Abstract:
An optical array containing a system of absorptive filters and a system of interference filters. For the sun light the spectral characteristics of transmission of the optical array is close to the world-wide accepted Diffey Standard. That standard models human skin sensitivity to UV burning. The invention allows making inexpensive, miniature UV sensors that can be applied in miniature devices measuring burning power of UV contained in the sun light.

Description:
This invention is an optical array converting UV radiation, especially contained in sunlight. The spectral characteristic of the transmission of the filter is similar to the sensitivity of human skin to sun burning. That sensitivity is described by the widely recognized Diffey Standard, also called also the Erythema Action Spectrum. 
     The Roberston Berger UV meter has been widely used over the past two decades to measure UV in good approximation of the Diffey/Erythemal Spectral Response. This stationary device is based on a phosphore convertor screen as the principle means to reach a spectral response close to the Erythemal/Diffey Curve. 
     By now there are a few UV hand-held measuring devices known on the market that are targeting monitoring of LTV radiation for avoiding sunburning. CASIO Computer Ltd. manufactures a device called “CASIO UC-120 UV”, which has an optical array containing absorptive filter made of material similar to Schott UG-11 and a photodiode. The spectral characteristic of the device doesn&#39;t match the Diffey Standard. The device illuminated by sunlight is too sensitive to UV-A, that has low burning power. 
     U.S. Pat. No. 5,196,705 describes a device measuring the intensity and dose of UV. The device has an optical array containing: an absorptive filter made of material similar to Schott UG-11, a photo-luminescentive material and a photodiode. The spectral characteristic of the device doesn&#39;t match the Diffey Standard. The device is too sensitive to UV-A comparing to its sensitivity to UV-B. 
     Several others solutions for biologically oriented monitors of UV radiation were also proposed, among them: 
     U.S. Pat. No. 5,036,311 describes a UV-monitoring system in which a light sensing element is placed under a curved optical element with interference filters imposed on its surface. 
     U.S. Pat. No. 5,401,970 describes a UV-monitoring device which incorporates a UV-B sensor and a VIS sensor. The UV-B detector involved is described to be based on a phosphor convertor screen. 
     DESCRIPTION OF THE INVENTION 
     The invention solves the problem of constructing a device equipped with an optical array converting UV, visible and IR radiation that has the spectral characteristic of the transmission similar to the Diffey Standard. Definition of the relative internal transmission of a set of filters: 
     
       
           T   rel   int (λ)= T   int (λ)/ T   int (310)  (1) 
       
     
     where: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 λ 
                 wavelength in nano-meters 
               
               
                   
                 T rel   int (λ) 
                 relative internal transmission for λ wavelength 
               
               
                   
                 T int  (λ) 
                 internal transmission for λ wavelength 
               
               
                   
                 T int (310) 
                 internal transmission for 310 nm wavelength 
               
               
                   
                   
               
             
          
         
       
     
     Note that the total internal transmission of the set of absorptive filters is equal to the product of internal transmissions of each consecutive filter. 
     Definition of the relative transmission of a set of filters: 
     
       
           T   rel (λ)= T (λ)/ T (310)  (2) 
       
     
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 λ 
                 wavelength in nano-meters 
               
               
                   
                 T rel (γ) 
                 relative transmission for λ wavelength 
               
               
                   
                 T(λ) 
                 transmission for λ wavelength 
               
               
                   
                 T(310) 
                 transmission for 310 nm wavelength 
               
               
                   
                   
               
             
          
         
       
     
     The Diffey spectral characteristics will be denoted as D(λ) (3) where: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 λ 
                 wavelength in nano-meters 
               
               
                   
                   
               
             
          
         
       
     
     In the first solution the array contains a system of absorptive filters to block visible and IR radiation, a system of interference filters modifying transmission of UV and/or blocking visible and IR radiation, scattering elements, elements forming the light beam. Interference filter/filters is/are made of layers of materials having high and low UV refractive indexes. According to the invention one of the system of interference filters has layers made of Hafnium oxide and/or Zirconium oxide. A collimator placed in the optical path forms the light beam. The collimator can have surfaces highly absorbing light. At the beginning of the optical path a scatterer is placed to achieve non-directional characteristic of the array. The scatterer can be made of PTFE. 
     In the second solution the array contains the first system of absorptive filters to partly block UV-A, the second system of absorptive filters to block visible and IR radiation and may contain scattering elements and/or system/systems of interference filter/filters. The first system of absorptive filters has internal relative transmission T rel   int (λ): between 0 and 0.2 for λ=290 nm, between 0.34 and 0.7 for λ=300 nm, between 0.5 and 0.8 for λ=320 nm, between 0.04 and 0.36 for λ=330 nm, between 10E-3 and 0.1 for λ=340 nm, between 7*10E-6 and 0.02 for λ=350 nm, between 2*10E-7 and 7*10E-3 for λ=360 nm, between 2*10E-7 and 7*10E-3 for λ=370 nm, between 2*10E-5 and 0.03 for λ=380 nm, between 2*10E-3 and 0.14 for λ=390 nm. The total optical thickness of the first system of absorptive filters is between 0.5 and 2 mm. 
     The second system of absorptive filters has internal relative transmission T rel   int (λ): between 0 and 0.3 for λ=290 nm, between 0.7 and 0.8 for λ=300 nm, between 1 and 1.3 for λ=320 nm, between 1 and 1.4 for λ=330 nm, between 1 and 1.3 for λ=340 nm, between 1 and 1.12 for λ=350 nm, between 0.6 and 0.8 for λ=360 nm, between 0.14 and 0.3 for λ=370 nm, between 10E-3 and 0.015 for λ=380 nm, between 10E-10 and 10E-6 for λ=390 nm. The total optical thickness of the first system of absorptive filters is between 0.5 and 10 mm. 
     At the beginning of the optical path a scatterer is placed to achieve non-directional characteristic of the array. The scatterer can be made of PTFE. In the optical path additional system/systems of interference filters can be placed to block visible and IR radiation and/or to modify transmission in UV range. 
     This invention allows producing a cheap and simple optical array with a spectral characteristics in the UV-A and TV-B range following the human skin sensitivity described by Diffey Standard. The scatterer ensures non-directional characteristics of the array. Other standards of skin sensitivity to UV-A and UV-B burning can also be easily followed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is presented on the block diagrams where 
     FIG. 1 presents the construction of the version 1 of the optical array, 
     FIG. 2 presents the construction of another variant of the invention presented on FIG. 1, 
     FIG. 3 presents the construction of the version  2  of the optical array, 
     FIG. 4 presents the construction of the of the version  3  of the optical array. 
     FIG. 5 presents T rel (λ)*D(310)/T rel (310) for optical array from FIG. 2 in comparison with the Diffey Standard D(λ), 
     FIG. 6 presents T rel (λ)*D(310)/T rel (310) for optical array from FIG. 3 in comparison with the Diffey Standard D(λ), 
     FIG. 7 presents T rel (λ)*D(310)/T rel (310) for optical array from FIG. 4 in comparison with the Diffey Standard D(λ). 
    
    
     DESCRIPTION OF THE VERSION 1 
     The array contains: the layer  1  that scatters light, a collimator  2  an absorptive filter  3  that makes a system of absorptive filters, a set of interference filters  4  that makes a system of interference filters. The absorptive filter  3  is made of material transparent to UV and blocking visible and IR radiation. That property has M1 material, with a characteristics presented in the table below. 
     In that example a scatterer  1  is made of PTFE, and the absorptive filter  3  is a plano-parallel plate, 8 mm thick, made of M1 material Schott UG-11 like. The set of interference filters  4  that is placed on the absorptive filter&#39;s  3  surface consists of 38 layers of Hafnium oxide and/or Zirconium oxide and Silica oxide. 
     The scatterer  1  ensures non-directional characteristics of the array. The collimator  2  forms the light beam. To achieve desired spectral characteristics the light beam passes through the absorptive filter  3  and the interference filter  4 . 
     In the other variant of the version 1, that is shown on the FIG. 2, the array contains: the layer  5  that scatters light, a collimator  6 , absorptive filter  7  that makes a system of absorptive filters and a first set of interference filters  8  and a second set of interference filters  9  that both make a system of interference filters. The absorptive filter  7  is made of material transparent to UV and blocking visible and IR radiation. That property has M1 material, with a characteristics presented in the table below. 
     In that example a scatterer  5  is made of PTFE, and absorptive filter  7  is a plano-parallel plate, 8 mm thick, made of M1 material, Schott UG-11 like. The first set of interference filters  8  and the second set of interference filters  9  are placed on the absorptive filter&#39;s  7  surfaces and together consists of 62 layers of Hafnium oxide and/or Zirconium oxide and Silica oxide. 
     The scatterer  5  ensures non-directional characteristics of the array. The collimator  6  forms the light beam. To achieve desired spectral characteristics the light beam passes through the first interference filter  8 , the absorptive filter  7  and the second interference filter  9 . 
     On the FIG. 5 chart the T rel (λ)*D(310)/T rel (310) characteristics of the array is plotted as a broken line, the Diffey Standard is plotted as a solid line. On the chart these two curves are close to each other in the 310-325 nm range. 
     DESCRIPTION OF THE VERSION 2 
     The array contains: the layer  10  that scatters light, a first absorptive filter  11  that makes a first system of absorptive filters, a second absorptive filter  12  that makes a second system of absorptive filters. The first absorptive filter  11  is made of material transparent to UV with decreasing transmission when the wavelength is changed from 320 to 350 nm, the second absorptive filter  12  is made of material transparent to UV and blocking visible and IR radiation. That property have materials M2 and M1 respectively, with characteristics presented in the table below. 
     In that example a scatterer  10  is made of PTFE, the first absorptive filter  11  is a plano-parallel plate, 1.5 mm thick, made of M2 material, Schott GG-19 like, the second absorptive filter  12  is a plano-parallel plate, 8 mm thick, made of M1 material, Schott UG-11 like. 
     The scatterer  10  ensures non-directional characteristics of the array. To achieve desired spectral characteristics the light beam passes through the first absorptive filter  11  and the second absorptive filter  12 . 
     On the FIG. 6 chart T rel (λ)*D(310)/T rel (310) characteristics of the array is plotted as a broken line, the Diffey Standard is plotted as a solid line. 
     DESCRIPTION OF THE VERSION 3 
     The array contains: a first absorptive filter  13  that makes a first system of absorptive filters, a second absorptive filter  14  that makes a second system of absorptive filters and a first set of interference filters  15  and a second set of interference filters  16  that both make a system of interference filters. The first absorptive filter  13  is made of material transparent to UV with decreasing transmission when wavelength is changed from 320 to 350 nm, the second absorptive filter  14  is made of material transparent to UV and blocking visible and IR radiation. That property have materials M2 and M1 respectively, with characteristics presented in the table below. Interference filters are constructed to block visible and IR radiation and/or to modify transmission characteristics in UV. 
     In that example the first absorptive filter  13  is a plano-parallel plate, 1.5 mm thick, made of M2 material, Schott GG-19 like. The second absorptive filter  14  with interference filters  15 ,  16  placed on the filter  14  surfaces are made together by Schott as Schott DUG-11 filter. 
     To achieve desired spectral characteristics the light beam passes through the first absorptive filter  13 , the first interference filter  15 , the second absorptive filter  14  and the second interference filter  16 . 
     On the FIG. 7 chart T rel (λ)*D(310)/T rel (310) characteristics of the array is plotted as a broken line, the Diffey Standard is plotted as a solid line. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 TABLE of relative internal transmission T rel  int(λ) 
               
             
          
           
               
                 λ [nm] 
                 290 
                 300 
                 310 
                 320 
                 330 
                 340 
                 350 
                 360 
                 370 
                 380 
                 390 
               
               
                   
               
             
          
           
               
                 M1 glass, 
                 Minimal value 
                 0 
                 0.7 
                 1 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 0.6 
                 0.14 
                 10E−3 
                 10E−10 
               
               
                 8 mm thick 
                 Maximal value 
                 0.3 
                 0.8 
                 1 
                 1.3 
                 1.4 
                 1.3 
                 1.12 
                 0.8 
                 0.3 
                 0.015 
                 10E−6 
               
               
                 M2 glass, 
                 Minimal value 
                 0 
                 0.34 
                 1 
                 0.5 
                 0.04 
                 10E−3 
                 7 * 10E−6 
                 2 * 10E−7 
                 2 * 10E−7 
                 2 * 10E−5 
                 2 * 10E−3 
               
               
                 1.5 mm thick 
                 Maximal value 
                 0.2 
                 0.7 
                 1 
                 0.8 
                 0.36 
                 0.1 
                 0.02 
                 7 * 10E−3 
                 7 * 10E−3 
                 0.03 
                 0.14 
               
               
                   
               
             
          
         
       
     
     Data in tables above are T rel   int (λ) characteristics of plano-paralel plates made of M1, M2 with given thickness. 
     The exact values of T rel   int (λ) are described in the example constructions. These data are example values and it is obvious that the invention is not restricted to them. The optical array in the example constructions has the spectral characteristics similar to human skin sensitivity to UV contained in sunlight. FIG. 5 presents T rel (λ)*D(310)/T rel (310) chart for optical array from FIG. 2 in comparison with the Diffey Standard D(λ), FIG. 6 presents T rel (λ)*D(310)/T rel (310) chart for optical array from FIG. 3 in comparison with the Diffey Standard D(λ), FIG. 7 presents T rel (λ)*D(310)/T rel (310) chart for optical array from FIG. 4 in comparison with the Diffey Standard D(λ). The biggest discrepancies between the characteristics and the Diffey Standard are for UV-C that is absent in sunlight and UV-A that has a minimal burning power comparing with total burning power of sun UV.