidifier showing the operation of the tank level switch in accordance with an exemplary embodiment of the present invention; 
       FIGS. 8A ,  8 B and  8 C are diagrams depicting cross-sectional views of an ultrasonic transducer installed in a portion of the nebulizer section of a repellent humidifier showing in accordance with various exemplary embodiments of the present invention; and 
       FIG. 9  is a diagram depicting a cross-sectional view of a repellent humidifier showing the air flow and repellent vapor paths in accordance with an exemplary embodiment of the present invention. 
   

   Other features of the present invention will be apparent from the accompanying drawings and from the following detailed description. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Element Reference Number Designations 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               100: Ultrasonic Humidifier 
             
             
                 
               110: Lid Section 
             
             
                 
               112: Tank Fill Cover 
             
             
                 
               114: Tank Fill Opening 
             
             
                 
               120: Tank Section 
             
             
                 
               121: Insect Repellant 
             
             
                 
               122: Tank Valve 
             
             
                 
               124: Tank Float Assembly 
             
             
                 
               125: Tank Float 
             
             
                 
               126: Float Assembly Pedestal 
             
             
                 
               127: Switch Actuating Rod 
             
             
                 
               128: Tank Handle 
             
             
                 
               130: Humidifier Section 
             
             
                 
               131: Nebulizer Volume 
             
             
                 
               132: Repellant Well 
             
             
                 
               133: Sump 
             
             
                 
               134: Ultrasonic Transducer Assembly 
             
             
                 
               135: Ultrasonic Transducer Assembly 
             
             
                 
               136: Well Level Switch 
             
             
                 
               137: Well Level Sensor 
             
             
                 
               138: Tank Level Switch 
             
             
                 
               139: Tank Level Switch Cover 
             
             
                 
               140: Fan 
             
             
                 
               141: Fan Shroud 
             
             
                 
               142: Shroud Louver 
             
             
                 
               143: Fan Motor Support 
             
             
                 
               144: Fan Motor 
             
             
                 
               145: Fan Impeller 
             
             
                 
               146: Optional Battery 
             
             
                 
               147: Optional Battery Charger/Rectifier 
             
             
                 
               148: Optional Low Voltage Input 
             
             
                 
               150: Transformer 
             
             
                 
               151: AC Input 
             
             
                 
               152: GFI Power Switch 
             
             
                 
               163: Well Float Contact 
             
             
                 
               164: Well Float Assembly 
             
             
                 
               165: Well Float 
             
             
                 
               166: Well Assembly Pedestal 
             
             
                 
               170: Control Panel 
             
             
                 
               171: Display 
             
             
                 
               172: Panel Input Buttons/Switches 
             
             
                 
               174: Motion Sensor 
             
             
                 
               184: Optional Diverter 
             
             
                 
               186: Vapor Duct 
             
             
                 
               188: Vapor Vents/Register 
             
             
                 
               190: Bottom Section 
             
             
                 
               192: Legs 
             
             
                 
               194: Air Vent 
             
             
                 
               196: Fan Shroud 
             
             
                 
               202: Transducer Case 
             
             
                 
               204: Silicon Rubber 
             
             
                 
               206: Transducer Jacket 
             
             
                 
               208: Transducer (Piezoelectric Crystal) 
             
             
                 
               210: Ceramic Cover 
             
             
                 
               212: Seal/O-ring 
             
             
                 
                 
             
          
         
       
     
   
   Humidifiers are a well known devices for saturating air with water vapor and are of generally two types: evaporative and mechanical. Evaporative humidifiers evaporate water molecules in the air either by raising the temperature of the water (by using a heat coil) or by increasing the surface area of the water and decreasing its surface tension (by using a wick or filter). Vapor type evaporative humidifiers have many disadvantages such as high energy use, residue and scale accumulation and they are often incompatible with ingredients in the water that result from the thermal energy breaking down or altering certain chemical components. Wick-type humidifiers are relatively inefficient in the moderate to high relative humidity range and the wick demands constant cleaning. Mechanical type humidifiers utilize either a spinning impeller or an ultrasonic element to disperse small droplets of water in the air without heating. In the first type, a rotating drum is partially immersed in a water bath and as it spins, it picks up water and flings it at a diffuser, which breaks the water into fine particles that float in the air. 
   Ultrasonic humidifiers and nebulizers are well known devices for exciting a liquid to such a level that the liquid evaporates without the addition of any thermal energy. Certain medications have a synergistic effect when vaporized, such as vaporizing water with eucalyptus oil for use as a decongestant. One of the selling points of ultrasonic nebulizers is that the vapor they produce has more consistent, uniform and smaller particle size compared to other types of nebulizer technology. Particle size with the impeller type nebulizers can be more varied and larger, simply because of the interaction between the water droplets traveling at different speeds from the drum to the diffuser, whereas ultrasonic vibrations are constant, reliable and steady. It has long been understood that the more uniform, smaller particle sizes makes the medicated mist penetrate more deeply into the lungs. Ultrasonic humidifiers generally operate by imparting mechanical energy to a liquid thereby exciting the liquid molecules without increasing the intrinsic heat of the liquid. Thus, a liquid may be subjected to a rapidly vibrating (or oscillating) component in order to absorb enough mechanical energy to change its physical state through a process known as inertial cavitation. Although the cavitation process appears rather mundane, it is a violent process that sets up mechanical energy fields, such as acoustical, that can damage surrounding mechanisms and is a major source of wear for propellers and impellers. Cavitation occurs at an ultrasonic transducer which vibrates rapidly, first oscillating in the negative direction which creates an ultra-low pressure void in the water adjacent to the transducer that pulls in water vapor and then in the positive direction that forces the water vapors into bubbles and away from the transducer; the result is often referred to as ‘pulverized water.’ This vibrating energy also has a detrimental effect of breaking down certain unstable components into potentially harmful subspecies and ions which may damage certain components of the device, in much the same manner as heating the liquid might. Therefore, humidifiers are not suitable for vaporizing every type of liquid. Furthermore, the entire device is subjected to emersion in the vaporized liquid, so every part of the device is exposed to potentially detrimental effects of the vaporized liquid compounds. Consequently, humidification and nebulizing devices are typically employed in highly structured environments and under supervised conditions. 
   Ultrasonic type humidifiers are well known in the prior art as exemplified by U.S. Pat. Nos. 4,752,422, 4,752,423 and 4,921,639, which are incorporated herein by reference in their entireties. These describe, generally, a unit with a water well in which a high frequency ultrasonic transducer is immersed. The transducer typically comprises a piezoelectric crystal which vibrates rapidly, producing a fine water vapor which is dispersed into the atmosphere by an air current from a blower fan. 
   Mechanical humidifiers do not selectively atomize only water but they disperse water and whatever contaminants are contained in the water at approximately proportional concentrations. Therefore, mechanical humidifiers will disperse repellants effectively without some of the disadvantages associated with heating the liquid repellent. However, because ultrasonic humidifiers do not thermally vaporize only the water molecules, or disinfect it, they also disperse any suspended material in the water to the air such as microorganisms and minerals. 
   The present invention relates to an ultrasonic humidifier suitable for dispersing repellents for repelling nuisance insects in an exterior environment.  FIGS. 1 through 5  are diagrams of the different views of an ultrasonic repellent humidifier in accordance with exemplary embodiments of the present invention.  FIGS. 1A and 1B  show the front and side views of the external features of repellent humidifier  100 . As will be discussed below, repellent humidifier  100  generally comprises four discrete sections: lid section  110 ; tank section  120  shown in  FIG. 4 ; nebulizer section  130  shown in  FIG. 3 ; and bottom section  190  shown in  FIG. 5  (see also the exploded cross-sectional views shown in  FIG. 2 ). Repellent humidifier  100  is an automated repellent dispersing system for exterior usage that is relatively maintenance free. It disperses cool vaporized repellent in the air having particle sizes between 0.03 microns and 15.0 microns depending on the surface tension and viscosity of the repellent and the operating frequency of the ultrasonic transducer. The transducer, which will be discussed in greater detail below with regard to  FIG. 8 , will operate at the resonance frequency of the piezoelectric crystal it is made from, but optimally will operate between 1600 kHz to 1750 kHz, which may be excited by a drive current oscillating at approximating the resonance frequency of the piezoelectric crystal. In operation, repellent humidifier  100  is intended for exterior use only, therefore all of the components should be sealed and water tight to avoid humidity related failures and should meet Underwriters Laboratories Inc. certification requirements. 
   Turning to  FIGS. 1A and 1B , repellent humidifier  100  has control panel  170  with buttons/switches  172  for programming its operation and display  171  for monitoring inputs and operating parameters. Buttons/switches  172  of control panel  170  is depicted in the exemplary embodiments as being attached to repellent humidifier  100 , but in accordance with other embodiments buttons/switches  172  may be an detachable handheld remote for programming control panel  170 . For simplicity, all of the processing, memory, control, timing and safety components for repellent humidifier  100  are represented by control panel  170 . Optionally, repellent humidifier  100  may have motion sensor  174  for sensing local motion and initiating an automated run sequence for dispensing repellent at vents  188  (depicted in the exemplary embodiment as being stationary but may be louvered and/or adjustable for dispersing the repellent in a particular direction). Tank fill cover  112  is provided in lid  110  that exposes fill opening  114  for replenishing the volume of tank  120  with repellent  121 . Tank fill cover  112  is provided with a water resistant sealing gasket for forming a water tight bond with lid  110  and around fill opening  114 . As the unit is designed for exterior usage, it will be exposed to direct and indirect ultraviolet (UV) rays from the sun, so the outer shell material must resist ultraviolet light or have a UV protective coating added. Furthermore, repellent  121  may also be sensitive to ultraviolet light, so the entire structure of the unit should be opaque to block harmful UV rays from reaching repellent  121 . The inner compartments, tank section  120  should be constructed from chemical resistant material, such as polyethylene, in order to resist damage from repellents. 
   One exemplary repellent for use in repellent humidifier  100  is a composition of geraniol (sometimes referred to as rhodinol which is derived from the Geranium plant but also may occur naturally in lemon, citronella and other essential oils), cedarwood oil and a surfactant (approximate concentrations geraniol 4%, cedarwood Oil 1%, surfactant, such as sodium lauryl sulfate 0.75% with inert ingredients of xanthan gum, citric acid and water in the remaining 94.25%). The insect repelling properties of geranium plants have been long understood and Geraniol, an ingredient extracted from geranium oil, provides a natural, safe and extremely effective insect repellent. Geraniol has been tested by the University of Florida, and has been proven in various laboratory and field tests to be the best available flying insect repellent available, even better than DEET. Geraniol is a natural, pesticide-free product, which requires no EPA registration. Cedarwood oil, which has been touted as being an effective treatment for many hair and skin disorders, congestion and coughs, also has proven repellent properties. In addition, it lends a light musky wood scent to the fragrance of the Geraniol. Because both geraniol and cedarwood oil are lighter than water, a surfactant must be used as a wetting agent that lowers the surface tension of the two oils with the water, allowing for easier mixing and lowering of the interfacial tension between the oils and water. Other natural repellents that may be substituted or used in addition to those above are citronella oil ( Cymbopogon Winterianus ), lemongrass oil ( Cymbopogon Citratus ), rosemary oil ( Rosemarinus Officinalis ), Wintergreen oil ( Gaultheria Procumbens ) and thyme oil ( Thymus Vulgaris ). 
   One disadvantage of using an oil based repellent is that it tends to reduce the effective life expectancy of the ultrasonic transducer and other electrical components. The repellent oil readily adheres to metal surfaces. As the repellent is atomized, a residue of oil and oil byproducts is left on the vibrating part of the transducer (the diaphragm). This coating immediately reduces the efficiency of the energy transfer between the transducer and liquid and left untreated, it thermally isolates the transducer from the liquid, thereby accelerating thermal failure. Another problem is that the humidifier components that come in contact with the repellent vapor will eventually exhibit a thin oil film. While this film is easily cleaned from the exterior, its conductive properties will shorten the life expectancy of high voltage and electronic components it contacts. 
   In accordance with one exemplary embodiment of the present invention, repellent humidifier  100  comprises nebulizer volume  131  which contains all of the electrical components, has forced ventilation for air cooling, but is isolated from the repellent vapor generated in nebulizer section  130 ; see nebulizer section  230  of  FIG. 3 . Nebulizer volume  131  is defined by the horizontal portion and lower sides of nebulizer section  130  and base section  190 . As depicted in  FIGS. 2 and 3A  through  3 D, contained within nebulizer volume  131  is transformer  150  that receives AC power from three-pronged external power cord  151  coupled through GFI power switch  152 . Control panel  170  that receives power from transformer  150  and both ultrasonic transducer assembly  134  and blower assembly  140  receive controlled power and/or drive currents from control panel  170 . Although the present repellent humidifier  100  is depicted as a stationary device that receives power from a household AC power supply, the device consumes relatively little electricity and can, therefore, be powered by optional battery  146  that is recharged via optional battery charger/rectifier  147 , or instead receive power directly from a 12 VDC source through optional low voltage input  148 . Thus, repellent humidifier  100  may be operated from a car battery for trips to the beach or camping, tailgating or picnicking. 
   Blower assembly  140  is depicted as comprising motor  144 , mechanically coupled to squirrel cage fan  145  and which is enclosed on the lateral and top sides by fan shroud  141 . Fan shroud  141  has an air intake inlet (not shown) in a center portion of shroud  141  proximate to the axle of motor  144  and an exhaust outlet above the horizontal portion of nebulizer section  130  (the lowermost portion of the fan shroud is affixed to base section  190 , shown in  FIGS. 5A through 5C  as lower fan shroud  196 ). That exhaust opening is movably covered by shroud louver  142  when blower assembly  140  is idle, thereby isolating nebulizer volume  131  from any vaporized repellent that may be present in the nebulizer section  130  and protecting the electrical components located therein. Blower assembly  140  is depicted as a squirrel cage fan but may be any type fan system. 
   Briefly turning to  FIG. 9 , air from blower  140  is directed toward the surface of repellant  121  in well  132  proximate to the vibrating surface of ultrasonic transducer  134 . As repellent is vaporized, it is forced out of well  132  and into the stream of air from shroud  141 . Directing the air stream toward the vibrating surface of ultrasonic transducer  134  keeps the upper level of repellent in well  132  agitated, thereby lessening instances of oil and other contaminants adhering to the vibrating surface of the transducer. The repellent vapor mixes with the moving air and is swept upward into vapor duct  186  and egresses repellent humidifier  100  at vapor vents/register  188 . While vents  188  are depicted in the figures as stationary openings, they may instead be comprised of louvers and/or repositionable register vents for altering the direction and dispersing pattern of the repellent. 
   The present invention is intended to disperse a micro fine vapor of repellent particles into a control area. However, directing the air stream toward the surface of the repellent sometimes causes larger droplets of repellent to enter vapor duct  186  with the repellent vapor. This condition is more prevalent at higher air velocities and with the use of high energy transducers that tend to form tall water cones over the vibrating disc (see  FIG. 8A ). Repellent adhering to the sides of vapor duct  186  may be also swept out of the humidifier as large droplets of repellent. Any type of dispersal pattern other than a micro fine vapor of repellent particles is an inefficient use of the repellent. Slotted inverted cone-shape diverter  184  may be installed in the throat of vapor duct  186  as shown in  FIG. 9 . Slots in inverted cone-shape diverter  184  provide high speed paths for channeling micro particles of repellent that are away from the sidewalls and away from the center of the duct. The obstructions along the circumference and center of inverted cone-shape diverter  184  collect larger and slower droplets and provide a path of relatively calm air for the larger droplets to return to well  132  either along the sidewalls of duct  186  or at the center of the cone. 
   During operation, repellent  121  resides in repellent well  132 , completely covering the vibrating portion of ultrasonic transducer assembly  134  and well level sensor  137  (which is electrically coupled to switch  136 ). At least a portion of well float  165  of float assembly  164  is also immersed in repellent  121  of well  132 . Well float  165  tracks the level of the repellent  121 ; as the repellent is vaporized from well  132 , the fluid level drops causing well float contact  163  to engage and actuate tank valve  122  (see  FIGS. 5A and 5B ). Once actuated, tank valve  122  releases repellent from tank section  120 , thereby replenishing repellent  121  in well  132  to a predetermined level (see  FIGS. 7A and 7B ). Optimally, the level of repellent  121  in well  132  is approximately 1.0 in. to 1.75 in. above the vibrating surface of transducer assembly  134 , depicted as distance h 1  in  FIGS. 6A and 6B . 
   Those of ordinary skill in the art will readily understand that the present embodiment is exemplary in nature designed for ease in understanding the present invention and than many of the components may be substituted with equivalent components or eliminated altogether. For instance, the mechanical level indicators (tank float assembly  124  and well float assembly  164 ) described herein may be substituted with electronic fluid level measurement devices. However, one advantage of using a mechanical device for maintaining the repellent level in well  132  is that the well will be filled regardless of whether or not repellent humidifier  100  is connected to an electrical power source. Anytime the repellent evaporates, an oil residue is left on the surfaces. Thus, if repellent  121  evaporates from well  132 , a film residue will be left on the upper surface of the transducer, which may lower its efficiency, or worse, lower its operational life. 
   The repellent level in well  132  should remain at least 0.25 in. to 0.5 in. above the vibrating surface of transducer assembly  134 , depicted as distance h 2  in  FIGS. 6A and 6B . Therefore, well float assembly  164  should actuate tank valve  122  where h 2 &gt;0.25 in., preferably 1.0 in.&gt;h 2 &gt;0.5 in. The heat generated by transducer assembly  134  during operation is dissipated by repellent  121  in well  132 . If the surface of transducer assembly  134  is uncovered, the transducer will fail in short order. As a safety precaution, well level sensor  137  is positioned approximately 0.125 in. to 0.25 in. above the surface of transducer assembly  134 , depicted as distance h 3  in  FIGS. 6A and 6B . When well level sensor  137  senses well  132  is running dry and the vibrating surface of transducer  134  is in jeopardy of becoming uncovered, i.e., h 3 ≈0.125 in., well level sensor  137  will actuate well level switch  136 , which in turn signals control panel  170  to deactivate the ultrasonic transducer. In order to prevent repellent humidifier  100  from cycling on and off, control panel  170  may delay any action until it receives a constant signal from well level switch  136  for five or ten seconds, thereby ensuring that well  132  is running dry and not receiving a false report from well level sensor  137  from being temporarily uncovered by a combination of a low repellent level and turbulence in the repellent from the air flow. Once the signal has been accepted, control panel  170  will then immediately turn off the ultrasonic transducer and flash a low fluid warning across display  171 . Control panel  170  may also immediately turn off the blower assembly, or in accordance with another exemplary embodiment of the present invention, control panel  170  may instead delay disengaging blower  140  for a few seconds. By allowing the blower to continue running for a few seconds after the ultrasonic transducer is switched off, any repellent vapor still inside repellent humidifier  100  is exhausted to the atmosphere before it can settle down into nebulizer volume  131  and contaminate the electrical components there within. Control panel  170  may run blower  140  for a few seconds following any run cycle to vent repellent vapor from repellent humidifier  100 . 
   Also located within nebulizer volume  131  is tank level switch  138  which is a second safety switch for alerting the user that the repellent tank is in need of refilling, thereby avoiding an unnecessary interruption in dispensing repellent. Tank level switch  138  is a spring loaded, normally open switch that protrudes through the horizontal surface of nebulizer section  130  at tank level switch cover  139 . Tank switch level cover  139  seals nebulizer volume  131  but does not impede the movement of the switch. Turning to  FIGS. 4A ,  4 B,  4 C,  7 A and  7 B notice that tank float assembly  124  is hingedly attached to float assembly pedestal  126  above the highest level for repellent  121  within tank section  120 . Switch actuating rod  127  extends from tank float assembly  124 , through the interior of float assembly pedestal  126  and engages tank level switch  138  through tank level switch cover  139 . As the level of repellent  121  in tank section  120  recedes, ball  125  tracks the fluid level causing switch actuating rod  127  to move up. At some point, switch actuating rod  127  displaces tank level switch  138  enough to activate the switch and signal the control panel  170  and thus the user that the repellent should be replenished. 
   Tuning again to  FIGS. 5A through 5C , base section  190  of repellent humidifier  100  is shown in accordance with an exemplary embodiment of the present invention. Base section  190  seals the lowermost portion of nebulizer volume  131  and should form an air and water-tight seal. When in place, lower fan shroud  196  cooperates with fan shroud  141  of nebulizer section  130  completely enclosing fan impeller  145  except for the intake opening (not shown). Blower assembly  140  draws fresh air from the exterior of repellent humidifier  100  through air vent  194  and into nebulizer volume  131 . The fresh air circulates around the electrical components prior to being captured by fan  145  and forces through shroud  141 , past open louver  142  and into nebulizer section  130 . Because repellent humidifier  100  draws air from beneath base section  190 , legs  192  should provide clearance of approximately 2.0 in. In accordance with other embodiments, air vent  194  may be located on a sidewall of nebulizer section  130 , below its horizontal surface. 
   In the exemplary configuration using a single ultrasonic transducer, repellent humidifier  100  will continuously repel insects from a 1,000 sq. ft. control area for thirty hours while consuming approximately two gallons of repellent. Control panel  170  includes a programmable menu for scheduling repellent treatment at a predetermined time, such as in the morning and evening hours of weekends when people are about and insects are most active. Control panel  170  also incorporates a programmable countdown time for activating the device for a preset time period. Then, a user merely activates button  172  labeled AUTO, and repellent humidifier  100  disperses repellent for the preset time period. One method of extending the repellent is by dispersing it in short cycles for a preset time period, rather than in a continuous dispersion, for instance alternating cycles of ten minutes ON and five minutes OFF, or cycles of five minutes ON and ten minutes OFF. Alternatively, a manual override RUN button may also be included for running the unit longer than the preset time period. Humidifiers designed for internal use will often have a moisture sensitive rheostat for deactivating the run cycle at a predetermined relative humidity, and thus not inducing too much moisture into the air. Because repellent humidifier  100  is designed for outdoor use, sensing the surrounding relative humidity may be of little importance since the outdoor relative humidity would probably override the dispersing time period causing the device to shut off too early, especially in humid climates. Furthermore, because the present invention disperses micro fine particles of repellent, only a small amount of repellent is necessary for controlling nuisance insects, and the moisture content of the ambient air (the relative humidity) may not be affected. Instead, repellent humidifier  100  may include an optional motion detector  174  for sensing movement and dispersing repellent in conjunction with movement. This feature is even more important for use in areas that need insect control when humans are not present to activate the device. These are places where parasitic insects may be attracted for nonhuman hosts, and may transmit Lyme disease, heart worms, viral encephalitis, Eastern and Western equine encephalitis, West Nile virus and the like to their nonhuman hosts. Included in these places are aviaries, barns, kennels, stables and dairies. 
   As depicted in the figures of the exemplary embodiments, tank section  120  will accommodate one and a half to four gallons of repellent, but in accordance with other exemplary embodiments of the present invention the tank may hold ten or more gallons of repellent. Repellent humidifier  100  is depicted as having only a single ultrasonic transducer  134 . The exposed portion of the vibrating surface should be approximately 2.0 in. in diameter to vaporize enough repellent to efficiently repel insects from a 1,000 sq. ft. control area. In accordance with other exemplary embodiments depicted in  FIGS. 3A and 3C , the repellent humidifier may be configured with multiple ultrasonic transducers, either to increase its capacity or longevity. There, exemplary ultrasonic transducer  134  is depicted as being supplemented with a second transducer, exemplary ultrasonic transducer  135 , but others may also be included. In accordance with one exemplary embodiment, the multiple ultrasonic transducers may be activated simultaneously in order to increase the capacity of the unit for control areas greater than 1,000 sq. ft. Alternatively, the multiple ultrasonic transducers may be activated alternatively in order to extend that time between transducer services. The present configuration of repellent humidifier  100  may be further optimized by using a dual speed blower for more rapidly dispersing repellent at start up. After a predetermined time has elapsed, the blower reverts to its normal and slower run speed. 
   Turning now to  FIGS. 8A ,  8 B and  8 C, the construction and operation of an ultrasonic transducer is shown in accordance with exemplary embodiments of the present invention. As mentioned elsewhere above, ultrasonic transducers for vaporizing water abound and are extremely well known. However, those designs are intended for interior usage and for vaporizing water having a purity consistent with drinking or pool water. Using such humidifier designs out-of-doors for oily repellents will result in failure from a variety of factors. All else being equal, the purity of the air ingested by the present repellent humidifier also presents a serious challenge as outdoor air contains large concentrations of dust, pollen, spores, mold and bacteria not usually present indoors. These contaminants present two separate problems: hygiene and maintenance. One solution to molds and bacteria is to deposit aqueous silver ions to well  132 , such as by using the Ionic Silver Stick water purification technology (Ionic Silver Stick is registered by and available from Plaston AG of Switzerland). These silver ion cartridges last approximately one year and then must be replaced. Additionally, the interior surfaces of the humidifier may be coated or impregnated with an antimicrobial substance such as Microban (Microban is registered to and available from Microban International Ltd. of New York, N.Y.). 
   Even though these solutions will suppress the growth of harmful bacteria, mold and some viruses, they do little to stem the inordinate amount of contaminants ingested into the unit from the air stream. Obviously, filtering air at air vent  194  will reduce the amount of contaminants entering the system, but a filter adds an additional maintenance item for the user. As a practical matter, the vast majority of contaminates will travel straight through the device, and while they will have an effect on particle size, they will not reduce the effectiveness of the particle size to any measurable amount. Some particles will, however, be captured by liquid repellent  121  in well  132 . Those contaminants are first addressed by the design of well  132 . A reservoir well in a typical humidifier is usually an inch deep or less. The vibrating surface of the ultrasonic transducer is positioned near the bottom of the well (with the exception of perhaps the fluid level indicator, the transducer is near the deepest portion of the reservoir). Any contaminates captured in the water of the reservoir will settle out and saturate the bottom of the reservoir, while the upper level of the reservoir water will be relatively free of contaminates. The contaminants will cover the vibrating surface of the transducer and after periods of inactivity, the contaminants will adhere to the transducer, thereby lowering its efficiency. The oils and oil byproducts in the repellent further bind the contaminants to any metal surfaces present in the well, such as the transducer diaphragm. 
   This problem is partially overcome in the present invention by providing a sump below the level of the vibrating surface of the transducer. Turning again to  FIGS. 6A and 6B , the depth of the water column above the vibrating surface of the transducer is shown as h 1  and h 2 , depending on the level of water in the well. Sump distance, shown as h 4 , is typically only a few millimeters in prior art humidifiers, perhaps up to 0.25 in. In accordance with an exemplary embodiment of the present invention, the depth of sump  133  h 4  is deepened to create a low energy environment conducive to holding contaminates. In the present invention, sump depth h 4  may exceed 1.0 in. depending on the air velocity and the type and concentration of contaminates in the air. While the bottom of the sump  133  in well  132  must be cleaned from time to time, the cleaning frequency is much less than the maintenance cycle of the ultrasonic transducer. 
   The second solution to contaminates, and for anything that might stick to the vibrating surface of ultrasonic transducer assembly  134 , is to select a nonstick surface that does not inhibit the transfer of ultrasonic energy to the repellent or causes heat to accumulate in the piezoelectric crystal of the transducer. Turning now to  FIG. 8A , ultrasonic transducer assembly  134  is shown in accordance with an exemplary embodiment of the present invention. Ultrasonic transducers take many forms, but the exemplary transducer comprises mounting case  202  with a flanged opening for securely holding the transducer in place. Mounting case  202  is secured to the bottom of well  132  by fasteners with seal/o-ring  212  there between. The transducer comprises piezoelectric crystal  208  that converts electrical energy to high frequency mechanical energy (inaudible sound) and is usually silver soldered to a pair of electrical leads. Piezoelectric crystal  208  is not usually exposed to the water in humidifiers but is separated by metal disc  206  (the disc may be of any shape and in some applications a screen is substituted for a solid disc). The disc may actually be in the form of a cap or encase the entire piezoelectric crystal. The energy created by piezoelectric crystal  208  vibrates metal disc  206 , causing the water to cavitate. Piezoelectric crystal  208  and metal disc  206  are held securely by UL approved silicon rubber  204  that surrounds the opening in mounting case  202 . Metal disc  206  is typically fabricated from stainless steel, nickel plated or layered steel, or titanium. In either case, the oils and oil byproducts of the repellent readily adhere to the surface of metal disc  206  and its efficiency rapidly degrades. It appears that the metal surface attracts the oils and/or repels the surfactant in the repellent, resulting in an oil residue on the metal. The oil residue can usually be cleaned, but adds another maintenance item for the user. Oil mixed with airborne contaminants, and biological material is far more stubborn to clean. Often, the most expeditious solution is to simply replace the entire ultrasonic transducer assembly  134 , thereby greatly increasing the cost of operation of the unit. In accordance with an exemplary embodiment of the present invention, piezoelectric crystal  208  is separated from repellent  121  by ceramic disc  210  rather than the metal jacket. The repellent oils and oil byproducts are not attracted to the ceramic material in the manner of the metal disc and the surface of the ceramic disc remains pristine longer. Contaminants and particulate matter that does settle on ceramic disc  210  does not adhere to the ceramic to the extent as with the metal. In most cases, any oil residue that is present can usually be brushed off of the surface of ceramic disc  210  without replacing it. Metal disc  206  may be interposed between piezoelectric crystal  208  and ceramic disc  210  without any loss of efficiency. Therefore, in accordance with still another exemplary embodiment of the present invention, ceramic disc  210  may be separately replicable from piezoelectric crystal  208 . In that case, ceramic disc  210  may be separately cleaned or replaced without disturbing ultrasonic transducer assembly  134  and without incurring the costs. 
   As mentioned elsewhere above, during operation ultrasonic transducer assembly  134  forms a water cone that tends to induce the formation of larger sized particle droplets. The force of the forced air from blower  140  sweeps these large repellent droplets into the exhaust duct  186  and out of the machine causing a spray of repellent. Aside from using a diverter in the duct, ultrasonic transducer assembly  134  can be oriented for maximum vapor product with a minimally sized water cone. Cavitation efficiency is severely decreased as angle a diverges from horizontal. On the other hand, the size of the water cone in the air stream can be decreased by increasing angle θ in the direction of the air stream, see  FIG. 8B . With the water cone oriented away from the air stream, less repellent is spattered and drawn up into the duct as large sized droplets. Decreasing angle θ in the direction of the air stream tends to build the water column like an offshore breeze causes ocean waves to build, see  FIG. 8C . Not only is the water column taller with more surface area for creating larger droplets, but it presents a larger obstacle to the air stream that induces a low pressure zone on the backside of the water cone that is further conducive for droplet formation. Therefore, piezoelectric crystal  208  and ceramic disc  210  should be oriented slightly in the direction of the air flow, thereby reducing the size of the water cone. Optimally, angle should be between 5.0 and 9.0 degrees, preferably around 7.0 degrees off horizontal. 
   The exemplary embodiments described below were selected and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. The particular embodiments described below are in no way intended to limit the scope of the present invention as it may be practiced in a variety of variations and environments without departing from the scope and intent of the invention. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein. 
   The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.