at their heart , air purification and sterilization devices represent a series of engineering compromises . the devices should ideally maintain high air flow , so as to be able to continually process the air in a room or dwelling at high enough rates so as process most of the air in a room at least multiple times over the period of a day . the filtration and sterilization of the device should be high , but not at the expense of reducing the air flow rate to the point where the device &# 39 ; s ability to process air is insufficient . the devices should run quietly , air purification and sterilization devices typically contain multiple components , each with a limited lifetime . air filtration components can include hepa filters , pre - filters , activated carbon filters , and other types of filters , which eventually will become clogged with many small air particles or otherwise inactivated and must eventually be replaced . the limited - lifetime uv photocatalytic ( here called “ sterilizing ” to distinguish this function from a simple filter function ) components can include uv light sources and electronic power supplies , such as the electronic uv germicidal lamps and ballasts ( or other electronic circuitry ) used to produce uv light . even the catalytic surfaces , used in conjunction with uv light and often moisture and / or oxygen in the air to create anti - microbial oxidizing agents , can eventually become “ poisoned ” or inactivated by airborne dust and chemicals , and can lose effectiveness . as previously discussed , the invention is designed to overcome these difficulties by providing a unitized device that packages the limited lifetime components of a photocatalytic air purifier / sterilizer , namely the uv light source , limited - lifetime electronics ( such as a ballast ) that manage or power the uv light source , and the catalytic support , into a single handheld unit . this combined unit can ideally then be easily inserted or removed from an air purifier unit in a single operation , ideally without the need for extra tools . the invention is also designed for maximum air flow , ideally allowing the air in a room or vehicle to be recirculated many times over the course of a day , thus rapidly diluting the concentration of unwanted airborne contaminants . nomenclature : for brevity , the uv photocatalytic devices will often be referred to in the alternative form as uv air sterilizer devices , uv sterilization devices , or even as sterilizers . again , all applications of the use of hydroxyl radicals and super - oxide ions for breaking down or destroying a wide variety of different contaminants , including both living and non - living contaminants , is encompassed by this “ sterilization ” term . fig1 shows an overview showing the exterior of one embodiment of the unitized uv air sterilization device ( 100 ), and a cutaway view of the interior of the same device ( 102 ) in this figure , the device is shown with a plurality ( here 44 ) of metal ( aluminum ) plates ( 104 ) stacked parallel to each other . although these plates will often be referred to in this specification as metal plates or catalytic metal plates , in fact there is no requirement that the underlying material of the plates be metal at all . in alternative configurations , other non - catalytic structural materials , such as plastic or metal coated plastic , may also be used . for simplicity however , since such plates are often made of metal materials such as aluminum or steel , these plates will be otherwise referred to in this specification as “ catalytic metal plates ”. in the particular embodiment exemplified by fig1 , each catalytic metal plate has a square shape with dimensions of roughly 70 mm × 70 mm × 0 . 5 mm , and each metal plate also has a central hole ( here circular ) ( 106 ) about 15 mm in diameter . one or more uv light sources ( here a single uv germicidal lamp in a common fluorescent light tube form factor is shown ) ( 108 ) runs in the center of the device through the various central holes . the metal plates are stacked with a separation of about 5 mm between plates , and all of the metal plates have roughly the same size and shape . the metal plates are typically coated with a uv light activated catalyst , which are often particles of semiconductors such as titanium dioxide . due to the configuration of the plates relative to the uv light source , which enables the uv light source to shine on both sides of the plates , both plates are typically coated with the uv light activated catalyst , effectively doubling the efficiency of this design over prior art devices that used one side of the plate as a uv activated catalyst . as previously discussed , when activated by uv light from the central light source ( s ), the catalytic particles can in turn react with trace amounts of moisture from the air , and / or oxygen from the air , and produce oxidant molecules ( e . g . hydroxyl radicals , super - oxide ions ) capable of destroying microbes ( e . g . bacteria , molds ) and viruses often carried in microscopic airborne particles . such catalytic particles can also be useful for neutralizing unwanted airborne allergens ( e . g . pollen , pet dander , dust ) volatile organic compounds ( voc ) as well . as previously discussed , typically both sides of the metal plates will be coated with semiconductor material in order to maximize sterilization , allergen breakdown and voc neutralization efficiency . as previously discussed , the term “ sterilization ” will here also encompass allergen and voc neutralization capability as well . the separation between the catalytic metal plates ( 110 ) is typically chosen to be a balance between maximizing the amount of air flow past the plates , and maximizing sterilization efficiency . as the separation between the catalytic metal plates decreases , two undesirable things happen . one undesirable effect is that there is a proportionally lesser amount of uv light flux available to each plate , since typically only the uv light source originating from that portion of the light source between the gap between the plates will be available to contribute uv light . the other undesirable effect is that there will be a greater surface area of the catalytic metal plates available to obstruct air flow . this can result in both higher noise generation , and also a decrease in the amount of air the device can process over any period of time . the beneficial effect of a lesser separation , however is that the chance of a microbial or viral particle contacting the catalytic surface of the catalytic metal plate will increase as the gap between the plates decreases . in general , for the purposes of this invention , gaps ( 110 ) in the 1 to 20 mm range , often in the 2 to 10 mm range , preferably between 3 to 7 mm , and here drawn as 5 mm separation have been found to offer a good compromise between optimizing air flow and sterilization efficiency . the device has a number of other design features intended to optimize air flow . as can be seen in fig1 , the catalytic metal sheets are connected by their edges to support plates ( 112 ), so that the catalytic metal sheet ( 104 ) is connected by one edge side of the square metal catalytic sheet to the support plate ( 112 ) at a roughly 90 degree angle ( perpendicular ). in this embodiment , six catalytic metal sheets are connected to each support plate , and the arrangement of the support plates is such that the support plates are alternately positioned with one support plate ( 112 ) on one side of the catalytic metal plates , then another support plate on the opposite side of a different group of metal plates , so that although ultimately , all catalytic metal plates are supported by attachment to their particular support plate , the arrangement of support plates is such that there is never a full “ wall ” of support plates capable of totally restricting air flow from any angle . in this embodiment , for example , at most only about 50 % of one side is obstructed to air at any given time . the advantages of this approach will be discussed in more detail in the discussion of fig9 . although the support plates ( 112 ) need not be themselves covered with a catalytic material , there is some benefit to doing so because the overall catalytic surface area of the unitized air sterilizer device will increase somewhat . in some embodiments , it may be useful to first manufacture all plates ( e . g . both support plates and catalytic plates ) and support plates out of a metal , ( such as aluminum ), plastic , or metal coated plastic , and then apply the semiconductor catalyst in a second operation by a spraying or dipping process , in which case often the support plate will be coated with the semiconducting material as well . although the catalytic metal plates ( 104 ) are shown in this embodiment as being square in shape , other shapes , such as rectangular shapes , triangular shapes , pentagons , etc . may also be used . ideally the shape and central hole ( 106 ) for the uv lamp ( 108 ) will be chosen as to efficiently utilize the light emitted by the uv lamp . thus in a preferred embodiment , the plates will have rectangular shape close to that or equal to that of a square . the actual size of the plates may also differ , and may be as low as 10 mm in diameter ( or per side ) for some miniaturized applications up to 500 mm by 500 mm in diameter ( or per side ) or greater for purifying the air in extremely large rooms . the number of individual plates will typically vary from as few as 2 to as many as 1000 or more , with plate numbers in the 10 to 300 , and still more preferably in the 20 to 100 range being preferred . modern uv light sources , such as uv germicidal lamps ( again often made in a fluorescent tube form factor ), often have use lifetimes of about 10 , 000 to 20 , 000 hours , which coincidentally is often roughly similar to the use lifetime of the electronic circuits , such as ballast circuits , used to drive these uv light sources . indeed , as previously discussed , even the semiconductor catalyst coating itself has a finite lifetime because gradually it can become contaminated or “ poisoned ” by a gradual buildup of various compounds and particles from the air . as previously discussed , one problem associated with prior art uv air sterilization devices was the problem of maintenance . typically each individual element of the device , such as the uv light source , the electronics that drive the uv light source , and the catalytic surfaces were designed as individual stand - alone devices , and installed into larger air purifier devices in a way that made maintenance difficult . a user would have to perform a first maintenance operation to open up the device and extract the uv light source from the uv light source holder , catalytic material , and power supply electronics . then perform a separate operation to service the power supply , and a third operation to service the catalytic material . by contrast , if this prior art practice of producing discrete components is dropped in favor of producing a new type of unitized air uv sterilizer device , a number of distinct advantages result . to begin with , user servicing of the air purifier device that holds the uv light source , uv light source electronics , and catalytic material can be greatly simplified . for example , in one embodiment , a simple “ clip in ” ( and perhaps disposable or recyclable ) air uv sterilizer device can be produced that can be easily replaced by the user in a simple one - step , and ideally tool - free , operation . an additional advantage of this unitized uv photocatalytic light source , electronics , catalytic device ( air uv sterilizer device ) is that it can greatly simplify the design of the larger air purifier device that holds the air uv sterilizer device as well . for example , if the electronics section or module of the unitized air uv sterilizer device ( 114 ) is designed to handle typical international ac voltages ( which typically run from about 100 to 240 volts , at either 50 or 60 hz ), then a single type of air purifier device ( that holds the air uv sterilizer device ) can be inexpensively constructed that can work in all countries worldwide , irrespective of local ac voltages . this can lead to manufacturing efficiencies , as well as sales , marketing , distribution and servicing efficiencies as well . in fig1 , electronics section ( 114 ) holds the electronics used to drive the uv light source ( 108 ). as previously discussed , the “ metal ” plates ( 104 ) will typically be converted to catalytic metal plates ( or catalytic plates ) by coating with a suitable semiconductor , such as titanium dioxide ( tio 2 ) or other material ( s ), chosen for their ability to accept uv light , water molecules , and alternatively oxygen as input , and produce sterilizing oxidizing molecules as output . although titanium dioxide is given as an example , this example is not intended to be limiting , and other types of semiconducting particles may be used . additionally other types of materials , such as water absorbing agents , other antimicrobial materials , and other chemicals ( i . e . binders , preservatives , reflective materials , etc .) may also be used . examples of suitable catalytic semiconductors and other materials useful for this purpose include the hydrophilic agent ( s ) titanium dioxide , silver / copper / rhodium materials and methods taught by fink et . al ., us application 2005 / 0186124 , the contents of which are included herein by reference . other suitable catalytic materials and methods are taught by the materials and methods of morrow et . al ., us application 2007 / 0243114 , the contents of which are incorporated herein by reference . the wavelengths of the uv light sources ( uv germicidal light ) will usually be in the uvc wavelength of around 100 to 280 to 300 nm . at the longer wavelength end , the maximum energy ( maximum wavelength ) of the uv light useful for this purpose is about 385 nm , which represents the band gap energy of semiconductor catalysts such as tio 2 . often wavelengths such as 245 nm and / or 185 nm may be used . for example , morrow teaches the utility of coating no more than 5 % of the surface of a reflective metal with photocatalytic particles in order to maintain the uv reflective characteristics of the underlying reflective material ( such as the non - catalytic metal base ), and morrow wishes to have the uv light bounce back and forth many times within morrow &# 39 ; s reflecting cavity . these methods may also be useful in some embodiments of the unitized uv photocatalytic device as well . this is because although the disclosure &# 39 ; s parallel metal plates do not form a completely enclosed uv reflective cavity , the relatively large size ( e . g . 70 × 70 mm ) of the plates coupled with their typically close spacing ( e . g . 5 mm ) means that the uv light may also bounce back and forth between an first plate and a second plate may times before the uv light is either absorbed or else escapes through the open sides at the edge of the plates . thus morrow &# 39 ; s methods , such as the utility of using water absorbing materials ( such as silica gel or other dielectric material ) on the surface of the reflecting cavity to help promote the desired uv stimulated catalytic activity can be useful in some embodiments of the unitized uv photocatalytic device as well . fig2 shows a top cut away view of the interior of the unitized uv air sterilization device previously shown in fig1 ( 102 ). here the uv light source , here depicted as a single linear uv germicidal lamp with a fluorescent tube form factor ( 108 ) is shown , as well as a cross section of the catalytic metal plates and support plates . on the right , the section of the case that holds the power electronics needed to drive the uv light source ( 114 ), such as ballast ( 202 ) and appropriate power connectors ( 204 ), are shown . on the right , the holder ( 206 ) that caps the end of the device and protects and holds the end of the uv light source is shown . fig3 shows an alternate cross section through the device , exposing the details of one of the catalytic metal plates ( 104 ) and its central hole ( 106 ). note that one edge of the catalytic plate ( 104 ) is attached to a support plate ( 112 ) at a right angle . the portion of the device that holds the electronics ( 114 ) is also shown with the top of the electronics case attached . fig4 shows a detail of the electronics portion of the unitized device ( 114 ), in which the top has been removed in order to show additional details . here the uv light source ( 108 ) is again shown as a single uv germicidal lamp with a fluorescent light tube form factor that has been inserted into the central holes of the parallel catalytic metal plates , and the power plugs of this light source ( 400 ) are protruding into the electronics portion . ( for clarity , the connecting wires and plugs are not drawn .) in this example , the electronics again includes ballast ( 202 ) and suitable power connecting plugs ( 204 ). typically prongs or jacks from an external purifier device ( not shown ) will supply external power to these power connecting plugs ( 204 ). this can be seen in more detail later in fig8 ( 812 ). fig5 shows a detail of the holder end of the device ( 206 ), showing the distal end of the uv light source ( 108 ) being capped and protected by the holder . again , the top portion of the holder has been cut away to allow for better visualization . usually , the unitized uv air sterilization devices ( 100 ) will be mounted on the interior of a larger air purifier device . often it may be useful to mount the unitized uv light sterilization devices ( 100 ) using clips or other type of holding fixture that can allow the sterilization devices to be easily mounted to an interior wall of the air purifier device , and removed by unskilled users without the need to use additional tools . fig6 shows a 3d view of a clip fixture ( 600 ) that can hold two unitized uv air sterilization devices ( 100 ). in this embodiment , the clip fixture can hold the unitized uv air sterilization device ( s ) by a first clip ( 602 ) that attaches to the electronics portion ( 114 ) of device ( 100 ), and a second clip ( 604 ) that attaches to the holder portion ( 205 ) of device ( 100 ). clip fixture ( 600 ) may additionally contain wall mounting brackets ( 606 ) to attach the fixture ( 600 ) and attached unitized uv air sterilization devices ( 100 ) to an interior wall of an air purification device . fig7 shows a top view of the same dual clip fixture , here shown mounted on an interior wall ( 700 ) of an air purifier device ( 800 ). this interior wall ( 700 ) will usually have one or more holes ( 702 ) so that air ( often driven by the force of a motor driven air blower ), may be driven to pass through the slots of the unitized uv air sterilizer devices ( 100 ) and out through the other side . here the dual clip fixture is drawn with dotted lines in order to better distinguish the fixture from the unitized uv air sterilization device ( 100 ). note that one aspect of this design is that rather than attempting to sterilize 100 % of the air in one pass through the air purifier and the unitized uv air sterilization device , the design instead emphasizes high air flow , so that the air may pass through the air purifier many times over the course of a day , each time reducing the amount of microbial or viral particles , allergens , or voc present in the air . parts of fig7 may be best understood by also comparing fig7 with fig8 . in this embodiment , an air filter , such as a hepa filter ( 802 ), may optionally be mounted on top of ( or in front of ) the unitized uv air sterilizer devices ( 100 ), clip fixture , and wall ( 700 ), and a motor driven air blower ( 804 ) may be mounted behind ( or in back of ) the wall ( 700 ). the sides of the wall ( 700 ) will normally be covered by an enclosure ( 806 ) that forces the outside air ( 808 ) to travel through the air filter ( 802 ), the unitized uv air sterilization device ( 100 ), the hole ( 702 ), before allowing the now purified and partially sterilized outside air ( 810 ) to exit the air purifier device . fig8 shows an alternate view of an embodiment of the air purifier device ( 800 ), showing more details of the optional air filter ( 802 ), the unitized uv air sterilization device ( s ) ( 100 ), and the motor driven air blower ( 804 ). here the power plugs or prongs ( 812 ) that supply power to the electronics module ( 114 ) of the unitized uv air sterilization device ( 100 ) are also shown ( 812 ). as previously discussed , the air purifier unit ( 800 ) consists of an enclosure ( 806 ) with a front air intake , often through an optional air filter such as a hepa filter ( 802 ) that removes larger air particles . after passing through the optional filter , the air then passes through a wall one or more holes ( 702 ) in interior wall ( 700 ). however before doing so , in this embodiment , the air also flows through the catalytic plates ( 104 ) of the unitized uv sterilization device ( 100 ). to do this , the mounting clips ( 602 ) hold the one or more unitized uv light sterilization devices ( 100 ) are mounted on wall ( 700 ), and the unitized uv light sterilization devices themselves ( 100 ), are then clipped to the mounting clips . to force the air to move , in this in this embodiment , a motor driven air blower ( 804 ), mounted on the opposite side of wall ( 700 ) and hole ( 702 ) operates to suck air from the outside ( 808 ) through the optional hepa filter ( or other type of air filter ) ( 802 ), then through the unitized uv light sterilization devices ( 802 ), and then through the hole in the wall ( 702 ) and out ( 810 ) the other side of the motor driven air blower ( 804 ). as a result of this process , the airborne contaminants , such as the voc , allergens , microbes , and viruses are neutralized by the action of the uv activated catalyst as the air passes through the series of metal catalytic plates ( 104 ). fig9 shows various drawings of the air purifier wall ( 700 ) and overall air purifier device arrangements previously shown in fig7 and 8 , showing the air flow through the device ( s ) in both the preferred embodiment ( 900 ), ( 902 ) where the support plates ( 112 ) are arranged so as to never to create a major block to air flow from any direction , and a less preferred embodiment ( 904 ), ( 906 ) in which the support plates ( 112 ) are arranged so as to create a major block to air flow from one direction . note that in the preferred air purifier configuration , air may pass through the catalytic plates ( 104 ) in the unitized uv air sterilizing device ( 100 ) from both the side of the sterilizing device that faces the hepa filter , and from the sides of the sterilizing device that are at right angles to the hepa filters , because at most only about 50 % of these right angle sides are blocked by the support plates ( 112 ). thus air can flow in through gaps between the catalytic plates ( 104 ) from the sides as well as from the top ( 908 ). this results in a greater amount of air flow through the unitized uv sterilization device ( 100 ). by contrast , in the less preferred embodiment ( 904 ), ( 906 ), in which all of the support plates ( 112 ) are arranged on the same side of the device ( 100 ), the support plates will act to substantially limit the free flow of air into the unitized uv sterilization device ( 100 ) from at least the side of the device facing at a right angle to the optional hepa filter . although air can still enter the gaps between the catalytic plates ( 104 ) from the top or filter side of the sterilization device ( 100 ), the total amount of air flow is substantially less , because the air from the side is blocked by the support plates ( 112 ). this blocked air is shown as ( 910 ). in order to illustrate the improved catalytic efficiency of this device over prior art devices , such as the device of morrow et . al . ( u . s . pat . no . 7 , 303 , 612 , the contents of which are incorporated herein by reference ), a few calculations will be given . if an alternative prior - art box shaped structure with dimensions 70 mm × 70 mm × 230 mm was produced with a central uv lamp , then the total surface area of the interior of this box that would be available for catalytic activity would be the four walls of the box alone ( since the top and bottom would presumably have to be open for air flow ). this would be 70 × 230 × 4 = 64 , 440 square millimeters . ( keep in mind that in the morrow design , these four catalytic walls are solid , and totally obstruct air flow past these walls ). by contrast , the invention , using the embodiment shown in fig1 , would have an effective catalytic area , per plate , of 70 mm × 70 mm ( plate dimensions )× 2 ( sides per plate )− πr 2 ( the diameter of the inner circle , which is 3 . 14 *( 15 / 2 ) 2 or 422 mm2 )= 9 , 378 square millimeters per plate . since in this example , 44 plates are placed in the same 230 mm length , the total surface area of the device in fig1 is thus 44 * 9 , 378 = 412 , 632 . thus , relative to the prior art design of morrow , the present invention has 6 . 40 times greater surface area . note also that in the fig1 design , none of the sides of the device are completely obstructed , and thus air may flow from all sides . thus the invention both has a larger catalytic area , and it also impedes air flow less than the morrow device . neglecting the obstructing effects of the uv light source , the morrow device has an effective air opening ( free air flow area ) of only 70 × 70 mm ( i . e . the top or bottom of the device ), which is 4 , 900 square millimeters . by contrast , the embodiment shown in fig1 has an effective air opening ( free air flow area ) of at least 70 × 230 mm ( minus 44 × 70 × 0 . 5 mm if the plates are 0 . 5 mm thick ) or 16 , 100 − 1 , 540 or 14 , 560 mm . a high air flow is of course critical to the proper operation of the device . for example , a device with a very high catalytic surface area , but no openings to allow air to flow , will of course be useless . in general , the amount of air flowing past an opening will be proportional to the surface area of the opening , times the flow velocity of air ( often expressed in cubic feet per minute or cfm ). assuming equal uv light flux , the net catalytic efficiency will roughly be proportional to the amount of catalytic surface and the amount of free air flow past the catalytic surface . here , the differences between the embodiment shown in fig1 and the prior art morrow device become still more striking . note that when comparing differences between units otherwise similarly situated , the cfm value cancels out , and we can just compare catalytic area * free air flow area . the morrow device has an overall efficiency of catalytic surface area * free air flow area of 64 , 440 * 4 , 900 = 315 , 756 , 000 mm 2 catalyst * mm 2 airflow . by contrast , the device in fig1 has an overall efficiency of 412 , 632 * 14 , 560 = 6 , 007 , 921 , 920 mm 2 catalyst * mm 2 airflow . the ratio of the catalytic efficiency of the two units is thus roughly 19 : 1 in favor of the device shown in fig1 . this catalytic efficiency measurement can also be a useful way to compare the invention with prior art meshwork or fabric devices , since although some of these alternative meshwork or fabric devices may have a larger catalytic surface area , they will also have a far smaller free airflow area , and / or be exposed to a far smaller amount of incident uv light flux . thus the overall catalytic efficiency of these prior art devices is again sub - optimal ( as compared to the invention ) due to reduced air flow and lesser uv light flux . although some specific embodiments of the invention have been disclosed , these embodiments and examples are not intended to be limiting . other embodiments will also be clear to those skilled in the art . for example , although the particular embodiments discussed here disclosed use of the unitized uv air sterilization device in the context of an air purifier device that also used other filters , such as hepa filters , to pre - purify the air , use of such filters is not obligatory . thus in alternative embodiments of the invention , such air filters may be omitted , or alternatively different types of air filters may be used . further , although some embodiments of the invention may be configured with relatively wide spacing between the catalytic elements ( e . g . catalytic plates ) to enable high levels of air flow , this is just one of many potential embodiments . in other embodiments , the requirement for high air flow may be reduced or dropped . in this case , alternative catalytic elements employing foams , meshes , fabrics , narrowly spaced catalytic plates , or other lower air flow configurations may also be used .
a uv photocatalytic air purifier / sterilizer in which the multiple limited - lifetime components of a photocatalytic uv air purifier / sterilizer are packaged together to form a single , handheld , unitized package , designed for easy insertion and removal into an air purifier . the invention may be configured enable maximum air flow through the photocatalytic portions of the device , thus further improving air cleaning efficiency by allowing many volumes of room air to be recirculated through the device and cleaned / purified / sterilized over the course of a day . in a preferred embodiment , the device may package a series of stacked tio2 coated parallel metal catalytic plates , a uv germicidal lamp with a fluorescent tube form factor , and a uv lamp ballast into a single disposable or recyclable unit . this disposable unit can be easily clipped into a motorized air purifier unit designed for rapid servicing .